
<PAGE>
                          SUPPLEMENTAL TRUST INDENTURE
                                      FROM
                         NORTHERN STATES POWER COMPANY
 
                                       TO
                         HARRIS TRUST AND SAVINGS BANK
                                    TRUSTEE
                                 --------------
                              DATED APRIL 1, 1997
                                 --------------
                        SUPPLEMENTAL TO TRUST INDENTURE
                             DATED FEBRUARY 1, 1937
                                      AND
                           SUPPLEMENTAL AND RESTATED
                                TRUST INDENTURE
                               DATED MAY 1, 1988

<PAGE>

                               TABLE OF CONTENTS
                                 --------------
 
<TABLE>
<S>             <C>                                                                     <C>
Parties................................................................................  1
 
Recitals...............................................................................  1
 
Form of Bonds of Pollution Control Series M, N, O and P................................   5
 
Form of Trustee's Certificate..........................................................   8
 
Further Recitals.......................................................................   8
 
ARTICLE I       SPECIFIC SUBJECTION OF ADDITIONAL PROPERTY TO THE LIEN OF THE ORIGINAL
                INDENTURE..............................................................   8
 
Section 1.01    Grant of certain property, including personal property to comply with
                the Uniform Commercial Code, subject to permitted liens and other
                exceptions contained in 1937 Indenture.................................   8
 
ARTICLE II      PROVISIONS OF BONDS OF POLLUTION CONTROL SERIES M, N, O AND P..........   9
 
Section 2.01    Terms of Bonds of Pollution Control Series M...........................   9
 
Section 2.02    Payment of principal and interest of Bonds of Pollution Control Series
                M......................................................................  10
 
Section 2.03    Bonds of Pollution Control Series M deemed fully paid upon payment of
                Series 1989-A Pollution Control Revenue Bonds..........................  11
 
Section 2.04    Terms of Bonds of Pollution Control Series N...........................  11
 
Section 2.05    Payment of principal and interest of Bonds of Pollution Control Series
                N......................................................................  11
 
Section 2.06    Bonds of Pollution Control Series N deemed fully paid upon payment of
                Series 1992-A Pollution Control Revenue Bonds..........................  12
 
Section 2.07    Terms of Bonds of Pollution Control Series O...........................  13
 
Section 2.08    Payment of principal and interest of Bonds of Pollution Control Series
                O......................................................................  13
 
Section 2.09    Bonds of Pollution Control Series O deemed fully paid upon payment of
                Series 1993-A Pollution Control Revenue Bonds..........................  14
 
Section 2.10    Terms of Bonds of Pollution Control Series P...........................  14
 
Section 2.11    Payment of principal and interest of Bonds of Pollution Control Series
                P......................................................................  14
 
Section 2.12    Bonds deemed fully paid upon payment of Series 1993-B Pollution Control
                Revenue Bonds..........................................................  15
 
Section 2.13    Interchangeability of bonds............................................  16
 
Section 2.14    Charges upon exchange or transfer of bonds.............................  16
 
ARTICLE III     FINANCING STATEMENT TO COMPLY WITH THE UNIFORM COMMERCIAL CODE.........  17
 
Section 3.01    Names and addresses of debtor and secured party........................  17
 
Section 3.02    Property subject to lien...............................................  17
 
Section 3.03    Maturity dates and principal amounts of obligations secured............  17
 
Section 3.04    Financing Statement adopted for all First Mortgage Bonds listed in
                Section 3.03...........................................................  17
 
Section 3.05    Recording data for the 1937 Indenture and prior Supplemental Trust
                Indentures.............................................................  17
 
Section 3.06    Financing Statement covers additional series of First Mortgage Bonds...  18
</TABLE>
<PAGE>
 
                                       ii
 
<TABLE>
<S>             <C>                                                                      <C>
ARTICLE IV      AMENDMENTS TO INDENTURE................................................  19
 
Section 4.01    Consent of holders of Bonds............................................  19
 
ARTICLE V       MISCELLANEOUS..........................................................  19
 
Section 5.01    Recitals of fact, except as stated, are statements of the Company......  19
 
Section 5.02    Supplemental Trust Indenture to be construed as a part of the 1937
                Indenture, as supplemented.............................................  19
 
Section         Trust Indenture Act to control.........................................  19
5.03(a)
 
    (b)         Severability of conditions contained in Supplemental Trust Indenture
                and bonds..............................................................  19
 
Section 5.04    Word "Indenture" as used herein includes in its meaning the 1937
                Indenture and all indentures supplemental thereto......................  19
 
Section 5.05    References to either party in Supplemental Trust Indenture include
                successors or assigns..................................................  19
 
Section         Provision for execution in counterparts................................  20
5.06(a)
 
          (b)   Table of Contents and descriptive headings of Articles not to affect
                meaning................................................................  20
 
Schedule A.............................................................................  A-1
</TABLE>

<PAGE>

                                       1
 
    Supplemental Trust Indenture, MADE AS OF THE 1ST DAY OF APRIL, 1997, BY AND
BETWEEN NORTHERN STATES POWER COMPANY, 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, Minnesota (the "Company"), party of the first
part, and HARRIS TRUST AND SAVINGS BANK, 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, Illinois, as Trustee (the "Trustee"),
party of the second part;
 
WITNESSETH:
 
    WHEREAS, the Company has heretofore executed and delivered to the Trustee
its Trust Indenture (the "1937 Indenture"), made as of February 1, 1937, whereby
the 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 Company (except as therein
excepted from the lien thereof) and subject to the rights reserved by the
Company in and by the provisions of the 1937 Indenture, to be held by said
Trustee in trust in accordance with the provisions of the 1937 Indenture for the
equal pro rata benefit and security of all and each of the bonds issued and to
be issued thereunder in accordance with the provisions thereof; and
 
    WHEREAS, the Company heretofore has executed and delivered to the Trustee a
Supplemental Trust Indenture, made as of June 1, 1942, whereby the 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 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:
 
<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
January 1, 1973                 Series due February 1, 2003
</TABLE>
<PAGE>
 
                                       2
 
<TABLE>
<CAPTION>
     DATE OF SUPPLEMENTAL
       TRUST INDENTURE                            DESIGNATION OF SERIES
- ------------------------------  ----------------------------------------------------------
<S>                             <C>
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
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
April 1, 1993                   Series due April 1, 2003
December 1, 1993                Series due December 1, 2000, and December 1, 2005
February 1, 1994                Series due February 1, 1999
October 1, 1994                 Series due October 1, 2001
June 1, 1995                    Series due July 1, 2025
April 1, 1997                   Pollution Control Series M, N, O and P; and
</TABLE>
 
    WHEREAS, the 1937 Indenture and all of the foregoing Supplemental Trust
Indentures are referred to herein collectively as the "Original Indenture"; and
 
    WHEREAS, the 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; 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, the City of Becker, in the County of Sherburne, a municipal
corporation existing under the Constitution and laws of the State of Minnesota
(the "City") has issued $60,000,000 principal amount of its Pollution Control
Revenue Refunding Bonds (Northern States Power Company--Sherburne County
Generating Station Units 1 and 2 Project), Series 1989-A (the "Series 1989-A
Pollution Control Revenue Bonds") pursuant to the provisions of the Indenture of
Trust, dated as of July 1, 1989, as supplemented by Supplemental Indenture No. 1
dated as of April 1, 1997 (as supplemented, the "Series 1989-A Pollution Control
Indenture"), between the City and First Trust National Association, as Trustee
(said Trustee or any successor trustee under the Series 1989-A Pollution Control
Indenture being hereinafter referred to as the "Series 1989-A Pollution Control
Trustee"); and
<PAGE>
                                       3
 
    WHEREAS, the net proceeds of the Series 1989-A Pollution Control Revenue
Bonds were loaned by the City to the Company pursuant to the provisions of a
Loan Agreement dated as of July 1, 1989 as amended by Amendment No. 1 dated as
of April 1, 1997, between the City and the Company (as amended the "Series
1989-A Agreement"), to provide a portion of the funds to finance the
acquisition, construction and equipping of certain pollution control facilities
relating to the first and second electric generating units located in the City
at the Company's Sherburne County Generating Station, owned jointly by the
Company and Southern Minnesota Municipal Power Agency; and
 
    WHEREAS, payments by the Company under and pursuant to the Series 1989-A
Agreement have been assigned by the City to the Series 1989-A Pollution Control
Trustee in order to secure the payment of the Series 1989-A Pollution Control
Revenue Bonds; and
 
    WHEREAS, in order to further secure the payment of the Series 1989-A
Pollution Control Revenue Bonds, the Company desires to provide for the issuance
under the Indenture to the Series 1989-A Pollution Control Trustee of a new
series of bonds designated "First Mortgage Bonds, Pollution Control Series M"
(sometimes called "Bonds of Pollution Control Series M"), in a principal amount
equal to the principal amount of the Series 1989-A Pollution Control Revenue
Bonds, and with corresponding terms and maturity, the Bonds of Pollution Control
Series M to be issued as registered bonds without coupons in denominations of a
multiple of $5,000; and
 
    WHEREAS, the City has issued $27,900,000 principal amount of its Pollution
Control Revenue Bonds (Northern States Power Company--Sherburne County
Generating Station Unit 3 Project), Series 1992-A (the "Series 1992-A Pollution
Control Revenue Bonds") pursuant to the provisions of the Indenture of Trust,
dated as of March 1, 1992, as supplemented by Supplemental Indenture No. 1 dated
as of April 1, 1997 (as supplemented, the "Series 1992-A Pollution Control
Indenture"), between the City and Norwest Bank Minnesota, National Association,
as Trustee (said Trustee or any successor trustee under the Series 1992-A
Pollution Control Indenture being hereinafter referred to as the "Series 1992-A
Pollution Control Trustee"); and
 
    WHEREAS, the net proceeds of the Series 1992-A Pollution Control Revenue
Bonds were loaned by the City to the Company pursuant to the provisions of a
Loan Agreement dated as of March 1, 1992, as amended by Amendment No. 1 dated as
of April 1, 1997, between the City and the Company (as amended, the "Series
1992-A Agreement"), to provide a portion of the funds to finance the
acquisition, construction and equipping of certain pollution control facilities
relating to the third electric generating unit located in the City at the
Company's Sherburne County Generating Station, owned jointly by the Company and
Southern Minnesota Municipal Power Agency; and
 
    WHEREAS, payments by the Company under and pursuant to the Series 1992-A
Agreement have been assigned by the City to the Series 1992-A Pollution Control
Trustee in order to secure the payment of the Series 1992-A Pollution Control
Revenue Bonds; and
 
    WHEREAS, in order to further secure the payment of the Series 1992-A
Pollution Control Revenue Bonds, the Company desires to provide for the issuance
under the Indenture to the Series 1992-A Pollution Control Trustee of a new
series of bonds designated "First Mortgage Bonds, Pollution Control Series N"
(sometimes called "Bonds of Pollution Control Series N"), in a principal amount
equal to the principal amount of the Series 1992-A Pollution Control Revenue
Bonds, and with corresponding terms and maturity, the Bonds of Pollution Control
Series N to be issued as registered bonds without coupons in denominations of a
multiple of $5,000; and
 
    WHEREAS, the City has issued $50,000,000 principal amount of its Pollution
Control Revenue Bonds (Northern States Power Company--Sherburne County
Generating Station Unit 3 Project), Series 1993-A (the "Series 1993-A Pollution
Control Revenue Bonds") pursuant to the provisions of the Indenture of Trust,
dated as of September 1, 1993, as supplemented by Supplemental Indenture No. 1
dated as of April 1, 1997 (as supplemented, the "Series 1993-A Pollution Control
Indenture"), between the City and Norwest Bank Minnesota, National Association,
as Trustee (said Trustee or any successor trustee under the Series 1993-A
Pollution Control Indenture being hereinafter referred to as the "Series 1993-A
Pollution Control Trustee"); and
<PAGE>
                                       4
 
    WHEREAS, the net proceeds of the Series 1993-A Pollution Control Revenue
Bonds were loaned by the City to the Company pursuant to the provisions of a
Loan Agreement dated as of September 1, 1993, as amended by Amendment No. 1
dated as of April 1, 1997, between the City and the Company (as amended, the
"Series 1993-A Agreement"), to provide a portion of the funds to finance the
acquisition, construction and equipping of certain pollution control facilities
relating to the third electric generating unit located in the City at the
Company's Sherburne County Generating Station, owned jointly by the Company and
Southern Minnesota Municipal Power Agency; and
 
    WHEREAS, payments by the Company under and pursuant to the Series 1993-A
Agreement have been assigned by the City to the Series 1993-A Pollution Control
Trustee in order to secure the payment of the Series 1993-A Pollution Control
Revenue Bonds; and
 
    WHEREAS, in order to further secure the payment of the Series 1993-A
Pollution Control Revenue Bonds, the Company desires to provide for the issuance
under the Indenture to the Series 1993-A Pollution Control Trustee of a new
series of bonds designated "First Mortgage Bonds, Pollution Control Series O"
(sometimes called "Bonds of Pollution Control Series O"), in a principal amount
equal to the principal amount of the Series 1993-A Pollution Control Revenue
Bonds, and with corresponding terms and maturity, the Bonds of Pollution Control
Series O to be issued as registered bonds without coupons in denominations of a
multiple of $5,000; and
 
    WHEREAS, the City has issued $50,000,000 principal amount of its Pollution
Control Revenue Bonds (Northern States Power Company--Sherburne County
Generating Station Unit 3 Project), Series 1993-B (the "Series 1993-B Pollution
Control Revenue Bonds") pursuant to the provisions of the Indenture of Trust,
dated as of September 1, 1993, as supplemented by Supplemental Indenture No. 1
dated as of April 1, 1997 (as supplemented, the "Series 1993-B Pollution Control
Indenture"), between the City and Norwest Bank Minnesota, National Association,
as Trustee (said Trustee or any successor trustee under the Series 1993-B
Pollution Control Indenture being hereinafter referred to as the "Series 1993-B
Pollution Control Trustee"); and
 
    WHEREAS, the net proceeds of the Series 1993-B Pollution Control Revenue
Bonds were loaned by the City to the Company pursuant to the provisions of a
Loan Agreement dated as of September 1, 1993, as amended by Amendment No. 1
dated as of April 1, 1997 between the City and the Company (as amended, the
"Series 1993-B Agreement"), to provide a portion of the funds to finance the
acquisition, construction and equipping of certain pollution control facilities
relating to the third electric generating unit located in the City at the
Company's Sherburne County Generating Station, owned jointly by the Company and
Southern Minnesota Municipal Power Agency; and
 
    WHEREAS, payments by the Company under and pursuant to the Series 1993-B
Agreement have been assigned by the City to the Series 1993-B Pollution Control
Trustee in order to secure the payment of the Series 1993-B Pollution Control
Revenue Bonds; and
 
    WHEREAS, in order to further secure the payment of the Series 1993-B
Pollution Control Revenue Bonds, the Company desires to provide for the issuance
under the Indenture to the Series 1993-B Pollution Control Trustee of a new
series of bonds designated "First Mortgage Bonds, Pollution Control Series P"
(sometimes called "Bonds of Pollution Control Series P"), in a principal amount
equal to the principal amount of the Series 1993-B Pollution Control Revenue
Bonds, and with corresponding terms and maturity, the Bonds of Pollution Control
Series P to be issued as registered bonds without coupons in denominations of a
multiple of $5,000; and
<PAGE>
                                       5
 
    WHEREAS, the Bonds of Pollution Control Series M, the Bonds of Pollution
Control Series N, the Bonds of Pollution Control Series O and the Bonds of
Pollution Control Series P are to be substantially in the form and tenor
following, to-wit:
 
           (Form of Bonds of Pollution Control Series M, N, O and P)
 
    This Bond has not been registered under the Securities Act of 1933, as
amended, and may not be offered or sold in contravention of said Act and is not
transferable except to a successor Trustee under the Indenture of Trust dated as
of          from the City of Becker, Minnesota (the "City"), to
         , as Trustee.
 
                         NORTHERN STATES POWER COMPANY
            (Incorporated under the laws of the State of Minnesota)
                              First Mortgage Bond
                            Pollution Control Series
No. ______________                                              $ ______________
 
    Northern States Power Company, a corporation organized and existing under
and by virtue of the laws of the State of Minnesota (herein called the
"Company"), for value received, hereby promises to pay to                    ,
          , Minnesota, as Trustee under the Indenture of Trust dated as of
         , as supplemented by Supplemental Indenture No. 1 dated as of April 1,
1997 (as supplemented, the "Pollution Control Indenture") from the City of
Becker, Minnesota, to                    ,           , Minnesota, or any
successor trustee under the Pollution Control Indenture (the "Pollution Control
Trustee") and at the office of Harris Trust and Savings Bank, Chicago, Illinois
(the "Trustee") the sum of                    Million Dollars in lawful money of
the United States of America on the Demand Redemption Date, as hereinafter
defined, and to pay on the Demand Redemption Date to the Pollution Control
Trustee, interest hereon from the Initial Interest Accrual Date, as hereinafter
defined, to the Demand Redemption Date at the same rate or rates per annum then
and thereafter from time to time borne by the Pollution Control Revenue
[Refunding] Bonds (Northern States Power Company--Sherburne County Generating
Station Unit    Project), Series          (the "Pollution Control Revenue
Bonds"), in like money, said interest being payable at the office of the Trustee
in Chicago, Illinois, subject to the provisions hereinafter set forth in the
event of a rescission of a Redemption Demand, as hereinafter defined.
 
    This bond is one of a duly authorized issue of bonds of the Company, known
as its First Mortgage Bonds, unlimited in aggregate principal amount, which
issue of bonds consists, or may consist of several series of varying
denominations, dates and tenors, all issued and to be issued under and equally
secured (except in so far 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 44 supplemental trust indentures
(the "Supplemental Indentures"), a Supplemental and Restated Trust Indenture
dated May 1, 1988 (the "Restated Indenture") and a new supplemental trust
indenture for the bonds of this series (the "New Supplemental Indenture"),
executed by the Company to the Trustee. The 1937 Indenture, as supplemented by
the Supplemental Indentures, the Restated Indenture and the New Supplemental
Indenture, is referred to as the "Indenture". Reference is hereby 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 in the Indenture provided.
 
    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/or the
holders of the bonds, and/or the terms and provisions of the Indenture and/or of
any instruments supplemental thereto may be modified or altered by affirmative
vote of the holders of at least 80% in principal amount of the bonds then
outstanding under the Indenture and any
<PAGE>
                                       6
 
instruments supplemental thereto (excluding bonds 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
foregoing 80% requirement will be reduced to 66 2/3% when all bonds of each
series issued under the Indenture prior to May 1, 1985, shall have been retired
or all the holders thereof shall have consented to such reduction.
 
    The Restated Indenture amends and restates the 1937 Indenture and the
Supplemental Indentures. 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.
 
    This bond is one of a series of bonds of the Company issued under the
Indenture and designated as First Mortgage Bonds, Pollution Control Series     .
The bonds of this Series have been issued to the Pollution Control Trustee under
the Pollution Control Indenture to secure payment of the Pollution Control
Revenue Bonds issued by the City under the Pollution Control Indenture, the
proceeds of which have been or are to be loaned to the Company pursuant to the
provisions of the Loan Agreement dated as of          , as amended by Amendment
No. 1 dated as of April 1, 1997 (as amended, the "Agreement") between the
Company and the City. The maturity of the obligation represented by the bonds of
this Series is               . The date of maturity of the obligation
represented by the bonds of this Series is hereinafter referred to as the Final
Maturity Date. The bonds of this Series shall bear interest from the Initial
Interest Accrual Date, as hereinafter defined, at the same rate or rates per
annum then and thereafter from time to time borne by the Pollution Control
Revenue Bonds.
 
    Except as provided in the next succeeding paragraph, in the event of a
default under Section 8.01 of the Agreement or in the event of a default in the
payment of the principal of, premium, if any, or interest [(and such default in
the payment of interest continues for the full grace period, if any, permitted
by the Pollution Control Indenture and the Pollution Control Revenue Bonds)] on
the Pollution Control Revenue Bonds, whether at maturity, by acceleration, by
sinking fund, redemption or otherwise, as and when the same becomes due, the
bonds of this Series shall be redeemable in whole upon receipt by the Trustee of
a written demand (hereinafter called a "Redemption Demand") from the Pollution
Control Trustee stating that there has been such a default, stating that it is
acting pursuant to the authorization granted by Section [8.03][8-3] of the
Pollution Control Indenture, specifying the last date to which interest on the
Pollution Control Revenue Bonds has been paid (such date being hereinafter
referred to as the "Initial Interest Accrual Date") and demanding redemption of
the bonds of this Series. The Trustee shall, within 10 days after receiving such
Redemption Demand, mail a copy thereof to the Company marked to indicate the
date of its receipt by the Trustee. Promptly upon receipt by the Company of such
copy of a Redemption Demand, the Company shall fix a date on which it will
redeem the bonds of this Series so demanded to be redeemed (hereinafter called
the "Demand Redemption Date"). Notice of the date fixed as and for the Demand
Redemption Date shall be mailed by the Company to the trustee at least 30 days
prior to such Demand Redemption Date. The date to be fixed by the Company as and
for the Demand Redemption Date may be any date up to and including the earlier
of (i) the 120th day after receipt by the Trustee of the Redemption Demand or
(ii) the Final Maturity Date, PROVIDED that if the Trustee shall not have
received such notice fixing the Demand Redemption Date within 90 days after
receipt by it of the Redemption Demand, the Demand Redemption Date shall be
deemed to be the earlier of (i) the 120th day after receipt by the Trustee of
the Redemption Demand or (ii) the Final Maturity Date. The Trustee shall mail
notice of the Demand Redemption Date (such notice being hereafter called the
"Demand Redemption Notice") to the Pollution
<PAGE>
                                       7
 
Control Trustee not more than 10 nor less than five days prior to the Demand
Redemption Date. Notwithstanding the foregoing, if a default to which this
paragraph is applicable is existing on the Final Maturity Date, such date shall
be deemed to be the Demand Redemption Date without further action (including
actions specified in this paragraph) by the Pollution Control Trustee, the
Trustee or the Company. The bonds of this Series shall be redeemed by the
Company on the Demand Redemption Date, upon surrender thereof by the Pollution
Control Trustee to the Trustee, at a redemption price equal to the principal
amount thereof, plus accrued interest thereon at the rate per annum set forth in
the first paragraph of this Bond, from the Initial Interest Accrual Date to the
Demand Redemption Date. If a Redemption Demand is rescinded by the Pollution
Control Trustee by written notice to the Trustee prior to the Demand Redemption
Date, no Demand Redemption Notice shall be given, or, if already given, shall be
automatically annulled, and interest on the bonds of this Series shall cease to
accrue, all interest accrued thereon shall be automatically rescinded and
cancelled and the Company shall not be obligated to make any payments of
principal of or interest on the bonds of this Series; but no such rescission
shall extend to or affect any subsequent default or impair any right consequent
thereon.
 
    In the event that all of the bonds outstanding under the Indenture shall
have become immediately due and payable, whether by declaration or otherwise,
and such acceleration shall not have been annulled, the bonds of this Series
shall bear interest at the rate per annum set forth in the first paragraph of
this Bond, from the Initial Interest Accrual Date, as specified in a written
notice to the Trustee from the Pollution Control Trustee, and the principal of
and interest on the bonds of this Series from the Initial Interest Accrual Date
shall be payable in accordance with the provisions of the Indenture.
 
    Upon payment of the principal of and premium, if any, and interest on the
Pollution Control Revenue Bonds, whether at maturity or prior to maturity by
redemption or otherwise, and the surrender thereof to and cancellation thereof
by the Pollution Control Trustee (other than any Pollution Control Revenue Bond
that was cancelled by the Pollution Control Trustee and for which one or more
other Pollution Control Revenue Bonds were delivered and authenticated pursuant
to the Pollution Control Indenture in lieu of or in exchange or substitution for
such cancelled Pollution Control Revenue Bond), or upon provision for the
payment thereof having been made in accordance with the Pollution Control
Indenture, bonds of this Series in a principal amount equal to the principal
amount of the Pollution Control Revenue Bonds so surrendered and cancelled or
for the provision for which payment has been made shall be deemed fully paid and
the obligations of the Company thereunder shall be terminated, and such bonds of
this Series shall be surrendered by the Pollution Control Trustee to the Trustee
and shall be cancelled by the Trustee.
 
    No recourse shall be had for the payment of, or interest, if any, on this
bond, or any part thereof, or of any claim based hereon or in respect hereof or
of the Indenture, against any incorporator, or any past, present or future
stockholder, 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.
 
    The 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 Harris Trust and Savings Bank, as Trustee under the Indenture, or its
successor thereunder.
 
    IN WITNESS WHEREOF, NORTHERN STATES POWER COMPANY has caused this instrument
to be signed 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 ___________________________________
         _________ Secretary                       _________ President
<PAGE>
                                       8
 
                        (Form of Trustee's Certificate)
 
    This bond is one of the bonds of the Series designated thereon, described in
the within-mentioned Indenture.
 
                                          HARRIS TRUST AND SAVINGS BANK,
 
                                                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 June 1,
1995; 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 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;

<PAGE>
                                       9
 
    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 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.
         PROVISIONS OF BONDS OF POLLUTION CONTROL SERIES M, N, O AND P
 
    SECTION 2.01. There is hereby created, for issuance under the Indenture, a
series of bonds designated Pollution Control Series M, each of which shall bear
the descriptive title "First Mortgage Bonds, Pollution Control Series M" and the
form thereof shall contain suitable provisions with respect to the matters
specified in this section. The Bonds of Pollution Control Series M shall be
printed, lithographed or typewritten and shall be substantially of the tenor and
purport previously recited. The Bonds of Pollution Control Series M shall be
<PAGE>
                                       10
 
issued as registered bonds without coupons in denominations of a multiple of
$5,000 and shall be registered in the name of the Series 1989-A Pollution
Control Trustee. The Bonds of Pollution Control Series M shall be dated as of
the date of their authentication.
 
    The Bonds of Pollution Control Series M shall be payable, both as to
principal and interest, at the office of the Trustee in Chicago, Illinois, in
lawful money of the United States of America. The maturity of the obligation
represented by the Bonds of Pollution Control Series M is April 1, 2007. The
date of maturity of the obligation represented by the Bonds of Pollution Control
Series M is hereinafter referred to as the Series M Final Maturity Date. The
Bonds of Pollution Control Series M shall bear interest from the Series M
Initial Interest Accrual Date, as hereinafter defined, at the same rate or rates
then and thereafter from time to time borne by the Series 1989-A Pollution
Control Revenue Bonds.
 
    SECTION 2.02. Except as provided in the next succeeding paragraph of this
Section 2.02, in the event of a default under Section 8.01 of the Series 1989-A
Agreement or in the event of a default in the payment of the principal of,
premium, if any, or interest on the Series 1989-A Pollution Control Revenue
Bonds, whether at maturity, by acceleration, by sinking fund, redemption or
otherwise, as and when the same becomes due, the Bonds of Pollution Control
Series M shall be redeemable in whole upon receipt by the Trustee of a written
demand (hereinafter called a "Series M Redemption Demand") from the Series
1989-A Pollution Control Trustee stating that there has been such a default,
stating that it is acting pursuant to the authorization granted by Section 8-3
of the Series 1989-A Pollution Control Indenture, specifying the last date to
which interest on the Series 1989-A Pollution Control Revenue Bonds has been
paid (such date being hereinafter referred to as the "Series M Initial Interest
Accrual Date") and demanding redemption of the Bonds of Pollution Control Series
M. The Trustee shall, within 10 days after receiving such Series M Redemption
Demand, mail a copy thereof to the Company marked to indicate the date of its
receipt by the Trustee. Promptly upon receipt by the Company of such copy of a
Series M Redemption Demand, the Company shall fix a date on which it will redeem
the Bonds of Pollution Control Series M so demanded to be redeemed (hereinafter
called the "Series M Demand Redemption Date"). Notice of the date fixed as the
Series M Demand Redemption Date shall be mailed by the Company to the Trustee at
least 30 days prior to such Series M Demand Redemption Date. The date to be
fixed by the Company as and for the Series M Demand Redemption Date may be any
date up to and including the earlier of (i) the 120th day after receipt by the
Trustee of the Series M Redemption Demand or (ii) the Series M Final Maturity
Date; PROVIDED that if the Trustee shall not have received such notice fixing
the Series M Demand Redemption Date within 90 days after receipt by it of the
Series M Redemption Demand, the Series M Demand Redemption Date shall be deemed
to be the earlier of (i) the 120th day after receipt by the Trustee of the
Series M Redemption Demand or (ii) the Series M Final Maturity Date. The Trustee
shall mail notice of the Series M Demand Redemption Date (such notice being
hereinafter called the "Series M Demand Redemption Notice") to the Series 1989-A
Pollution Control Trustee not more than 10 nor less than five days prior to the
Series M Demand Redemption Date. Notwithstanding the foregoing, if a default to
which this paragraph is applicable is existing on the Series M Final Maturity
Date, such date shall be deemed to be the Series 1989-A Demand Redemption Date
without further action (including actions specified in this paragraph) by the
Series 1989-A Pollution Control Trustee, the Trustee or the Company. The Bonds
of Pollution Control Series M shall be redeemed by the Company on the Series M
Demand Redemption Date, upon surrender thereof by the Series 1989-A Pollution
Control Trustee to the Trustee, at a redemption price equal to the principal
amount thereof, plus accrued interest thereon at the rate per annum set forth in
Section 2.01 hereof, from the Series M Initial Interest Accrual Date to the
Series M Demand Redemption Date. If a Series M Redemption Demand is rescinded by
the Series 1989-A Pollution Control Trustee by written notice to the Trustee
prior to the Series M Demand Redemption Date, no Series M Demand Redemption
Notice shall be given, or, if already given, shall be automatically annulled,
and interest on the Bonds of Pollution Control Series M shall cease to accrue,
all interest accrued thereon shall be automatically rescinded and cancelled and
the Company shall not be obligated to make any payments of principal of or
interest on the Bonds of Pollution Control Series M; but no such rescission
shall extend to or affect any subsequent default or impair any right consequent
thereon.
<PAGE>
                                       11
 
    In the event that all of the bonds outstanding under the Indenture shall
have become immediately due and payable, whether by declaration or otherwise,
and such acceleration shall not have been annulled, the Bonds of Pollution
Control Series M shall bear interest at the rate per annum set forth in Section
2.01 hereof, from the Series M Initial Interest Accrual Date, as specified in a
written notice to the Trustee from the Series 1989-A Pollution Control Trustee,
and the principal of and interest on the Bonds of Pollution Control Series M
from the Series M Initial Interest Accrual Date shall be payable in accordance
with the provisions of the Indenture.
 
    Anything herein contained to the contrary notwithstanding, the Trustee is
not authorized to take any action pursuant to a Series M Redemption Demand or a
rescission thereof or a written notice required by this Section 2.02, and such
Series M Redemption Demand, rescission or notice shall be of no force or effect,
unless it is executed in the name of the Series 1989-A Pollution Control Trustee
by one of its Vice Presidents.
 
    SECTION 2.03. Upon payment of the principal of and premium, if any, and
interest on the Series 1989-A Pollution Control Revenue Bonds, whether at
maturity or prior to maturity by redemption or otherwise, and the surrender
thereof to and cancellation thereof by the Series 1989-A Pollution Control
Trustee (other than any Series 1989-A Pollution Control Revenue Bond that was
cancelled by the Series 1989-A Pollution Control Trustee and for which one or
more other Series 1989-A Pollution Control Revenue Bonds were delivered and
authenticated pursuant to the Series 1989-A Pollution Control Indenture), or
upon provision for the payment thereof having been made in accordance with the
Series 1989-A Pollution Control Indenture, Bonds of Pollution Control Series M
in a principal amount equal to the principal amount of the Series 1989-A
Pollution Control Revenue Bonds so surrendered and cancelled or for the
provision for which payment has been made shall be deemed fully paid and the
obligations of the Company thereunder shall be terminated, and such Bonds of
Pollution Control Series M shall be surrendered by the Series 1989-A Pollution
Control Trustee to the Trustee and shall be cancelled and destroyed by the
Trustee, and a certificate of such cancellation and destruction shall be
delivered to the Company.
 
    SECTION 2.04. There is hereby created, for issuance under the Indenture, a
series of bonds designated Pollution Control Series N, each of which shall bear
the descriptive title "First Mortgage Bonds, Pollution Control Series N" and the
form thereof shall contain suitable provisions with respect to the matters
specified in this section. The Bonds of Pollution Control Series N shall be
printed, lithographed or typewritten and shall be substantially of the tenor and
purport previously recited. The Bonds of Pollution Control Series N shall be
issued as registered bonds without coupons in denominations of a multiple of
$5,000 and shall be registered in the name of the Series 1992-A Pollution
Control Trustee. The Bonds of Pollution Control Series N shall be dated as of
the date of their authentication.
 
    The Bonds of Pollution Control Series N shall be payable, both as to
principal and interest, at the office of the Trustee in Chicago, Illinois, in
lawful money of the United States of America. The maturity of the obligation
represented by the Bonds of Pollution Control Series N is March 1, 2019. The
date of maturity of the obligation represented by the Bonds of Pollution Control
Series N is hereinafter referred to as the Series N Final Maturity Date. The
Bonds of Pollution Control Series N shall bear interest from the Series N
Initial Interest Accrual Date, as hereinafter defined, at the same rate or rates
then and thereafter from time to time borne by the Series 1992-A Pollution
Control Revenue Bonds.
 
    SECTION 2.05. Except as provided in the next succeeding paragraph of this
Section 2.05, in the event of a default under Section 8.01 of the Series 1992-A
Agreement or in the event of a default in the payment of the principal of,
premium, if any, or interest (and such default in the payment of interest
continues for the full grace period, if any, permitted by the Series 1992-A
Pollution Control Indenture and the Series 1992-A Pollution Control Revenue
Bonds) on the Series 1992-A Pollution Control Revenue Bonds, whether at
maturity, by acceleration, by sinking fund, redemption or otherwise, as and when
the same becomes due, the Bonds of Pollution Control Series N shall be
redeemable in whole upon receipt by the Trustee of a written demand (hereinafter
called a "Series N Redemption Demand") from the Series 1992-A Pollution Control
Trustee stating that there has been such a default, stating that it is acting
pursuant to the authorization granted by Section 8.03 of the Series 1992-A
Pollution Control Indenture, specifying the last date to which interest on the
Series 1992-A Pollution Control Revenue Bonds has been paid (such date being
hereinafter referred to as the "Series N Initial
<PAGE>
                                       12
 
Interest Accrual Date") and demanding redemption of the Bonds of Pollution
Control Series N. The Trustee shall, within 10 days after receiving such Series
N Redemption Demand, mail a copy thereof to the Company marked to indicate the
date of its receipt by the Trustee. Promptly upon receipt by the Company of such
copy of a Series N Redemption Demand, the Company shall fix a date on which it
will redeem the Bonds of Pollution Control Series N so demanded to be redeemed
(hereinafter called the "Series N Demand Redemption Date"). Notice of the date
fixed as the Series N Demand Redemption Date shall be mailed by the Company to
the Trustee at least 30 days prior to such Series N Demand Redemption Date. The
date to be fixed by the Company as and for the Series N Demand Redemption Date
may be any date up to and including the earlier of (i) the 120th day after
receipt by the Trustee of the Series N Redemption Demand or (ii) the Series N
Final Maturity Date; PROVIDED that if the Trustee shall not have received such
notice fixing the Series N Demand Redemption Date within 90 days after receipt
by it of the Series N Redemption Demand, the Series N Demand Redemption Date
shall be deemed to be the earlier of (i) the 120th day after receipt by the
Trustee of the Series N Redemption Demand or (ii) the Series N Final Maturity
Date. The Trustee shall mail notice of the Series N Demand Redemption Date (such
notice being hereinafter called the "Series N Demand Redemption Notice") to the
Series 1992-A Pollution Control Trustee not more than 10 nor less than five days
prior to the Series N Demand Redemption Date. Notwithstanding the foregoing, if
a default to which this paragraph is applicable is existing on the Series N
Final Maturity Date, such date shall be deemed to be the Series 1992-A Demand
Redemption Date without further action (including actions specified in this
paragraph) by the Series 1992-A Pollution Control Trustee, the Trustee or the
Company. The Bonds of Pollution Control Series N shall be redeemed by the
Company on the Series N Demand Redemption Date, upon surrender thereof by the
Series 1992-A Pollution Control Trustee to the Trustee, at a redemption price
equal to the principal amount thereof, plus accrued interest thereon at the rate
per annum set forth in Section 2.04 hereof, from the Series N Initial Interest
Accrual Date to the Series M Demand Redemption Date. If a Series N Redemption
Demand is rescinded by the Series 1992-A Pollution Control Trustee by written
notice to the Trustee prior to the Series N Demand Redemption Date, no Series N
Demand Redemption Notice shall be given, or, if already given, shall be
automatically annulled, and interest on the Bonds of Pollution Control Series N
shall cease to accrue, all interest accrued thereon shall be automatically
rescinded and cancelled and the Company shall not be obligated to make any
payments of principal of or interest on the Bonds of Pollution Control Series N;
but no such rescission shall extend to or affect any subsequent default or
impair any right consequent thereon.
 
    In the event that all of the bonds outstanding under the Indenture shall
have become immediately due and payable, whether by declaration or otherwise,
and such acceleration shall not have been annulled, the Bonds of Pollution
Control Series N shall bear interest at the rate per annum set forth in Section
2.04 hereof, from the Series N Initial Interest Accrual Date, as specified in a
written notice to the Trustee from the Series 1992-A Pollution Control Trustee,
and the principal of and interest on the Bonds of Pollution Control Series N
from the Series N Initial Interest Accrual Date shall be payable in accordance
with the provisions of the Indenture.
 
    Anything herein contained to the contrary notwithstanding, the Trustee is
not authorized to take any action pursuant to a Series N Redemption Demand or a
rescission thereof or a written notice required by this Section 2.05, and such
Series N Redemption Demand, rescission or notice shall be of no force or effect,
unless it is executed in the name of the Series 1992-A Pollution Control Trustee
by one of its Vice Presidents.
 
    SECTION 2.06. Upon payment of the principal of and premium, if any, and
interest on the Series 1992-A Pollution Control Revenue Bonds, whether at
maturity or prior to maturity by redemption or otherwise, and the surrender
thereof to and cancellation thereof by the Series 1992-A Pollution Control
Trustee (other than any Series 1992-A Pollution Control Revenue Bond that was
cancelled by the Series 1992-A Pollution Control Trustee and for which one or
more other Series 1992-A Pollution Control Revenue Bonds were delivered and
authenticated pursuant to the Series 1992-A Pollution Control Indenture), or
upon provision for the payment thereof having been made in accordance with the
Series 1992-A Pollution Control Indenture, Bonds of Pollution Control Series N
in a principal amount equal to the principal amount of the Series 1992-A
Pollution Control Revenue Bonds so surrendered and cancelled or for the
provision for which payment has been made shall be deemed fully paid and the
obligations of the Company thereunder shall be terminated, and such Bonds of
<PAGE>
                                       13
 
Pollution Control Series N shall be surrendered by the Series 1992-A Pollution
Control Trustee to the Trustee and shall be cancelled and destroyed by the
Trustee, and a certificate of such cancellation and destruction shall be
delivered to the Company.
 
    SECTION 2.07. There is hereby created, for issuance under the Indenture, a
series of bonds designated Pollution Control Series O, each of which shall bear
the descriptive title "First Mortgage Bonds, Pollution Control Series O" and the
form thereof shall contain suitable provisions with respect to the matters
specified in this section. The Bonds of Pollution Control Series O shall be
printed, lithographed or typewritten and shall be substantially of the tenor and
purport previously recited. The Bonds of Pollution Control Series O shall be
issued as registered bonds without coupons in denominations of a multiple of
$5,000 and shall be registered in the name of the Series 1993-A Pollution
Control Trustee. The Bonds of Pollution Control Series O shall be dated as of
the date of their authentication.
 
    The Bonds of Pollution Control Series O shall be payable, both as to
principal and interest, at the office of the Trustee in Chicago, Illinois, in
lawful money of the United States of America. The maturity of the obligation
represented by the Bonds of Pollution Control Series O is September 1, 2019. The
date of maturity of the obligation represented by the Bonds of Pollution Control
Series O is hereinafter referred to as the Series O Final Maturity Date. The
Bonds of Pollution Control Series O shall bear interest from the Series O
Initial Interest Accrual Date, as hereinafter defined, at the same rate or rates
then and thereafter from time to time borne by the Series 1993-A Pollution
Control Revenue Bonds.
 
    SECTION 2.08. Except as provided in the next succeeding paragraph of this
Section 2.08, in the event of a default under Section 8.01 of the Series 1993-A
Agreement or in the event of a default in the payment of the principal of,
premium, if any, or interest (and such default in the payment of interest
continues for the full grace period, if any, permitted by the Series 1993-A
Pollution Control Indenture and the Series 1993-A Pollution Control Revenue
Bonds) on the Series 1993-A Pollution Control Revenue Bonds, whether at
maturity, by acceleration, by sinking fund, redemption or otherwise, as and when
the same becomes due, the Bonds of Pollution Control Series O shall be
redeemable in whole upon receipt by the Trustee of a written demand (hereinafter
called a "Series O Redemption Demand") from the Series 1993-A Pollution Control
Trustee stating that there has been such a default, stating that it is acting
pursuant to the authorization granted by Section 8.03 of the Series 1993-A
Pollution Control Indenture, specifying the last date to which interest on the
Series 1993-A Pollution Control Revenue Bonds has been paid (such date being
hereinafter referred to as the "Series O Initial Interest Accrual Date") and
demanding redemption of the Bonds of Pollution Control Series O. The Trustee
shall, within 10 days after receiving such Series O Redemption Demand, mail a
copy thereof to the Company marked to indicate the date of its receipt by the
Trustee. Promptly upon receipt by the Company of such copy of a Series O
Redemption Demand, the Company shall fix a date on which it will redeem the
Bonds of Pollution Control Series O so demanded to be redeemed (hereinafter
called the "Series O Demand Redemption Date"). Notice of the date fixed as the
Series O Demand Redemption Date shall be mailed by the Company to the Trustee at
least 30 days prior to such Series O Demand Redemption Date. The date to be
fixed by the Company as and for the Series O Demand Redemption Date may be any
date up to and including the earlier of (i) the 120th day after receipt by the
Trustee of the Series O Redemption Demand or (ii) the Series O Final Maturity
Date; PROVIDED that if the Trustee shall not have received such notice fixing
the Series O Demand Redemption Date within 90 days after receipt by it of the
Series O Redemption Demand, the Series O Demand Redemption Date shall be deemed
to be the earlier of (i) the 120th day after receipt by the Trustee of the
Series O Redemption Demand or (ii) the Series O Final Maturity Date. The Trustee
shall mail notice of the Series O Demand Redemption Date (such notice being
hereinafter called the "Series O Demand Redemption Notice") to the Series 1993-A
Pollution Control Trustee not more than 10 nor less than five days prior to the
Series O Demand Redemption Date. Notwithstanding the foregoing, if a default to
which this paragraph is applicable is existing on the Series O Final Maturity
Date, such date shall be deemed to be the Series 1993-A Demand Redemption Date
without further action (including actions specified in this paragraph) by the
Series 1993-A Pollution Control Trustee, the Trustee or the Company. The Bonds
of Pollution Control Series O shall be redeemed by the Company on the Series O
Demand Redemption Date, upon surrender thereof by the Series 1993-A Pollution
Control Trustee to the Trustee, at a redemption price equal to the principal
amount
<PAGE>
                                       14
 
thereof, plus accrued interest thereon at the rate per annum set forth in
Section 2.07 hereof, from the Series O Initial Interest Accrual Date to the
Series O Demand Redemption Date. If a Series O Redemption Demand is rescinded by
the Series 1993-A Pollution Control Trustee by written notice to the Trustee
prior to the Series O Demand Redemption Date, no Series O Demand Redemption
Notice shall be given, or, if already given, shall be automatically annulled,
and interest on the Bonds of Pollution Control Series O shall cease to accrue,
all interest accrued thereon shall be automatically rescinded and cancelled and
the Company shall not be obligated to make any payments of principal of or
interest on the Bonds of Pollution Control Series O; but no such rescission
shall extend to or affect any subsequent default or impair any right consequent
thereon.
 
    In the event that all of the bonds outstanding under the Indenture shall
have become immediately due and payable, whether by declaration or otherwise,
and such acceleration shall not have been annulled, the Bonds of Pollution
Control Series O shall bear interest at the rate per annum set forth in Section
2.07 hereof, from the Series O Initial Interest Accrual Date, as specified in a
written notice to the Trustee from the Series 1993-A Pollution Control Trustee,
and the principal of and interest on the Bonds of Pollution Control Series O
from the Series O Initial Interest Accrual Date shall be payable in accordance
with the provisions of the Indenture.
 
    Anything herein contained to the contrary notwithstanding, the Trustee is
not authorized to take any action pursuant to a Series O Redemption Demand or a
rescission thereof or a written notice required by this Section 2.08, and such
Series O Redemption Demand, rescission or notice shall be of no force or effect,
unless it is executed in the name of the Series 1993-A Pollution Control Trustee
by one of its Vice Presidents.
 
    SECTION 2.09. Upon payment of the principal of and premium, if any, and
interest on the Series 1993-A Pollution Control Revenue Bonds, whether at
maturity or prior to maturity by redemption or otherwise, and the surrender
thereof to and cancellation thereof by the Series 1993-A Pollution Control
Trustee (other than any Series 1993-A Pollution Control Revenue Bond that was
cancelled by the Series 1993-A Pollution Control Trustee and for which one or
more other Series 1993-A Pollution Control Revenue Bonds were delivered and
authenticated pursuant to the Series 1993-A Pollution Control Indenture), or
upon provision for the payment thereof having been made in accordance with the
Series 1993-A Pollution Control Indenture, Bonds of Pollution Control Series O
in a principal amount equal to the principal amount of the Series 1993-A
Pollution Control Revenue Bonds so surrendered and cancelled or for the
provision for which payment has been made shall be deemed fully paid and the
obligations of the Company thereunder shall be terminated, and such Bonds of
Pollution Control Series O shall be surrendered by the Series 1993-A Pollution
Control Trustee to the Trustee and shall be cancelled and destroyed by the
Trustee, and a certificate of such cancellation and destruction shall be
delivered to the Company.
 
    SECTION 2.10. There is hereby created, for issuance under the Indenture, a
series of bonds designated Pollution Control Series P, each of which shall bear
the descriptive title "First Mortgage Bonds, Pollution Control Series P" and the
form thereof shall contain suitable provisions with respect to the matters
specified in this section. The Bonds of Pollution Control Series P shall be
printed, lithographed or typewritten and shall be substantially of the tenor and
purport previously recited. The Bonds of Pollution Control Series P shall be
issued as registered bonds without coupons in denominations of a multiple of
$5,000 and shall be registered in the name of the Series 1993-B Pollution
Control Trustee. The Bonds of Pollution Control Series P shall be dated as of
the date of their authentication.
 
    The Bonds of Pollution Control Series P shall be payable, both as to
principal and interest, at the office of the Trustee in Chicago, Illinois, in
lawful money of the United States of America. The maturity of the obligation
represented by the Bonds of Pollution Control Series P is September 1, 2019. The
date of maturity of the obligation represented by the Bonds of Pollution Control
Series P is hereinafter referred to as the Series P Final Maturity Date. The
Bonds of Pollution Control Series P shall bear interest from the Series P
Initial Interest Accrual Date, as hereinafter defined, at the same rate or rates
then and thereafter from time to time borne by the Series 1993-B Pollution
Control Revenue Bonds.
 
    SECTION 2.11. Except as provided in the next succeeding paragraph of this
Section 2.11, in the event of a default under Section 8.01 of the Series 1993-B
Agreement or in the event of a default in the payment of the principal of,
premium, if any, or interest (and such default in the payment of interest
continues for the full grace
<PAGE>
                                       15
 
period, if any, permitted by the Series 1993-B Pollution Control Indenture and
the Series 1993-B Pollution Control Revenue Bonds) on the Series 1993-B
Pollution Control Revenue Bonds, whether at maturity, by acceleration, by
sinking fund, redemption or otherwise, as and when the same becomes due, the
Bonds of Pollution Control Series P shall be redeemable in whole upon receipt by
the Trustee of a written demand (hereinafter called a "Series P Redemption
Demand") from the Series 1993-B Pollution Control Trustee stating that there has
been such a default, stating that it is acting pursuant to the authorization
granted by Section 8.03 of the Series 1993-B Pollution Control Indenture,
specifying the last date to which interest on the Series 1993-B Pollution
Control Revenue Bonds has been paid (such date being hereinafter referred to as
the "Series P Initial Interest Accrual Date") and demanding redemption of the
Bonds of Pollution Control Series P. The Trustee shall, within 10 days after
receiving such Series P Redemption Demand, mail a copy thereof to the Company
marked to indicate the date of its receipt by the Trustee. Promptly upon receipt
by the Company of such copy of a Series P Redemption Demand, the Company shall
fix a date on which it will redeem the Bonds of Pollution Control Series P so
demanded to be redeemed (hereinafter called the "Series P Demand Redemption
Date"). Notice of the date fixed as the Series P Demand Redemption Date shall be
mailed by the Company to the Trustee at least 30 days prior to such Series P
Demand Redemption Date. The date to be fixed by the Company as and for the
Series P Demand Redemption Date may be any date up to and including the earlier
of (i) the 120th day after receipt by the Trustee of the Series P Redemption
Demand or (ii) the Series P Final Maturity Date; PROVIDED that if the Trustee
shall not have received such notice fixing the Series P Demand Redemption Date
within 90 days after receipt by it of the Series P Redemption Demand, the Series
P Demand Redemption Date shall be deemed to be the earlier of (i) the 120th day
after receipt by the Trustee of the Series P Redemption Demand or (ii) the
Series P Final Maturity Date. The Trustee shall mail notice of the Series P
Demand Redemption Date (such notice being hereinafter called the "Series P
Demand Redemption Notice") to the Series 1993-B Pollution Control Trustee not
more than 10 nor less than five days prior to the Series P Demand Redemption
Date. Notwithstanding the foregoing, if a default to which this paragraph is
applicable is existing on the Series P Final Maturity Date, such date shall be
deemed to be the Series 1993-B Demand Redemption Date without further action
(including actions specified in this paragraph) by the Series 1993-B Pollution
Control Trustee, the Trustee or the Company. The Bonds of Pollution Control
Series P shall be redeemed by the Company on the Series P Demand Redemption
Date, upon surrender thereof by the Series 1993-B Pollution Control Trustee to
the Trustee, at a redemption price equal to the principal amount thereof, plus
accrued interest thereon at the rate per annum set forth in Section 2.10 hereof,
from the Series P Initial Interest Accrual Date to the Series P Demand
Redemption Date. If a Series P Redemption Demand is rescinded by the Series
1993-B Pollution Control Trustee by written notice to the Trustee prior to the
Series P Demand Redemption Date, no Series P Demand Redemption Notice shall be
given, or, if already given, shall be automatically annulled, and interest on
the Bonds of Pollution Control Series P shall cease to accrue, all interest
accrued thereon shall be automatically rescinded and cancelled and the Company
shall not be obligated to make any payments of principal of or interest on the
Bonds of Pollution Control Series P; but no such rescission shall extend to or
affect any subsequent default or impair any right consequent thereon.
 
    In the event that all of the bonds outstanding under the Indenture shall
have become immediately due and payable, whether by declaration or otherwise,
and such acceleration shall not have been annulled, the Bonds of Pollution
Control Series P shall bear interest at the rate per annum set forth in Section
2.10 hereof, from the Series P Initial Interest Accrual Date, as specified in a
written notice to the Trustee from the Series 1993-B Pollution Control Trustee,
and the principal of and interest on the Bonds of Pollution Control Series P
from the Series P Initial Interest Accrual Date shall be payable in accordance
with the provisions of the Indenture.
 
    Anything herein contained to the contrary notwithstanding, the Trustee is
not authorized to take any action pursuant to a Series P Redemption Demand or a
rescission thereof or a written notice required by this Section 2.11, and such
Series P Redemption Demand, rescission or notice shall be of no force or effect,
unless it is executed in the name of the Series 1993-B Pollution Control Trustee
by one of its Vice Presidents.
 
    SECTION 2.12 Upon payment of the principal of and premium, if any, and
interest on the Series 1993-B Pollution Control Revenue Bonds, whether at
maturity or prior to maturity by redemption or otherwise, and the surrender
thereof to and cancellation thereof by the Series 1993-B Pollution Control
Trustee (other than any
<PAGE>
                                       16
 
Series 1993-B Pollution Control Revenue Bond that was cancelled by the Series
1993-B Pollution Control Trustee and for which one or more other Series 1993-B
Pollution Control Revenue Bonds were delivered and authenticated pursuant to the
Series 1993-B Pollution Control Indenture), or upon provision for the payment
thereof having been made in accordance with the Series 1993-B Pollution Control
Indenture, Bonds of Pollution Control Series P in a principal amount equal to
the principal amount of the Series 1993-B Pollution Control Revenue Bonds so
surrendered and cancelled or for the provision for which payment has been made
shall be deemed fully paid and the obligations of the Company thereunder shall
be terminated, and such Bonds of Pollution Control Series P shall be surrendered
by the Series 1993-B Pollution Control Trustee to the Trustee and shall be
cancelled and destroyed by the Trustee, and a certificate of such cancellation
and destruction shall be delivered to the Company.
 
    SECTION 2.13 The Series 1989-A Pollution Control Trustee, the Series 1992-A
Pollution Control Trustee, the Series 1993-A Pollution Control Trustee and the
Series 1993-B Pollution Control Trustee as the registered holder of the Bonds of
Pollution Control Series M, Bonds of Pollution Control Series N, Bonds of
Pollution Control Series O and Bonds of Pollution Control Series P,
respectively, at its option may surrender the same at the office of the Trustee,
in Chicago, Illinois, or elsewhere, if authorized by the Company, for
cancellation, in exchange for other bonds of the same series of the same
aggregate principal amount. Thereupon, and upon receipt of any payment required
under the provisions of Section 2.14 hereof, the Company shall execute and
deliver to the Trustee and the Trustee shall authenticate and deliver such other
registered bonds to such registered holder at its office or at any other place
specified as aforesaid.
 
    SECTION 2.14 No charge shall be made by the Company for any exchange or
transfer of Bonds of Pollution Control Series M, Bonds of Pollution Control
Series N, Bonds of Pollution Control Series O or Bonds of Pollution Control
Series P other than for taxes or other governmental charges, if any, that may be
imposed in relation thereto.

<PAGE>
                                       17
 
                                  ARTICLE III.
         FINANCING STATEMENT TO COMPLY WITH THE UNIFORM COMMERCIAL CODE
 
    SECTION 3.01 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: Harris Trust and Savings Bank, Trustee
                       111 West Monroe Street
                       Chicago, Illinois 60603
 
    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 3.02 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 3.03 The maturity dates and respective principal amounts of
obligations of the debtor secured and presently to be secured by the 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:
 
<TABLE>
<CAPTION>
FIRST MORTGAGE BONDS                                                          PRINCIPAL AMOUNT
- ----------------------------------------------------------------------------  ----------------
<S>                                                                           <C>
Series due October 1, 1997..................................................   $  100,000,000
Series due February 1, 1999.................................................   $  200,000,000
Series due October 1, 2001..................................................   $  150,000,000
Series due December 1, 2000.................................................   $  100,000,000
Series due March 1, 2002....................................................   $   50,000,000
Series due February 1, 2003.................................................   $   50,000,000
Series due April 1, 2003....................................................   $   80,000,000
Series due December 1, 2005.................................................   $   70,000,000
Resource Recovery Series I..................................................   $   19,800,000
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 M..................................................   $   60,000,000
Pollution Control Series N..................................................   $   27,900,000
Pollution Control Series O..................................................   $   50,000,000
Pollution Control Series P..................................................   $   50,000,000
</TABLE>
 
    SECTION 3.04 This Financing Statement is hereby adopted for all of the First
Mortgage Bonds of the series mentioned above secured by said Indenture.
 
    SECTION 3.05 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 June 1, 1952
 
    Supplemental Indenture
      Dated October 1, 1954
 
    Supplemental Indenture
      Dated September 1, 1956
<PAGE>
                                       18
 
    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, 1945
 
    Supplemental Indenture
      Dated July 1, 1948
 
    Supplemental Indenture
      Dated August 1, 1949
 
    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
 
    Supplemental Indenture
      Dated September 1, 1985
 
    Supplemental Indenture
      Dated May 1, 1988
 
    Supplemental Indenture
      Dated July 1, 1989
 
    Supplemental Indenture
      Dated October 1, 1969
 
    Supplemental Indenture
      Dated February 1, 1971
 
    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 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
 
    SECTION 3.06 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.
<PAGE>
                                       19
 
                                  ARTICLE IV.
                            AMENDMENTS TO INDENTURE
 
    SECTION 4.01 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 Trust Indenture dated May 1, 1985. Each holder or registered owner
of a bond of any series (including Bonds of Pollution Control Series M, Bonds of
Pollution Control Series N, Bonds of Pollution Control Series O and Bonds of
Pollution Control Series P) 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 V.
                                 MISCELLANEOUS
 
    SECTION 5.01 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 5.02 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, 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 and
April 1, 1997.
 
    SECTION 5.03 (a) If any provision of 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 provision shall control.
 
    (b) In case any one or more of the provisions contained in this Supplemental
Indenture or in the bonds issued hereunder shall 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 5.04 Wherever in this Supplemental Trust Indenture the word
"Indenture" is used without either 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 5.05 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
<PAGE>
                                       20
 
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 5.06 (a) This Supplemental Trust Indenture may be simultaneously
executed 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 amount of obligations to be issued forthwith under the Indenture is
$187,900,000.
 
                                 --------------
<PAGE>
                                       21
 
    IN WITNESS WHEREOF, on this 10th day of April, A.D. 1997, 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 dated April 1, 1997, 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 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 dated April 1, 1997, 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.
 
<TABLE>
<S>                                       <C>
                                          NORTHERN STATES POWER COMPANY
 
                                          BY: EDWARD J. MCINTYRE, VICE PRESIDENT
 
Attest:
 
                                                                (CORPORATE SEAL)
 
GARY R. JOHNSON, SECRETARY
 
Executed by Northern States
Power Company in the presence of:
 
MARY SCHELL, WITNESS
 
DEAN SCHAFER, WITNESS
 
                                                  HARRIS TRUST AND SAVINGS BANK,
                                                                      as Trustee
 
                                          BY: J. BARTOLINI, VICE PRESIDENT
 
Attest:
 
                                                                (CORPORATE SEAL)
 
D.G. DONOVAN, ASSISTANT SECRETARY
 
Executed by Harris Trust and Savings
Bank in the presence of:
 
K. RICHARDSON, WITNESS
 
R. JOHNSON,  WITNESS
</TABLE>
 
<PAGE>
                                       22
 
<TABLE>
<S>                   <C>
STATE OF MINNESOTA
COUNTY OF HENNEPIN    ss.:
</TABLE>
 
    On this 10th day of April A.D. 1997, before me, FAYE WAHLSTRAND, a Notary
Public in and for said County in the State aforesaid, personally appeared Edward
J. McIntyre, and Gary R. Johnson, to me personally known, and to me known to be
the Vice President and 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 Edward J. McIntyre is a Vice President, and
he, the said Gary R. Johnson is the 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 Edward J. McIntyre and Gary R. Johnson 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 10th day of April, A.D. 1997.
 
FAYE WAHLSTRAND
NOTARY PUBLIC IN HENNEPIN COUNTY, MINNESOTA.
MY COMMISSION EXPIRES JANUARY 31, 2000
 
                        (NOTARY SEAL)
 
<TABLE>
<S>                   <C>
STATE OF MINNESOTA
COUNTY OF HENNEPIN    ss.:
</TABLE>
 
    Edward J. McIntyre and Gary R. Johnson, being severally duly sworn, each
deposes and says that he, the said Edward J. McIntyre is Vice President, and he,
the said Gary R. Johnson is Secretary, 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.
 
<TABLE>
<S>                                       <C>
EDWARD J. MCINTYRE
 
GARY R. JOHNSON
</TABLE>
 
    Subscribed and sworn to before me this 10th day of April, A.D. 1997.
 
<TABLE>
<S>                                       <C>
FAYE WAHLSTRAND
 
NOTARY PUBLIC, HENNEPIN COUNTY, MINN.
MY COMMISSION EXPIRES JANUARY 31, 2000
 
                        (NOTARY SEAL)
</TABLE>
 
<PAGE>
                                       23
 
<TABLE>
<S>                <C>
STATE OF ILLINOIS
COUNTY OF COOK)    ss.:
</TABLE>
 
    On this 10th day of April, A.D. 1997, before me, T. MUZQUIZ, a Notary Public
in and for said County in the State aforesaid, personally appeared J. BARTOLINI
and D.G. DONOVAN to me personally known, and to me known to be the Vice
President and Assistant Secretary, respectively, of Harris Trust and Savings
Bank, 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 she, the said J. BARTOLINI is a Vice President, and he, the said D.G.
DONOVAN, is the Assistant Secretary, of said Harris Trust and Savings Bank, 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 J.
BARTOLINI and D.G. DONOVAN 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 10th day of April, A.D. 1997.
 
                                          T. MUZQUIZ
                                          NOTARY PUBLIC, COOK COUNTRY, ILLINOIS.
                                          MY COMMISSION EXPIRES JULY 12, 1997.
 
(NOTARY SEAL)
 
<TABLE>
<S>                <C>
STATE OF ILLINOIS
COUNTY OF COOK     ss.:
</TABLE>
 
    J. BARTOLINI and D.G. DONOVAN, being severally duly sworn, each for himself
deposes and says that she, the said J. BARTOLINI, is Vice President, and he, the
said D.G. DONOVAN, is Assistant Secretary, of Harris Trust and Savings Bank, 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.
 
<TABLE>
<S>                                       <C>
J. BARTOLINI
 
D.G. DONOVAN
</TABLE>
 
    Subscribed and sworn to before me this 10th day of April, A.D. 1997.
 
                                          T. MUZQUIZ
 
                                          NOTARY PUBLIC, COOK COUNTY, ILLINOIS.
                                          MY COMMISSION EXPIRES JULY 12, 1997
 
                        (NOTARY SEAL)

<PAGE>
                                      A-1
 
                                   SCHEDULE A
 
    The property referred to in Article I of the foregoing Supplemental Trust
Indenture from Northern States Power Company to Harris Trust and Savings Bank,
Trustee, made as of April 1, 1997, includes the following property hereafter
more specifically described. Such description, however, is not intended to limit
or impair the scope of intention of the general description contained in the
granting clauses or elsewhere in the Original Indenture.
 
                    I.  PROPERTIES IN THE STATE OF MINNESOTA
 
    The following described real property, situate, lying and being in the
County of Dakota, to-wit:
 
    (1) That part of the NE1/4 of the SE1/4 of Section 30, Township 115 North,
       Range 17 West described as follows: Commencing at the Northeast corner of
       said quarter-quarter; thence South along the East line thereof 153.90
       feet to the South right-of-way line of Trunk Highway No. 55 and the point
       of beginning of the land to be described; thence continuing South along
       said East line 603.00 feet; thence deflecting 90 degrees 00 minutes 00
       seconds right 495.00 feet; thence deflecting 90 degrees 00 minutes 00
       seconds right to said South highway right-of-way line; thence East along
       said highway right-of-way line to the point of beginning. Excepting and
       reserving unto Seller, their heirs and assigns, the perpetual right,
       privilege and easement to construct improve, use, maintain and dedicate
       to the public a roadway upon the North 125 feet and the East 40 feet of
       the above-described parcel of land provided that said roadways do not
       interfere with NSP's electrical facilities, landscaping or right of
       access to the land granted herein.
 
    The following described real property; situate, lying and being in the
County of Hennepin, to-wit:
 
    (1) Lot 1, Block 1, Schany 2nd Addition.
 
    The following described real property; situate, lying and being in the
County of Murray, to-wit:
 
    (1) The North 220 feet of the East 200 feet of the West 235 feet of the
       NE1/4 of Section 24, Township 106 North, Range 43 West.
 
    The following described real property; situate, lying and being in the
County of Rice, to-wit:
 
    (1) Lot 1, Block 1, Cannon Road Substation.
 
    The following described real property; situate, lying and being in the
County of Sherburne, to-wit:
 
    (1) The SW1/4 of Section 6, Township 33 North, Range 28 West, excepting
       therefrom the West 500 feet of the SW1/4 of the SW1/4 of said Section 6.
 
       And
 
       The NE1/4 of the NW1/4 of Section 7, Township 33 North, Range 28 West,
       excepting therefrom the East 153 feet of the North 163 feet.
 
    (2) Beginning at the Northwest corner of the NE1/4 of Section 35, Township
       34 North, Range 29 West; thence North 89 degrees 07 minutes 33 seconds
       East along the North line of said NE1/4 of Section 35 (assumed bearing) a
       distance of 495.01 feet; thence South 00 degrees 10 minutes 53 seconds
       West a distance of 440.07 feet to the South line of the North 440 feet of
       the NW1/4 of the NE1/4; thence South 89 degrees 07 minutes 33 seconds
       West a distance of 495.02 feet to the West line of the NE1/4 of Section
       35; thence North 00 degrees 10 minutes 53 seconds East along said West
       line to the point of beginning, and there terminating.
 
       And
 
       Commencing at the Northwest corner of the NE1/4 of Section 35, Township
       34 North, Range 29 West; thence North 89 degrees 07 minutes 33 seconds
       East along the North line of said NE1/4 of Section 35 (assumed bearing) a
       distance of 819.97 feet to the point of beginning of the land to be
       described;
<PAGE>
                                      A-2
 
       thence continuing North 89 degrees 07 minutes 33 seconds East a distance
       of 497.96 feet to the East line of the NW1/4 of the NE1/4 of said Section
       35; thence South 00 degrees 11 minutes 30 seconds West along the East
       line of said NW1/4 of the NE1/4 a distance of 440.07 feet to the South
       line of the North 440 feet thereof; thence South 89 degrees 07 minutes 33
       seconds West a distance of 495.00 feet; thence North 00 degrees 11
       minutes 31 seconds East a distance of 440.07 feet to the point of
       beginning and there terminating.
 
    The following described real property; situate, lying and being in the
County of Washington, to-wit:
 
    (1) Lots Nine (9) and Ten (10), Block Eight (8), of OAK PARK.
 
    (2) All that part of the Northwest Quarter of the Northwest Quarter (NW1/4
       of the NW1/4) of Section Three (3), in Township Twenty-nine (29) North,
       of Range Twenty (20) West of the Fourth Meridian, described as follows,
       to-wit:
 
          Beginning at an iron monument set at the intersection of the Southerly
           right-of-way line of Minnesota State Highway 212 with a line drawn
           parallel to and Three Hundred Seventy-nine and Two-tenths (379.2)
           feet East of the West line of said tract, and running thence South
           along said parallel line One Hundred (100) feet to an iron monument;
           thence Easterly on a straight line to an iron monument; said monument
           being set on a line drawn parallel to and Five Hundred Ninety-seven
           (597) feet East of said West line of said tract, at a point One
           Hundred (100) feet South of the intersection of said parallel line
           with said Southerly right-of-way line of said highway; thence North
           along said parallel line just described One Hundred (100) feet to an
           iron monument set on said Southerly right-of-way line of said
           highway; thence Westerly along said right of way line to the point of
           beginning, containing Five-tenths (0.5) acres, more or less,
           according to the United States Government Survey thereof.
 
    The following described real property; situate, lying and being in the
County of Waseca, to-wit:
 
    (1) Lot Five (5), Block One (1), South Addition to the City of Waseca, and
       the West (10) feet of the South Fifty (50) feet of Lot Four (4), in Block
       One (1), South Addition to the City of Waseca.
<PAGE>
                                      A-3
 
                                 --------------
 
                          MORTGAGOR'S RECEIPT FOR COPY
 
    The undersigned Northern States Power Company, the Mortgagor described in
the foregoing Mortgage, hereby acknowledges that at the time of the execution of
the Mortgage, Harris Trust and Savings Bank, Trustee, the Mortgagee described
therein, surrendered to it a full, true, complete, and correct copy of said
instrument, with signatures, witnesses, and acknowledgments thereon shown.
 
                                              NORTHERN STATES POWER COMPANY
 
                                          BY EDWARD J. MCINTYRE, VICE PRESIDENT
 
Attest:
 
GARY R. JOHNSON, SECRETARY
                                 --------------
 
    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.

