SC 13D/A

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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

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                                 SCHEDULE 13D/A
                                 (RULE 13d-101)

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                                 AMENDMENT NO. 7

                       COGENERATION CORPORATION OF AMERICA
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                                (Name of Issuer)

                     Common Stock, par value $.01 per share
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                         (Title of Class of Securities)

                                 628950 10 7
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                                (CUSIP number)

         James J. Bender                         John P. Moore, Jr.
Vice President and General Counsel              Corporate Secretary
         NRG Energy, Inc.                  Northern States Power Company
  1221 Nicollet Mall, Suite 700           414 Nicollet Mall, Fourth Floor
      Minneapolis, MN 55403                    Minneapolis, MN 55401
          (612) 373-5300                           (612) 330-5500
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                  (Name, address and telephone number of person
                authorized to receive notices and communications)

                               October 27, 1998
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             (Date of event which requires filing of this statement)

         If the filing person has previously filed a statement on Schedule 13G
to report the acquisition which is the subject of this Schedule 13D, and is
filing this schedule because of Rule 13d-1(b)(3) or (4), check the following box
/ /.

         Note. Six copies of this statement, including all exhibits, should be
filed with the Commission. See Rule 13d-1(a) for other parties to whom copies
are to be sent.

         *The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which would
alter disclosures provided in a prior cover page.

         The information required on the remainder of this cover page shall not
be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of
the Act but shall be subject to all other provisions of the Act (however, see
the Notes).


                                 (Page 1 of 4)
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         Item 4 of Schedule 13D is hereby amended and restated as follows:

ITEM 4.  PURPOSE OF TRANSACTION

         NRG Energy, Inc. ("NRG") acquired a 41.86% interest in Cogeneration
Corporation of America (formerly named "NRG Generating (U.S.) Inc." and "O'Brien
Environmental Energy, Inc.") (the "Company") pursuant to the Composite Fourth
Amended and Restated Plan of Reorganization (the "Plan") for O'Brien
Environmental Energy, Inc., confirmed by order of the United States Bankruptcy
Court for the District of New Jersey under Chapter 11 of the United States
Bankruptcy Code on February 22, 1996, and pursuant to the Amended and Restated
Stock Purchase and Reorganization Agreement dated as of January 31, 1996 (the
"Purchase Agreement"). Copies of the Plan and the Purchase Agreement were filed
as exhibits to Schedule 13D filed by NRG on May 10, 1996.

         In connection with the negotiation and consummation of the Plan, on
March 8, 1996, NRG entered into a loan agreement (the "Loan Agreement") with
O'Brien (Schuylkill) Cogeneration, Inc. ("Schuylkill"), a wholly owned
subsidiary of the Company, pursuant to which NRG agreed to make a loan in the
principal amount of $10,000,000 available to Schuylkill upon Schuylkill's
request. As part of the consideration for entering into the Loan Agreement, the
Company entered into an option agreement dated March 8, 1996 (the "Option
Agreement") with NRG. Pursuant to the Option Agreement, the Company agreed that,
on the date on which NRG made a loan to Schuylkill pursuant to the Loan
Agreement, NRG would have the right, upon 15 business days' notice, to reduce
the outstanding principal amount of the note payable to NRG by Schuylkill by
$3,000,000 in exchange for the 396,255 shares (the "Conversion Shares") of the
Company's common stock, par value $0.01 per share (the "Common Stock").

         In June 1997, NRG agreed to allow Schuylkill to borrow funds under the
Loan Agreement on an "as needed" basis rather than requiring that Schuylkill
borrow the full $10,000,000 on the funding date. On August 22, 1997, NRG made a
loan of $2,700,000 to Schuylkill pursuant to the Loan Agreement, bringing the
total outstanding principal amount under the Loan Agreement to $4,500,000 and
thereby vesting in NRG an option, exercisable on 15 business days' notice to the
Company, to acquire the Conversion Shares. On August 28, 1997, NRG notified the
Company of its intention to exercise its option to acquire the Conversion Shares
(the "Exercise Notice"). On November 25, 1997, NRG acquired the Conversion
Shares. Copies of the Option Agreement and the Exercise Notice were filed as
exhibits to Amendment No. 1 to Schedule 13D filed by NRG on August 29, 1997.

         On August 3, 1998, NRG received an irrevocable proxy (the "Proxy")
granting it the right for a limited period of time to vote 147,676 shares of
Common Stock. NRG obtained the Proxy in order to increase its voting control
over the Company. A copy of the Form of Proxy was filed as an exhibit to
Amendment No. 4 to Schedule 13D filed by NRG on August 3, 1998. As a result of
its receipt of the Proxy, NRG now beneficially owns an aggregate of 3,254,288,
or 47.60%, of the Common Stock.

         NRG intends to review its investment in the Company on a continuing
basis and may, at any time, consistent with NRG's obligations under the federal
securities laws and the Company's Certificate of Incorporation, determine to
increase or decrease its ownership of shares of the Common Stock through
purchases or sales of the Common Stock in the open market or in privately
negotiated transactions. NRG's review of its investment in the Company will
depend on various factors, including the Company's business prospects, other
developments concerning the Company, general economic conditions, money and
stock market conditions, and any other facts and circumstances that may become
known to NRG regarding its investment in the Company. At the time of filing this
Amendment No. 7, NRG has no plans to purchase additional shares of Common Stock
in the open market or in privately negotiated transactions.

         On September 14, 1998, NRG sent a letter, a copy of which is attached
hereto as Exhibit 6, to the Company's Chairman requesting that he call a special
meeting of the Company's shareholders to consider the removal of Robert Sherman
from the Company's Board of Directors. NRG also filed definitive solicitation
materials with the Securities and Exchange Commission pursuant to Section 14(a)
of the Securities Exchange Act of 1934, as amended, relating to a proposed
solicitation of proxies and consents from the Company's stockholders to remove
Mr. Sherman from the Company's Board. On October 26, 1998, consents of over 50% 
of the Company's shareholders in favor of Mr. Sherman's removal from the 
Company's Board of Directors were filed with the Company and Mr. Sherman was 
removed from the Board of Directors.

                                 (Page 2 of 4)
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         On October 27, 1998 the resulting vacancy was filled with Michael
O'Sullivan, who is Vice President of NRG's North American division, resulting in
five of the Company's eight directors now being employees of NRG. On the same
day, Mr. Sherman's employment agreement with the Company was terminated for
cause and Ms. Julie A. Jorgensen, senior counsel of NRG and a director of the
Company, was elected as the Company's interim president and chief executive
officer. Also on October 27, 1998, NRG entered into a letter agreement with
Wexford Management LLC, a holder of approximately 6.4% of the outstanding Common
Stock. This agreement is attached as Exhibit No. 7 to this Amendment No. 7 to
Schedule 13D, and its terms are hereby incorporated by reference in answer to
this Item.

         Except as described in this Item 4, NRG has no present plans or
proposals which relate to or would result in (i) an extraordinary corporate
transaction, such as a merger, reorganization or liquidation, involving the
Company or any of its subsidiaries, (ii) a sale or transfer of a material amount
of assets of the Company or any of its subsidiaries, (iii) any change in the
board of directors or management of the Company or any of its subsidiaries, (iv)
any material change in the present capitalization or dividend policy of the
Company, (v) any other material change in the Company's business or corporate
structure; (vi) changes in the Company's charter or bylaws or other actions
which may impede the acquisition of control of the Company by any person, (vii)
causing a class of securities of the Company to be delisted from a national
securities exchange or cease to be quoted in an inter-dealer quotation system of
a registered national securities association, (viii) a class of equity
securities of the Company becoming eligible for termination of registration
pursuant to Section 12(g)(4) of the Securities Exchange Act of 1934 or (ix) any
action similar to any of those described above. However, NRG retains its rights
to modify its plans with respect to the transactions described in this Item 4,
to acquire or dispose of securities of the Company and to formulate plans and
proposals that could result in the occurrence of any such events, subject to
applicable laws and regulations.

                                      * * *

         Item 7 of Schedule 13D is hereby amended and restated as follows:

ITEM 7.  MATERIAL TO BE FILED AS EXHIBITS

         1.       Composite Fourth Amended and Restated Plan of Reorganization
                  for O'Brien Environmental Energy, Inc. (previously filed as an
                  exhibit to NRG's Schedule 13D on May 10, 1996).

         2.       Amended and Restated Stock Purchase and Reorganization
                  Agreement, dated as of January 31, 1996, between NRG Energy,
                  Inc. and O'Brien Environmental Energy, Inc. (previously filed
                  as an exhibit to NRG's Schedule 13D on May 10, 1996).

         3.       Option Agreement, dated March 8, 1996, between O'Brien
                  Environmental Energy, Inc. and NRG Energy, Inc. (previously
                  filed as an exhibit to Amendment No. 1 to NRG's Schedule 13D
                  on August 29, 1997).

         4.       Option Exercise Notice, dated August 28, 1997, from NRG
                  Energy, Inc. to NRG Generating (U.S.), Inc. (previously filed
                  as an exhibit to Amendment No. 1 to NRG's Schedule 13D on
                  August 29, 1997).

         5.       Form of Proxy to be executed by Halcyon Alchemy Fund, L.P.,
                  Halcyon Special Situations, L.P., Gryphon Hidden Values
                  Limited and Gryphon Hidden Values II Limited (previously filed
                  as an exhibit to Amendment No. 4 to NRG's Schedule 13D on
                  August 3, 1998).

         6.       Letter, dated September 14, 1998, from NRG Energy, Inc. to
                  David H. Peterson, Chairman of the Board of Directors of
                  Cogeneration Corporation of America (previously filed as an
                  exhibit to Amendment No. 5 to NRG's Schedule 13D on October
                  15, 1998).

         7.       Letter Agreement, dated October 27, 1998, between NRG and
                  Wexford Management LLC.


                                 (Page 3 of 4)




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                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                   NRG ENERGY, INC.

Dated:   October 30, 1998          /s/ James J. Bender
                                   -------------------------------------------
                                   Name:  James J. Bender
                                   Title:  Vice President and General Counsel



                                   NORTHERN STATES POWER COMPANY

                                   /s/ John P. Moore, Jr.
                                   -------------------------------------------
                                   Name:  John P. Moore, Jr.
                                   Title:  Corporate Secretary


                                (Page 4 of 4)

EX-7

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                      [WEXFORD MANAGEMENT LLC LETTERHEAD]




October 27, 1998



James J. Bender
Vice President & General Counsel
NRG Energy, Inc.
1221 Nicollet Mall
Suite 700
Minneapolis, MN  55403-2445



                         Cogeneration Corp. of America


Dear Jim:

We are writing to set forth the terms of the agreement between Wexford 
Management LLC ("Wexford") and NRG Energy, Inc. ("NRG") with respect to certain 
matters concerning Cogeneration Corp. of America ("CCA").

1.   Wexford is the investment advisor to certain investment funds that hold 
approximately 443,976 shares of stock of CCA (the "Wexford Shares").  Wexford 
has a nominee serving as a member of the board of directors of CCA.

2.   NRG holds approximately 3,106,612 shares of stock of CCA.  NRG has four 
nominees (the "NRG Directors") serving as members of the board of directors of 
CCA.  NRG and/or the NRG Directors are participants in a proxy solicitation 
relating to CCA (the "Proxy Solicitation").

3.   Wexford has agreed to provide NRG with proxies and consents with respect 
to the Wexford Shares solely for purposes of voting in connection with the 
Proxy Solicitation.  The parties agree that Wexford's grant of such proxies and 
consents shall be irrevocable, subject to the limitations set forth herein on 
the use of such proxies and consents, until November 30, 1998.  The parties 
further agree that NRG's ability to utilize the proxies and consents shall 
terminate and NRG shall have no right to vote the Wexford Shares in connection 
with the Proxy Solicitation (a) after the conclusion of the CCA shareholders' 
meeting scheduled for November 12, 1998 or any postponement or adjournment 
thereof, but in no event after November 30, 1998 or (b) on such earlier date 
that NRG or the NRG Directors agrees (i) to a severance or other arrangement 
with Robert Sherman that provides him with compensation or other consideration 
in 
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James J. Bender
October 27, 1998 
Page 2

excess of the amounts set forth in his employment agreement dated March 28, 
1997, or (ii) to the payment by CCA in excess of an aggregate amount of 
$250,000 of the costs and expenses of the law firms, a public relations firm 
and printer retained by Robert Sherman and/or CCA in respect of the Proxy 
Solicitation.  Concurrently herewith Wexford is delivering executed proxy cards 
and consents with respect to the Proxy Solicitation, the use of which shall be 
subject to the terms and conditions set forth above.

4.   NRG agrees to use its best efforts not to oppose any nominee of Wexford as 
a member of the board of directors of CCA, subject to NRG's obligations under 
the Co-Investment Agreement and CCA's charter documents and bylaws.

5.   NRG agrees to indemnity and hold harmless Wexford and its affiliates and 
each of their officers, directors, members, employees, agents and affiliates 
from any cost, expense or liability of any kind (including inside and outside 
attorney's fees) arising out of or relating in any manner to the granting of 
the proxies and consents provided for herein or the direction by Wexford to its 
nominee on the CCA board of directors to resign such position, other than such 
costs, expenses or liabilities arising out of or relating to any action or 
claim brought by or on behalf of Wexford's current nominee on the CCA board of 
directors.

If this agreement accurately reflects our understanding, please execute and 
return a copy of this letter to the undersigned.

Sincerely,

/s/ Arthur H. Amron

Arthur H. Amron
General Counsel

ACCEPTED & AGREED
this 27th day of October, 1998

NRG Energy, Inc.

By: /s/ James J. Bender
   ---------------------------
   Name:  James J. Bender
   Title:  V.P. & General Counsel