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The information in this preliminary prospectus supplement is not complete and may be changed. The preliminary prospectus supplement and the accompanying prospectus are part of an effective registration statement filed with the Securities and Exchange Commission. This preliminary prospectus supplement and the accompanying prospectus are not offers to sell nor solicitations of offers to buy these securities in any jurisdiction where such offer or sale is not permitted.

This is an offering of $ of % first mortgage bonds, series due September 1, 2048 to be issued by Northern States Power Company, a Wisconsin corporation. We will pay interest on the first mortgage bonds on March 1 and September 1 of each year, commencing on March 1, 2019. The first mortgage bonds will mature on September 1, 2048. The first mortgage bonds will be issued only in denominations of $1,000 and integral multiples in excess thereof. We may redeem the first mortgage bonds at any time, in whole or in part, at the applicable redemption price described in this prospectus supplement.

The first mortgage bonds will constitute a new issue of securities with no established trading market. We do not intend to apply for listing of the first mortgage bonds on any securities exchange or seek their quotation on any automated quotation system. Please read the information provided under the caption “Supplemental Description of the First Mortgage Bonds” in this prospectus supplement and under the caption “Description of the First Mortgage Bonds” in the accompanying prospectus for a more detailed description of the first mortgage bonds.

The first mortgage bonds will be our senior secured obligations and will be secured equally and ratably with all of our other first mortgage bonds from time to time outstanding.

Investing in the first mortgage bonds involves risks. See “Risk Factors” on page S-6 of this prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

The underwriters are offering the first mortgage bonds subject to various conditions. The underwriters expect to deliver the first mortgage bonds in book-entry form only through the facilities of The Depository Trust Company on or about September , 2018.

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of the first mortgage bonds we are offering in this prospectus supplement. The second part, the accompanying base shelf prospectus, gives more general information, some of which may not apply to the first mortgage bonds we are offering in this prospectus supplement. The accompanying base shelf prospectus dated April 18, 2018 is referred to as the “accompanying prospectus” in this prospectus supplement.

This prospectus supplement, the accompanying prospectus and any free writing prospectus that we prepare or authorize contain and incorporate by reference information that you should consider when making your investment decision. We have not, and the underwriters have not, authorized anyone to provide you with different information, and if given, you should not rely on it. We are not, and the underwriters are not, making an offer of these securities in any jurisdiction where the offer is not permitted. You should not assume that the information in this prospectus supplement, the accompanying prospectus or the documents incorporated by reference herein or therein is accurate as of any date other than the date on the front of those documents.

If this prospectus supplement is inconsistent with the accompanying prospectus, you should rely on the information in this prospectus supplement.

This prospectus supplement, the accompanying prospectus and the documents they incorporate by reference contain statements that are not historical fact and constitute “forward-looking statements.” When we use words like “anticipate,” “believe,” “could,” “estimate,” “expect,” “intend,” “may,” “objective,” “outlook,” “plan,” “project,” “possible,” “potential,” “should,” “will,” “would” and similar expressions, or when we discuss our strategy or plans, we are making forward-looking statements. Forward-looking statements are not guarantees of performance. They involve risks, uncertainties and assumptions. Our future results may differ materially from those expressed in these forward-looking statements. These statements are necessarily based upon various assumptions involving judgments with respect to the future and other risks, including, among others:

You are cautioned not to rely unduly on any forward-looking statements. These risks and uncertainties associated with forward-looking statements are discussed in detail under “Risk Factors,” “Business,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Notes to Consolidated Financial Statements” in our Annual Report on Form 10-K for the year ended December 31, 2017, as amended by Amendment No. 1 to our Annual Report on Form 10-K for the year ended December 31, 2017 (our “2017 Form 10-K”), and in our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2018 and June 30, 2018, and in other documents on file with the SEC and incorporated by reference in this prospectus supplement and the accompanying prospectus. You may obtain copies of these documents as described in the accompanying prospectus under the caption “Where You Can Find More Information.”

We undertake no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. The foregoing review of factors should not be construed as exhaustive.

PROSPECTUS SUPPLEMENT SUMMARY

The following information supplements, and should be read together with, the information contained or incorporated by reference in other parts of this prospectus supplement and the accompanying prospectus. This summary highlights selected information from this prospectus supplement and the accompanying prospectus. As a result, it does not contain all of the information you should consider before investing in the first mortgage bonds offered by this prospectus supplement. You should carefully read this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference, which are described under the caption “Where You Can Find More Information” in the accompanying prospectus. In this prospectus supplement, except as otherwise indicated or as the context otherwise requires, the “Company,” “we,” “us” and “our” refer to Northern States Power Company, a Wisconsin corporation.

The Company

General

We were incorporated in 1901 under the laws of the State of Wisconsin. We are a utility primarily engaged in the generation, transmission, distribution and sale of electricity in portions of northwestern Wisconsin and in the western portion of the Upper Peninsula of Michigan. We also purchase, transport, distribute and sell natural gas to retail customers and transport customer-owned natural gas in the same service territory. As of December 31, 2017, we provided electric utility service to approximately 259,000 customers and natural gas utility service to approximately 114,000 customers.

Our electric production and transmission system is managed as an integrated system with that of Northern States Power Company, a Minnesota corporation, or “NSP-Minnesota”, jointly referred to as the NSP System. The electric production and transmission costs of the entire NSP System are shared by us and NSP-Minnesota. A FERC approved agreement between the two companies, called the Interchange Agreement, provides for the sharing of all generation and transmission costs of the NSP System. Such costs include current and potential obligations of NSP-Minnesota related to its nuclear generating facilities.

We own the following direct subsidiaries: Chippewa and Flambeau Improvement Co., which operates hydro reservoirs; Clearwater Investments Inc., which owns interests in affordable housing; and NSP Lands, Inc., which holds real estate.

We are a wholly owned subsidiary of Xcel Energy Inc., or “Xcel Energy,” a Minnesota corporation. Among Xcel Energy’s other subsidiaries are NSP-Minnesota, Public Service Company of Colorado and Southwestern Public Service Company. Xcel Energy is a publicly held company and files periodic reports and other documents with the SEC. All of the members of our board of directors and many of our executive officers also are executive officers of Xcel Energy.

Our principal executive offices are located at 1414 W. Hamilton Avenue, Eau Claire, Wisconsin 54701, and our telephone number is (715) 737-2625.

The Offering

The following summary contains basic information about this offering. Because this is only a summary, it does not contain all of the information that may be important to you. For a more complete understanding of this offering, we encourage you to read this entire prospectus supplement, including the information under the caption “Supplemental Description of the First Mortgage Bonds,” the accompanying prospectus, including the information under the caption “Description of the First Mortgage Bonds,” and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus.

Issuer

Northern States Power Company, a Wisconsin corporation.

Securities Offered

$ principal amount of % first mortgage bonds, series due September 1, 2048.

Maturity

September 1, 2048.

Interest Rate

% per year.

Interest Payment Dates

March 1 and September 1 of each year, beginning on March 1, 2019.

Ranking

The first mortgage bonds will be our senior secured obligations and will be secured equally and ratably with all of our other outstanding first mortgage bonds and any first mortgage bonds hereafter issued under our Indenture dated as of April 1, 1947, as supplemented and restated, or the “Mortgage Indenture”, from us to U.S. Bank National Association, as successor trustee, or the “Mortgage Trustee”. As of June 30, 2018, there were five series of first mortgage bonds outstanding under the Mortgage Indenture in an approximate aggregate principal amount of $750 million.

Collateral

The first mortgage bonds are secured by a first mortgage lien on substantially all of our real and fixed properties, subject to limited exceptions.

Optional Redemption

At any time prior to March 1, 2048 (which is the date that is six months prior to the maturity of the first mortgage bonds (the “Par Call Date”)), we may redeem, in whole or in part, the first mortgage bonds at a “make whole” redemption price equal to the greater of (i) 100% of the principal amount of such first mortgage bonds being redeemed or (ii) the sum of the present values of the remaining scheduled payments of principal and interest on the first mortgage bonds being redeemed that would be due if such first mortgage bonds matured on the Par Call Date (excluding the portion of any such accrued and unpaid interest to but excluding the date fixed for redemption), discounted to the date fixed for redemption on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate (as defined below) plus basis points, plus, in each case, accrued and unpaid interest thereon to but excluding the date fixed for redemption. At any time on or after the Par Call Date, we may redeem, in whole or in part, the first mortgage bonds, at

100% of the principal amount of the first mortgage bonds being redeemed plus accrued and unpaid interest thereon to but excluding the date fixed for redemption. See “Supplemental Description of the First Mortgage Bonds—Optional Redemption” in this prospectus supplement for more information.

Sinking Fund

None.

Use of Proceeds

We intend to add the net proceeds from the sale of the first mortgage bonds offered by this prospectus supplement to our general corporate funds and apply a portion of such net proceeds to fund the repayment at maturity of our $150 million of 5.25% First Mortgage Bonds, Series B due October 1, 2018 and the repayment of short-term debt borrowings. The balance of the net proceeds will be used for general corporate purposes. Until the net proceeds from the sale of the first mortgage bonds have been used, we may invest them temporarily in interest-bearing obligations. See “Use of Proceeds” in this prospectus supplement for more information.

Mortgage Trustee

U.S. Bank National Association.

You should carefully consider the risks and uncertainties described below as well as any cautionary language or other information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus, including the information under the caption “Item 1A. Risk Factors” in our 2017 Form 10-K, as modified by our quarterly reports on Form 10-Q and other SEC filings filed after such annual report and the information under the caption “Critical Accounting Policies” in this prospectus supplement, before purchasing the first mortgage bonds offered by this prospectus supplement. Those risks and the risks set forth below are those that we consider to be the most significant to your decision whether to invest in the first mortgage bonds. If any of the events described therein or set forth below occur, our business, financial condition or results of operations could be materially harmed. In addition, we may not be able to make payments on the first mortgage bonds, and this could result in your losing all or part of your investment.

Any lowering of the credit ratings on the first mortgage bonds would likely reduce their value.

As described under the caption “Item 1A. Risk Factors” in our 2017 Form 10-K, our credit ratings could be lowered or withdrawn entirely by a rating agency in the future. Any lowering of the credit ratings on our first mortgage bonds would likely reduce the value of the first mortgage bonds offered by this prospectus supplement.

The first mortgage bonds offered by this prospectus supplement have no prior public market, and we cannot assure you that any public market will develop or be sustained after the offering.

Although the first mortgage bonds offered by this prospectus supplement generally may be resold or otherwise transferred by holders who are not our affiliates, the first mortgage bonds will constitute a new issue of securities without an established trading market. We have been advised by the underwriters that they may make a market in the first mortgage bonds, but they have no obligation to do so and may discontinue market making at any time without providing notice. There can be no assurance that a market for the first mortgage bonds will develop or, if it does develop, that it will continue. If an active public market does not develop, the market price and liquidity of the first mortgage bonds may be adversely affected. Furthermore, we do not intend to apply for listing of the first mortgage bonds on any securities exchange or seek their quotation on any automated quotation system.

We estimate that our net proceeds from the sale of the first mortgage bonds, less the underwriting discount and the offering expenses for such bonds, will be approximately $ . We intend to add the net proceeds from the sale of the first mortgage bonds offered by this prospectus supplement to our general corporate funds and apply a portion of such net proceeds to fund the repayment at maturity of our $150 million of 5.25% First Mortgage Bonds, Series B due October 1, 2018 and the repayment of short-term debt borrowings. The balance of the net proceeds will be used for general corporate purposes. Until the net proceeds from the sale of the first mortgage bonds have been used, we may invest them temporarily in interest-bearing obligations. At June 30, 2018, we had approximately $30 million of short-term debt borrowings outstanding, with a weighted average interest rate of approximately 2.29%.

The table below sets forth our ratios of consolidated earnings to consolidated fixed charges for the periods indicated.

For purposes of computing the ratios of consolidated earnings to consolidated fixed charges, (1) earnings consist of income from continuing operations before income taxes plus fixed charges; and (2) fixed charges consist of interest charges, including interest on long-term debt, the interest component on leases, other interest charges and amortization of debt discount, premium and expense.

The following selected consolidated financial data as of December 31, 2017 and 2016, and for the years ended December 31, 2017, 2016 and 2015, has been derived from our audited consolidated financial statements and the related notes. The selected consolidated financial data as of June 30, 2018 and for the six months ended June 30, 2018 and 2017 has been derived from our unaudited consolidated financial statements and the related notes. The information set forth below should be read together with “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” our audited and unaudited consolidated financial statements and related notes and other information contained in our 2017 Form 10-K and our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2018 and June 30, 2018, which we incorporate by reference in this prospectus supplement and the accompanying prospectus. See “Where You Can Find More Information” in the accompanying prospectus. The historical financial information may not be indicative of our future performance.

You should consider the financial data and other information contained in our audited and unaudited consolidated financial statements and the related notes, “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and other financial information contained in our 2017 Form 10-K and our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2018 and June 30, 2018, which we incorporate by reference in this prospectus supplement and the accompanying prospectus, before making a decision to invest in the first mortgage bonds.

Preparation of the consolidated financial statements and related disclosures in compliance with generally accepted accounting principles requires the application of accounting rules and guidance, as well as the use of estimates. The application of these policies involves judgments regarding future events, including the likelihood of success of particular projects, legal and regulatory challenges and anticipated recovery of costs. These judgments could materially impact the consolidated financial statements and disclosures, based on varying assumptions. In addition, the financial and operating environment also may have a significant effect on the operation of the business and on the results reported. The following is a list of accounting policies and estimates that are most significant to the portrayal of our financial condition and results, and require management’s most difficult, subjective or complex judgments. Each of these has a higher likelihood of resulting in materially different reported amounts under different conditions or using different assumptions. Each critical accounting policy has been discussed with the audit committee of Xcel Energy’s board of directors.

We are a rate-regulated entity that is subject to the accounting for regulated operations, which provides that rate-regulated entities report assets and liabilities consistent with the recovery of those incurred costs in rates, if the competitive environment makes it probable that such rates will be charged and collected. Our rates are derived through the ratemaking process, which results in the recording of regulatory assets and liabilities based on the probability of future cash flows. Regulatory assets generally represent incurred or accrued costs that have been deferred because future recovery from customers is probable. Regulatory liabilities generally represent amounts that are expected to be refunded to customers in future rates or amounts collected in current rates for future costs. In other businesses or industries, regulatory assets and regulatory liabilities would generally be charged to net income or other comprehensive income.

Each reporting period we assess the probability of future recoveries and obligations associated with regulatory assets and liabilities. Factors such as the current regulatory environment, recently issued rate orders and historical precedents are considered. Decisions made by regulatory agencies can directly impact the amount and timing of cost recovery as well as the rate of return on invested capital and may materially impact our results of operations, financial condition, or cash flows.

As of June 30, 2018 and December 31, 2017, we had recorded regulatory assets of $302.7 million and $305.3 million, respectively. As of June 30, 2018 and December 31, 2017, we had recorded regulatory liabilities of $432.4 million and $407.5 million, respectively. We are subject to regulation that varies from jurisdiction to jurisdiction. If future recovery of costs, in any such jurisdiction, ceases to be probable, we would be required to charge these assets to current net income or other comprehensive income. There are no current or expected proposals or changes in the regulatory environment that we anticipate will materially impact the probability of future recovery of these assets.

Judgment, uncertainty, and estimates are a significant aspect of the income tax accrual process that accounts for the effects of current and deferred income taxes. Uncertainty associated with the application of tax statutes

and regulations and the outcomes of tax audits and appeals require that judgment and estimates be made in the accrual process and in the calculation of the effective tax rates. Changes in tax laws and rates may affect recorded deferred tax assets and liabilities and our future effective tax rates. The Tax Cuts and Jobs Act (as defined below) reduced the federal income tax rate from 35 percent to 21 percent, significantly impacting the recorded amounts of deferred tax assets and liabilities and reducing the effective tax rate applicable to future periods.

Effective tax rates are highly impacted by assumptions. Effective tax rate calculations are revised every quarter based on best available year-end tax assumptions (income levels, deductions, credits, etc.); adjusted in the following year after returns are filed, with the tax accrual estimates being trued-up to the actual amounts claimed on the tax returns; and further adjusted after examinations by taxing authorities have been completed.

In accordance with the interim period reporting guidance, income tax expense for the first three quarters in a year is based on the forecasted annual effective tax rates. The forecasted effective tax rates reflect a number of estimates including forecasted annual income, permanent tax adjustments and tax credits.

Valuation allowances are applied to deferred tax assets if it is more likely than not that at least a portion may not be realized based on an evaluation of expected future taxable income.

Accounting for income taxes also requires that only tax benefits that meet the more likely than not recognition threshold can be recognized or continue to be recognized. The change in the unrecognized tax benefits needs to be reasonably estimated based on evaluation of the nature of uncertainty, the nature of the event that could cause the change and an estimated range of reasonably possible changes. Management will use prudent business judgment to derecognize appropriate amounts of tax benefits at any period end, and as new developments occur. Unrecognized tax benefits can be recognized as issues are favorably resolved and loss exposures decline.

We may adjust our unrecognized tax benefits and interest accruals to the updated estimates as disputes with the Internal Revenue Service and state tax authorities are resolved. These adjustments may increase or decrease earnings.

Xcel Energy offers various benefit plans to its subsidiaries’ employees, including our employees. Xcel Energy’s pension and postretirement health care costs are based on an actuarial calculation that includes a number of key assumptions, most notably the annual return level that pension and postretirement health care investment assets are expected to earn in the future and the interest rate used to discount future pension benefit payments to a present value obligation. In addition, the pension cost calculation uses an asset-smoothing methodology to reduce the volatility of varying investment performance over time. A portion of Xcel Energy’s pension and postretirement health care costs are attributable to its operating subsidiaries, including us.

Pension costs are expected to decrease in 2018 and continue to decline in the following few years. Funding requirements in 2018 are expected to be consistent with 2017 and continue at that level in the following years. While investment returns were below the assumed levels in 2015 and 2016, investment returns exceeded the assumed levels in 2017. The pension cost calculation uses a market-related valuation of pension assets. Xcel Energy uses a calculated value method to determine the market-related value of the plan assets. The market-related value is determined by adjusting the fair market value of assets at the beginning of the year to reflect the investment gains and losses (the difference between the actual investment return and the expected investment return on the market-related value) during each of the previous five years at the rate of 20 percent per year. As these differences between the actual investment returns and the expected investment returns are incorporated into the market-related value, the differences are recognized in pension cost over the expected average remaining years of service for active employees, which was approximately 12 years in 2017.

Based on current assumptions and the recognition of past investment gains and losses, Xcel Energy currently projects the pension costs recognized for financial reporting purposes will be $117 million in 2018 and $106 million in 2019, of which $7 million in 2018 and $6 million in 2019 is expected to be attributable to us, while the actual pension costs were $139 million in 2017 and $122 million in 2016. The expected decrease in 2018 and future year costs is due primarily to reductions in loss amortizations, plan design changes and an increase in expected return on assets due to planned future contributions and expected return of current assets.

In 2014, the Society of Actuaries published a new mortality table (RP-2014) that increased the overall life expectancy of males and females. In 2014, Xcel Energy adopted this mortality table, with modifications, based on its population and specific experience. During 2017, a new projection table was released (MP-2017). Xcel Energy evaluated the updated projection table and concluded that the methodology currently in use and adopted in 2016 is consistent with the recently updated 2017 table and continues to be representative of Xcel Energy’s population.

At December 31, 2017, Xcel Energy set the rate of return on assets used to measure pension costs at 6.87 percent, which is consistent with the rate set at December 31, 2016. The rate of return used to measure postretirement health care costs is 5.80 percent at December 31, 2017 and this is consistent with December 31, 2016. Xcel Energy’s ongoing pension investment strategy is based on plan-specific investments that seek to minimize potential investment and interest rate risk as a plan’s funded status increases over time. The investments result in a greater percentage of interest rate sensitive securities being allocated to specific plans having relatively higher funded status ratios and a greater percentage of growth assets being allocated to plans having relatively lower funded status ratios.

Xcel Energy set the discount rates used to value the December 31, 2017 pension at 3.63 percent and postretirement health care obligations at 3.62 percent, which represents a 50 basis point and a 51 basis point decrease from December 31, 2016, respectively. Xcel Energy uses a bond matching study as its primary basis for determining the discount rate used to value pension and postretirement health care obligations. The bond matching study utilizes a portfolio of high grade (Aa or higher) bonds that matches the expected cash flows of Xcel Energy’s benefit plans in amount and duration. The effective yield on this cash flow matched bond portfolio determines the discount rate for the individual plans. The bond matching study is validated for reasonableness against the Merrill Lynch Corporate 15+ Bond Index. At December 31, 2017, this reference point supported the selected rate. In addition to this reference point, Xcel Energy also reviews general actuarial survey data to assess the reasonableness of the discount rate selected.

The following are the pension funding contributions across all four of Xcel Energy’s pension plans, both voluntary and required, for 2015 through 2018:

For future years, Xcel Energy and we anticipate contributions will be made as necessary.

If alternative assumptions were used at December 31, 2017, a one-percent change would result in the following impact on our 2017 pension costs:

Beginning with the December 31, 2017 measurement date, Xcel Energy separated its initial medical trend assumption for pre-Medicare (Pre-65) and post-Medicare (Post-65) claims costs, and assumed 7.0 percent and 5.5 percent, respectively. Xcel Energy separated the trends in order to reflect different short-term expectations based on recent experiences with Pre-65 and Post-65 claims cost increases for Xcel Energy’s retiree medical plan. The ultimate trend assumption remained at 4.5 percent for both Pre-65 and Post-65 claims costs as similar long-term trend rates are expected for both populations. The period from initial trend rate until the ultimate rate is reached is five years. Xcel Energy bases its medical trend assumption on the long-term cost inflation expected in the health care market, considering the levels projected and recommended by industry experts, as well as recent actual medical cost experienced by Xcel Energy’s retiree medical plan.

Xcel Energy recovers employee benefits costs in its regulated utility operations consistent with accounting guidance except that in 2017, the Public Service Commission of Wisconsin, or the “PSCW,” approved our request for deferred accounting treatment of the 2017 pension settlement accounting expense.

Xcel Energy recognizes liabilities for the expected cost of retiring tangible long-lived assets for which a legal obligation exists. These asset retirement obligations, or “AROs”, are recognized at fair value as incurred and are capitalized as part of the cost of the related long-lived assets. In the absence of quoted market prices, Xcel Energy estimates the fair value of its AROs using present value techniques, in which it makes various assumptions including estimates of the amounts and timing of future cash flows associated with retirement activities, credit-adjusted risk free rates and cost escalation rates. When Xcel Energy revises any assumptions used to estimate AROs, it adjusts the carrying amount of both the ARO liability and the related long-lived asset. Xcel Energy accretes ARO liabilities to reflect the passage of time using the interest method.

A significant portion of Xcel Energy’s AROs relates to the future decommissioning of NSP-Minnesota’s nuclear facilities. The total obligation for nuclear decommissioning is expected to be funded by the external decommissioning trust fund. The difference between regulatory funding (including depreciation expense less returns from the external trust fund) and expense recognized under current accounting guidance is deferred as a regulatory asset. The amounts recorded for AROs related to future nuclear decommissioning were $1.874 billion and $2.249 billion as of December 31, 2017 and 2016, respectively. Based on their significance, the following discussion relates specifically to the AROs associated with nuclear decommissioning.

NSP-Minnesota obtains periodic cost studies in order to estimate the cost and timing of planned nuclear decommissioning activities. These independent cost studies are based on relevant information available at the time performed. Estimates of future cash flows for extended periods of time are by nature highly uncertain and may vary significantly from actual results. NSP-Minnesota is required to file a nuclear decommissioning filing every three years. The filing covers all expenses over the decommissioning period of the nuclear plants, including decontamination and removal of radioactive material. The Minnesota Public Utility Commission, or the “MPUC”, approved NSP-Minnesota’s currently effective decommissioning filing in October 2015. The most recent filing was submitted in December 2017 and is currently pending with the MPUC, with an order expected in 2018.

The following key assumptions have a significant effect on the estimated nuclear obligation:

Significant uncertainties exist in estimating the future cost of nuclear decommissioning including the method to be utilized, the ultimate costs to decommission, and the planned method of disposing spent fuel. If different cost estimates, life assumptions or cost escalation rates were utilized, the AROs could change materially. However, changes in estimates should have minimal impact on results of operations as NSP-Minnesota expects to continue to recover all costs in future rates.

We continually make judgments and estimates related to these critical accounting policy areas, based on an evaluation of the varying assumptions and uncertainties for each area. The information and assumptions underlying many of these judgments and estimates will be affected by events beyond the control of Xcel Energy, or otherwise change over time. This may require adjustments to recorded results to better reflect the events and updated information that becomes available. The financial statements contained in our 2017 Form 10-K along with expenses and contributions as reported on our Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2018, reflect management’s best estimates and judgments of the impact of these factors as of June 30, 2018.

These policies are further discussed in the “Notes to Consolidated Financial Statements” in our 2017 Form 10-K and our Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2018.

Net cash provided by operating activities decreased $1.0 million for the six months ended June 30, 2018 compared with the six months ended June 30, 2017. The decrease was primarily due to timing of accounts payable, partially offset by a regulatory liability for refunds to customers related to the Tax Cuts and Jobs Act as well as an increase in other current liabilities.

Net cash provided by operating activities decreased by $21.0 million for 2017 compared to 2016. The decrease was primarily from regulatory assets and liabilities as well as current and noncurrent liabilities, taxes paid, and lower cash provided by accounts receivable, partially offset by an increase in net income, excluding amounts related to non-cash operating charges (e.g., depreciation and deferred tax expense).

Net cash used in investing activities increased $29.5 million for the six months ended June 30, 2018 compared with the six months ended June 30, 2017. The increase was primarily the result of higher capital expenditures related to transmission projects in 2018.

Net cash used in investing activities increased by $13.2 million for 2017 compared to 2016. The increase was primarily the result of higher capital expenditures related to transmission projects in 2017.

Net cash used in financing activities decreased by $31.0 million for the six months ended June 30, 2018 compared with the six months ended June 30, 2017. The change was primarily due to net proceeds from short-term debt in 2018 compared to 2017, partially offset by lower capital contributions from Xcel Energy.

Net cash provided by financing activities was $32.3 million in 2017 compared to net cash used in financing activities of $1.3 million in 2016. The change was primarily due to a bond issuance in 2017 and increased capital contributions from Xcel Energy, partially offset by net repayments of short term debt.

Capital Expenditures. The estimated cost, as of December 31, 2017, of our capital expenditure program is approximately $250 million in 2018, approximately $250 million in 2019, approximately $240 million in 2020, approximately $280 million in 2021, and approximately $290 million in 2022.

Our capital expenditure programs are subject to continuing review and modification. Actual utility capital expenditures may vary from the estimates due to changes in electric and natural gas projected load growth,

regulatory decisions, legislative initiatives, reserve margin requirements, the availability of purchased power, alternative plans for meeting long-term energy needs, compliance with environmental requirements, renewable portfolio standards, and merger, acquisition and divestiture opportunities.

Contractual Obligations and Other Commitments. We have a variety of contractual obligations and other commitments that will need to be funded in the future, in addition to our capital expenditure programs. The following is a summarized table of contractual obligations as of December 31, 2017:

Historically, we have paid quarterly dividends to Xcel Energy. In the first six months of 2018 and in fiscal years 2017, 2016 and 2015, we paid dividends to Xcel Energy of $32 million, $64 million, $53 million and $54 million, respectively. The amount of dividends that we can pay to Xcel Energy is limited to some extent by our equity-to-total capitalization ratio approved by the PSCW. The payment of dividends is also subject to the FERC’s jurisdiction under the Federal Power Act, which prohibits the payment of dividends out of capital accounts; payment of dividends is allowed out of retained earnings only.

We expect to meet future financing requirements by periodically issuing long-term debt and short-term debt and by receiving equity contributions from Xcel Energy to maintain desired capitalization ratios. In the first six

months of 2018 and in fiscal years 2017, 2016 and 2015, we received equity contributions from Xcel Energy of $3.3 million, $48.0 million, $1.9 million and $69.2 million, respectively. Our current authority from the PSCW requires us to maintain a 13 month average financial common equity ratio of at least 51.5 percent. For these purposes, our 13 month average financial common equity ratio as of December 31, 2017 was 53.1 percent of our total capitalization. To the extent Xcel Energy experiences constraints on available capital sources, it may limit its equity contributions to us.

We have a $150 million revolving credit facility that expires in June 2021. We have the right to request an extension of the revolving termination date for an additional one-year period, subject to majority bank group approval. The credit facility serves as back-up liquidity for general corporate purposes including letters of credit and refinancing indebtedness outstanding from time to time. After considering short-term debt borrowings, as of June 30, 2018, we had $120 million available under this revolving credit facility. We expect to use a portion of the net proceeds from this offering to repay the outstanding short-term debt borrowings. See “Use of Proceeds” in this prospectus supplement for more information.

Historically, we have used a number of sources to fulfill short-term funding needs, including operating cash flow, notes payable, commercial paper and bank lines of credit. The amount and timing of short-term funding needs depend in large part on financing needs for utility capital expenditures and working capital as discussed above under the caption “—Capital Requirements.”

Operating cash flow as a source of short-term funding is affected by such operating factors as weather; regulatory requirements, including rate recovery of costs, environmental regulation compliance and industry deregulation; changes in the trends for energy prices; and supply and operational uncertainties, all of which are difficult to predict.

Short-term borrowing as a source of short-term funding is affected by access to the capital markets on reasonable terms. Our access varies based on our financial performance and existing debt levels. If our current debt levels are perceived to be at or higher than standard industry levels or those levels that can be sustained by our current operating performance, our access to reasonable short-term borrowings could be limited. These factors are evaluated by credit rating agencies that review our and Xcel Energy’s operations on an ongoing basis.

Our cost of capital and access to capital markets for both long-term and short-term funding are dependent in part on credit rating agency reviews. As discussed above under the caption “Risk Factors,” our credit ratings could be lowered or withdrawn in the future.

As of June 30, 2018, we had cash and cash equivalents of approximately $1.6 million.

Please read the following information concerning the first mortgage bonds offered by this prospectus supplement in conjunction with the statements under the caption “Description of the First Mortgage Bonds” in the accompanying prospectus, which the following information supplements and, in the event of any inconsistencies, supersedes. The following description does not purport to be complete and is subject to, and is qualified in its entirety by reference to, the description in the accompanying prospectus and the Mortgage Indenture, as supplemented by the Supplemental Trust Indenture dated as of September 1, 2018 relating to the first mortgage bonds offered by this prospectus supplement. The Mortgage Indenture, as supplemented and restated, is described in the accompanying prospectus and is filed as an exhibit to the registration statement under which the first mortgage bonds are being offered and sold. As of June 30, 2018, there were five series of first mortgage bonds outstanding under the Mortgage Indenture in an aggregate principal amount of $750 million.

We will offer $ million principal amount of the first mortgage bonds, as a series of first mortgage bonds under the Mortgage Indenture. The entire principal amount of the first mortgage bonds will mature and become due and payable, together with any accrued and unpaid interest thereon, on September 1, 2048.

The first mortgage bonds will bear interest at the annual rate set forth on the cover page of this prospectus supplement from September , 2018, payable semi-annually on March 1 and September 1 of each year, beginning on March 1, 2019 to the person in whose name the first mortgage bond is registered at the close of business on the February 15 or August 15 immediately preceding such March 1 and September 1. Interest at maturity will be paid to the person to whom principal is paid. So long as the first mortgage bonds are in book-entry only form, we will wire any payments of principal, interest and premium to The Depository Trust Company, or “DTC”, as depository, or its nominee. See “Book-Entry System” in the accompanying prospectus for a discussion of the procedures for payment to the beneficial owners of the first mortgage bonds. The amount of interest payable will be computed on the basis of a 360-day year of twelve 30-day months based on the actual number of days elapsed. In the event that any date on which interest is payable on the first mortgage bonds is not a business day, then payment of the interest payable on such date will be made on the next succeeding day that is a business day (and without any interest or other payment in respect of any such delay), with the same force and effect as if made on such date. The term “business day” means any day other than a Saturday or Sunday or a day on which the offices of the Mortgage Trustee in the city of St. Paul, Minnesota, are closed pursuant to authorization of law.

We may, from time to time, without the consent of the holders of the first mortgage bonds offered by this prospectus supplement, reopen the first mortgage bonds and issue additional first mortgage bonds with the same terms (including the maturity date and interest rate), except for the public offering price, the issue date and, if applicable, the first interest accrual and payment dates, as such first mortgage bonds offered by this prospectus supplement. Any such additional first mortgage bonds, together with the first mortgage bonds offered by this prospectus supplement, will constitute a single series under the Mortgage Indenture and will have the same CUSIP provided they are fungible for U.S. federal income tax purposes.

At any time prior to March 1, 2048, the Par Call Date, we may redeem, in whole or in part, the first mortgage bonds at a “make whole” redemption price equal to the greater of (i) 100% of the principal amount of such first mortgage bonds being redeemed or (ii) the sum of the present values of the remaining scheduled

payments of principal and interest on the first mortgage bonds being redeemed that would be due if such first mortgage bonds matured on the Par Call Date (excluding the portion of any such accrued and unpaid interest to but excluding the date fixed for redemption), discounted to the date fixed for redemption on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate (as defined below) plus basis points, plus, in each case, accrued and unpaid interest thereon to but excluding the date fixed for redemption. At any time on or after the Par Call Date, we may redeem, in whole or in part, the first mortgage bonds at 100% of the principal amount of the first mortgage bonds being redeemed plus accrued and unpaid interest thereon to but excluding the date fixed for redemption.

For purposes of these redemption provisions with respect to the first mortgage bonds, the following terms have the following meanings:

“Comparable Treasury Issue” means the U.S. Treasury security selected by an Independent Investment Banker as having a maturity comparable to the remaining term of the first mortgage bonds being redeemed (assuming, for this purpose, that the first mortgage bonds matured on the Par Call Date) that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of the first mortgage bonds being redeemed.

“Comparable Treasury Price” means (1) the average of the Reference Treasury Dealer Quotations for such date fixed for redemption, after excluding the highest and lowest of such Reference Treasury Dealer Quotations for such date fixed for redemption, or (2) if we obtain fewer than four of such Reference Treasury Dealer Quotations for the date fixed for redemption, the average of all of such Reference Treasury Dealer Quotations for the date fixed for redemption.

“Independent Investment Banker” means one of the Reference Treasury Dealers appointed by us.

“Primary Treasury Dealer” means any primary U.S. Government securities dealer in the United States.

“Reference Treasury Dealer” means (1) each of Mizuho Securities USA LLC and a Primary Treasury Dealer selected by U.S. Bancorp Investments, Inc., or their respective affiliates or successors, provided, however, that if any of the foregoing or any of their respective designees ceases to be a Primary Treasury Dealer, we will appoint another Primary Treasury Dealer as a substitute and (2) any other Primary Treasury Dealers selected by us after consultation with an Independent Investment Banker.

“Reference Treasury Dealer Quotations” means, for each Reference Treasury Dealer and any date fixed for redemption, the average, as determined by an Independent Investment Banker, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to an Independent Investment Banker by the Reference Treasury Dealer at 5:00 p.m., Eastern time, on the third business day preceding the date fixed for redemption.

“Treasury Rate” means, with respect to any date fixed for redemption, the rate per annum equal to the semiannual equivalent yield to maturity of the Comparable Treasury Issue, calculated using a price for such Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to such Comparable Treasury Price for such date fixed for redemption. The Treasury Rate will be calculated on the third business day preceding the date fixed for redemption.

If we elect to redeem fewer than all of the first mortgage bonds, the Mortgage Trustee will select, in a manner as it deems fair and appropriate (and in accordance with the procedures of the Depository), the particular first mortgage bonds or portions of them to be redeemed. Notice of redemption will be given by mail not less than 30 days prior to the date fixed for redemption to the holders of first mortgage bonds to be redeemed (which, as long as the first mortgage bonds are held in the book-entry only system, will be the Depository, its nominee or a successor depository). On and after the date fixed for redemption (unless we default in the payment of the redemption price and interest accrued thereon to such date), interest on the first mortgage bonds called for redemption or the portions of them so called for redemption will cease to accrue.

The first mortgage bonds will be issued as one or more global securities in the name of DTC or a nominee of DTC and will be available only in book-entry form. See “Book-Entry System” in the accompanying prospectus. The first mortgage bonds will be issued only in denominations of $1,000 and integral multiples in excess thereof.

See “Description of the First Mortgage Bonds—Defaults” in the accompanying prospectus.

The underwriters will pay us and settle for the first mortgage bonds in immediately available funds. We will make all payments of principal and interest in immediately available funds.

The first mortgage bonds will trade in DTC’s same-day funds settlement system until maturity or until the first mortgage bonds are issued in certificated form, and secondary market trading activity in the first mortgage bonds will therefore be required by DTC to settle in immediately available funds. No assurance can be given as to the effect, if any, of settlement in immediately available funds on trading activity in the first mortgage bonds.

The Mortgage Indenture is, and the first mortgage bonds will be, governed by and construed in accordance with the laws of the State of Wisconsin.

U.S. Bank National Association is the Mortgage Trustee under the Mortgage Indenture.

The following discussion is a summary of certain material U.S. federal income tax consequences relevant to the purchase, beneficial ownership and disposition of the first mortgage bonds offered by this prospectus supplement. This summary is based on the U.S. Internal Revenue Code of 1986, as amended (the “Code”), Treasury regulations promulgated thereunder, administrative pronouncements of the U.S. Internal Revenue Service (the “IRS”), and judicial decisions, all as currently in effect and all of which are subject to change and to different interpretations. Changes to any of the foregoing authorities could apply on a retroactive basis, and could affect the U.S. federal income tax consequences described below. We have not sought and will not seek a ruling from the IRS with respect to the matters discussed in this section, and we cannot assure you that the IRS will not challenge one or more of the tax consequences described below.

This summary does not address all of the U.S. federal income tax considerations that may be relevant to a particular investor’s circumstances (such as the effects of section 451(b) of the Code, as revised by the 2017 legislation known as the “Tax Cuts and Jobs Act, ” or the fact (if applicable) that such investor purchases first mortgage bonds and also holds our 5.25% First Mortgage Bonds, Series B due October 1, 2018) and does not discuss any aspect of U.S. federal tax law other than income tax law or any state, local or non-U.S. tax consequences of the purchase, beneficial ownership and disposition of the first mortgage bonds. This summary addresses only first mortgage bonds purchased for cash pursuant to this offering at their “issue price” (i.e., the first price at which a substantial amount of the first mortgage bonds are sold to investors, excluding sales to bond houses, brokers or similar persons or organizations acting in the capacity as underwriters, placement agents or wholesalers) and held as capital assets and does not address U.S. federal income tax considerations applicable to investors that may be subject to special tax rules, such as:

As used herein, a “U.S. Holder” is a beneficial owner of first mortgage bonds that is, for U.S. federal income tax purposes, (i) an individual citizen or resident of the United States, (ii) a corporation created or organized in or under the laws of the United States, any state thereof or the District of Columbia, (iii) an estate whose income is subject to U.S. federal income tax regardless of its source, or (iv) a trust if (A) a United States court has the authority to exercise primary supervision over the administration of the trust and one or more “United States persons” (as defined in the Code) are authorized to control all substantial decisions of the trust or (B) it has a valid election in place to be treated as a United States person.

A “Non-U.S. Holder” is any beneficial owner of the first mortgage bonds that is neither a U.S. Holder nor a partnership (including an entity or arrangement treated as a partnership for U.S. federal income tax purposes).

If a partnership (or other entity or arrangement treated as a partnership for U.S. federal income tax purposes) holds first mortgage bonds, the U.S. federal income tax treatment of a partner generally will depend on the status of the partner and the activities of the partnership. A partnership holding first mortgage bonds, and partners in such a partnership, should consult their own tax advisors with regard to the U.S. federal income tax consequences of the purchase, ownership and disposition of the first mortgage bonds by the partnership.

THIS DISCUSSION OF CERTAIN MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF THE FIRST MORTGAGE BONDS IS NOT INTENDED TO BE, NOR SHOULD IT BE CONSTRUED TO BE, LEGAL OR TAX ADVICE TO ANY PARTICULAR PERSON. ACCORDINGLY, ALL PROSPECTIVE INVESTORS ARE URGED TO CONSULT THEIR TAX ADVISORS WITH RESPECT TO THE U.S. FEDERAL, STATE AND LOCAL AND NON-U.S. TAX CONSEQUENCES RELATING TO THE PURCHASE, OWNERSHIP AND DISPOSITION OF THE FIRST MORTGAGE BONDS BASED ON THEIR PARTICULAR CIRCUMSTANCES, INCLUDING THE EFFECTS OF THE RECENTLY ENACTED TAX CUTS AND JOBS ACT, THE EFFECTS OF ANY TAX TREATIES AND THE POTENTIAL EFFECTS OF ANY CHANGES IN LAW.

Payments of Interest. Interest on first mortgage bonds generally will be taxable to a U.S. Holder as ordinary income from U.S. sources at the time that such interest is paid or accrued, in accordance with the U.S. Holder’s regular method of accounting for U.S. federal income tax purposes.

It is expected, and this discussion assumes, that the first mortgage bonds will be issued with no more than de minimis original issue discount for U.S. federal income tax purposes.

Sale, Retirement or Other Taxable Disposition of First Mortgage Bonds. Upon the sale, retirement or other taxable disposition of first mortgage bonds, a U.S. Holder generally will recognize U.S.-source gain or loss equal to the difference between the amount realized upon the sale, retirement or other taxable disposition (other than amounts representing accrued and unpaid qualified stated interest, which will be taxable as ordinary interest income to the extent not previously included in gross income) and the U.S. Holder’s adjusted tax basis in the first mortgage bonds. In general, the U.S. Holder’s adjusted tax basis in the first mortgage bonds will equal the U.S. Holder’s initial investment in first mortgage bonds, reduced by any cash payments previously received in respect of the first mortgage bonds (other than qualified stated interest payments). Such gain or loss generally will be capital gain or loss and will be long-term capital gain or loss if at the time of sale, retirement or other taxable disposition the first mortgage bonds have been held for more than one year. Under current U.S. federal income tax law, certain non-corporate U.S. Holders, including individuals, are eligible for preferential rates of U.S. federal income taxation in respect of long-term capital gains. The deductibility of capital losses is subject to limitations.

Medicare Tax. A U.S. Holder that is an individual or estate, or a trust that does not fall into a special class of trusts that is exempt from such tax, is subject to a 3.8% tax on the lesser of (1) the U.S. Holder’s “net investment income” (in the case of individuals) or “undistributed net investment income” (in the case of estates and trusts) for the relevant taxable year and (2) the excess of the U.S. Holder’s “modified adjusted gross income” (in the case of individuals) or “adjusted gross income” (in the case of estates and trusts) for the taxable year over a certain threshold (which, in the case of individuals, will be between $125,000 and $250,000, depending on the individual’s circumstances). A U.S. Holder’s net investment income will generally include its interest income from the first mortgage bonds and net gain from the disposition of the first mortgage bonds, unless such interest income and net gain is derived in the ordinary course of the conduct of a trade or business (other than a trade or business that consists of certain passive or trading activities). Net investment income may, however, be reduced

by properly allocable deductions to such income. U.S. Holders that are individuals, estates or trusts are urged to consult their tax advisors regarding the applicability of the Medicare tax to their income and gains from the first mortgage bonds.

(a) Payments of interest on the first mortgage bonds by us or our paying agent to any Non-U.S. Holder generally will be exempt from U.S. federal income tax and the 30% U.S. federal withholding tax (or lower applicable treaty rate), provided that:

The certification requirement referred to above will be fulfilled if (i) the beneficial owner of the first mortgage bonds certifies on a properly executed IRS Form W-8BEN or W-8BEN-E, as applicable, or applicable successor form, under penalties of perjury, that such beneficial owner is not a U.S. person, provides its name and address and certifies the other relevant factual information supporting its exemption, and (ii) the beneficial owner files IRS Form W-8BEN or W-8BEN-E, as applicable, or applicable successor form with the paying agent, or in the case of first mortgage bonds held on behalf of the beneficial owner by a securities clearing organization, bank, or other financial institution holding customers’ securities in the ordinary course of its trade or business, such financial institution files with the paying agent a statement that it has received the IRS Form W-8BEN or W-8BEN-E, as applicable, or applicable successor form, from the beneficial owner and furnishes the paying agent with a copy. Prospective investors should consult their tax advisors regarding possible additional reporting requirements.

(b) A Non-U.S. Holder generally will not be subject to U.S. federal income tax on gain realized on the sale, redemption, retirement or other taxable disposition of the first mortgage bonds, unless:

If a Non-U.S. Holder is as described in the first bullet in paragraph (b) above, such Non-U.S. Holder generally will be subject to U.S. federal income tax at a rate of 30% on the amount by which such Non-U.S. Holder’s capital gains allocable to United States sources, including gain from such disposition, exceed any capital losses allocable to United States sources, except as otherwise specified by an applicable income tax treaty.

To the extent the amount realized on a sale, redemption, retirement or other taxable disposition of the first mortgage bonds is attributable to accrued but unpaid interest on the first mortgage bonds, this amount generally will be treated in the same manner as described in paragraph (a) above.

With regard to paragraphs (a) and (b) above, if a Non-U.S. Holder of first mortgage bonds is engaged in the conduct of a trade or business in the United States, and interest on the first mortgage bonds, or gain realized on

its sale, retirement or other taxable disposition of the first mortgage bonds, is effectively connected with the conduct of such trade or business (and, if required by an applicable tax treaty, is attributable to a permanent establishment or fixed base maintained by the Non-U.S. Holder in the United States), the Non-U.S. Holder, although exempt from the withholding tax discussed in the preceding paragraphs, will be subject to U.S. federal income tax on its effectively connected income, generally in the same manner as a U.S. Holder (but without regard to the Medicare tax described above). See “Certain U.S. Federal Income Tax Considerations—U.S. Federal Income Taxation of U.S. Holders” above. In addition, a Non-U.S. Holder that is a corporation for U.S. federal income tax purposes may be subject to a 30% branch profits tax (unless reduced or eliminated by an applicable tax treaty) on its effectively connected earnings and profits, subject to certain adjustments. In lieu of the IRS forms described above, such a Non-U.S. Holder will be required to provide to the paying agent a properly completed and executed IRS Form W-8ECI or applicable successor form to claim an exemption from withholding.

U.S. Holders. In general, a U.S. Holder (other than an exempt recipient) will be subject to information reporting requirements with respect to payments of principal and interest in respect of, and the proceeds from a sale, redemption or other disposition before maturity of the first mortgage bonds. In addition, a U.S. Holder may be subject to backup withholding on such payments if the U.S. Holder (i) fails to provide an accurate taxpayer identification number to the payor; (ii) has been notified by the IRS of a failure to report all interest or dividends required to be shown on its U.S. federal income tax returns; or (iii) otherwise fails to comply with applicable certification requirements.

Any amounts withheld under the backup withholding rules will be allowed as a refund or a credit against a U.S. Holder’s U.S. federal income tax liability, provided the required information is furnished to the IRS on a timely basis. U.S. Holders should consult their tax advisors regarding the application of information reporting and backup withholding rules in their particular situations, the availability of an exemption therefrom and the procedure for obtaining such an exemption, if applicable.

Non-U.S. Holders. In general, we or our paying agent must report to the IRS and to a Non-U.S. Holder the amount of interest on the first mortgage bonds paid to the Non-U.S. Holder and the amount of U.S. federal withholding tax, if any, deducted from those payments. Copies of the information returns reporting such interest payments and any associated U.S. federal withholding tax also may be made available to the tax authorities in the country in which the Non-U.S. Holder resides under the provisions of an applicable tax treaty. A Non-U.S. Holder generally will not be subject to backup withholding with respect to payments that we make on the first mortgage bonds provided that we or our paying agent does not have actual knowledge or reason to know that the Non-U.S. Holder is a U.S. person, and we or our paying agent has received from the Non-U.S. Holder an appropriate certification establishing non-U.S. status or other exemption from backup withholding (i.e., IRS Form W-8BEN or W-8BEN-E, as applicable, W-8ECI or other applicable IRS Form W-8 or applicable successor form). Information reporting and, depending on the circumstances, backup withholding will apply to the payment of the proceeds of a sale of first mortgage bonds that is effected within the United States or effected outside the United States through certain U.S.-related financial intermediaries, unless the Non-U.S. Holder certifies under penalty of perjury as to its non-U.S. status, and the payor does not have actual knowledge or reason to know that the beneficial owner is a U.S. person, or the Non-U.S. Holder otherwise establishes an exemption.

Any amounts withheld under the backup withholding rules will be allowed as a refund or a credit against a Non-U.S. Holder’s U.S. federal income tax liability, provided the required information is furnished to the IRS on a timely basis. Non-U.S. Holders of first mortgage bonds should consult their tax advisors regarding the application of information reporting and backup withholding in their particular situations, the availability of an exemption therefrom, and the procedure for obtaining an exemption, if applicable.

Pursuant to the Foreign Account Tax Compliance Act, or “FATCA,” foreign financial institutions (which term includes most foreign banks, hedge funds, private equity funds, mutual funds, securitization vehicles and other investment vehicles) and certain other foreign entities generally must comply with certain information reporting rules with respect to their U.S. account holders and investors or confront a withholding tax on U.S.-source payments made to them (whether received as a beneficial owner or as an intermediary for another party). A foreign financial institution or such other foreign entity that does not comply with the FATCA reporting requirements will generally be subject to a 30% withholding tax with respect to any “withholdable payments.” For this purpose, withholdable payments generally include U.S.-source payments otherwise subject to nonresident withholding tax (e.g., U.S.-source interest) and also include the entire gross proceeds from the sale or other disposition of any debt instruments of U.S. issuers, even if the payment would otherwise not be subject to U.S. nonresident withholding tax (e.g., because it is capital gain). Under the applicable final Treasury regulations, withholding under FATCA, if required, generally will apply to payments of U.S.-source interest on the first mortgage bonds, although withholding will be deferred until January 1, 2019 for gross proceeds (including principal payments) from dispositions (including redemptions) of the first mortgage bonds. Foreign financial institutions located in jurisdictions that have an intergovernmental agreement with the United States pursuant to FATCA may be subject to different rules with respect to information reporting and related requirements.

We will not pay any additional amounts to Non-U.S. Holders in respect of any amounts withheld, including pursuant to FATCA. Under certain circumstances, a Non-U.S. Holder might be eligible for refunds or credits of such taxes. Non-U.S. Holders are urged to consult with their own tax advisors regarding the effect, if any, of the FATCA provisions to them based on their particular circumstances.

The preceding discussion of material U.S. federal income tax consequences is general information only and is not tax advice. Accordingly, you should consult your own tax advisor as to the U.S. federal, state and local and non-U.S. tax consequences to you of purchasing, holding or disposing of first mortgage bonds, including the applicability and effect of the recently enacted Tax Cuts and Jobs Act, any tax treaties and any changes or proposed changes in applicable law.

Subject to the terms and conditions set forth in the underwriting agreement dated the date of this prospectus supplement, we have agreed to sell to each of the underwriters named below, and each of the underwriters has severally, but not jointly, agreed to purchase, the respective principal amounts of first mortgage bonds set forth opposite its name below:

The underwriters have agreed to purchase all of the first mortgage bonds sold under the underwriting agreement if any of the first mortgage bonds are purchased. The underwriting agreement provides that the obligations of the several underwriters to purchase the first mortgage bonds offered by this prospectus supplement are subject to the approval of specified legal matters by their counsel and several other specified conditions. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the non-defaulting underwriter may be increased or the underwriting agreement may be terminated.

The underwriters have advised us that they propose to offer the first mortgage bonds offered by this prospectus supplement to the public at the initial public offering price set forth on the cover of this prospectus supplement and may offer the first mortgage bonds to certain securities dealers at such price less a concession not in excess of % of the principal amount of the first mortgage bonds. The underwriters may allow, and such dealers may reallow, a concession not in excess of % of the principal amount of the first mortgage bonds, on sales to certain other brokers and dealers. After the initial offering of the first mortgage bonds, the underwriters may change the offering price and the other selling terms. The offering of the first mortgage bonds by the underwriters is subject to receipt and acceptance and subject to the underwriters’ right to reject any order in whole or in part.

The following table shows the underwriting discount that we will pay to the underwriters in connection with this offering of first mortgage bonds (expressed as a percentage of the principal amount of the first mortgage bonds):

We estimate that our share of the total expenses of this offering, excluding the underwriting discount, will be approximately $650,000. Prior to the offering, there has been no public market for the first mortgage bonds.

The first mortgage bonds are a new issue of securities with no established trading market. The underwriters have informed us that they may make a market in the first mortgage bonds from time to time. The underwriters are not obligated to do this, and they may discontinue this market making for the first mortgage bonds at any time without notice. Therefore, no assurance can be given concerning the liquidity of the trading market for the first mortgage bonds or that an active market for the first mortgage bonds will develop. We do not intend to apply for listing of the first mortgage bonds on any securities exchange or seek their quotation on any automated quotation system.

In connection with the offering of the first mortgage bonds, the underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the first mortgage bonds. Specifically, the underwriters may

sell a greater number of first mortgage bonds than they are required to purchase in connection with the offering of the first mortgage bonds, creating a syndicate short position. In addition, the underwriters may bid for, and purchase, first mortgage bonds in the open market to cover syndicate short positions or to stabilize the price of the first mortgage bonds. Finally, the underwriting syndicate may reclaim selling concessions allowed for distributing the first mortgage bonds in the offering of the first mortgage bonds, if the syndicate repurchases previously distributed first mortgage bonds in syndicate covering transactions, stabilization transactions or otherwise. Any of these activities may stabilize or maintain the market price of the first mortgage bonds above independent market levels. Neither we nor any of the underwriters make any representations or predictions as to the direction or magnitude of any effect that the transactions described above may have on the price of the first mortgage bonds. The underwriters are not required to engage in any of these transactions and may end any of them at any time.

The underwriters also may impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the underwriters have repurchased first mortgage bonds sold by or for the account of such underwriter in stabilizing or short-covering transactions.

We have agreed to indemnify the several underwriters against certain liabilities, including liabilities under the Securities Act of 1933, as amended, or contribute to payments that each underwriter may be required to make in respect thereof.

It is expected that delivery of the first mortgage bonds will be made against payment for the first mortgage bonds on or about the date specified on the cover page of this prospectus supplement, which is the fifth business day following the date of this prospectus supplement (such settlement cycle being referred to as “T+5”). Under Rule 15c6-1 under the Securities Exchange Act of 1934, as amended, trades in the secondary market generally are required to settle in two business days unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade the first mortgage bonds on the date of this prospectus supplement or the next two business days will be required, by virtue of the fact that the first mortgage bonds initially will settle in T+5, to specify an alternative settlement cycle at the time of any such trade to prevent failed settlement. Purchasers of the first mortgage bonds who wish to trade the first mortgage bonds on the date of this prospectus supplement or the next two business days should consult their own advisors.

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include sales and trading, commercial and investment banking, advisory, investment management, investment research, principal investment, hedging, market making, brokerage and other financial and non-financial activities and services. In the ordinary course of their respective businesses, the underwriters and their affiliates have engaged, and may in the future engage, in other investment banking or commercial banking transactions with us and our affiliates, including acting as lenders under our loan facilities and those of some of our affiliates. They have received or will receive customary fees and commissions for these transactions. U.S. Bancorp Investments, Inc., one of the underwriters, is an affiliate of U.S. Bank National Association, the Mortgage Trustee under the Mortgage Indenture.

In addition, in the ordinary course of their business activities, the underwriters and their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. Certain of the underwriters or their affiliates that have a lending relationship with us routinely hedge their credit exposure to us consistent with their customary risk management policies. Typically, such underwriters and their affiliates would hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities, including potentially the first mortgage bonds offered hereby. Any such short positions could adversely affect future trading prices of the first mortgage bonds offered hereby. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

No action has been or will be taken by us in any jurisdiction other than in the United States that would permit a public offering of the first mortgage bonds or the possession, circulation or distribution of any material relating to us in any jurisdiction where action for such purpose is required. The first mortgage bonds may not be offered or sold, directly or indirectly, nor may any offering material or advertisement in connection with the first mortgage bonds (including this prospectus supplement and the accompanying prospectus and any amendment or supplement hereto or thereto) be distributed or published, in or from any country or jurisdiction, except under circumstances that will result in compliance with any applicable rules and regulations of any such country or jurisdiction.

Legal opinions relating to the first mortgage bonds offered by this prospectus supplement will be rendered by our counsel, James L. Altman, Minneapolis, Minnesota, and Jones Day, Chicago, Illinois, counsel for the Company. Certain legal matters relating to the first mortgage bonds will be passed upon by Hunton Andrews Kurth LLP, New York, New York, for the underwriters. James L. Altman is our Vice President and Deputy General Counsel and is the beneficial owner of less than 1% of the common stock of our parent company, Xcel Energy.

We may offer and sell from time to time, in one or more offerings, together or separately, any combination of the securities listed above and described in this prospectus. We may offer and sell these securities to or through one or more underwriters, dealers and/or agents, or directly to purchasers, on a continuous or delayed basis.

This prospectus describes some of the general terms that may apply to the securities and the general manner in which they may be offered. The specific terms of any securities to be offered, and the specific manner in which they may be offered, will be described in a supplement to this prospectus. This prospectus may not be used to sell securities unless accompanied by a prospectus supplement.

You should carefully consider the risk factors set forth in the applicable prospectus supplement and certain of our filings with the Securities and Exchange Commission before making any decision to invest in any of the securities described in this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

This document is called a “prospectus” and it provides you with a general description of the securities we may offer. Each time we sell securities under this prospectus, we will provide a prospectus supplement containing specific information about the terms of the securities being offered. That prospectus supplement may include a discussion of any risk factors or other special considerations that apply to those securities. The prospectus supplement may also add, update or change the information in this prospectus. If there is any inconsistency between the information in this prospectus and in the prospectus supplement, you should rely on the information in the prospectus supplement. You should read this prospectus and the applicable prospectus supplement together with the additional information described under the caption “Where You Can Find More Information.” We may also prepare free writing prospectuses that describe particular securities. Any free writing prospectus should also be read in connection with this prospectus and with the prospectus supplement referred to therein. For purposes of this prospectus, any reference to an applicable prospectus supplement may also refer to a free writing prospectus, unless the context otherwise requires.

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the “SEC,” using a shelf registration process. As permitted by SEC rules, this prospectus does not contain all of the information included in the registration statement and the accompanying exhibits and schedules we filed with the SEC. You should read the registration statement and the related exhibits and schedules for more information about us and our securities. The registration statement and the related exhibits and schedules can be read at the SEC’s website or at the SEC’s offices. The SEC’s website and street addresses are provided under the caption “Where You Can Find More Information.”

The distribution of this prospectus and the applicable prospectus supplement and the offering of the securities in certain jurisdictions may be restricted by law. Persons into whose possession this prospectus and the applicable prospectus supplement come should inform themselves about and observe any such restrictions. This prospectus and the applicable prospectus supplement do not constitute, and may not be used in connection with, an offer or solicitation by anyone in any jurisdiction in which such offer or solicitation is not authorized or in which the person making such offering or solicitation is not qualified to do so or to any person to whom it is unlawful to make such offer or solicitation.

This prospectus, the applicable prospectus supplement and any free writing prospectus that we prepare or authorize contain and incorporate by reference information that you should consider when making your investment decision. No one is authorized to provide you with information different from that which is contained, or deemed to be contained, in this prospectus and applicable prospectus supplement. We are not making an offer of these securities in any jurisdiction where the offer is not permitted. You should not assume that the information in this prospectus or the documents incorporated by reference is accurate as of any date other than the date on the front of those documents.

Unless otherwise specified or unless the context requires otherwise, all references in this prospectus to “Northern States Power Company,” “NSP,” “we,” “us,” “our,” “the Company,” or similar terms refer to Northern States Power Company.

We file annual, quarterly and current reports and other information with the SEC. Our SEC filings are available to the public on the SEC’s website at http://www.sec.gov. You may also read and copy any document we file with the SEC at the SEC’s Public Reference Room located at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the Public Reference Room.

The SEC allows us to “incorporate by reference” the information we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference our Annual Report on Form 10-K for the year ended December 31, 2017, including information specifically incorporated by reference into our Form 10-K from Xcel Energy Inc.’s definitive Proxy Statement for its 2018 Annual Meeting of Shareholders, and any future filings made with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, from the date of the prospectus until we sell all of the securities (other than, in each case, documents or information deemed to have been furnished and not filed in accordance with SEC rules).

We will provide, without charge, to each person, including any beneficial owner of our securities to whom this prospectus is delivered, upon written or oral request, a copy of any or all documents referred to above that have been incorporated by reference into this prospectus, excluding exhibits to those documents unless they are specifically incorporated by reference into those documents. You may request these documents from:

Our electric production and transmission system is managed as an integrated system with that of Northern States Power Company, a Minnesota corporation, or “NSP-Minnesota”, jointly referred to as the NSP System. The electric production and transmission costs of the entire NSP System are shared by us and NSP-Minnesota. A Federal Energy Regulatory Commission-approved agreement between the two companies, called the Interchange Agreement, provides for the sharing of all generation and transmission costs of the NSP System. Such costs include current and potential obligations of NSP-Minnesota related to its nuclear generating facilities.

Our principal executive offices are located at 1414 W. Hamilton Avenue, Eau Claire, Wisconsin 54701, and our telephone number is (715) 839-2625.

Investing in our securities involves certain risks. You are urged to carefully read and consider the risk factors relating to an investment in our securities described in our annual, quarterly and current reports filed with the SEC under the Securities Exchange Act of 1934, as amended, which are incorporated by reference into this prospectus. Before making an investment decision, you should carefully consider these risks, as well as any other information that we include or incorporate by reference in this prospectus or any prospectus supplement. The prospectus supplement applicable to each type or series of securities we offer may contain a discussion of additional risks applicable to an investment in our securities and the particular type of securities we are offering under that prospectus supplement.

Unless otherwise indicated in the applicable prospectus supplement, we intend to use the net proceeds from the sale of the securities offered by this prospectus for general corporate purposes, including meeting our working capital requirements, funding capital expenditures and acquisitions, repaying short-term debt and refunding long-term debt at maturity or otherwise. Until the net proceeds from the sale of the offered securities have been used, we may invest them temporarily in interest-bearing obligations.

For purposes of computing the ratio of consolidated earnings to consolidated fixed charges, (1) earnings consist of pre-tax income from continuing operations plus fixed charges; and (2) fixed charges consist of interest on long-term debt, other interest charges, the interest component on leases and amortization of debt discount, premium and expense.

The description below contains a summary of selected provisions of the indenture, including supplemental indentures, under which the first mortgage bonds will be issued. This summary is not complete. The indenture and the form of supplemental indenture applicable to the first mortgage bonds have been filed as exhibits to the registration statement of which this prospectus constitutes a part. You should read them for provisions that may be important to you. In the summary below, we have included references to section numbers of the indenture so that you can easily locate these provisions.

We are not required to issue future issues of indebtedness under the indenture described below. We are free to use other indentures or documentation, containing provisions different from those described in this prospectus, in connection with future issues of other indebtedness not issued under this prospectus.

The first mortgage bonds will be represented either by global securities registered in the name of The Depository Trust Company, or DTC, as depository, or Depository, or its nominee, or by securities in certificated form issued to the registered owners, as set forth in the applicable prospectus supplement. See the information under the caption “Book-Entry System” in this prospectus.

We may issue the first mortgage bonds from time to time in one or more new series under the Supplemental and Restated Trust Indenture dated March 1, 1991, which we refer to as the Restated Indenture, as previously supplemented by nine supplemental trust indentures and as to be supplemented by one or more new supplemental indentures for the first mortgage bonds, which we collectively refer to as the Mortgage Indenture, all from us to U.S. Bank National Association, as successor trustee, which we refer to as the Mortgage Trustee. The Mortgage Indenture will govern the first mortgage bonds offered by this prospectus. As of December 31, 2017, there were five series of first mortgage bonds in an aggregate principal amount of $750 million outstanding under the Mortgage Indenture.

The holders of the outstanding first mortgage bonds do not, and, unless the prospectus supplement that describes a particular series of first mortgage bonds provides otherwise with respect to that series, the holders of any first mortgage bonds offered by this prospectus will not, have the right to require us to repurchase the first mortgage bonds if we become involved in a highly leveraged or change in control transaction. The Mortgage Indenture does not have any provision that is designed specifically in response to highly leveraged or change in control transactions.

When we offer to sell a particular series of first mortgage bonds, we will describe the specific terms of that series in a prospectus supplement relating to that series, including the following terms:

Unless the prospectus supplement that describes a particular series of first mortgage bonds provides otherwise, we may from time to time, without the consent of the holders of that series of first mortgage bonds, reopen such series of first mortgage bonds and issue additional first mortgage bonds with the same terms (including maturity and interest payment terms) as such series of first mortgage bonds.

Unless the prospectus supplement that describes a particular series of first mortgage bonds provides otherwise, the amount of interest payable will be computed on the basis of a 360-day year of twelve 30-day months. In the event that any date on which such interest is payable on the first mortgage bonds is not a business day, then payment of the interest payable on such date will be made on the next succeeding day which is a business day (and without any interest or other payment in respect of any such delay), with the same force and effect as if made on such date.

The prospectus supplement that describes a particular series of first mortgage bonds will set forth any terms for the optional or mandatory redemption of that particular series.

The first mortgage bonds being issued pursuant to this prospectus will be secured equally and ratably with all of our other outstanding first mortgage bonds, subject to the provisions relating to any sinking fund for any particular series of first mortgage bonds, by a valid and direct first mortgage lien on all of the real and fixed properties, leasehold rights, franchises and permits then owned by us subject only to permitted encumbrances (as discussed below). The lien of the Mortgage Indenture does not cover securities, cash, contracts, receivables, motor vehicles, merchandise, equipment and supplies and specified non-utility property.

The Mortgage Indenture subjects to the lien of the Mortgage Indenture all of our property, rights and franchises, except as otherwise expressly provided. These provisions might not be effective as to property acquired within 90 days prior and subsequent to the filing of a case by us under the U.S. Bankruptcy Code.

We have not made any appraisal of the properties subject to the lien of the Mortgage Indenture. The value of the properties in the event of liquidation will depend on market and economic conditions, the availability of buyers and other factors.

The Mortgage Indenture provides that no liens prior or equal to the lien of the Mortgage Indenture, other than permitted encumbrances, may be created or permitted to exist on the mortgaged and pledged property whether now owned or acquired in the future. (Section 8.04 of the Restated Indenture.)

With the consent of the holders of 66 2/3% of the principal amount of first mortgage bonds outstanding, the Company may (1) permit the creation or existence of a prior lien with respect to up to 50% of the sum of our depreciable property and land, after giving effect to the prior lien and the acquisition of the property subject to the prior lien or (2) terminate the lien of the Mortgage Indenture with respect to up to 50% of the sum of our depreciable property and land. (Section 19.02(e) of the Restated Indenture.)

We currently do not have any outstanding first mortgage bonds that are, and, unless the prospectus supplement that describes a particular series of first mortgage bonds provides otherwise with respect to that series, the first mortgage bonds offered by this prospectus will not be, subject to a sinking fund.

As a maintenance fund for the first mortgage bonds, we have agreed to pay to the Mortgage Trustee on each May 1 an amount equal to 2.50% of our completed depreciable property as of the end of the preceding calendar year, after deducting credits at our option for the following:

We may withdraw moneys from the maintenance fund in amounts equal to retirements of first mortgage bonds and permanent additions. Cash on deposit in the maintenance fund may be used for the purchase or redemption of first mortgage bonds. Any redemption of this nature would be at the applicable regular redemption price of the first mortgage bonds to be redeemed and subject to any restrictions on the redemption of the first mortgage bonds. (Sections 9.03 and 9.04 of the Restated Indenture).

The Restated Indenture further provides that to the extent that maintenance fund credits exceed 2.50% of our completed depreciable property for any year after 1990, such excess credits may be applied in future years (1) to offset any maintenance fund deficiency or (2) to increase the amount of established permanent additions available for use under the Mortgage Indenture in an aggregate amount equal to the lesser of such excess credits or the amount of permanent additions used after 1990 for the maintenance fund. (Section 9.05 of the Restated Indenture.)

We have agreed to maintain our properties in adequate repair, working order and condition. (Section 8.06 of the Restated Indenture.)

The maximum principal amount of first mortgage bonds that we may issue under the Mortgage Indenture is not limited, except as described below. We may issue additional first mortgage bonds in an aggregate principal amount not exceeding (1) 66 2/3% of the cost or fair value, whichever is less, of permanent additions after deducting retirements (Article V of the Restated Indenture); (2) the aggregate principal amount of retired first mortgage bonds, which have not been otherwise used under the Mortgage Indenture (Article VI of the Restated Indenture); or (3) the amount of cash deposited with the Mortgage Trustee, which cash may be withdrawn on the same basis as additional first mortgage bonds may be issued under clauses (1) and (2) above (Article VII of the Restated Indenture).

At December 31, 2017, the amount of net permanent additions available for the issuance of first mortgage bonds was approximately $1.767 billion, which could be used to authenticate up to approximately $1.178 billion principal amount of the first mortgage bonds. As of December 31, 2017, $11.000 million of retired first mortgage bonds were available to authenticate up to $11.000 million of first mortgage bonds.

We may not issue any additional first mortgage bonds on the basis of clause (1), clause (2) under specified conditions or clause (3) above, unless the earnings applicable to bond interest for a specified 12-month period are equal to at least twice the annual interest requirements on the first mortgage bonds, including those about to be issued, any permitted indebtedness and any obligations secured by prior liens. (Sections 1.03, 5.03, 5.06, 6.02 and 7.01 of the Restated Indenture.) The calculation of earnings applicable to bond interest includes all of our gross revenue, including our nonutility revenues. (Section 1.03 of the Restated Indenture.)

Earnings applicable to bond interest for the 12 months ended December 31, 2017 would be 4.30 times the annual interest requirements on our first mortgage bonds and any obligations secured by prior liens and any permitted indebtedness secured by permitted encumbrances. Additional first mortgage bonds may vary as to maturity, interest rate, redemption prices and sinking fund provisions, among other things. (Article II of the Restated Indenture.)

The Mortgage Indenture does not restrict our ability to pay dividends on our common stock.

The Mortgage Indenture permits the release from its lien of any property upon depositing or pledging cash or certain other property of comparable fair value. The Mortgage Indenture also permits the following, in each case without any release or consent by the Mortgage Trustee or accountability to the Mortgage Trustee for any consideration received by us:

Any of the mortgaged and pledged property may be released from the lien of the Mortgage Indenture if, after the release, the fair value of the remaining mortgaged and pledged property of the character of permanent additions equals or exceeds a sum equal to 150% of the aggregate principal amount of first mortgage bonds outstanding. (Section 11.03(k) of the Restated Indenture.) Upon satisfaction of the requirements set forth in the Mortgage Indenture, this provision would permit us to spin off or otherwise dispose of a substantial amount of assets or a line of business, including all or a portion of our electric generation, transmission or distribution assets, or our gas storage and distribution assets, without depositing cash or property with the Mortgage Trustee or obtaining the consent of the holders of the first mortgage bonds.

We and the Mortgage Trustee may modify and amend the Mortgage Indenture from time to time. We will not need the consent of the holders of the first mortgage bonds for the following types of amendments, among others:

With our consent, other provisions of the Mortgage Indenture may be changed by the affirmative vote of the holders of 66 2/3% in principal amount of the first mortgage bonds outstanding except that, among other things, the following may not be done without the consent of the holder of each first mortgage bond so affected:

The following is a summary of events defined in the Mortgage Indenture as completed defaults:

Notice of Default. The Mortgage Trustee is required to give notice to bondholders within 90 days after the occurrence of a default, unless the default has been cured or waived before giving its notice; provided that, except in the case of a default in payment of principal or interest on any first mortgage bond or to make any sinking fund payment, the Mortgage Trustee may withhold the notice if it determines in good faith that withholding the notice is in the interest of the bondholders. Any notice of default of the covenants contained in Section 8.11 of the Restated Indenture regarding bankruptcy, insolvency, assignment or receivership may not be given until at least 90 days after the occurrence of the default. (Section 17.02 of the Restated Indenture.)

Acceleration of Maturity. In case of a completed default, the Mortgage Trustee may, and upon request of the holders of 25% in principal amount of the first mortgage bonds outstanding will, declare the first mortgage bonds due and payable, subject to the right of the holders of a majority of the first mortgage bonds then-outstanding to rescind or annul such action. Further, the Mortgage Trustee is obligated to take the actions provided in the Mortgage Indenture to enforce payment of the first mortgage bonds and the lien of the Mortgage Indenture upon being requested to do so by the holders of a majority in principal amount of the first mortgage bonds. However, the holders of a majority in principal amount of the first mortgage bonds may direct the taking

of any of these actions or the refraining from these actions as is not in violation of the law or the Mortgage Indenture. Before taking these actions, the Mortgage Trustee may require adequate indemnity against the costs, expenses and liabilities to be incurred in connection with these actions. (Article XIV of the Restated Indenture.)

Compliance Certificate. We are required to furnish with the Mortgage Trustee information, documents and reports regarding our compliance with the conditions and covenants of the Mortgage Indenture as may be required by the rules and regulations of the SEC, including a certificate, furnished at least annually, as to whether, to the knowledge of the officer signing such certificate, we are in compliance with the conditions and covenants under the Mortgage Indenture. (Section 8.18 of the Restated Indenture.)

Whenever all indebtedness secured by the Mortgage Indenture has been paid, or adequate provision for payment has been made, the Mortgage Trustee will cancel and discharge the Mortgage Indenture. (Article XVIII of the Restated Indenture.) We may deposit with the Mortgage Trustee any combination of cash or government obligations in order to provide for the payment of any series or all of the first mortgage bonds outstanding. This deposit could constitute a taxable event as to holders of those first mortgage bonds, creating possible adverse tax consequences. The Mortgage Indenture also provides that we must furnish to the Mortgage Trustee officers’ certificates, certificates of an engineer, appraiser or other expert and, in some cases, accountants’ certificates in connection with the authentication of first mortgage bonds, the release or release and substitution of property and some other matters, and opinions of counsel as to the lien of the Mortgage Indenture and some other matters. (Articles IV, V, VI, VII, XI and XVIII and Section 21.08 of the Restated Indenture.)

U.S. Bank National Association is the Mortgage Trustee under the Mortgage Indenture. We maintain banking relationships with the Mortgage Trustee in the ordinary course of business. The Mortgage Trustee also acts as trustee for our senior unsecured debt securities discussed below under “Description of the Senior Unsecured Debt Securities.”

The Mortgage Indenture and first mortgage bonds to be issued pursuant to this prospectus are governed by, and construed in accordance with, the laws of the State of Wisconsin.

The description below contains a summary of selected provisions of the indenture, including supplemental indentures, under which the senior unsecured debt securities, which we refer to as debt securities, will be issued. This summary is not complete. The indenture and the form of supplemental indenture applicable to the debt securities have been filed as exhibits to the registration statement of which this prospectus is a part. You should read them for provisions that may be important to you. In the summary below, we have included references to section numbers of the indenture so that you can easily locate these provisions.

The debt securities will be represented either by global securities registered in the name of DTC, as Depository, or its nominee, or by securities in certificated form issued to the registered owners, as set forth in the applicable prospectus supplement. See the information under the caption “Book-Entry System” in this prospectus.

We may issue the debt securities from time to time in one or more new series under the Indenture dated September 1, 2000, as previously supplemented by one supplemental indenture and as to be supplemented by one or more new supplemental indentures for the debt securities, which we collectively refer to as the Senior Indenture, all from us to U.S. Bank National Association, as successor trustee, which we refer to as the Senior Trustee. The Senior Indenture will govern the debt securities offered by this prospectus. As of December 31, 2017, there were no debt securities outstanding under the Senior Indenture.

The holders of the outstanding debt securities do not, and, unless the supplemental indenture that describes a particular series of debt securities provides otherwise with respect to that series, the holders of any debt securities offered by this prospectus will not, have the right to require us to repurchase the debt securities if we become involved in a highly leveraged or change in control transaction. The Senior Indenture does not have any provision that is designed specifically in response to highly leveraged or change in control transactions.

The debt securities will be our senior unsecured obligations and will rank on a parity with our other existing and future senior unsecured indebtedness. Our secured debt will have a prior claim on the assets pledged to secure such debt and, therefore, our debt securities will be effectively subordinated to all of our current and future secured debt, including our first mortgage bonds to the extent of the value of the properties securing them. As of December 31, 2017, we had $750 million of secured debt outstanding. The amount of debt securities that we may issue under the Senior Indenture is not limited.

When we offer to sell a particular series of debt securities, we will describe the specific terms of that series in a prospectus supplement relating to that series, including the following terms:

Unless the prospectus supplement that describes a particular series of debt securities provides otherwise, we may from time to time, without the consent of the holders of that series of debt securities, reopen such series and issue additional debt securities with the same terms (including maturity and interest payment terms) as such series of debt securities.

Unless the prospectus supplement that describes a particular series of debt securities provides otherwise, the amount of interest payable will be computed on the basis of a 360-day year of twelve 30-day months. In the event that any date on which such interest is payable on the debt securities is not a business day, then payment of the interest payable on such date will be made on the next succeeding day which is a business day (and without any interest or other payment in respect of any such delay), with the same force and effect as if made on such date.

Debt securities of any series may be exchanged for one or more new securities of any authorized denomination and of like aggregate principal amount, series and stated maturity and having the same terms and issue date or dates. (Section 2.6 of the Senior Indenture).

Unless the prospectus supplement that describes a particular series of debt securities provides otherwise with respect to that series, debt securities may be presented for registration of transfer (duly endorsed or accompanied by a duly executed written instrument of transfer) at the office of the Senior Trustee maintained for that purpose and referred to in the applicable prospectus supplement, without service charge and upon payment of any taxes and other governmental charges as described in the Senior Indenture. Any transfer or exchange will be effected upon the Senior Trustee’s satisfaction with the documents of title and indemnity of the person making the request. (Sections 2.6 and 2.7 of the Senior Indenture.)

The Senior Trustee will not be required to exchange or register a transfer of any debt securities of a series selected, called or being called for redemption except, in the case of any debt security to be redeemed in part, the portion of that debt security not to be so redeemed. (Section 2.6 of the Senior Indenture.) See the information under the caption “Book-Entry System.”

Principal, interest and premium, if any, on debt securities issued in the form of global securities will be paid in the manner described below under the caption “Book-Entry System.” Unless the prospectus supplement that describes a particular series of debt securities provides otherwise with respect to that series, principal, interest and premium, if any, on debt securities that are in the form of certificated securities will be paid by check mailed to the holder at that person’s address as it appears in the register for the debt securities maintained by the Senior Trustee; however, a holder of $10,000,000 or more of the debt securities having the same interest payment dates will be entitled to receive payments of interest by wire transfer, if appropriate wire transfer instructions have been received by the Senior Trustee on or prior to the applicable record date. Unless the prospectus supplement that describes a particular series of debt securities provides otherwise with respect to that series, the principal, interest at maturity and premium, if any, on debt securities in the form of certificated securities will be payable in immediately available funds at the office of the Senior Trustee. (Section 2.12 of the Senior Indenture.)

All monies paid by us to a paying agent for the payment of principal, interest or premium, if any, on any debt securities that remain unclaimed at the end of two years after that principal, interest or premium has become due and payable will be repaid to us, and the holder of those debt securities will thereafter look only to us for payment of that principal, interest or premium. (Section 4.4 of the Senior Indenture.)

The following is a summary of events that constitute events of default under the Senior Indenture:

If an event of default occurs and is continuing, either the Senior Trustee or the holders of a majority in principal amount of the outstanding debt securities may declare the principal amount of all debt securities to be due and payable immediately. At any time after an acceleration of the debt securities has been declared, but before a judgment or decree of the immediate payment of the principal amount of the debt securities has been obtained, if we pay or deposit with the Senior Trustee a sum sufficient to pay all matured installments of interest and the principal and any premium that has become due otherwise than by acceleration and all defaults have been cured or waived, then that payment or deposit will cause an automatic rescission and annulment of the acceleration of the debt securities. (Section 7.1 of the Senior Indenture.)

The Senior Trustee generally will be under no obligation to exercise any of its rights or powers under the Senior Indenture at the request or direction of any of the holders of debt securities unless such holders have offered reasonable indemnity to the Senior Trustee. (Section 8.2 of the Senior Indenture.) The holders of a majority in principal amount of the outstanding debt securities generally will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the Senior Trustee, or of exercising any trust or power conferred on the Senior Trustee, relating to the debt securities. (Section 7.7 of the Senior Indenture.) Each holder of a debt security has the right to institute a proceeding relating to the Senior Indenture, but this right is subject to conditions precedent specified in the Senior Indenture. (Section 7.4 and 7.7 of the Senior Indenture.) The Senior Trustee is required to give the holders of the debt securities notice of the occurrence of a default within 90 days of the occurrence of the default, unless the default is cured. Except in the case of a payment default on any debt securities, however, the Senior Trustee may withhold notice if it determines in good faith that it is in the interest of such holders to do so. (Section 7.8 of the Senior Indenture.) We are required to deliver to the Senior Trustee each year a certificate as to whether, to the knowledge of the officers signing such certificate, we are in compliance with the conditions and covenants under the Senior Indenture. (Section 5.5 of the Senior Indenture.)

We and the Senior Trustee may modify and amend the Senior Indenture from time to time.

We will not need the consent of the holders of debt securities for the following types of amendments, among others:

We will need the consent of the holders of each debt security so affected to do any of the following, among others:

Additionally, we may not modify these requirements or reduce the percentage of outstanding securities necessary to consent to the modification or amendment of the Senior Indenture or to waive past defaults without the consent of the holders of all of the outstanding debt securities.

Amendments requiring holders’ consent, other than those described in the above paragraph, will require the approval of the holders of a majority in aggregate principal amount of the outstanding securities. (Section 12.2 of the Senior Indenture.)

We may be discharged from all obligations relating to the debt securities and the Senior Indenture (except for specified obligations such as obligations to register the transfer or exchange of debt securities, replace stolen, lost or mutilated debt securities and maintain paying agencies) if we irrevocably deposit with the Senior Trustee, in trust for the benefit of holders of debt securities, cash or U.S. government obligations (or any combination thereof) sufficient to make all payments of principal, premium, if any, and interest on all outstanding debt securities on the dates those payments are due. To discharge these obligations, we must deliver to the Senior Trustee an opinion of counsel that the holders of the debt securities will not recognize income, gain or loss for federal income tax purposes as a result of the defeasance or discharge of the Senior Indenture. If we discharge our obligations as described above, the holders of debt securities must look only to the funds deposited with the Senior Trustee, and not us, for payments on the debt securities. (Section 4.1 of the Senior Indenture.)

We will not merge into any other corporation or sell or otherwise transfer all or substantially all of our assets unless (1) the successor or transferee corporation assumes by supplemental indenture our obligations to pay the principal, interest and premium, if any, on all of the debt securities and our obligation to perform every covenant of the Senior Indenture that we are to perform or observe and (2) we or the successor or transferee corporation, as applicable, are not, immediately following such merger, sale or transfer, in default in the performance of any of those covenants. Upon any merger, sale or transfer of all or substantially all of our assets, the successor or transferee corporation will succeed to, and be substituted for, and may exercise all of our rights and powers under the Senior Indenture with the same effect as if the successor corporation had been named as us in the Senior Indenture, and we will be released from all obligations under the Senior Indenture. Unless the prospectus supplement that describes a particular series of debt securities provides otherwise with respect to that series, the Senior Indenture will define all or substantially all of our assets as being 50% or more of our total assets as shown on our balance sheet as of the end of the prior calendar year and specifically will permit any sale, transfer or disposition during a calendar year of less than 50% of our total assets without the consent of the holders of the securities. (Sections 11.1 and 11.2 of the Senior Indenture.)

Unless the prospectus supplement that describes a particular series of debt securities provides otherwise with respect to that series, the Senior Indenture will not contain any financial or other similar restrictive covenants.

The Senior Trustee may resign at any time by notifying us in writing and specifying the day upon which the resignation is to take effect. The resignation will not take effect, however, until a successor trustee has been appointed. (Section 8.10 of the Senior Indenture.)

The holders of a majority in principal amount of the outstanding securities may remove the Senior Trustee at any time. In addition, so long as no event of default or event that, with the giving of notice or lapse of time or both, would become an event of default has occurred and is continuing, we may remove the Senior Trustee upon notice to the holder of each debt security outstanding and appointment of a successor Senior Trustee. (Section 8.10 of the Senior Indenture.)

U.S. Bank National Association is the Senior Trustee. We maintain banking relationships with the Senior Trustee in the ordinary course of business. The Senior Trustee also acts as trustee for our first mortgage bonds discussed above under “Description of the First Mortgage Bonds.”

Unless otherwise specified in the applicable prospectus supplement, each series of securities offered by this prospectus will be issued as fully-registered global securities representing all or part of that series of securities. This means that we will not issue certificates for that series of securities to the holders. Instead, a global security representing that series of securities will be deposited with, or on behalf of, DTC or its successor, as the depository. The global securities will be registered at the request of DTC in the name of Cede & Co., DTC’s nominee, or such other name as may be requested by an authorized representative of DTC.

DTC will keep an electronic record of its participants (for example, your broker) whose clients have purchased securities represented by a global security. Unless a global security is exchanged in whole or in part for a certificated security, a global security may not be transferred, except that DTC, its nominees and successors may transfer a global security as a whole to one another.

Beneficial interests in global securities will be shown on, and transfers of interests will be made only through, records maintained by DTC and its participants. The laws of some jurisdictions require that some purchasers take physical delivery of securities in definitive form. These laws may impair the ability to transfer beneficial interests in a global security.

We will make payments of principal, interest, if any, and premium, if any, to DTC or its nominee. We, the applicable trustee and any paying agent will treat DTC or its nominee as the owner of the global security for all purposes, including any notices and voting. Accordingly, neither we nor any trustee nor any paying agent will have any direct responsibility or liability to pay amounts due on a global security to owners of beneficial interests in a global security.

DTC is a limited-purpose trust company organized under the New York Banking Law, a “banking organization” within the meaning of the New York Banking Law, a member of the Federal Reserve System, a “clearing corporation” within the meaning of the New York Uniform Commercial Code and a “clearing agency” registered pursuant to the provisions of Section 17A of the Exchange Act. DTC holds securities that its participants, or “direct participants,” deposit with DTC. DTC also facilitates the post-trade settlement among direct participants of sales and other securities transactions in deposited securities through electronic computerized book-entry transfers and pledges between direct participants’ accounts. This eliminates the need for physical movement of securities certificates. Direct participants include both U.S. and non-U.S. securities brokers and dealers, banks, trust companies, clearing corporations and certain other organizations. DTC is a wholly owned subsidiary of The Depository Trust & Clearing Corporation, or “DTCC.” DTCC is the holding company for DTC, National Securities Clearing Corporation and Fixed Income Clearing Corporation, all of which are registered clearing agencies. DTCC is owned by the users of its regulated subsidiaries. Access to the DTC system is also available to others such as both U.S. and non-U.S. securities brokers and dealers, banks, trust companies and clearing corporations that clear through or maintain a custodial relationship with a direct participant either directly or indirectly, an “indirect participant.” Direct participants and indirect participants are referred to collectively as “participants.” The DTC Rules applicable to its participants are on file with the SEC.

Purchases of global securities under the DTC system must be made by or through direct participants, which will receive a credit for the securities on DTC’s records. The ownership interest of each actual purchaser of each security, or “beneficial owner,” is in turn to be recorded on the direct and indirect participants’ records. Beneficial owners will not receive written confirmation from DTC of their purchase. Beneficial owners are, however, expected to receive written confirmations providing details of the transaction, as well as periodic statements of their holdings, from the direct or indirect participant through which the beneficial owner entered into the transaction. Transfers of ownership interests in the global securities are to be accomplished by entries made on the books of direct and indirect participants acting on behalf of beneficial owners. Beneficial owners will not receive certificates representing their ownership interests in the global securities, except in the event that use of the book-entry system for the global securities is discontinued.

To facilitate subsequent transfers, all securities deposited by direct participants with DTC are registered in the name of Cede & Co. or such other name as may be requested by an authorized representative of DTC. The deposit of securities with DTC and their registration in the name of Cede & Co. or such other nominee do not effect any change in beneficial ownership. DTC has no knowledge of the actual beneficial owners of the securities. DTC’s records reflect only the identity of the direct participants to whose accounts such securities are credited, which may or may not be the beneficial owners. The direct and indirect participants remain responsible for keeping account of their holdings on behalf of their customers.

Conveyance of notices and other communications by DTC to direct participants, by direct participants to indirect participants and by direct participants and indirect participants to beneficial owners will be governed by arrangements among them, subject to any statutory or regulatory requirements as may be in effect from time to time.

If a particular series of securities is redeemable at our option or at the option of the holder, redemption notices will be sent to DTC. If less than all of the securities of a series are being redeemed, DTC’s practice is to determine by lot the amount of the interest of each direct participant in such series to be redeemed. Redemption proceeds and distributions on global securities will be made to Cede & Co. or such other nominee as may be requested by an authorized representative of DTC. Upon DTC’s receipt of funds and corresponding detail information from us, any trustee or any paying agent, DTC’s practice is to credit direct participants’ accounts in accordance with the holdings information shown on DTC’s records on the payment date. Payments by participants to beneficial owners of securities will be governed by standing instructions and customary practices, as is the case with securities held for the accounts of customers in bearer form or registered in “street name.” Payments will be the responsibility of such participant and not of DTC nor its nominee, any trustee, any paying agent or us, subject to any statutory or regulatory requirements. Payment of redemption proceeds and distributions to Cede & Co. or such other nominee as may be requested by an authorized representative of DTC is the responsibility of us, the applicable trustee or the applicable paying agent, disbursement of such payments to direct participants will be the responsibility of DTC, and disbursement of such payments to the beneficial owners will be the responsibility of direct and indirect participants.

Neither DTC nor Cede & Co. or any other DTC nominee will consent or vote with respect to global securities unless authorized by a direct participant in accordance with DTC’s procedures. Under its usual procedures, DTC mails an omnibus proxy to us as soon as possible after the record date. The omnibus proxy assigns Cede & Co.’s consenting or voting rights to those direct participants to whose accounts the securities are credited on the record date as identified in a listing attached to the omnibus proxy.

Global securities will be exchangeable for corresponding certificated securities registered in the name of persons other than DTC or its nominee if (1) DTC (a) notifies us that it is unwilling or unable to continue as depository for any of the global securities or (b) at any time ceases to be a clearing agency registered under the Exchange Act, (2) an event of default occurs and is continuing with respect to the applicable series of securities or (3) we execute and deliver to the applicable trustee an order that the global securities will be so exchangeable.

The information in this section concerning DTC and DTC’s book-entry system has been obtained from DTC, and we and any underwriters, dealers or agents are not responsible for the accuracy of the information or for the performance by DTC of its obligations under the rules and procedures governing its operations or otherwise.

Any underwriters, dealers or agents of any securities may be direct participants of DTC.

We may sell the securities offered under this prospectus through underwriters or dealers, through agents or directly to one or more purchasers. The terms under which the securities are offered and the method of distribution will be set forth in the applicable prospectus supplement.

Underwriters, dealers and agents that participate in the distribution of the securities offered under this prospectus may be underwriters as defined in the Securities Act of 1933, as amended, the “Securities Act,” and any discounts or commissions received by them from us and any profit on the resale of the offered securities by them may be treated as underwriting discounts and commissions under the Securities Act. Any underwriters or agents will be identified and their compensation, including any underwriting discount or commission, will be described in the applicable prospectus supplement. The applicable prospectus supplement will also describe other terms of the offering, including the initial public offering price and any discounts or concessions allowed or reallowed to dealers.

The distribution of the securities described in this prospectus may be effected from time to time in one or more transactions at a fixed price or prices, which may be changed, at market prices prevailing at the time of sale, at prices related to the prevailing market prices or at negotiated prices.

We may determine the price or other terms of the securities offered under this prospectus by use of an electronic auction. We will describe in the applicable prospectus supplement how any auction will be conducted to determine the price or any other terms of the securities, how potential investors may participate in the auction and, where applicable, the nature of the underwriters’ obligations with respect to the auction.

Each series of securities will be a new issue of securities and will have no established trading market. Any underwriters to whom securities are sold for public offering and sale may make a market in such securities, but such underwriters will not be obligated to do so and may discontinue any market making at any time without notice. The securities may or may not be listed on a national securities exchange.

Under agreements into which we may enter in connection with the sale of the securities, underwriters, dealers and agents who participate in the distribution of the securities may be entitled to indemnification by us against specified liabilities, including liabilities under the Securities Act.

Unless otherwise indicated in the applicable prospectus supplement, legal opinions relating to the validity of the securities being offered by this prospectus will be rendered by our counsel, James L. Altman, Minneapolis, Minnesota. Unless otherwise indicated in the prospectus supplement relating to a particular series of securities, certain legal matters will be passed upon for the underwriters, dealers or agents named in a prospectus supplement by Hunton Andrews Kurth LLP, New York, New York. James L. Altman is the Vice President and Deputy General Counsel of Xcel Energy Services Inc., and is the beneficial owner of less than 1% of the common stock of our parent company, Xcel Energy Inc.

The consolidated financial statements, and the related financial statement schedule, incorporated in this prospectus by reference from Northern States Power Company’s, a Wisconsin corporation, Annual Report on Form 10-K have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report, which is incorporated herein by reference. Such consolidated financial statements and financial statement schedule have been so incorporated in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.


	Page
Special Note Regarding Forward-Looking Statements		S-1
Prospectus Supplement Summary		S-3
Risk Factors		S-6
Use of Proceeds		S-7
Ratio of Consolidated Earnings to Consolidated Fixed Charges		S-7
Selected Consolidated Financial Data		S-8
Critical Accounting Policies		S-10
Liquidity and Capital Resources		S-15
Supplemental Description of the First Mortgage Bonds		S-18
Certain Material U.S. Federal Income Tax Considerations		S-21
Underwriting		S-26
Legal Opinions		S-29
Prospectus
About This Prospectus		i
Where You Can Find More Information		ii
Our Company		1
Risk Factors		1
Use of Proceeds		1
Ratio of Consolidated Earnings to Consolidated Fixed Charges		1
Description of the First Mortgage Bonds		2
Description of the Senior Unsecured Debt Securities		8
Book-Entry System		14
Plan of Distribution		16
Legal Opinions		17
Experts		17


	Six Months Ended June 30, 2018		Year Ended December 31,
	Six Months Ended June 30, 2018		2017		2016		2015		2014		2013
Ratio of Consolidated Earnings to Consolidated Fixed Charges		4.2		4.5		4.2		4.6		4.8		4.4


	Six months ended June 30,				Year ended December 31,
	2018		2017 ^(a)		2017		2016		2015
	(unaudited)
	(Thousands of Dollars)
Consolidated Statements of Income Data:
Operating revenues	$	504,898	$	494,957	$	1,005,451	$	957,233	$	956,541
Operating expenses		428,432		421,759		857,223		817,305		816,582

Operating income		76,466		73,198		148,228		139,928		139,959

Other income, net		3,232		2,011		7,540		4,738		8,136
Interest charges and financing costs		17,513		16,039		32,180		32,629		29,221
Income taxes		15,580		22,510		44,172		42,902		44,238

Net income	$	46,605	$	36,660	$	79,416	$	69,135	$	74,636


	June 30, 2018		December 31,
	June 30, 2018		2017		2016
	(unaudited)
	(Thousands of Dollars)
Consolidated Balance Sheet Data:
Current assets	$	187,250	$	207,682	$	175,386
Property, plant and equipment, net		2,150,296		2,088,728		1,947,637
Other assets		282,835		285,310		289,817

Total assets	$	2,620,381	$	2,581,720	$	2,412,840

Current portion of long-term debt	$	151,067	$	151,080	$	1,123
Short-term debt and notes payable to affiliates		30,500		11,500		60,500
Other current liabilities		180,636		177,154		174,196

Total current liabilities		362,203		339,734		235,819

Deferred credits and other liabilities		753,704		755,297		703,225
Long-term debt		610,161		610,100		661,946
Common stockholder’s equity		894,313		876,589		811,850

Total liabilities and equity	$	2,620,381	$	2,581,720	$	2,412,840


	Pension Costs
	+1%			-1%
	(Millions of Dollars)
Rate of Return	$	(1.3	)	$	1.3
Discount Rate ^(a)	$	(0.8	)	$	1.0


	Six months ended June 30,				Year ended December 31,
	2018		2017		2017		2016
	(Thousands of Dollars)
Net cash provided by operating activities	$	126,985	$	127,943	$	179,737	$	200,732


	Payments Due by Period
Contractual Obligations	Total		Less than 1 Year		1 – 3 Years		3 – 5 Years		After 5 Years
	(Thousands of Dollars)
Long-term debt, principal and interest payments ⁽¹⁾	$	1,291,145	$	184,941	$	55,951	$	73,729	$	976,524
Operating leases		8,941		943		1,782		1,663		4,553
Unconditional purchase obligations ⁽²⁾		104,258		29,055		24,357		19,570		31,276
Other long-term obligations, including current portion ⁽³⁾		7,076		2,655		3,777		644		—
Payments to vendors in process		3,300		3,300		—		—		—
Short-term debt		11,000		11,000		—		—		—

Total contractual cash obligations ^(4)(5)(6)	$	1,425,720	$	231,894	$	85,867	$	95,606	$	1,012,353


Underwriters		Principal amount of the first mortgage bonds
Mizuho Securities USA LLC		$
U.S. Bancorp Investments, Inc.


Total		$


	Page
ABOUT THIS PROSPECTUS		i

WHERE YOU CAN FIND MORE INFORMATION		ii

OUR COMPANY		1

RISK FACTORS		1

USE OF PROCEEDS		1

RATIO OF CONSOLIDATED EARNINGS TO CONSOLIDATED FIXED CHARGES		1

DESCRIPTION OF THE FIRST MORTGAGE BONDS		2

DESCRIPTION OF THE SENIOR UNSECURED DEBT SECURITIES		8

BOOK-ENTRY SYSTEM		14

PLAN OF DISTRIBUTION		16

LEGAL OPINIONS		17

EXPERTS		17


Mizuho Securities		US Bancorp