Document:

<PAGE>
                                                                    EXHIBIT 4.01

                          SUPPLEMENTAL TRUST INDENTURE

                                      FROM

                          NORTHERN STATES POWER COMPANY
                            (A MINNESOTA CORPORATION)

                                       TO

                            BNY MIDWEST TRUST COMPANY

                                   ----------

                              DATED AUGUST 1, 2003

                                   ----------

                         SUPPLEMENTAL TO TRUST INDENTURE
                             DATED FEBRUARY 1, 1937

                                       AND

                            SUPPLEMENTAL AND RESTATED
                                 TRUST INDENTURE

                                DATED MAY 1, 1988

<PAGE>

                                TABLE OF CONTENTS

<Table>
<Caption>
                                                                                                              PAGE
<S>      <C>                                                                                                  <C>
PARTIES..........................................................................................................1

RECITALS.........................................................................................................1

ARTICLE I             SPECIFIC SUBJECTION OF ADDITIONAL PROPERTY TO THE LIEN OF THE ORIGINAL INDENTURE..........10

         SECTION 1.01...........................................................................................10

ARTICLE II            FORM AND EXECUTION OF SERIES 2006 BONDS AND SERIES 2010 BONDS.............................11

         SECTION 2.01...........................................................................................11

         SECTION 2.02...........................................................................................13

         SECTION 2.03...........................................................................................14

         SECTION 2.04...........................................................................................16

         SECTION 2.05...........................................................................................16

         SECTION 2.06...........................................................................................16

         SECTION 2.07...........................................................................................17

ARTICLE III           APPOINTMENT OF AUTHENTICATING AGENT.......................................................20

         SECTION 3.01...........................................................................................20

         SECTION 3.02...........................................................................................20

         SECTION 3.03...........................................................................................20

         SECTION 3.04...........................................................................................21

ARTICLE IV            FINANCING STATEMENT TO COMPLY WITH THE UNIFORM COMMERCIAL CODE............................21

         SECTION 4.01...........................................................................................21

         SECTION 4.02...........................................................................................21

         SECTION 4.03...........................................................................................21

         SECTION 4.04...........................................................................................22

         SECTION 4.05...........................................................................................22

         SECTION 4.06...........................................................................................26

ARTICLE V             AMENDMENTS TO INDENTURE...................................................................26

         SECTION 5.01...........................................................................................26

ARTICLE VI            MISCELLANEOUS.............................................................................26

         SECTION 6.01...........................................................................................26
</Table>

                                      -i-
<PAGE>

                                TABLE OF CONTENTS
                                   (continued)

<Table>
<Caption>
                                                                                                               PAGE
<S>                                                                                                            <C>

         SECTION 6.02...........................................................................................26

         SECTION 6.03...........................................................................................27

         SECTION 6.04...........................................................................................27

         SECTION 6.05...........................................................................................27

         SECTION 6.06...........................................................................................27

SCHEDULE A - PROPERTIES
</Table>

                                      -ii-
<PAGE>

         Supplemental Trust Indenture, made effective as of the 1st day of
August, 2003, by and between NORTHERN STATES POWER COMPANY (formerly Northern
Power Corporation), a corporation duly organized and existing under and by
virtue of the laws of the State of Minnesota, having its principal office in the
City of Minneapolis in said State (the "Company"), party of the first part, and
BNY MIDWEST TRUST COMPANY, a corporation duly organized and existing under and
by virtue of the laws of the State of Illinois, having its principal office in
the City of Chicago in said State (as successor Trustee to Harris Trust and
Savings Bank), as Trustee (the "Trustee"), party of the second part;

                                   WITNESSETH:

         WHEREAS, a predecessor in interest to the Company, Xcel Energy Inc.
(formerly Northern States Power Company), a corporation duly organized and
existing under and by virtue of the laws of the State of Minnesota (the
"Predecessor Company") heretofore has executed and delivered to the Trustee its
Trust Indenture (the "1937 Indenture"), made as of February 1, 1937, whereby the
Predecessor Company granted, bargained, sold, warranted, released, conveyed,
assigned, transferred, mortgaged, pledged, set over and confirmed to the Trustee
and to its respective successors in trust, all property, real, personal and
mixed then owned or thereafter acquired or to be acquired by the Predecessor
Company (except as therein excepted from the lien thereof) and subject to the
rights reserved by the Predecessor Company in and by the provisions of the 1937
Indenture, to be held by said Trustee in trust in accordance with provisions of
the 1937 Indenture for the equal pro rata benefit and security of all and each
of the bonds issued thereunder in accordance with the provisions thereof; and

         WHEREAS, the Predecessor Company heretofore has executed and delivered
to the Trustee a Supplemental Trust Indenture, made as of June 1, 1942, whereby
the Predecessor Company conveyed, assigned, transferred, mortgaged, pledged, set
over and confirmed to the Trustee, and its respective successors in said trust,
additional property acquired by it subsequent to the date of the 1937 Indenture;
and

         WHEREAS, the Predecessor Company heretofore has executed and delivered
to the Trustee the following additional Supplemental Trust Indentures which, in
addition to conveying, assigning, transferring, mortgaging, pledging, setting
over and confirming to the Trustee, and its respective successors in said trust,
additional property acquired by it subsequent to the preparation of the next
preceding Supplemental Trust Indenture and adding to the covenants, conditions
and agreements of the 1937 Indenture certain additional covenants, conditions
and agreements to be observed by the Company, created the following series of
First Mortgage Bonds:

<PAGE>

<Table>
<Caption>
              DATE OF SUPPLEMENTAL
                 TRUST INDENTURE                                   DESIGNATION OF SERIES
              --------------------                                 ---------------------
<S>                                                          <C>
               February 1, 1944                              Series due February 1, 1974 (retired)
               October 1, 1945                               Series due October 1, 1975 (retired)
               July 1, 1948                                  Series due July 1, 1978 (retired)
               August 1, 1949                                Series due August 1, 1979 (retired)
               June 1, 1952                                  Series due June 1, 1982 (retired)
               October 1, 1954                               Series due October 1, 1984 (retired)
               September 1, 1956                             Series due 1986 (retired)
               August 1, 1957                                Series due August 1, 1987 (redeemed)
               July 1, 1958                                  Series due July 1, 1988 (retired)
               December 1, 1960                              Series due December 1, 1990 (retired)
               August 1, 1961                                Series due August 1, 1991 (retired)
               June 1, 1962                                  Series due June 1, 1992 (retired)
               September 1, 1963                             Series due September 1, 1993 (retired)
               August 1, 1966                                Series due August 1, 1996 (redeemed)
               June 1, 1967                                  Series due June 1, 1995 (redeemed)
               October 1, 1967                               Series due October 1, 1997 (redeemed)
               May 1, 1968                                   Series due May 1, 1998 (redeemed)
               October 1, 1969                               Series due October 1, 1999 (redeemed)
               February 1, 1971                              Series due March 1, 2001 (redeemed)
               May 1, 1971                                   Series due June 1, 2001 (redeemed)
               February 1, 1972                              Series due March 1, 2002 (redeemed)
               January 1, 1973                               Series due February 1, 2003 (redeemed)
               January 1, 1974                               Series due January 1, 2004 (redeemed)
               September 1, 1974                             Pollution Control Series A (redeemed)
               April 1, 1975                                 Pollution Control Series B (redeemed)
               May 1, 1975                                   Series due May 1, 2005 (redeemed)
               March 1, 1976                                 Pollution Control Series C (retired)
               June 1, 1981                                  Pollution Control Series D, E and F (redeemed)
               December 1, 1981                              Series due December 1, 2011 (redeemed)
               May 1, 1983                                   Series due May 1, 2013 (redeemed)
               December 1, 1983                              Pollution Control Series G (redeemed)
               September 1, 1984                             Pollution Control Series H (redeemed)
               December 1, 1984                              Resource Recovery Series I (redeemed)
               May 1, 1985                                   Series due June 1, 2015 (redeemed)
               September 1, 1985                             Pollution Control Series J, K and L
               July 1, 1989                                  Series due July 1, 2019 (redeemed)
               June 1, 1990                                  Series due June 1, 2020 (redeemed)
               October 1, 1992                               Series due October 1, 1997 (retired)
               April 1, 1993                                 Series due April 1, 2003 (retired)
               December 1, 1993                              Series due December 1, 2000 (retired), and
                                                             December 1, 2005
</Table>

                                      -2-
<PAGE>

<Table>
<Caption>
              DATE OF SUPPLEMENTAL
                 TRUST INDENTURE                                   DESIGNATION OF SERIES
              --------------------                                 ---------------------
<S>                                                          <C>
               February 1, 1994                              Series due February 1, 1999 (retired)
               October 1, 1994                               Series due October 1, 2001 (retired)
               June 1, 1995                                  Series due July 1, 2025
               April 1, 1997                                 Pollution Control Series M (redeemed), N, O and P
               March 1, 1998                                 Series due March 1, 2003 (retired), and
                                                             March 1, 2028
               May 1, 1999                                   Resource Recovery Series Q
               June 1, 2000                                  Resource Recovery Series R; and
</Table>

         WHEREAS, on August 18, 2000, New Centuries Energies, Inc. was merged
with and into the Predecessor Company and the Predecessor Company changed its
corporate name from Northern States Power Company to Xcel Energy Inc.; and

         WHEREAS, pursuant to an Assignment and Assumption Agreement dated as of
August 18, 2000 between the Predecessor Company and the Company, substantially
all the assets of the Predecessor Company (other than the stock of the
Predecessor Company's subsidiaries) were conveyed to, and substantially all the
liabilities of the Predecessor Company, including liabilities created under the
Indenture, were assumed by, the Company (the "Assignment"); and

         WHEREAS, pursuant to the Supplemental Trust Indenture dated as of
August 1, 2000 among the Predecessor Company, the Company and Harris Trust and
Savings Bank, as trustee, the requirements and conditions precedent set forth in
the Original Indenture and the Restated Indenture (each as hereinafter defined)
with respect to the Assignment were satisfied; and

         WHEREAS, the Company heretofore has executed and delivered to the
Trustee the following additional Supplemental Trust Indentures which, in
addition to conveying, assigning, transferring, mortgaging, pledging, setting
over and confirming to the Trustee, and its respective successors in said trust,
additional property acquired by it (or, as the case may be, the Predecessor
Company) subsequent to the preparation of the next preceding Supplemental Trust
Indenture and adding to the covenants, conditions and agreements of the 1937
Indenture certain additional covenants, conditions, and agreements to be
observed by the Company, created the following series of First Mortgage Bonds:

<Table>
<Caption>
              DATE OF SUPPLEMENTAL
                 TRUST INDENTURE                                   DESIGNATION OF SERIES
              --------------------                                 ---------------------
<S>                                                          <C>
             June 1, 2002                                    Series due August 15, 2003
             July 1, 2002                                    Pollution Control Series S
             August 1, 2002                                  Series A and Series B due August 28, 2012
             May 1, 2003                                     Series due 2004, extendible through 2006; and
</Table>

         WHEREAS, the 1937 Indenture and all of the foregoing Supplemental Trust
Indentures are referred to herein collectively as the "Original Indenture"; and

                                      -3-
<PAGE>

         WHEREAS, the Predecessor Company heretofore has executed and delivered
to the Trustee a Supplemental and Restated Trust Indenture, dated May 1, 1988
(the "Restated Indenture"), which, in addition to conveying, assigning,
transferring, mortgaging, pledging, setting over and confirming to the Trustee,
and its respective successors in said trust additional property acquired by it
subsequent to the preparation of the next preceding Supplemental Trust
Indenture, amended and restated the Original Indenture (except for those
Supplemental Trust Indentures executed after May 1, 1988); and

         WHEREAS, the Restated Indenture will not become effective and operative
until all bonds of each series issued under the Original Indenture prior to May
1, 1988, shall have been retired through payment or redemption (including those
bonds "deemed to be paid" within the meaning of that term as used in Article
XVII of the 1937 Indenture) or until, subject to certain exceptions, the holders
of the requisite principal amount of such bonds shall have consented to the
amendments contained in the Restated Indenture (such date being herein called
the "Effective Date"); and

         WHEREAS, the Original Indenture and the Restated Indenture are referred
to herein collectively as the "Indenture"; and

         WHEREAS, pursuant to the Agreement of Resignation, Appointment and
Acceptance dated as of May 1, 2002 among the Company, BNY Midwest Trust Company,
as successor trustee, and Harris Trust and Savings Bank, the Trustee accepted
the rights, powers, duties and obligations of the trustee under the Indenture
effective as of May 9, 2002; and

         WHEREAS, the Indenture provides that bonds may be issued thereunder in
one or more series, each series to have such distinctive designation as the
Board of Directors of the Company may select for such series; and

         WHEREAS, the Company is desirous of providing for the creation of (a) a
new series of First Mortgage Bonds, said new series of bonds to be designated
"First Mortgage Bonds, Series due August 1, 2006" (the "Series 2006 Bonds") and
(b) a new series of First Mortgage Bonds, said new series of bonds to be
designated "First Mortgage Bonds, Series due August 1, 2010" (the "Series 2010
Bonds," and collectively with the Series 2006 Bonds, the "Bonds"), the bonds of
each series to be issued as registered bonds without coupons in denominations of
a multiple of $1,000, and the bonds of each series to be substantially in the
form and of the tenor following with the redemption prices inserted therein in
conformity with the provisions of Section 2.03 hereof, to-wit:

                (Form of Series 2006 Bonds and Series 2010 Bonds)
                          NORTHERN STATES POWER COMPANY
             (Incorporated under the laws of the State of Minnesota)
                               First Mortgage Bond
                        Series due August 1, [2006][2010]

No. _______________                                          $________________

                                      -4-
<PAGE>

         [Unless this certificate is presented by an authorized representative
of The Depository Trust Company, a New York corporation, to the Company or its
agent for registration of transfer, exchange or payment, and any certificate
issued is registered in the name of Cede & Co. or such other name as is
requested by an authorized representative of The Depository Trust Company (and
any payment is made to Cede & Co. or to such other entity as is requested by an
authorized representative of The Depository Trust Company), ANY TRANSFER, PLEDGE
OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL since
the registered owner hereof, Cede & Co., has an interest herein.]*

         NORTHERN STATES POWER COMPANY, a corporation organized and existing
under the laws of the State of Minnesota (the "Company"), for value received,
hereby promises to pay to [_____________] or its registered assigns, at the
office of the Trustee, in Chicago, Illinois, or, at the option of the registered
owner, at the agency of the Company in the Borough of Manhattan, City and State
of New York, an amount equal to [_________] Dollars in lawful money of the
United States of America, on the 1st day of August, [2006]** [2010]***, and to
pay interest hereon from the date hereof at the rate of [2.875]** [4.75]***
percent per annum, in like money, until the Company's obligation with respect to
the payment of such principal sum shall be discharged; said interest being
payable at the option of the person entitled to such interest either at the
office of the Trustee, in Chicago, Illinois, or at the agency of the Company in
the Borough of Manhattan, City and State of New York, on the 1st day of February
and on the 1st day of August in each year provided that as long as there is no
existing default in the payment of interest and except for the payment of
defaulted interest, the interest payable on any February 1 or August 1 will be
paid to the person in whose name this bond was registered at the close of
business on the record date (the January 15 prior to such February 1 or the July
15 prior to such August 1 (whether or not a business day)).

         [EXCEPT UNDER THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE,
THESE GLOBAL BONDS MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE REGISTERED
DEPOSITORY OR BY A NOMINEE OF THE REGISTERED DEPOSITORY TO THE REGISTERED
DEPOSITORY, ANOTHER NOMINEE OF THE REGISTERED DEPOSITORY, A SUCCESSOR OF THE
REGISTERED DEPOSITORY OR A NOMINEE OF SUCH SUCCESSOR.]*

         This bond is one of a duly authorized issue of bonds of the Company, of
the series and designation indicated on the face hereof, which issue of bonds
consists, or may consist, of several series of varying denominations, dates and
tenor, all issued and to be issued under and equally secured (except insofar as
a sinking fund, or similar fund, established in accordance with the provisions
of the Indenture may afford additional security for the bonds of any specific
series) by a Trust Indenture dated February 1, 1937 (the "1937 Indenture"), as
supplemented by 53 supplemental trust indentures (collectively, the
"Supplemental Indentures"), a Supplemental and Restated Trust Indenture dated
May 1, 1988 (the "Restated Indenture") and a new

----------
*   This legend to be included if the Bonds are issued as a global bond in
    book-entry form.
**  To be inserted in Series 2006 Bonds.

*** To be inserted in Series 2010 Bonds.

                                      -5-
<PAGE>

supplemental trust indenture for the bonds of this series effective as of August
1, 2003 (the "New Supplemental Indenture"), executed by the Company to BNY
MIDWEST TRUST COMPANY (as successor to Harris Trust and Savings Bank), as
trustee (the "Trustee"). The 1937 Indenture, as supplemented by the Supplemental
Indentures, the Restated Indenture and the New Supplemental Indenture, is
referred to herein collectively as the "Indenture". Reference hereby is made to
the Indenture for a description of the property mortgaged and pledged, the
nature and extent of the security, the rights of the holders of the bonds as to
such security and the terms and conditions upon which the bonds may be issued
under the Indenture and are secured. The principal hereof may be declared or may
become due on the conditions, in the manner and at the time set forth in the
Indenture upon the happening of a default as provided in the Indenture.

         With the consent of the Company and to the extent permitted by and as
provided in the Indenture, the rights and obligations of the Company and of the
holders of the bonds and the terms and provisions of the Indenture and of any
instruments supplemental thereto may be modified or altered by affirmative vote
of the holders of at least 66 2/3% in principal amount of the bonds then
outstanding under the Indenture and any instruments supplemental thereto
(excluding bonds challenged and disqualified from voting by reason of the
Company's interest therein as provided in the Indenture); provided that without
the consent of all holders of all bonds affected no such modification or
alteration shall permit the extension of the maturity of the principal of any
bond or the reduction in the rate of interest thereon or any other modification
in the terms of payment of such principal or interest.

         The Restated Indenture amends and restates the 1937 Indenture and the
Supplemental Indentures executed prior to May 1, 1988. The Restated Indenture
will become effective and operative (the "Effective Date") when all bonds of
each series issued under the Indenture prior to May 1, 1988 shall have been
retired through payment or redemption (including those bonds "deemed to be paid"
within the meaning of that term as used in Article XVII of the 1937 Indenture)
or until, subject to certain exceptions, the holders of the requisite principal
amount of such bonds shall have consented to the amendments contained in the
Restated Indenture. Holders of the bonds of this series and of each subsequent
series of bonds issued under the Indenture likewise will be bound by the
amendments contained in the Restated Indenture when they become effective and
operative. Reference is made to the Restated Indenture for a complete
description of the amendments contained therein to the 1937 Indenture and to the
Supplemental Indentures.

         The Company and the Trustee may deem and treat the person in whose name
this bond is registered as the absolute owner hereof for the purpose of
receiving payment and for all other purposes and shall not be affected by any
notice to the contrary.

         The bonds of this series shall be redeemable at the option of the
Company, as a whole or in part, on any date upon not less than 30 days' previous
notice to be given in the manner and with the effect provided in Section 2 of
Article X of the 1937 Indenture (except that, on and after the Effective Date,
such notice shall be given in the manner and effect provided in Section 10.02 of
the Indenture) at a redemption price equal to the greater of (a) the principal
amount being redeemed or (b) the sum of the present values of the remaining
scheduled payments of principal and interest on the bonds of this series that
are being redeemed, discounted to the redemption date on a semi-annual basis
(assuming a 360-day year consisting of twelve 30-day months) at the

                                      -6-
<PAGE>

Treasury Yield plus [12.5]** [20]*** basis points, plus in each case accrued and
unpaid interest to the redemption date.

         "Treasury Yield" means, with respect to any redemption date, (i) the
yield, under the heading which represents the average for the immediately
preceding week, appearing in the most recently published statistical release
designated "H.15(519)" or any successor publication which is published weekly by
the Board of Governors of the Federal Reserve System and which establishes
yields on actively traded U.S. Treasury securities adjusted to constant maturity
under the caption "Treasury Constant Maturities", for the maturity corresponding
to the Comparable Treasury Issue (if no maturity is within three months before
or after the Remaining Term, yields for the two published maturities most
closely corresponding to the Comparable Treasury Issue will be determined and
the Treasury Yield will be interpolated or extrapolated from such yields on a
straight line basis, rounding to the nearest month); or (ii) if such release (or
any successor release) is not published during the week preceding the
calculation date or does not contain such yields, the rate per annum equal to
the semi-annual equivalent yield to maturity of the Comparable Treasury Issue,
calculated using a price for the Comparable Treasury Issue (expressed as a
percentage of its principal amount) equal to the Comparable Treasury Price for
such redemption date. The Treasury Yield will be calculated on the third
business day preceding the date fixed for redemption.

         "Comparable Treasury Issue" means the United States Treasury security
selected by an Independent Investment Banker as having a maturity comparable to
the remaining term (the "Remaining Term") of the bonds of this series 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 bonds of this series.

         "Comparable Treasury Price" means (i) the average of the Reference
Treasury Dealer Quotations for such redemption date, after excluding the highest
and lowest of such Reference Treasury Dealer Quotations for such redemption
date, or (ii) if the Trustee obtains fewer than four such Reference Treasury
Dealer Quotations, the average of all such Reference Treasury Dealer Quotations.

         "Independent Investment Banker" means Barclays Capital Inc. or J.P.
Morgan Securities Inc. or their successors or, if such firms or their successors
are unwilling or unable to select the Comparable Treasury Issue, an independent
investment banking institution of national standing appointed by the Trustee
after consultation with the Company.

         "Reference Treasury Dealer Quotations" means, for each Reference
Treasury Dealer and any redemption date, the average, as determined by the
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 the Independent Investment Banker by such Reference
Treasury Dealer at 5:00 p.m. on the third business day preceding such redemption
date.

----------
** To be inserted in Series 2006 Bonds.

*** To be inserted in Series 2010 Bonds.

                                      -7-

<PAGE>

         "Reference Treasury Dealer" means (i) Barclays Capital Inc. or J.P.
Morgan Securities Inc. and any other primary U.S. Government securities dealer
in New York City (a "Primary Treasury Dealer") designated by, and not affiliated
with, Barclays Capital Inc., J.P. Morgan Securities Inc. and their respective
successors, provided, however, that if Barclays Capital Inc. or J.P. Morgan
Securities Inc. or any of their designees ceases to be a Primary Treasury
Dealer, the Company shall appoint another Primary Treasury Dealer as a
substitute, and (ii) any other Primary Treasury Dealers selected by the Company
after consultation with the Independent Investment Banker.

         Bonds of this series are not subject to a sinking fund.

         This bond is transferable as prescribed in the Indenture by the
registered owner hereof in person, or by his duly authorized attorney, at the
office of the Trustee in Chicago, Illinois, or at the option of the owner at the
agency of the Company in the Borough of Manhattan, City and State of New York,
or elsewhere if authorized by the Company, upon surrender and cancellation of
this bond, and thereupon a new bond or bonds of the same series and of a like
aggregate principal amount will be issued to the transferee in exchange therefor
as provided in the Indenture, upon payment of taxes or other governmental
charges, if any, that may be imposed in relation thereto.

         Bonds of this series are interchangeable as to denominations in the
manner and upon the conditions prescribed in the Indenture.

         No charge shall be made by the Company for any exchange or transfer of
bonds of this series, other than for taxes or other governmental charges, if
any, that may be imposed in relation thereto.

         The Company shall not be required to issue, transfer or exchange any
bond of this series during a period of 10 days immediately preceding any
selection of bonds of this series to be redeemed. The Company shall not be
required to transfer or exchange any bond of this series called or being called
for redemption in its entirety or to transfer or exchange the called portion of
a bond of this series which has been called for partial redemption.

         No recourse shall be had for the payment of the principal of or the
interest on this bond, or any part thereof, or of any claim based hereon or in
respect hereof or of said Indenture, against any incorporator, or any past,
present, or future shareholder, officer or director of the Company or of any
predecessor or successor corporation, either directly or through the Company, or
through any such predecessor or successor corporation, or through any receiver
or a trustee in bankruptcy, whether by virtue of any constitution, statute, or
rule of law or by the enforcement of any assessment or penalty or otherwise, all
such liability being, by the acceptance hereof and as part of the consideration
for the issue hereof, expressly waived and released, as more fully provided in
the Indenture.

         This bond shall not be valid or become obligatory for any purpose
unless and until the certificate of authentication hereon shall have been signed
by or on behalf of BNY Midwest Trust Company (as successor trustee to Harris
Trust and Savings Bank), as Trustee under the Indenture, or its successor
thereunder.

                                      -8-
<PAGE>

         IN WITNESS WHEREOF, NORTHERN STATES POWER COMPANY has caused this bond
to be executed in its name by its President or a Vice President and its
corporate seal, or a facsimile thereof, to be hereto affixed and attested by its
Secretary or an Assistant Secretary.

Dated: ____________                       NORTHERN STATES POWER COMPANY

     Attest:                              By:
            ------------------------         ----------------------------------
                                             President

                         (Form of Trustee's Certificate)

         This bond is one of the bonds of the series designated thereon,
described in the within-mentioned Indenture.

                                          BNY MIDWEST TRUST COMPANY, as Trustee

                                          By:
                                             ----------------------------------
                                             Authorized Officer

and

         WHEREAS, the Company is desirous of conveying, assigning, transferring,
mortgaging, pledging, setting over and confirming to the Trustee and to its
respective successors in trust, additional property acquired by it subsequent to
the date of the preparation of the Supplemental Trust Indenture dated as of May
1, 2003; and

         WHEREAS, the Indenture provides in substance that the Company and the
Trustee may enter into indentures supplemental thereto for the purposes, among
others, of creating and setting forth the particulars of any new series of bonds
and of providing the terms and conditions of the issue of the bonds of any
series not expressly provided for in the Indenture and of conveying, assigning,
transferring, mortgaging, pledging, setting over and confirming to the Trustee
additional property of the Company, and for any other purpose not inconsistent
with the terms of the Indenture; and

         WHEREAS, the execution and delivery of this Supplemental Trust
Indenture have been duly authorized by a resolution adopted by the Board of
Directors of the Company;

         WHEREAS, the Trustee has duly determined to execute this Supplemental
Trust Indenture and to be bound, insofar as it may lawfully do so, by the
provisions hereof;

         NOW, THEREFORE, Northern States Power Company, in consideration of the
premises and of one dollar duly paid to it by the Trustee at or before the
ensealing and delivery of these presents, the receipt of which is hereby
acknowledged, and other good and valuable considerations, does hereby covenant
and agree to and with BNY Midwest Trust Company (as

                                      -9-
<PAGE>

successor trustee to Harris Trust and Savings Bank), as Trustee, and its
successors in the trust under the Indenture for the benefit of those who hold or
shall hold the bonds, or any of them, issued or to be issued thereunder, as
follows:

                                   ARTICLE I
                   SPECIFIC SUBJECTION OF ADDITIONAL PROPERTY
                      TO THE LIEN OF THE ORIGINAL INDENTURE

         Section 1.01 . The Company, in order to better secure the payment, of
both the principal and interest, of all bonds of the Company at any time
outstanding under the Indenture according to their tenor and effect and the
performance of and compliance with the covenants and conditions contained in the
Indenture, has granted, bargained, sold, warranted, released, conveyed,
assigned, transferred, mortgaged, pledged, set over and confirmed, and by these
presents does grant, bargain, sell, warrant, release, convey, assign, transfer,
mortgage, pledge, set over and confirm, to the Trustee and to its respective
successors in said trust forever, subject to the rights reserved by the Company
in and by the provisions of the Indenture, all of the property described and
mentioned or enumerated in a schedule annexed hereto and marked Schedule A,
reference to said schedule being made hereby with the same force and effect as
if the same were incorporated herein at length; together with all and singular
the tenements, hereditaments and appurtenances belonging and in any way
appertaining to the aforesaid property or any part thereof with the reversion
and reversions, remainder and remainders, tolls, rents and revenues, issues,
income, products and profits thereof;

         Also, in order to subject the personal property and chattels of the
Company to the lien of the Indenture and to conform with the provisions of the
Uniform Commercial Code, all fossil, nuclear, hydro and other electric
generating plants, including buildings and other structures, turbines,
generators, exciters, boilers, reactors, nuclear fuel, other boiler plant
equipment, condensing equipment and all other generating equipment; substations;
electric transmission and distribution systems, including structures, poles,
towers, fixtures, conduits, insulators, wires, cables, transformers, services
and meters; steam heating mains and equipment; gas transmission and distribution
systems, including structures, storage facilities, mains, compressor stations,
purifier stations, pressure holders, governors, services and meters; telephone
plant and related distribution systems; trucks and trailers; office, shop and
other buildings and structures, furniture and equipment; apparatus and equipment
of all other kinds and descriptions; materials and supplies; all municipal and
other franchises, leaseholds, licenses, permits, privileges, patents and patent
rights; all shares of stock, bonds, evidences of indebtedness, contracts,
claims, accounts receivable, choses in action and other intangibles, all books
of account and other corporate records;

         Excluding, however, all merchandise and appliances heretofore or
hereafter acquired for the purpose of sale to customers and others;

         All the estate, right, title, interest and claim, whatsoever, at law as
well as in equity, which the Company now has or hereafter may acquire in and to
the aforesaid property and every part and parcel thereof subject, however, to
the right of the Company, until the happening of a completed default as defined
in Section 1 of Article XIII of the Original Indenture prior to the Effective
Date and upon the occurrence and continuation of a Completed Default as defined
in

                                      -10-
<PAGE>

the Indenture on and after the Effective Date, to retain in its possession all
shares of stock, notes, evidences of indebtedness, other securities and cash not
expressly required by the provisions hereof to be deposited with the Trustee, to
retain in its possession all contracts, bills and accounts receivable, motor
cars, any stock of goods, wares and merchandise, equipment or supplies acquired
for the purpose of consumption in the operation, construction or repair of any
of the properties of the Company, and to sell, exchange, pledge, hypothecate or
otherwise dispose of any or all of such property so retained in its possession,
free from the lien of the Indenture, without permission or hindrance on the part
of the Trustee, or any of the bondholders. No person in any dealings with the
Company in respect of any such property shall be charged with any notice or
knowledge of any such completed default (prior to the Effective Date) or
Completed Default (after the Effective Date) under the Indenture while the
Company is in possession of such property. Nothing contained herein or in the
Indenture shall be deemed or construed to require the deposit with, or delivery
to, the Trustee of any of such property, except such as is specifically required
to be deposited with the Trustee by some express provision of the Indenture;

         To have and to hold all said property, real, personal and mixed,
granted, bargained, sold, warranted, released, conveyed, assigned, transferred,
mortgaged, pledged, set over or confirmed by the Company as aforesaid, or
intended so to be, to the Trustee and its successors and assigns forever,
subject, however, to permitted liens as defined in Section 5 of Article I of the
1937 Indenture prior to the Effective Date and to Permitted Encumbrances on and
after the Effective Date and to the further reservations, covenants, conditions,
uses and trusts set forth in the Indenture; in trust nevertheless for the same
purposes and upon the same conditions as are set forth in the Indenture.

                                   ARTICLE II
          FORM AND EXECUTION OF SERIES 2006 BONDS AND SERIES 2010 BONDS

         Section 2.01 . There is hereby created, for issuance under the
Indenture, a series of bonds designated Series due August 1, 2006, each of which
shall bear the descriptive title "First Mortgage Bonds, Series due August 1,
2006", and the form thereof shall contain suitable provisions with respect to
the matters hereafter specified in this Section. The Series 2006 Bonds may
forthwith be executed by the Company substantially in the form set forth in the
recitals, including the relevant provisions as indicated therein, and delivered
to the Trustee for authentication and delivery by the Trustee in accordance with
the provisions of the Indenture and this Supplemental Indenture. The aggregate
principal amount of the Series 2006 Bonds outstanding at any time shall not
exceed $200,000,000. The Series 2006 Bonds shall mature on August 1, 2006, and
shall be issued as registered bonds without coupons in denominations of $1,000.
The Series 2006 Bonds shall bear interest at a rate of 2.875% per annum on the
principal amount thereof payable semi-annually on February 1 and August 1 of
each year, and the principal shall be payable at the office of the Trustee in
Chicago, Illinois, or at the option of the registered owner at the agency of the
Company in the Borough of Manhattan, City and State of New York, in lawful money
of the United States of America, and the interest shall be payable in like money
at the option of the person entitled to such interest either at said office of
the Trustee in Chicago, Illinois, or at the agency of the Company in the Borough
of Manhattan, City and State of New York. Interest on the Series 2006 Bonds
shall be calculated on the basis of a 360-day year consisting of twelve 30-day
months. The Series 2006 Bonds shall be dated as of the

                                      -11-
<PAGE>

interest payment date next preceding the authentication thereof by the Trustee
except that (i) if any Series 2006 Bond shall be authenticated before February
1, 2004, it shall be dated as of August 8, 2003, unless (iii) below is
applicable, (ii) if the Company shall at the time of the authentication of the
Series 2006 Bond be in default in the payment of interest upon the Series 2006
Bonds, such Series 2006 Bond shall be dated as of the date of the beginning of
the period for which such interest is so in default and (iii) as long as there
is no existing default in the payment of interest on the Series 2006 Bonds, if
any Series 2006 Bond shall be authenticated after the close of business on any
Record Date but on or prior to the interest payment date relating to such Record
Date, it shall be dated as of such interest payment date.

         As long as there is no existing default in the payment of interest on
the Series 2006 Bonds, the person in whose name any Series 2006 Bond is
registered at the close of business on any Record Date with respect to any
interest payment date shall be entitled to receive the interest payable on such
interest payment date notwithstanding any transfer or exchange of any such
Series 2006 Bond subsequent to the Record Date and on or prior to such interest
payment date, except as and to the extent the Company shall default in the
payment of the interest due on such interest payment date, in which case such
defaulted interest shall be paid to the person in whose name such Series 2006
Bond is registered on the Special Record Date for the payment of such defaulted
interest to be fixed by the Trustee, notice thereof shall be given to the
registered holder of any Series 2006 Bond not less than 10 days prior to such
Special Record Date, or may be paid at any time in any other lawful manner not
inconsistent with the requirements of any securities exchange on which the
Series 2006 Bonds may be listed, and upon such notice as may be required by such
exchange.

         The term "Record Date" as used in this Section 2.01 with respect to any
interest payment date (February 1 or August 1) shall mean the January 15 prior
to such February 1 or the July 15 prior to such August 1 (whether or not a
business day). The term "business day" shall mean any day other than a Saturday
or Sunday or a day on which the offices of the Trustee in the City of Chicago,
Illinois, are closed pursuant to authorization of law.

         As used in this Section 2.01, the term "default in the payment of
interest" means failure to pay interest on the applicable interest payment date
disregarding any period of grace permitted by the Indenture.

         The "Special Record Date" as used in this Section 2.01 shall be fixed
in the following manner. The Company shall notify the Trustee in writing of the
amount of defaulted interest proposed to be paid on each Series 2006 Bond and
the date of the proposed payment, and at the same time the Company shall deposit
with the Trustee an amount of money equal to the aggregate amount proposed to be
paid in respect of such defaulted interest or shall make arrangements
satisfactory to the Trustee for such deposit prior to the date of the proposed
payment, such money when deposited to be held in trust for the benefit of the
persons entitled to such defaulted interest as provided in this Section 2.01.
Thereupon the Trustee shall fix a Special Record Date for the payment of such
defaulted interest which shall be not more than 15 nor less than 10 days prior
to the date of the proposed payment and not less than 10 days after the receipt
by the Trustee of the notice of the proposed payment. The Trustee shall promptly
notify the Company of such Special Record Date and, in the name and at the
expense of the Company, shall cause notice of the proposed payment of such
defaulted interest and the Special Record

                                      -12-

<PAGE>

Date therefor to be mailed, first class postage prepaid, to each holder of the
Series 2006 Bonds, at his, her or its address as it appears in the bond
register, not less than 10 days prior to such Special Record Date. Notice of the
proposed payment of such defaulted interest and the Special Record Date therefor
having been mailed as aforesaid, such defaulted interest shall be paid to the
persons in whose names the Series 2006 Bonds are registered on such Special
Record Date and shall not be payable pursuant to the paragraph immediately
following in this Section 2.01.

         The Company may make payment of any defaulted interest in any other
lawful manner not inconsistent with the requirements of any securities exchange
on which the Series 2006 Bonds may be listed, and upon such notice as may be
required by such exchange, if, after notice is given by the Company to the
Trustee of the proposed payment pursuant to this Section 2.01, such payment
shall be deemed practicable by the Trustee.

         SECTION 2.02. There is hereby created, for issuance under the
Indenture, a series of bonds designated Series due August 1, 2010, each of which
shall bear the descriptive title "First Mortgage Bonds, Series due August 1,
2010", and the form thereof shall contain suitable provisions with respect to
the matters hereafter specified in this Section. The Series 2010 Bonds may
forthwith be executed by the Company substantially in the form set forth in the
recitals, including the relevant provisions as indicated therein, and delivered
to the Trustee for authentication and delivery by the Trustee in accordance with
the provisions of the Indenture and this Supplemental Indenture. The aggregate
principal amount of the Series 2010 Bonds outstanding at any time shall not
exceed $175,000,000. The Series 2010 Bonds shall mature on August 1, 2010, and
shall be issued as registered bonds without coupons in denominations of $1,000.
The Series 2010 Bonds shall bear interest at a rate of 4.750% per annum on the
principal amount thereof payable semi-annually on February 1 and August 1 of
each year, and the principal shall be payable at the office of the Trustee in
Chicago, Illinois, or at the option of the registered owner at the agency of the
Company in the Borough of Manhattan, City and State of New York, in lawful money
of the United States of America, and the interest shall be payable in like money
at the option of the person entitled to such interest either at said office of
the Trustee in Chicago, Illinois, or at the agency of the Company in the Borough
of Manhattan, City and State of New York. Interest on the Series 2010 Bonds
shall be calculated on the basis of a 360-day year consisting of twelve 30-day
months. The Series 2010 Bonds shall be dated as of the interest payment date
next preceding the authentication thereof by the Trustee except that (i) if any
Series 2010 Bond shall be authenticated before February 1, 2004, it shall be
dated as of August 8, 2003, unless (iii) below is applicable, (ii) if the
Company shall at the time of the authentication of the Series 2010 Bond be in
default in the payment of interest upon the Series 2010 Bonds, such Series 2010
Bond shall be dated as of the date of the beginning of the period for which such
interest is so in default and (iii) as long as there is no existing default in
the payment of interest on the Series 2010 Bonds, if any Series 2010 Bond shall
be authenticated after the close of business on any Record Date but on or prior
to the interest payment date relating to such Record Date, it shall be dated as
of such interest payment date.

         As long as there is no existing default in the payment of interest on
the Series 2010 Bonds, the person in whose name any Series 2010 Bond is
registered at the close of business on any Record Date with respect to any
interest payment date shall be entitled to receive the interest payable on such
interest payment date notwithstanding any transfer or exchange of any such
Series 2010 Bond subsequent to the Record Date and on or prior to such interest
payment date,

                                      -13-
<PAGE>

except as and to the extent the Company shall default in the payment of the
interest due on such interest payment date, in which case such defaulted
interest shall be paid to the person in whose name such Series 2010 Bond is
registered on the Special Record Date for the payment of such defaulted interest
to be fixed by the Trustee, notice thereof shall be given to the registered
holder of any Series 2010 Bond not less than 10 days prior to such Special
Record Date, or may be paid at any time in any other lawful manner not
inconsistent with the requirements of any securities exchange on which the
Series 2010 Bonds may be listed, and upon such notice as may be required by such
exchange.

         The term "Record Date" as used in this Section 2.02 with respect to any
interest payment date (February 1 or August 1) shall mean the January 15 prior
to such February 1 or the July 15 prior to such August 1 (whether or not a
business day). The term "business day" shall mean any day other than a Saturday
or Sunday or a day on which the offices of the Trustee in the City of Chicago,
Illinois, are closed pursuant to authorization of law.

         As used in this Section 2.02, the term "default in the payment of
interest" means failure to pay interest on the applicable interest payment date
disregarding any period of grace permitted by the Indenture.

         The "Special Record Date" as used in this Section 2.02 shall be fixed
in the following manner. The Company shall notify the Trustee in writing of the
amount of defaulted interest proposed to be paid on each Series 2010 Bond and
the date of the proposed payment, and at the same time the Company shall deposit
with the Trustee an amount of money equal to the aggregate amount proposed to be
paid in respect of such defaulted interest or shall make arrangements
satisfactory to the Trustee for such deposit prior to the date of the proposed
payment, such money when deposited to be held in trust for the benefit of the
persons entitled to such defaulted interest as provided in this Section 2.02.
Thereupon the Trustee shall fix a Special Record Date for the payment of such
defaulted interest which shall be not more than 15 nor less than 10 days prior
to the date of the proposed payment and not less than 10 days after the receipt
by the Trustee of the notice of the proposed payment. The Trustee shall promptly
notify the Company of such Special Record Date and, in the name and at the
expense of the Company, shall cause notice of the proposed payment of such
defaulted interest and the Special Record Date therefor to be mailed, first
class postage prepaid, to each holder of the Series 2010 Bonds, at his, her or
its address as it appears in the bond register, not less than 10 days prior to
such Special Record Date. Notice of the proposed payment of such defaulted
interest and the Special Record Date therefor having been mailed as aforesaid,
such defaulted interest shall be paid to the persons in whose names the Series
2010 Bonds are registered on such Special Record Date and shall not be payable
pursuant to the paragraph immediately following in this Section 2.02.

         The Company may make payment of any defaulted interest in any other
lawful manner not inconsistent with the requirements of any securities exchange
on which the Series 2010 Bonds may be listed, and upon such notice as may be
required by such exchange, if, after notice is given by the Company to the
Trustee of the proposed payment pursuant to this Section 2.02, such payment
shall be deemed practicable by the Trustee.

         SECTION 2.03. The Series 2006 Bonds and the Series 2010 Bonds shall be
redeemable at the option of the Company, as a whole or in part, on any date upon
not less than 30 days'

                                      -14-
<PAGE>

previous notice to be given in the manner and with the effect provided in
Section 2 of Article X of the 1937 Indenture (except that, on and after the
Effective Date, such notice shall be given in the manner and effect provided in
Section 10.02 of the Indenture) at a redemption price equal to the greater of
(a) the principal amount being redeemed or (b) the sum of the present values of
the remaining scheduled payments of principal and interest on the Series 2006
Bonds or Series 2010 Bonds, as applicable, that are being redeemed, discounted
to the redemption date on a semi-annual basis (assuming a 360-day year
consisting of twelve 30-day months) at the Treasury Yield plus 12.5 basis
points, in the case of the Series 2006 Bonds, and 20 basis points, in the case
of the Series 2010 Bonds, plus in each case accrued and unpaid interest to the
redemption date.

         "Treasury Yield" means, with respect to any redemption date, (i) the
yield, under the heading which represents the average for the immediately
preceding week, appearing in the most recently published statistical release
designated "H.15(519)" or any successor publication which is published weekly by
the Board of Governors of the Federal Reserve System and which establishes
yields on actively traded U.S. Treasury securities adjusted to constant maturity
under the caption "Treasury Constant Maturities", for the maturity corresponding
to the Comparable Treasury Issue (if no maturity is within three months before
or after the Remaining Term, yields for the two published maturities most
closely corresponding to the Comparable Treasury Issue will be determined and
the Treasury Yield will be interpolated or extrapolated from such yields on a
straight line basis, rounding to the nearest month); or (ii) if such release (or
any successor release) is not published during the week preceding the
calculation date or does not contain such yields, the rate per annum equal to
the semi-annual equivalent yield to maturity of the Comparable Treasury Issue,
calculated using a price for the Comparable Treasury Issue (expressed as a
percentage of its principal amount) equal to the Comparable Treasury Price for
such redemption date. The Treasury Yield will be calculated on the third
business day preceding the date fixed for redemption.

         "Comparable Treasury Issue" means the United States Treasury security
selected by an Independent Investment Banker as having a maturity comparable to
the remaining term (the "Remaining Term") of the bonds of the series to be
redeemed 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 bonds of the series being
redeemed.

         "Comparable Treasury Price" means (i) the average of the Reference
Treasury Dealer Quotations for such redemption date, after excluding the highest
and lowest of such Reference Treasury Dealer Quotations for such redemption
date, or (ii) if the Trustee obtains fewer than four such Reference Treasury
Dealer Quotations, the average of all such Reference Treasury Dealer Quotations.

         "Independent Investment Banker" means Barclays Capital Inc. or J.P.
Morgan Securities Inc. or their successors or, if such firms or their successors
are unwilling or unable to select the Comparable Treasury Issue, an independent
investment banking institution of national standing appointed by the Trustee
after consultation with the Company.

         "Reference Treasury Dealer Quotations" means, for each Reference
Treasury Dealer and any redemption date, the average, as determined by the
Independent Investment Banker, of the

                                      -15-
<PAGE>

bid and asked prices for the Comparable Treasury Issue (expressed in each case
as a percentage of its principal amount) quoted in writing to the Independent
Investment Banker by such Reference Treasury Dealer at 5:00 p.m. on the third
business day preceding such redemption date.

         "Reference Treasury Dealer" means (i) Barclays Capital Inc. or J.P.
Morgan Securities Inc. and any other primary U.S. Government securities dealer
in New York City (a "Primary Treasury Dealer") designated by, and not affiliated
with, Barclays Capital Inc., J.P. Morgan Securities Inc. and their respective
successors, provided, however, that if Barclays Capital Inc. or J.P. Morgan
Securities Inc. or any of their designees ceases to be a Primary Treasury
Dealer, the Company shall appoint another Primary Treasury Dealer as a
substitute and (ii) any other Primary Treasury Dealers selected by the Company
after consultation with the Independent Investment Banker.

         Neither the Series 2006 Bonds nor the Series 2010 Bonds are subject to
a sinking fund.

         The redemption prices of the Series 2006 Bonds and the Series 2010
Bonds, as applicable, need not be specified in any temporary bond of said series
if an appropriate reference be made in said temporary bond to the provision of
this Section.

         SECTION 2.04. The registered owner of any Bond or Bonds, at his, her,
or its option, may surrender the same with other Bonds of such series at the
office of the Trustee in Chicago, Illinois, or at the agency of the Company in
the Borough of Manhattan, City and State of New York, or elsewhere if authorized
by the Company, for cancellation, in exchange for other Bonds of such series of
higher or lower authorized denominations, but of the same aggregate principal
amount, bearing interest from its date, and upon receipt of any payment required
under the provisions of Section 2.05 hereof. Thereupon the Company shall execute
and deliver to the Trustee and the Trustee shall authenticate and deliver such
other registered Bonds to such registered owner at its office or at any other
place specified as aforesaid.

         Notwithstanding the provisions of Section 11 of Article II of the 1937
Indenture, the Company shall not be required to issue, transfer or exchange any
Bond during a period of ten (10) days next preceding any selection of Bonds to
be redeemed. The Company shall not be required to transfer or exchange any Bond
called or being called for redemption in its entirety or to transfer or exchange
the called portion of a Bond which has been called for partial redemption.

         SECTION 2.05. No charge shall be made by the Company for any exchange
or transfer of Bonds other than for taxes or other governmental charges, if any,
that may be imposed in relation thereto.

         SECTION 2.06. The Bonds shall be executed on behalf of the Company by
the manual signature of its President or one of its Vice Presidents or with the
facsimile signature of its President, and its corporate seal shall be thereunto
affixed, or printed, lithographed, or engraved thereon, in facsimile, and
attested by the manual signature of its Secretary or one of its Assistant
Secretaries or with the facsimile signature of its Secretary. In case any of the
officers who shall have signed any Bonds or attested the seal thereon or whose
facsimile signature shall be borne by the Bonds shall cease to be such officers
of the Company before the Bonds so signed and sealed

                                      -16-
<PAGE>

actually shall have been authenticated by the Trustee or delivered by the
Company, such Bonds nevertheless may be issued, authenticated, and delivered
with the same force and effect as though the person or persons who signed such
Bonds and attested the seal thereon or whose facsimile signature is borne by the
Bonds had not ceased to be such officer or officers of the Company. Any Bond
issuable hereunder may be signed or attested by manual or facsimile signature in
behalf of the Company by such person as at the actual date of the execution of
such Bond shall be the proper officer of the Company, although at the date of
such Bond such person shall not have been an officer of the Company.

         SECTION 2.07. (a) Except as provided in subsections (c) and (g) below,
the registered holder of all of the Series 2006 Bonds and the Series 2010 Bonds
shall be The Depository Trust Company ("DTC") and such Bonds shall be registered
in the name of Cede & Co., as nominee for DTC. Payment of principal of, premium,
if any, and interest on any Bonds registered in the name of Cede & Co. shall be
made by transfer of New York Federal or equivalent immediately available funds
with respect to the Bonds to the account of Cede & Co. on each such payment date
for the Bonds at the address indicated for Cede & Co. in the bond register kept
by the Trustee.

         (b) The Series 2006 Bonds and the Series 2010 Bonds shall each be
initially issued in the form of one or more separate single authenticated fully
registered certificates in the respective aggregate principal amount of such
series of Bonds. Upon initial issuance, the ownership of such Bonds shall be
registered in the bond register kept by the Trustee in the name of Cede & Co.,
as nominee of DTC. The Trustee and the Company may treat DTC (or its nominee) as
the sole and exclusive registered holder of the Bonds registered in its name for
the purposes of payment of the principal of, premium, if any, and interest on
the Bonds and of giving any notice permitted or required to be given to holders
under the Indenture, except as provided in Section 2.07(g) below; and neither
the Trustee nor the Company shall be affected by any notice to the contrary.
Neither the Trustee nor the Company shall have any responsibility or obligation
to any of DTC's participants (each a "Participant"), any person claiming a
beneficial ownership in the Bonds under or through DTC or any Participant (each
a "Beneficial Owner") or any other person which is not shown on the bond
register maintained by the Trustee as being a registered holder, with respect to
(1) the accuracy of any records maintained by DTC or any Participant; (2) the
payment by DTC or any Participant of any amount in respect of the principal of,
premium, if any, or interest on the Bonds; (3) the delivery by DTC or any
Participant of any notice to any Beneficial Owner which is permitted or required
to be given to registered holders under the Indenture of the Bonds; (4) the
selection of the Beneficial Owners to receive payment in the event of any
partial redemption of the Bonds; or (5) any consent given or other action taken
by DTC as bondholder. The Trustee shall pay all principal of, premium, if any,
and interest on the Bonds registered in the name of Cede & Co. only to or "upon
the order of" (as that term is used in the Uniform Commercial Code as adopted in
Minnesota and New York) DTC, and all such payments shall be valid and effective
to fully satisfy and discharge the Company's obligations with respect to the
principal of, premium, if any, and interest on such Bonds to the extent of the
sum or sums so paid. Except as otherwise provided in Sections 2.07(c) and (g)
below, no person other than DTC shall receive authenticated bond certificates
evidencing the obligation of the Company to make payments of principal of and
interest on the Bonds. Upon delivery by DTC to the Trustee of written notice to
the effect that DTC has determined to substitute a new nominee in place of Cede
& Co., and subject to the provisions of the Indenture

                                      -17-
<PAGE>

with respect to transfers of bonds, the word "Cede & Co." in this Supplemental
Trust Indenture shall refer to such new nominee of DTC.

         (c) If the Company in its discretion determines that it is in the best
interest of the Beneficial Owners that they be able to obtain bond certificates
for a series of Bonds or there shall have occurred and be continuing a completed
default with respect to a series of Bonds, the Company shall notify DTC and the
Trustee, whereupon DTC will notify the Participants of the availability through
DTC of bond certificates for such series of Bonds. In such event, the Trustee
shall issue, transfer and exchange bond certificates as requested by DTC in
appropriate amounts pursuant to Article II of the 1937 Indenture prior to the
Effective Date, Article II of the Restated Indenture on and after the Effective
Date and Section 2.04 of this Supplemental Trust Indenture. The Company shall
pay all costs in connection with the production of bond certificates if the
Company makes such a determination under this Section 2.07(c). DTC may determine
to discontinue providing its services with respect to a series of Bonds at any
time by giving written notice to the Company and the Trustee and discharging its
responsibilities with respect thereto under applicable law. Under such
circumstances (if there is no successor book-entry depository), the Company and
the Trustee shall be obligated (at the sole cost and expense of the Company) to
deliver bond certificates for such series of Bonds as described in this
Supplemental Trust Indenture. If bond certificates are issued, the provisions of
the Indenture shall apply to, among other things, the transfer and exchange of
such certificates and the method of payment of principal of, premium, if any,
and interest on such certificates. Whenever DTC requests the Company and the
Trustee to do so, the Company will direct the Trustee (at the sole cost and
expense of the Company) to cooperate with DTC in taking appropriate action after
reasonable notice (1) to make available one or more separate certificates
evidencing the Bonds to any Participant or (2) to arrange for another book-entry
depository to maintain custody of certificates evidencing the Bonds registered
in the name of such depository or its nominee. Any successor book-entry
depository must be a clearing agency registered with the Securities and Exchange
Commission pursuant to Section 17A of the Securities Exchange Act of 1934, as
amended, and must enter into an agreement with the Company and the Trustee
agreeing to act as the depository and clearing agency for such series of Bonds
(except as provided in Section 2.07(g) below). After such agreement has become
effective, DTC shall present the Bonds for registration of transfer in
accordance with Section 12 of Article II of the 1937 Indenture prior to the
Effective Date and Section 2.12 of the Restated Indenture on and after the
Effective Date, and the Trustee shall register them in the name of the successor
book-entry depository or its nominee and all references thereafter to DTC shall
be to such successor book-entry depository. If a successor book-entry depository
has not accepted such position before the effective date of DTC's termination of
its services, the book-entry system shall automatically terminate and may not be
reinstated without the consent of all registered holders of the Bonds.

         (d) Notwithstanding any other provision of this Supplemental Trust
Indenture to the contrary, so long as any Bonds are registered in the name of
Cede & Co., as nominee of DTC, all payments with respect to the principal of,
premium, if any, and interest on such Bonds and all notices with respect to such
Bonds shall be made and given, respectively, to DTC as provided in the
representation letter dated as of the date of delivery of the Bonds among DTC,
the Company and the Trustee. The Trustee is hereby authorized and directed to
comply with all terms of the representation letter.

                                      -18-
<PAGE>

         (e) In connection with any notice or other communication to be provided
pursuant to the Indenture for the Bonds by the Company or the Trustee with
respect to any consent or other action to be taken by the registered holders of
the Bonds, the Company or the Trustee, as the case may be, shall seek to
establish a record date to the extent permitted by the Indenture for such
consent or other action and give DTC notice of such record date not less than
fifteen (15) calendar days in advance of such record date to the extent
possible. Such notice to DTC shall be given only when DTC is the sole registered
holder.

         (f) NEITHER THE COMPANY NOR THE TRUSTEE WILL HAVE ANY RESPONSIBILITY OR
OBLIGATIONS TO THE PARTICIPANTS OR THE BENEFICIAL OWNERS WITH RESPECT TO (1) THE
ACCURACY OF ANY RECORDS MAINTAINED BY DTC OR ANY PARTICIPANT; (2) THE PAYMENT BY
DTC OR ANY PARTICIPANT OF ANY AMOUNT DUE TO ANY BENEFICIAL OWNER IN RESPECT OF
THE PRINCIPAL OF, PREMIUM, IF ANY, OR INTEREST ON THE BONDS; (3) THE DELIVERY BY
DTC OR ANY PARTICIPANT OF ANY NOTICE TO ANY BENEFICIAL OWNER WHICH IS REQUIRED
OR PERMITTED UNDER THE TERMS OF THE INDENTURE TO BE GIVEN TO REGISTERED HOLDERS;
(4) THE SELECTION OF THE BENEFICIAL OWNERS TO RECEIVE PAYMENT IN THE EVENT OF
ANY PARTIAL REDEMPTION OF THE BONDS; OR (5) ANY CONSENT GIVEN OR OTHER ACTION
TAKEN BY DTC AS A REGISTERED HOLDER.

         SO LONG AS CEDE & CO. IS THE REGISTERED HOLDER OF THE BONDS AS NOMINEE
OF DTC, REFERENCES HEREIN TO REGISTERED HOLDERS OF THE BONDS SHALL MEAN CEDE &
CO. AND SHALL NOT MEAN THE BENEFICIAL OWNERS OF THE BONDS NOR THE PARTICIPANTS.

         (g) The Company shall terminate the services of DTC with respect to a
series of Bonds if the Company determines that: (i) DTC (x) is unable to
discharge its responsibilities with respect to such series of Bonds or (y) at
any time ceases to be a clearing agency registered under the Securities Exchange
Act of 1934, as amended; or (ii) there shall have occurred and be continuing a
completed default with respect to any series of Bonds. The Company, in its sole
discretion, may terminate the services of DTC with respect to a series of Bonds
if the Company determines that a continuation of the requirement that all of the
outstanding Bonds be registered with the registration books kept by the Trustee
in the name of Cede & Co., as nominee of DTC, is not in the best interest of the
Beneficial Owners of the Bonds. After such event and if no substitute book-entry
depository is appointed by the Company, bond certificates will be delivered as
described in the Indenture.

         (h) Upon the termination of the services of DTC with respect to the
Bonds pursuant to subsections (c) or (g) of this Section 2.07 after which no
substitute book-entry depository is appointed, the Bonds shall be registered in
whatever name or names holders transferring or exchanging the Bonds shall
designate in accordance with the provisions of the Indenture.

                                      -19-
<PAGE>

                                   ARTICLE III
                       APPOINTMENT OF AUTHENTICATING AGENT

         SECTION 3.01. The Trustee shall, if requested in writing so to do by
the Company, promptly appoint an agent or agents of the Trustee who shall have
authority to authenticate registered Bonds in the name and on behalf of the
Trustee. Such appointment by the Trustee shall be evidenced by a certificate of
a vice-president of the Trustee delivered to the Company prior to the
effectiveness of such appointment.

         SECTION 3.02. (a) Any such authenticating agent shall be acceptable to
the Company and at all times shall be a corporation which is organized and doing
business under the laws of the United States or of any State, is authorized
under such laws to act as authenticating agent, has a combined capital and
surplus of at least $10,000,000 and is subject to supervision or examination by
Federal or State authority. If such corporation publishes reports of condition
at least annually, pursuant to law or to the requirements of the aforesaid
supervising or examining authority, then for the purposes of this Section 3.02
the combined capital and surplus of such corporation shall be deemed to be its
combined capital and surplus as set forth in its most recent report of condition
so published.

         (b) Any corporation into which any authenticating agent may be merged
or converted or with which it may be consolidated, or any corporation resulting
from any merger, conversion, or consolidation to which any authenticating agent
shall be a party, or any corporation succeeding to the corporate agency business
of any authenticating agent, shall continue to be the authenticating agent
without the execution or filing of any paper or any further act on the part of
the Trustee or the authenticating agent.

         (c) Any authenticating agent at any time may resign by giving written
notice of resignation to the Trustee and to the Company. The Trustee may at any
time, and upon written request of the Company to the Trustee shall, terminate
the agency of any authenticating agent by giving written notice of termination
to such authenticating agent and to the Company. Upon receiving such a notice of
resignation or upon such a termination, or in case at any time any
authenticating agent shall cease to be eligible in accordance with the
provisions of this Section 3.02, the Trustee, unless otherwise requested in
writing by the Company, promptly shall appoint a successor authenticating agent,
which shall be acceptable to the Company. Any successor authenticating agent
upon acceptance of its appointment hereunder shall become vested with all the
rights, powers, duties and responsibilities of its predecessor hereunder, with
like effect as if originally named. No successor authenticating agent shall be
appointed unless eligible under the provisions of this Section 3.02.

         (d) The Trustee agrees to pay to any authenticating agent, appointed in
accordance with the provisions of this Section 3.02, reasonable compensation for
its services, and the Trustee shall be entitled to be reimbursed for such
payments.

         SECTION 3.03. If an appointment is made pursuant to this Article III,
the registered Bonds shall have endorsed thereon, in addition to the Trustee's
Certificate, an alternate Trustee's Certificate in the following form:

                                      -20-
<PAGE>
         This bond is one of the bonds of the Series designated thereon,
described in the within-mentioned Indenture.

                                        BNY MIDWEST TRUST COMPANY, as Trustee

                                        By:
                                           ------------------------------------
                                                   Authenticating Agent

                                        By:
                                           ------------------------------------
                                                   Authorized Officer

         SECTION 3.04. No provision of this Article III shall require the
Trustee to have at any time more than one such authenticating agent for any one
State or to appoint any such authenticating agent in the State in which the
Trustee has its principal place of business.

                                   ARTICLE IV
                       FINANCING STATEMENT TO COMPLY WITH
                           THE UNIFORM COMMERCIAL CODE

         SECTION 4.01. The name and address of the debtor and secured party are
set forth below:

         Debtor:            Northern States Power Company
                            414 Nicollet Mall
                            Minneapolis, Minnesota  55401
         Secured Party:     BNY Midwest Trust Company, Trustee
                            2 North LaSalle Street
                            Suite 1020
                            Chicago, Illinois  60602

NOTE: Northern States Power Company, the debtor above named, is "a transmitting
utility" under the Uniform Commercial Code as adopted in Minnesota, North Dakota
and South Dakota.

         SECTION 4.02. Reference to Article I hereof is made for a description
of the property of the debtor covered by this Financing Statement with the same
force and effect as if incorporated in this Section at length.

         SECTION 4.03. The maturity dates and respective principal amounts of
obligations of the debtor secured and presently to be secured by the Indenture
and this Supplemental Trust Indenture, reference to all of which for the terms
and conditions thereof is hereby made with the same force and effect as if
incorporated herein at length, are as follows:

                                      -21-
<PAGE>

<Table>
<Caption>
                         FIRST MORTGAGE BONDS                                         PRINCIPAL AMOUNT
                         --------------------                                         ----------------
<S>                                                                                   <C>
Series due December 1, 2005..........................................                     $ 70,000,000
Pollution Control Series J...........................................                      $ 5,450,000
Pollution Control Series K...........................................                      $ 3,400,000
Pollution Control Series L...........................................                      $ 4,850,000
Series due July 1, 2025..............................................                     $250,000,000
Pollution Control Series N...........................................                     $ 27,900,000
Pollution Control Series O...........................................                     $ 50,000,000
Pollution Control Series P...........................................                     $ 50,000,000
Series due March 1, 2028.............................................                     $150,000,000
Resource Recovery Series Q...........................................                      $ 9,145,000
Resource Recovery Series R...........................................                     $ 14,090,000
Pollution Control Series S...........................................                     $ 69,000,000
Series A and Series B due August 28, 2012............................                     $450,000,000
Series due 2004, extendible through 2006.............................                     $275,000,000
Series due August 1, 2006............................................                     $200,000,000
Series due August 1, 2010............................................                     $175,000,000
</Table>

         SECTION 4.04. This Financing Statement is hereby adopted for all of
the First Mortgage Bonds of the Series mentioned above secured by said Indenture
and this Supplemental Trust Indenture.

         SECTION 4.05. The 1937 Indenture and the prior Supplemental Trust
Indentures, as set forth below, have been filed or recorded in each and every
office in the States of Minnesota, North Dakota, and South Dakota designated by
law for the filing or recording thereof in respect of all property of the
Company subject thereto:

Original Indenture
     Dated February 1, 1937

Supplemental Indenture
     Dated June 1, 1942

Supplemental Indenture
     Dated February 1, 1944

Supplemental Indenture
     Dated October 1, 1945

Supplemental Indenture
     Dated July 1, 1948

Supplemental Indenture
     Dated August 1, 1949

                                      -22-
<PAGE>

Supplemental Indenture
     Dated June 1, 1952

Supplemental Indenture
     Dated October 1, 1954

Supplemental Indenture
     Dated September 1, 1956

Supplemental Indenture
     Dated August 1, 1957

Supplemental Indenture
     Dated July 1, 1958

Supplemental Indenture
     Dated December 1, 1960

Supplemental Indenture
     Dated August 1, 1961

Supplemental Indenture
     Dated June 1, 1962

Supplemental Indenture
     Dated September 1, 1963

Supplemental Indenture
     Dated August 1, 1966

Supplemental Indenture
     Dated June 1, 1967

Supplemental Indenture
     Dated October  1, 1967

Supplemental Indenture
     Dated May 1, 1968

Supplemental Indenture
     Dated October 1, 1969

Supplemental Indenture
     Dated February 1, 1971

                                      -23-

<PAGE>

Supplemental Indenture
     Dated May 1, 1971

Supplemental Indenture
     Dated February 1, 1972

Supplemental Indenture
     Dated January 1, 1973

Supplemental Indenture
     Dated January 1, 1974

Supplemental Indenture
     Dated September 1, 1974

Supplemental Indenture
     Dated April 1, 1975

Supplemental Indenture
     Dated May 1, 1975

Supplemental Indenture
     Dated March 1, 1976

Supplemental Indenture
     Dated June 1, 1981

Supplemental Indenture
     Dated December 1, 1981

Supplemental Indenture
     Dated May 1, 1983

Supplemental Indenture
     Dated December 1, 1983

Supplemental Indenture
     Dated September 1, 1984

Supplemental Indenture
     Dated December 1, 1984

Supplemental Indenture
     Dated May 1, 1985

                                      -24-
<PAGE>

Supplemental Indenture
     Dated September 1, 1985

Supplemental Indenture
     Dated May 1, 1988

Supplemental Indenture
     Dated July 1, 1989

Supplemental Indenture
     Dated June 1, 1990

Supplemental Indenture
     Dated October 1, 1992

Supplemental Indenture
     Dated April 1, 1993

Supplemental Indenture
     Dated December 1, 1993

Supplemental Indenture
     Dated February 1, 1994

Supplemental Indenture
     Dated October 1, 1994

Supplemental Indenture
     Dated June 1, 1995

Supplemental Indenture
     Dated April 1, 1997

Supplemental Indenture
     Dated March 1, 1998

Supplemental Indenture
     Dated May 1, 1999

Supplemental Indenture
     Dated June 1, 2000

Supplemental Indenture
     Dated August 1, 2000

                                      -25-
<PAGE>

Supplemental Indenture
     Dated June 1, 2002

Supplemental Indenture
     Dated July 1, 2002

Supplemental Indenture
     Dated August 1, 2002

Supplemental Indenture
     Dated May 1, 2003

         SECTION 4.06. The property covered by this Financing Statement also
shall secure additional series of First Mortgage Bonds of the debtor which may
be issued from time to time in the future in accordance with the provisions of
the Indenture.

                                   ARTICLE V
                             AMENDMENTS TO INDENTURE

         SECTION 5.01. Each holder or registered owner of a bond of any series
originally authenticated by the Trustee and originally issued by the Company
subsequent to May 1, 1985 and of any coupon pertaining to any such bond, by the
acquisition, holding or ownership of such bond and coupon, thereby consents and
agrees to, and shall be bound by, the provisions of Article VI of the
Supplemental Indenture dated May 1, 1985. Each holder or registered owner of a
bond of any series (including the Series 2006 Bonds and the Series 2010 Bonds),
originally authenticated by the Trustee and originally issued by the Company
subsequent to May 1, 1988 and of any coupon pertaining to such bond, by the
acquisition, holding or ownership of such bond and coupon, thereby consents and
agrees to, and shall be bound by, the provisions of the Supplemental and
Restated Trust Indenture dated May 1, 1988 upon the Effective Date.

                                   ARTICLE VI
                                  MISCELLANEOUS

         SECTION 6.01. The recitals of fact herein, except the recital that the
Trustee has duly determined to execute this Supplemental Trust Indenture and be
bound, insofar as it may lawfully so do, by the provisions hereof and in the
bonds shall be taken as statements of the Company and shall not be construed as
made by the Trustee. The Trustee makes no representations as to the value of any
of the property subject to the lien of the Indenture, or any part thereof, or as
to the title of the Company thereto, or as to the security afforded thereby and
hereby, or as to the validity of this Supplemental Trust Indenture or of the
bonds issued under the Indenture by virtue hereof (except the Trustee's
certificate) and the Trustee shall incur no responsibility in respect of such
matters.

         SECTION 6.02. This Supplemental Trust Indenture shall be construed in
connection with and as a part of the 1937 Indenture, as supplemented by the
Supplemental Trust Indentures dated June 1, 1942, February 1, 1944, October 1,
1945, July 1, 1948, August 1, 1949, June 1,

                                      -26-
<PAGE>

1952, October 1, 1954, September 1, 1956, August 1, 1957, July 1, 1958, December
1, 1960, August 1, 1961, June 1, 1962, September 1, 1963, August 1, 1966, June
1, 1967, October 1, 1967, May 1, 1968, October 1, 1969, February 1, 1971, May 1,
1971, February 1, 1972, January 1, 1973, January 1, 1974, September 1, 1974,
April 1, 1975, May 1, 1975, March 1, 1976, June 1, 1981, December 1, 1981, May
1, 1983, December 1, 1983, September 1, 1984, December 1, 1984, May 1, 1985,
September 1, 1985, the Supplemental and Restated Trust Indenture dated May 1,
1988 and the Supplemental Trust Indentures dated July 1, 1989, June 1, 1990,
October 1, 1992, April 1, 1993, December 1, 1993, February 1, 1994, October 1,
1994, June 1, 1995, April 1, 1997, March 1, 1998, May 1, 1999, June 1, 2000,
August 1, 2000, June 1, 2002, July 1, 2002, August 1, 2002 and May 1, 2003.

         SECTION 6.03. (a) If any provision of the Indenture or this
Supplemental Trust Indenture limits, qualifies or conflicts with another
provision of the Indenture required to be included in indentures qualified under
the Trust Indenture Act of 1939, as amended (as enacted prior to the date of
this Supplemental Trust Indenture) by any of the provisions of Sections 310 to
317, inclusive, of the said Act, such required provisions shall control.

         (b) In case any one or more of the provisions contained in this
Supplemental Trust Indenture or in the bonds issued hereunder should be invalid,
illegal or unenforceable in any respect, the validity, legality and
enforceability of the remaining provisions contained herein and therein shall
not in any way be affected, impaired, prejudiced or disturbed thereby.

         SECTION 6.04. Wherever in this Supplemental Trust Indenture the word
"Indenture" is used without the prefix "1937", "Original" or "Supplemental",
such word was used intentionally to include in its meaning both the 1937
Indenture and all indentures supplemental thereto.

         SECTION 6.05. Wherever in this Supplemental Trust Indenture either of
the parties hereto is named or referred to, this shall be deemed to include the
successors or assigns of such party, and all the covenants and agreements in
this Supplemental Trust Indenture contained by or on behalf of the Company or by
or on behalf of the Trustee shall bind and inure to the benefit of the
respective successors and assigns of such parties, whether so expressed or not.

         SECTION 6.06. (a) This Supplemental Trust Indenture may be executed
simultaneously in several counterparts, and all said counterparts executed and
delivered, each as an original, shall constitute but one and the same
instrument.

         (b) The Table of Contents and the descriptive headings of the several
Articles of this Supplemental Trust Indenture were formulated, used and inserted
in this Supplemental Trust Indenture for convenience only and shall not be
deemed to affect the meaning or construction of any of the provisions hereof.

         The total aggregate amount of obligations to be issued forthwith under
this Supplemental Trust Indenture is $375,000,000, consisting of the Series 2006
Bonds in the aggregate principal amount of $200,000,000 and the Series 2010
Bonds in the aggregate principal amount of $175,000,000.

                                 ---------------

                                      -27-
<PAGE>

         IN WITNESS WHEREOF, on this 1st day of August, A.D. 2003, NORTHERN
STATES POWER COMPANY, a Minnesota corporation, party of the first part, has
caused its corporate name and seal to be hereunto affixed and this Supplemental
Trust Indenture effective August 1, 2003 to be signed by its President or a Vice
President, and attested by its Secretary or an Assistant Secretary, for and in
its behalf, and BNY MIDWEST TRUST COMPANY (as successor trustee to Harris Trust
and Savings Bank), an Illinois corporation, as Trustee, party of the second
part, to evidence its acceptance of the trust hereby created, has caused its
corporate name and seal to be hereunto affixed, and this Supplemental Trust
Indenture effective August 1, 2003, to be signed by its President, a Vice
President, or an Assistant Vice President, and attested by its Secretary or an
Assistant Secretary, for and in its behalf.

                                        NORTHERN STATES POWER COMPANY

                                          /S/ Benjamin G.S. Fowke III
                                        ---------------------------------------
                                        By: Benjamin G.S. Fowke III
                                        Its: Vice President
Attest:

    /S/ Peter F. Rechek
------------------------------------
Peter F. Rechek
Its:  Assistant Secretary
Executed by Northern States Power
Company in the presence of:                              (CORPORATE SEAL)

     /S/ Mary Schell
------------------------------------
Witness, Mary Schell

     /S/ Sharon Babcock
------------------------------------
Witness, Sharon Babcock

<PAGE>

                                                BNY MIDWEST TRUST COMPANY,
                                                as Trustee

                                                By:  /S/ D. G. Donovan
                                                   ----------------------------
                                                Its: Assistant Vice President
Attest:

        /S/ C. Potter
------------------------------------
Its:  Assistant Secretary
Executed by Northern States Power
Company in the presence of:                         (CORPORATE SEAL)

         /S/ Mary Callahan
------------------------------------
Witness Mary Callahan

         /S/ Linda Garcia
------------------------------------
Witness Linda Garcia

<PAGE>

STATE OF MINNESOTA               )
                                 )    SS.:
COUNTY OF HENNEPIN               )

         On this 1st day of August A.D. 2003, before me, Sharon Quellhorst, a
Notary Public in and for said County in the State aforesaid, personally appeared
Benjamin G.S. Fowke III and Peter F. Rechek, to me personally known, and to me
known to be the Vice President and Treasurer and Assistant Secretary,
respectively, of Northern States Power Company, one of the corporations
described in and which executed the within and foregoing instrument, and who,
being by me severally duly sworn, each for himself, did say that he, the said
Benjamin G.S. Fowke III is a Vice President and Treasurer, and Peter F. Rechek
is the Assistant Secretary, of said Northern States Power Company, a
corporation; that the seal affixed to the within and foregoing instrument is the
corporate seal of said corporation, and that said instrument was executed on
behalf of said corporation by authority of its stockholders and board of
directors; and said Benjamin G.S. Fowke III and Peter F. Rechek each
acknowledged said instrument to be the free act and deed of said corporation and
that such corporation executed the same.

         WITNESS my hand and notarial seal, this 1st day of August, A.D. 2003.

     /S/ Sharon Quellhorst
------------------------------------
Sharon Quellhorst
Notary Public
My commission expires:  January 31, 2005
                                                        (NOTARY SEAL)

<PAGE>

STATE OF MINNESOTA               )
                                 )    SS.:
COUNTY OF HENNEPIN               )

         Benjamin G.S. Fowke III and Peter F. Rechek, being severally duly
sworn, each deposes and says that they are Vice President and Treasurer and
Assistant Secretary respectively, of Northern States Power Company, the
corporation described in and which executed the within and foregoing
Supplemental Trust Indenture, as mortgagor; and each for himself further says
that said Supplemental Trust Indenture was executed in good faith, and not for
the purpose of hindering, delaying, or defrauding any creditor of the said
mortgagor.

    /S/ Benjamin G.S. Fowke III                          /S/ Peter F. Rechek
-----------------------------------                   -------------------------
Benjamin G.S. Fowke III                                    Peter F. Rechek

         Subscribed and sworn to before me this 1st day of August, A.D. 2003.

    /S/ Sharon Quellhorst
------------------------------------
Sharon Quellhorst
Notary Public
My commission expires:  January 31, 2005
                                                         (NOTARY SEAL)

<PAGE>

STATE OF ILLINOIS                )
                                 )    SS.:
COUNTY OF COOK                   )

         On this 1st day of August A.D. 2003, before me, K. Gibson, a Notary
Public in and for said County in the State aforesaid, personally appeared D. G.
Donovan and C. Potter to me personally known, and to me known to be the
Assistant Vice President and Assistant Secretary, respectively, of BNY Midwest
Trust Company, one of the corporations described in and which executed the
within and foregoing instrument, and who, being by me severally duly sworn,
each, did say that he, the said D. G. Donovan is Assistant Vice President, and
she, the said C. Potter, is the Assistant Secretary, of said BNY Midwest Trust
Company, a corporation; that the seal affixed to the within and foregoing
instrument is the corporate seal of said corporation, and that said instrument
was executed on behalf of said corporation by authority of its board of
directors; and said D. G. Donovan and C. Potter each acknowledged said
instrument to be the free act and deed of said corporation and that such
corporation executed the same.

         WITNESS my hand and notarial seal, this 1st day of August A.D. 2003.

         /S/ K. Gibson
------------------------------------
K. Gibson
Notary Public
My commission expires:  7/8/06
                                                      (NOTARY SEAL)

<PAGE>

STATE OF ILLINOIS                )
                                 )    SS.:
COUNTY OF COOK                   )

         D. G. Donovan and C. Potter, being severally duly sworn, each for
himself/herself deposes and says that he/she, the said D. G. Donovan, is
Assistant Vice President, and he/she, the said C. Potter, is Assistant
Secretary, of BNY Midwest Trust Company, the corporation described in and which
executed the within and foregoing Supplemental Trust Indenture, as mortgagee;
and each for himself further says that said Supplemental Trust Indenture was
executed in good faith, and not for the purpose of hindering, delaying, or
defrauding any creditor of the mortgagor.

       /S/ D. G. Donovan                                     /S/ C. Potter
------------------------------------                      ---------------------
D. G. Donovan                                                  C. Potter

         Subscribed and sworn to before me this 1st day of August, A.D. 2003.

         /S/ K. Gibson
------------------------------------
K. Gibson
Notary Public
My commission expires:  7/8/06
                                                    (NOTARY SEAL)

<PAGE>

                                   SCHEDULE A

         The property referred to in Article I of the foregoing Supplemental
Trust Indenture from Northern States Power Company to BNY Midwest Trust Company,
Trustee, effective as of August 1, 2003, includes the following property
hereafter more specifically described. Such description, however, is not
intended to limit or impair the scope or intention of the general description
contained in the granting clauses or elsewhere in the Original Indenture.

                      I. TRANSMISSION LINES OF THE COMPANY

         The electric transmission lines of the Company, including towers,
poles, pole lines, wire, switch racks, switchboards, insulators and other
appliances and equipment, and all other property forming a part thereof or
appertaining thereto, and all service lines extending therefrom; together with
all rights for or relating to the construction or maintenance of operation
thereof through, over, under or upon any private property of public streets or
highways within as well as without the corporate limits of any municipal
corporation, and particularly the following described lines, to-wit:

                          IN THE STATE OF NORTH DAKOTA

<Table>
<Caption>

Line 0920             56.41 Miles           Rugby - Manitoba Hydro
<S>                   <C>                   <C>    <C>    <C>    <C>    <C>
                                            Pierce Co., ND.
                                            Sec's  6, 7, T156  R72
                                            Sec's 3, 4, 10, 15, 21, 22, 28, 33, T157, R72
                                            Sec's 1, 12, 13, 14, 15, 16, 21, 28, 33, T158, R72
                                            Sec. 6, T158, R71

                                            Rolette Co., ND.
                                            Sec's 6, 7, 18, 19, 30, 31, T160,
                                            R71 Sec's 2, 3, 4, 8, 9, 17, 18, 19,
                                            30, 31, 36, T161, R71 Sec's 13, 14,
                                            21, 22, 23, 28, 29, 31, 32, T161,
                                            R70 Sec's 4, 5, 7, 8, T161, R69
                                            Sec's 2, 11, 14, 22, 23, 26, 33, 34,
                                            35, T162, R69 Sec's 2, 11, 14, 23,
                                            26, 35, T163, R69 Sec's 26, 35,
                                            T164, R69
</Table>

<PAGE>

         This instrument was drafted by Northern States Power Company, 414
Nicollet Mall, Minneapolis, Minnesota 55401.

         Tax statements for the real property described in this instrument
should be sent to Northern States Power Company, 414 Nicollet Mall, Minneapolis,
Minnesota 55401.

         Please return recorded document(s) to Lori R. Pagel, GO-Mezzanine, Xcel
Energy Inc., 414 Nicollet Mall, Minneapolis, Minnesota 55401.<PAGE>
                                 ACUSPHERE, INC.

                      2003 Stock Option and Incentive Plan

1.    Purpose and Eligibility

      The purpose of this 2003 Stock Option and Incentive Plan (the "Plan") of
Acusphere, Inc. (the "Company") is to provide stock options and other equity
interests in the Company (each an "Award") to employees, officers, directors,
consultants and advisors of the Company and its Subsidiaries, all of whom are
eligible to receive Awards under the Plan. Any person to whom an Award has been
granted under the Plan is called a "Participant." Additional definitions are
contained in Section 8.

2.    Administration

      a. Administration by Board of Directors. The Plan will be administered by
the Board of Directors of the Company (the "Board"). The Board, in its sole
discretion, shall have the authority to grant and amend Awards, to adopt, amend
and repeal rules relating to the Plan and to interpret and correct the
provisions of the Plan and any Award. All decisions by the Board shall be final
and binding on all interested persons. Neither the Company nor any member of the
Board shall be liable for any action or determination relating to the Plan.

      b. Appointment of Committees. To the extent permitted by applicable law,
the Board may delegate any or all of its powers under the Plan to one or more
committees or subcommittees of the Board (a "Committee"). All references in the
Plan to the "Board" shall mean such Committee or the Board.

      c. Delegation to Executive Officers. To the extent permitted by applicable
law, the Board may delegate to one or more executive officers of the Company the
power to grant Awards and exercise such other powers under the Plan as the Board
may determine, provided that the Board shall fix the maximum number of Awards to
be granted and the maximum number of shares issuable to any one Participant
pursuant to Awards granted by such executive officers.

3.    Stock Available for Awards

      a. Number of Shares. Subject to adjustment under Section 3(c), the
aggregate number of shares of Common Stock of the Company (the "Common Stock")
that may be issued pursuant to the Plan is fifteen million (15,000,000) shares.
If any Award expires, or is terminated, surrendered or forfeited, in whole or in
part, the unissued Common Stock covered by such Award shall again be available
for the grant of Awards under the Plan. If shares of Common Stock issued
pursuant to the Plan are repurchased by, or are surrendered or forfeited to, the
Company at no more than cost, such shares of Common Stock shall again be
available for the grant of Awards under the Plan; provided, however, that the
cumulative number of such shares that may be so reissued under the Plan will not
exceed fifteen million (15,000,000) shares.
<PAGE>
                                      -2-

Shares issued under the Plan may consist in whole or in part of authorized but
unissued shares or treasury shares.

      b. Per-Participant Limit. Subject to adjustment under Section 3(c), no
Participant may be granted Awards during any one fiscal year to purchase more
than three million five hundred thousand (3,500,000) shares of Common Stock.

      c. Adjustment to Common Stock. In the event of any stock split, stock
dividend, extraordinary cash dividend, recapitalization, reorganization, merger,
consolidation, combination, exchange of shares, liquidation, spin-off, split-up,
or other similar change in capitalization or event, (i) the number and class of
securities available for Awards under the Plan and the per-Participant share
limit, (ii) the number and class of securities, vesting schedule and exercise
price per share subject to each outstanding Option, (iii) the repurchase price
per security subject to repurchase, and (iv) the terms of each other outstanding
stock-based Award shall be adjusted by the Company (or substituted Awards may be
made) to the extent the Board shall determine, in good faith, that such an
adjustment (or substitution) is appropriate. If Section 7(e)(i) applies for any
event, this Section 3(c) shall not be applicable.

4.    Stock Options

      a. General. The Board may grant options to purchase Common Stock (each, an
"Option") and determine the number of shares of Common Stock to be covered by
each Option, the exercise price of each Option and the conditions and
limitations applicable to the exercise of each Option and the Common Stock
issued upon the exercise of each Option, including vesting provisions,
repurchase provisions and restrictions relating to applicable federal or state
securities laws, as it considers advisable.

      b. Incentive Stock Options. An Option that the Board intends to be an
"incentive stock option" as defined in Section 422 of the Code (an "Incentive
Stock Option") shall be granted only to employees of the Company and shall be
subject to and shall be construed consistently with the requirements of Section
422 of the Code. The Board and the Company shall have no liability if an Option
or any part thereof that is intended to be an Incentive Stock Option does not
qualify as such. An Option or any part thereof that does not qualify as an
Incentive Stock Option is referred to herein as a "Nonstatutory Stock Option."

      c. Exercise Price. The Board shall establish the exercise price (or
determine the method by which the exercise price shall be determined) at the
time each Option is granted and specify it in the applicable option agreement.

      d. Duration of Options. Each Option shall be exercisable at such times and
subject to such terms and conditions as the Board may specify in the applicable
option agreement.

      e. Exercise of Option. Options may be exercised only by delivery to the
Company of a written notice of exercise signed by the proper person together
with payment in full as specified in Section 4(f) for the number of shares for
which the Option is exercised.
<PAGE>
                                      -3-

      f. Payment Upon Exercise. Common Stock purchased upon the exercise of an
Option shall be paid for by one or any combination of the following forms of
payment:

            (i) by check payable to the order of the Company;

            (ii) except as otherwise explicitly provided in the applicable
option agreement, and only if the Common Stock is then publicly traded, delivery
of an irrevocable and unconditional undertaking by a creditworthy broker to
deliver promptly to the Company sufficient funds to pay the exercise price, or
delivery by the Participant to the Company of a copy of irrevocable and
unconditional instructions to a creditworthy broker to deliver promptly to the
Company cash or a check sufficient to pay the exercise price; or

            (iii) to the extent explicitly provided in the applicable option
agreement, by (x) delivery of shares of Common Stock owned by the Participant
valued at fair market value (as determined by the Board or as determined
pursuant to the applicable option agreement), (y) delivery of a promissory note
of the Participant to the Company (and delivery to the Company by the
Participant of a check in an amount equal to the par value of the shares
purchased), or (z) payment of such other lawful consideration as the Board may
determine.

5.    Restricted Stock

      a. Grants. The Board may grant Awards entitling recipients to acquire
shares of Common Stock, subject to (i) delivery to the Company by the
Participant of cash or other lawful consideration in an amount at least equal to
the par value of the shares purchased, and (ii) the right of the Company to
repurchase all or part of such shares at their issue price or other stated or
formula price from the Participant in the event that conditions specified by the
Board in the applicable Award are not satisfied prior to the end of the
applicable restriction period or periods established by the Board for such Award
(each, a "Restricted Stock Award").

      b. Terms and Conditions. The Board shall determine the terms and
conditions of any such Restricted Stock Award. Any stock certificates issued in
respect of a Restricted Stock Award shall be registered in the name of the
Participant and, unless otherwise determined by the Board, deposited by the
Participant, together with a stock power endorsed in blank, with the Company (or
its designee). After the expiration of the applicable restriction periods, the
Company (or such designee) shall deliver the certificates no longer subject to
such restrictions to the Participant or, if the Participant has died, to the
beneficiary designated by a Participant, in a manner determined by the Board, to
receive amounts due or exercise rights of the Participant in the event of the
Participant's death (the "Designated Beneficiary"). In the absence of an
effective designation by a Participant, Designated Beneficiary shall mean the
Participant's estate.

6.    Other Stock-Based Awards

      The Board shall have the right to grant other Awards based upon the Common
Stock having such terms and conditions as the Board may determine, including,
without limitation, the
<PAGE>
                                      -4-

grant of shares based upon certain conditions, the grant of securities
convertible into Common Stock and the grant of stock appreciation rights,
phantom stock awards or stock units.

7.    General Provisions Applicable to Awards

      a. Transferability of Awards. Except as the Board may otherwise determine
or provide in an Award, Awards shall not be sold, assigned, transferred, pledged
or otherwise encumbered by the person to whom they are granted, either
voluntarily or by operation of law, except by will or the laws of descent and
distribution, and, during the life of the Participant, shall be exercisable only
by the Participant. References to a Participant, to the extent relevant in the
context, shall include references to authorized transferees.

      b. Documentation. Each Award under the Plan shall be evidenced by a
written instrument in such form as the Board shall determine or as executed by
an officer of the Company pursuant to authority delegated by the Board. Each
Award may contain terms and conditions in addition to those set forth in the
Plan provided that such terms and conditions do not contravene the provisions of
the Plan.

      c. Board Discretion. The terms of each type of Award need not be
identical, and the Board need not treat Participants uniformly.

      d. Termination of Status. The Board shall determine the effect on an Award
of the disability, death, retirement, authorized leave of absence or other
change in the employment or other status of a Participant and the extent to
which, and the period during which, the Participant, or the Participant's legal
representative, conservator, guardian or Designated Beneficiary, may exercise
rights under the Award.

      e. Acquisition of the Company

            (i) Consequences of an Acquisition. Upon the consummation of an
Acquisition, the Board or the board of directors of the surviving or acquiring
entity (as used in this Section 7(e)(i), also the "Board"), shall, as to
outstanding Awards (on the same basis or on different bases as the Board shall
specify), make appropriate provision for the continuation of such Awards by the
Company or the assumption of such Awards by the surviving or acquiring entity
and by substituting on an equitable basis for the shares then subject to such
Awards either (a) the consideration payable with respect to the outstanding
shares of Common Stock in connection with the Acquisition, (b) shares of stock
of the surviving or acquiring corporation or (c) such other securities or other
consideration as the Board deems appropriate, the fair market value of which (as
determined by the Board in its sole discretion) shall not materially differ from
the fair market value of the shares of Common Stock subject to such Awards
immediately preceding the Acquisition. In addition to or in lieu of the
foregoing, with respect to outstanding Options, the Board may, on the same basis
or on different bases as the Board shall specify, upon written notice to the
affected optionees, provide that one or more Options then outstanding must be
exercised, in whole or in part, within a specified number of days of the date of
such notice, at the end of which period such Options shall terminate, or provide
that one or more Options then
<PAGE>
                                      -5-

outstanding, in whole or in part, shall be terminated in exchange for a cash
payment equal to the excess of the fair market value (as determined by the Board
in its sole discretion) for the shares subject to such Options over the exercise
price thereof; provided, however, that before terminating any portion of an
Option that is not vested or exercisable (other than in exchange for a cash
payment), the Board must first accelerate in full the exercisability of the
portion that is to be terminated. Unless otherwise determined by the Board (on
the same basis or on different bases as the Board shall specify), any repurchase
rights or other rights of the Company that relate to an Option or other Award
shall continue to apply to consideration, including cash, that has been
substituted, assumed or amended for an Option or other Award pursuant to this
paragraph. The Company may hold in escrow all or any portion of any such
consideration in order to effectuate any continuing restrictions.

            (ii) Acquisition Defined. An "Acquisition" shall mean: (x) the sale
of the Company by merger in which the shareholders of the Company in their
capacity as such no longer own a majority of the outstanding equity securities
of the Company (or its successor); or (y) any sale of all or substantially all
of the assets or capital stock of the Company (other than in a spin-off or
similar transaction) or (z) any other acquisition of the business of the
Company, as determined by the Board.

            (iii) Assumption of Options Upon Certain Events. In connection with
a merger or consolidation of an entity with the Company or the acquisition by
the Company of property or stock of an entity, the Board may grant Awards under
the Plan in substitution for stock and stock-based awards issued by such entity
or an affiliate thereof. The substitute Awards shall be granted on such terms
and conditions as the Board considers appropriate in the circumstances.

            (iv) Parachute Awards. If, in connection with an Acquisition
described therein, a tax under Section 4999 of the Code would be imposed on the
Participant (after taking into account the exceptions set forth in Sections
280G(b)(4) and 280G(b)(5) of the Code), then the number of Awards which shall
become exercisable, realizable or vested shall be reduced (or delayed), to the
minimum extent necessary, so that no such tax would be imposed on the
Participant (the Awards not becoming so accelerated, realizable or vested, the
"Parachute Awards"); provided, however, that if the "aggregate present value" of
the Parachute Awards would exceed the tax that, but for this sentence, would be
imposed on the Participant under Section 4999 of the Code in connection with the
Acquisition, then the Awards shall become immediately exercisable, realizable
and vested without regard to the provisions of this sentence. For purposes of
the preceding sentence, the "aggregate present value" of an Award shall be
calculated on an after-tax basis (other than taxes imposed by Section 4999 of
the Code) and shall be based on economic principles rather than the principles
set forth under Section 280G of the Code and the regulations promulgated
thereunder. All determinations required to be made under this Section 7(e)(iv)
shall be made by the Company.

      f. Withholding. Each Participant shall pay to the Company, or make
provisions satisfactory to the Company for payment of, any taxes required by law
to be withheld in connection with Awards to such Participant no later than the
date of the event creating the tax
<PAGE>
                                      -6-

liability. The Board may allow Participants to satisfy such tax obligations in
whole or in part by transferring shares of Common Stock, including shares
retained from the Award creating the tax obligation, valued at their fair market
value (as determined by the Board or as determined pursuant to the applicable
option agreement). The Company may, to the extent permitted by law, deduct any
such tax obligations from any payment of any kind otherwise due to a
Participant.

      g. Amendment of Awards. The Board may amend, modify or terminate any
outstanding Award including, but not limited to, substituting therefor another
Award of the same or a different type, changing the date of exercise or
realization, and converting an Incentive Stock Option to a Nonstatutory Stock
Option, provided that, the Participant's consent to such action shall be
required unless the Board determines that the action, taking into account any
related action, would not materially and adversely affect the Participant.

      h. Conditions on Delivery of Stock. The Company will not be obligated to
deliver any shares of Common Stock pursuant to the Plan or to remove
restrictions from shares previously delivered under the Plan until (i) all
conditions of the Award have been met or removed to the satisfaction of the
Company, (ii) in the opinion of the Company's counsel, all other legal matters
in connection with the issuance and delivery of such shares have been satisfied,
including any applicable securities laws and any applicable stock exchange or
stock market rules and regulations, and (iii) the Participant has executed and
delivered to the Company such representations or agreements as the Company may
consider appropriate to satisfy the requirements of any applicable laws, rules
or regulations, including any applicable withholding tax.

      i. Acceleration. The Board may at any time provide that any Options shall
become immediately exercisable in full or in part, that any Restricted Stock
Awards shall be free of some or all restrictions, or that any other stock-based
Awards may become exercisable in full or in part or free of some or all
restrictions or conditions, or otherwise realizable in full or in part, as the
case may be, despite the fact that the foregoing actions may (i) cause the
application of Sections 280G and 4999 of the Code if a change in control of the
Company occurs, or (ii) disqualify all or part of the Option as an Incentive
Stock Option.

8.    Miscellaneous

      a. Definitions.

            (i) "Company," for purposes of eligibility under the Plan, shall
include any present or future subsidiary corporations of Acusphere, Inc., as
defined in Section 424(f) of the Code (a "Subsidiary"), and any present or
future parent corporation of Acusphere, Inc., as defined in Section 424(e) of
the Code. For purposes of Awards other than Incentive Stock Options, the term
"Company" shall include any other business venture in which the Company has a
direct or indirect significant interest, as determined by the Board in its sole
discretion.

            (ii) "Code" means the Internal Revenue Code of 1986, as amended, and
any regulations promulgated thereunder.
<PAGE>
                                      -7-

            (iii) "employee" for purposes of eligibility under the Plan (but not
for purposes of Section 4(b)) shall include a person to whom an offer of
employment has been extended by the Company.

      b. No Right To Employment or Other Status. No person shall have any claim
or right to be granted an Award, and the grant of an Award shall not be
construed as giving a Participant the right to continued employment or any other
relationship with the Company. The Company expressly reserves the right at any
time to dismiss or otherwise terminate its relationship with a Participant free
from any liability or claim under the Plan.

      c. No Rights As Stockholder. Subject to the provisions of the applicable
Award, no Participant or Designated Beneficiary shall have any rights as a
stockholder with respect to any shares of Common Stock to be distributed with
respect to an Award until becoming the record holder thereof.

      d. Effective Date and Term of Plan. The Plan shall become effective on the
date on which it is adopted by the Board. No Awards shall be granted under the
Plan after the completion of ten years from the date on which the Plan was
adopted by the Board, but Awards previously granted may extend beyond that date.

      e. Amendment of Plan. The Board may amend, suspend or terminate the Plan
or any portion thereof at any time.

      f. Governing Law. The provisions of the Plan and all Awards made hereunder
shall be governed by and interpreted in accordance with the laws of Delaware,
without regard to any applicable conflicts of law.

                                          Adopted by the Board of Directors on
                                          August 4, 2003

                                          Approved by the stockholders on
                                          ---------------

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