<PAGE>
                                                                    Exhibit 10-H


                                CHANGE IN CONTROL
                               SEVERANCE AGREEMENT


     This Agreement is made as of the 8th day of April 2002, between Otter Tail
Corporation, a Minnesota corporation, with its principal offices at 215 South
Cascade Street, P.O. Box 496, Fergus Falls, Minnesota 56538-0496 (the
"Corporation") and George A. Koeck ("Employee"), residing at 1755 Ninth Street
South, Fargo, ND 58104.


                          W I T N E S S E T H    T H A T:

     WHEREAS, this Agreement is intended to specify the financial arrangements
that the Corporation will provide to Employee upon Employee's separation from
employment with the Corporation under any of the circumstances described herein;
and

     WHEREAS, this Agreement is entered into by the Corporation in the belief
that it is in the best interests of the Corporation and its shareholders to
provide stable conditions of employment for Employee notwithstanding the
possibility, threat or occurrence of certain types of change in control, thereby
enhancing the Corporation's ability to attract and retain highly qualified
people.

     NOW, THEREFORE, to assure the Corporation that it will have the continued
dedication of Employee notwithstanding the possibility, threat or occurrence of
a bid to take over control of the Corporation, and to induce Employee to remain
in the employ of the Corporation, and for other good and valuable
consideration, the Corporation and Employee agree as follows:

     1. Term of Agreement. The term of this Agreement shall commence on the date
hereof as first written above and shall continue through April 1, 2003; provided
that commencing on March 31, 2003 and each March 31 thereafter, the term of this
Agreement shall automatically be extended for one additional year unless 360
days prior to March 31, the Corporation shall have given notice that it does not
wish to extend this Agreement, and provided, further, that notwithstanding any
such notice by the Corporation not to extend, this Agreement shall continue in
effect for a period of 36 months beyond the term provided herein if a Change in
Control (as defined in Section 3(i) hereof) shall have occurred during such
term.

     2. Termination of Employment.

     (i) Prior to a Change in Control. Employee's rights upon termination of
employment prior to a Change in Control (as defined in Section 3(i) hereof)
shall be governed by the Corporation's standard employment termination policy
applicable to Employee in effect at the time of termination or the Employee's
Employment Agreement.
<PAGE>
     (ii) After a Change in Control.

         (a) From and after the date of a Change in Control (as defined in
Section 3(i) hereof) during the term of this Agreement, the Corporation shall
not terminate Employee from employment with the Corporation except as provided
in this Section 2(ii) or as a result of Employee's Disability (as defined in
Section 3(iv) hereof) or death.

         (b) From and after the date of a Change in Control (as defined in
Section 3(i) hereof) during the term of this Agreement, the Corporation shall
have the right to terminate Employee from employment with the Corporation at any
time during the term of this Agreement for Cause (as defined in Section 3(iii)
hereof), by written notice to Employee, specifying the particulars of the
conduct of Employee forming the basis for such termination.

         (c) From and after the date of a Change in Control (as defined in
Section 3(i) hereof) during the term of this Agreement: (x) the Corporation
shall have the right to terminate Employee's employment without Cause (as
defined in Section 3(iii) hereof), at any time; and (y) Employee shall, upon the
occurrence of such a termination by the Corporation without Cause, or upon the
voluntary termination of Employee's employment by Employee for Good Reason (as
defined in Section 3(ii) hereof), be entitled to receive the benefits provided
in Section 4 hereof. Employee shall evidence a voluntary termination for Good
Reason by written notice to the Corporation given within 60 days after the date
of the occurrence of any event that Employee knows or should reasonably have
known constitutes Good Reason for voluntary termination. Such notice need only
identify Employee and set forth in reasonable detail the facts and circumstances
claimed by Employee to constitute Good Reason.

     Any notice given by Employee pursuant to this Section 2 shall be effective
five business days after the date it is given by Employee.

     3. Definitions

     (i) A "Change in Control" shall mean:

         (a) a change in control of a nature that would be required to be
reported in response to Item 6(e) of Schedule 14A of Regulation 14A promulgated
under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or
successor provision thereto, whether or not the Corporation is then subject to
such reporting requirement;

         (b) any "person" (as such term is used in Sections 13(d) and 14(d) of
the Exchange Act) is or becomes the "beneficial owner" (as defined in Rule 13d-3
promulgated under the Exchange Act), directly or indirectly, of securities of
the Corporation representing 35% or more of the combined voting power of the
Corporation 's then outstanding securities;

         (c) the Continuing Directors (as defined in Section 3(v) hereof) cease
to constitute a majority of the Corporation's Board of Directors; provided that
such change is the


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direct or indirect result of a proxy fight and contested election or elections
for positions on the Board of Directors; or

         (d) the majority of the Continuing Directors (as defined in Section
3(v) hereof) determine in their sole and absolute discretion that there has been
a change in control of the Corporation.

     (ii) "Good Reason" shall mean the occurrence of any of the following
events, except for the occurrence of such an event in connection with the
termination or reassignment of Employee's employment by the Corporation for
Cause (as defined in Section 3(iii) hereof), for Disability (as defined in
Section 3(iv) hereof) or for death:

         (a) the assignment to Employee of employment responsibilities which are
not of comparable responsibility and status as the employment responsibilities
held by Employee immediately prior to a Change in Control;

         (b) a reduction by the Corporation in Employee's base salary as in
effect immediately prior to a Change in Control;

         (c) an amendment or modification of the Corporation 's incentive
compensation program (except as may be required by applicable law) which affects
the terms or administration of the program in a manner adverse to the interest
of Employee as compared to the terms and administration of such program
immediately prior to a Change in Control;

         (d) the Corporation's requiring Employee to be based anywhere other
than within 50 miles of Employee's office location immediately prior to a Change
in Control, except for requirements of temporary travel on the Corporation's
business to an extent substantially consistent with Employee's business travel
obligations immediately prior to a Change in Control;

         (e) except to the extent otherwise required by applicable law, the
failure by the Corporation to continue in effect any benefit or compensation
plan, stock ownership plan, stock purchase plan, stock incentive plan, bonus
plan, life insurance plan, health-and-accident plan, or disability plan in which
Employee is participating immediately prior to a Change in Control (or plans
providing Employee with substantially similar benefits), the taking of any
action by the Corporation which would adversely affect Employee's participation
in, or materially reduce Employee's benefits under, any of such plans or deprive
Employee of any material fringe benefit enjoyed by Employee immediately prior to
such Change in Control, or the failure by the Corporation to provide Employee
with the number of paid vacation days to which Employee is entitled immediately
prior to such Change in Control in accordance with the Corporation's vacation
policy as then in effect; or

         (f) the failure by the Corporation to obtain, as specified in Section
6(i) hereof, an assumption of the obligations of the Corporation to perform this
Agreement by any successor to the Corporation.



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     (iii) "Cause" shall mean termination by the Corporation of Employee's
employment based upon (a) the willful and continued failure by Employee
substantially to perform Employee's duties and obligations (other than any such
failure resulting from Employee's incapacity due to physical or mental illness
or any such actual or anticipated failure resulting from Employee's termination
for Good Reason) or (b) the willful engaging by Employee in misconduct which is
materially injurious to the Corporation, monetarily or otherwise. For purposes
of this Section 3(iii), no action or failure to act on Employee's part shall be
considered "willful" unless done, or omitted to be done, by Employee in bad
faith and without reasonable belief that such action or omission was in the best
interests of the Corporation.

     (iv) "Disability" shall mean any physical or mental condition which would
qualify Employee for a disability benefit under the Corporation 's long-term
disability plan.

     (v) "Continuing Director" shall mean any person who is a member of the
Board of Directors of the Corporation, while such person is a member of the
Board of Directors, who is not an Acquiring Person (as hereinafter defined) or
an Affiliate or Associate (as hereinafter defined) of an Acquiring Person, or a
representative of an Acquiring Person or of any such Affiliate or Associate, and
who (a) was a member of the Board of Directors on the date of this Agreement as
first written above or (b) subsequently becomes a member of the Board of
Directors, if such person's nomination for election or initial election to the
Board of Directors is recommended or approved by a majority of the Continuing
Directors. For purposes of this Section 3(v): "Acquiring Person" shall mean any
"person" (as such term is used in Sections 13(d) and 14(d) of the Exchange Act)
who or which, together with all Affiliates and Associates of such person, is the
"beneficial owner" (as defined in Rule 13d-3 promulgated under the Exchange Act)
of 20% or more of the shares of Common Stock of the Corporation then
outstanding, but shall not include the Corporation, any subsidiary of the
Corporation or any employee benefit plan of the Corporation or of any subsidiary
of the Corporation or any entity holding shares of Common Stock organized,
appointed or established for, or pursuant to the terms of, any such plan; and
"Affiliate" and "Associate" shall have the respective meanings ascribed to such
terms in Rule 12b-2 promulgated under the Exchange Act.

     4. Benefits upon Termination under Section 2(ii)(c)

     (i) Upon the termination (voluntary or involuntary) of the employment of
Employee pursuant to Section 2(ii)(c) hereof, Employee shall be entitled to
receive the benefits specified in this Section 4. The amounts due to Employee
under subparagraph (a) of this Section 4(i) shall be paid to Employee, at
Employee's election as specified in a written notice delivered by Employee to
the Corporation on the date of this Agreement and which is attached hereto as
Exhibit A and made a part hereof, either (a) in a lump sum not later than one
business day prior to the date that the termination of Employee's employment
becomes effective or (b) in 36 equal installments payable monthly, on the last
business day of the month, for 36 consecutive months following the date that the
termination of Employee's employment becomes effective. The amounts due to
Employee under subparagraphs (b), (c) and (d) of this Section 4(i) shall be paid
to Employee not later than one business day prior to the date that the
termination of Employee's employment


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becomes effective. Subject to the provisions of Section 4(ii) hereof, all
benefits to Employee pursuant to this Section 4(i) shall be subject to any
applicable payroll or other taxes required by law to be withheld.

         (a) The Corporation shall pay as severance pay to Employee an amount
equal to three times the sum of (1) Employee's highest annual rate of salary
from the Corporation in effect at any time during the 36 months preceding the
date that the termination of Employee's employment became effective and (2) the
average of the annual bonus paid or to be paid to Employee in respect of each of
the three fiscal years preceding the fiscal year when the termination of
Employee's employment became effective.

         (b) For a period of 36 months following the date that the termination
of Employee's employment became effective or until Employee reaches age 65 or
dies, whichever is the shorter period, the Corporation shall continue for
Employee, at the Corporation's expense, the health, disability and life
insurance coverage in effect for Employee immediately prior to the date that the
termination of Employee's employment became effective under the plans provided
by the Corporation for its executive personnel generally or, if such coverage
cannot by the terms of such plans be provided thereunder, then the Corporation
shall provide equivalent insurance coverage for Employee for such period under
specially obtained policies of insurance.

         (c) The Corporation shall pay to Employee (1) any amount earned by
Employee as a bonus with respect to the fiscal year of the Corporation preceding
the termination of Employee's employment if such bonus has not theretofore been
paid to Employee, and (2) an amount representing credit for any vacation earned
or accrued by him but not taken.

         (d) The Corporation shall also pay to Employee all legal fees and
expenses incurred by Employee as a result of such termination of employment
(including all fees and expenses, if any, incurred by Employee in seeking to
obtain or enforce any right or benefit provided to Employee by this Agreement
whether by arbitration or otherwise); and

         (e) Any and all contracts, agreements or arrangements between the
Corporation and Employee prohibiting or restricting Employee from owning,
operating, participating in, or providing employment or consulting services to,
any business or company competitive with the Corporation at any time or during
any period after the date the termination of Employee's employment becomes
effective, shall be deemed terminated and of no further force or effect as of
the date the termination of Employee's employment becomes effective, to the
extent, but only to the extent, such contracts, agreements or arrangements so
prohibit or restrict Employee; provided that the foregoing provision shall not
constitute a license or right to use any proprietary information of the
Corporation and shall in no way affect any such contracts, agreements or
arrangements insofar as they relate to nondisclosure and nonuse of proprietary
information of the Corporation notwithstanding the fact that such nondisclosure
and nonuse may prohibit or restrict Employee in certain competitive activities.

     (ii) In the event that any payment or benefit received or to be received by
Employee in connection with a Change in Control of the Corporation or
termination of Employee's


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employment (whether payable pursuant to the terms of this Agreement or any other
plan, contract, agreement or arrangement with the Corporation, with any person
whose actions result in a Change in Control of the Corporation or with any
person constituting a member of an "affiliated group" as defined in Section
280G(d)(5) of the Internal Revenue Code of 1986, as amended (the "Code"), with
the Corporation or with any person whose actions result in a Change in Control
of the Corporation (collectively, the "Total Payments")) would be subject to the
excise tax imposed by Section 4999 of the Code or any interest, penalties or
additions to tax with respect to such excise tax (such excise tax, together with
any such interest, penalties or additions to tax, are collectively referred to
as the "Excise Tax"), then Employee shall be entitled to receive from the
Corporation an additional cash payment (a "Gross-Up Payment") within thirty
business days of such determination in an amount such that after payment by
Employee of all taxes (including any interest, penalties or additions to tax
imposed with respect to such taxes), including any Excise Tax, imposed upon the
Gross-Up Payment, Employee retains an amount of the Gross-Up Payment equal to
the Excise Tax imposed upon the Total Payments. All determinations required to
be made under this Section 4(ii), including whether a Gross-Up Payment is
required and the amount of such Gross-Up Payment, shall be made by the
independent accounting firm retained by the Corporation on the date of the
Change in Control (the "Accounting Firm"), which shall provide detailed
supporting calculations both to the Corporation and Employee within 15 business
days of the date that the termination of Employee's employment becomes
effective, or such earlier time as is requested by the Corporation. If the
Accounting Firm determines that no Excise Tax is payable by Employee, it shall
furnish Employee with an opinion that Employee has substantial authority not to
report any Excise Tax on Employee's federal income tax return.

     Any uncertainty in the application of Section 4999 of the Code at the time
of the initial determination by the Accounting Firm hereunder shall be resolved
in favor of Employee. As a result of the uncertainty in the application of
Section 4999 of the Code at the time of the initial determination by the
Accounting Firm hereunder, it is possible that at a later time there will be a
determination that the Gross-Up Payments made by the Corporation were less than
the Gross-Up Payments that should have been made by the Corporation
("Underpayment"), consistent with the calculations required to be made
hereunder. In the event that Employee is required to make a payment of any
Excise Tax, the Accounting Firm shall determine the amount of the Underpayment,
if any, that has occurred and any such Underpayment shall be promptly paid by
the Corporation to or for the benefit of Employee. As a result of the
uncertainty in the application of Section 4999 of the Code at the time of the
initial determination by the Accounting Firm hereunder, it is possible that at a
later time there will be a determination that the Gross-Up Payments made by the
Corporation were more than the Gross-Up Payments that should have been made by
the Corporation ("Overpayment"), consistent with the calculations required to be
made hereunder. Employee agrees to refund to the Corporation the amount of any
Overpayment that the Accounting Firm shall determine has occurred hereunder. Any
determination by the Accounting firm as to the amount of any Gross-Up Payment,
including the amount of any Underpayment or Overpayment, shall be binding upon
the Corporation and Employee.

     (iii) Any payment not made to Employee when due hereunder shall thereafter,
until paid in full, bear interest at the rate of interest equal to the reference
rate announced from time to


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<PAGE>

time by U.S. Bank National Association, plus two percent, with such interest to
be paid to Employee upon demand or monthly in the absence of a demand.

     (iv) Employee shall not be required to mitigate the amount of any payment
provided for in this Section 4 by seeking other employment or otherwise. The
amount of any payment or benefit provided in this Section 4 shall not be reduced
by any compensation earned by Employee as a result of any employment by another
employer.

     5. Employee's Agreements.


        Employee agrees that:

     (i) Without the consent of the Corporation, Employee will not terminate
employment with the Corporation without giving 60 days prior notice to the
Corporation, and during such 60-day period Employee will assist the Corporation,
as and to the extent reasonably requested by the Corporation, in training the
successor to Employee's position with the Corporation. The provisions of this
Section 5(i) shall not apply to any termination (voluntary or involuntary) of
the employment of Employee pursuant to Section 2(ii)(c) hereof.

     (ii) Without the consent of the Corporation or except as may be required by
law, Employee will not at any time after termination of his employment with the
Corporation disclose to any person, corporation, firm, or other entity,
confidential information concerning the Corporation of which Employee has gained
knowledge during employment with the Corporation.

     (iii) In the event that Employee has received any benefits from the
Corporation under Section 4 of this Agreement, then, during the period of 36
months following the date that the termination of Employee's employment became
effective, Employee, upon request by the Corporation:

         (a) Will consult with one or more of the executive officers concerning
the business and affairs of the Corporation for not to exceed four hours in any
month at times and places selected by Employee as being convenient to him, all
without compensation other than what is provided for in Section 4 of this
Agreement; and

         (b) Will testify as a witness on behalf of the Corporation in any legal
proceedings involving the Corporation which arise out of events or circumstances
that occurred or existed prior to the date that the termination of Employee's
employment became effective (except for any such proceedings relating to this
Agreement), without compensation other than what is provided for in Section 4 of
this Agreement, provided that all out-of-pocket expenses incurred by Employee in
connection with serving as a witness shall be paid by the Corporation.

     Employee shall not required to perform Employee's obligations under this
Section 5(iii) if and so long as the Corporation is in default with respect to
performance of any of its obligations under this Agreement.

                                       7
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     6. Successors and Binding Agreement.


     (i) The Corporation will require any successor (whether direct or indirect,
by purchase, merger, consolidation or otherwise to all or substantially all of
the business and/or assets of the Corporation), by agreement in form and
substance satisfactory to Employee, to expressly assume and agree to perform
this Agreement in the same manner and to the same extent that the Corporation
would be required to perform it if no such succession had taken place. Failure
of the Corporation to obtain such agreement prior to the effectiveness of any
such succession shall be a breach of this Agreement and shall entitle Employee
to compensation from the Corporation in the same amount and on the same terms as
Employee would be entitled hereunder if employee terminated employment after a
Change in Control for Good Reason, except that for purposes of implementing the
foregoing, the date on which any such succession becomes effective shall be
deemed the date that the termination of Employee's employment becomes effective.
As used in this Agreement, "Corporation" shall mean the Corporation and any
successor to its business and/or assets which executes and delivers the
agreement provided for in this Section 6(i) or which otherwise becomes bound by
all the terms and provisions of this Agreement by operation of law.

     (ii) This Agreement is personal to Employee, and Employee may not assign or
transfer any part of Employee's rights or duties hereunder, or any compensation
due to him hereunder, to any other person. Notwithstanding the foregoing, this
Agreement shall inure to the benefit of and be enforceable by Employee's
personal or legal representatives, executors, administrators, heirs,
distributees, devisees, and legatees.

     7. Arbitration. Any dispute or controversy arising under or in connection
with this Agreement shall be settled exclusively by arbitration in the Fergus
Falls area, in accordance with the applicable rules of the American Arbitration
Association then in effect. Judgment may be entered on the arbitrator's award in
any court having jurisdiction.

     8. Modification; Waiver. No provisions of this Agreement may be modified,
waived, or discharged unless such waiver, modification, or discharge is agreed
to in a writing signed by Employee and such officer as may be specifically
designated by the Board of Directors of the Corporation. No waiver by either
party hereto at any time of any breach by the other party hereto of, or
compliance with, any condition or provision of this Agreement to be performed by
such other party shall be deemed a waiver of similar or dissimilar provisions or
conditions at the same or at any prior or subsequent time.

     9. Notice. All notices, requests, demands, and all other communications
required or permitted by either party to the other party by this Agreement
(including, without limitation, any notice of termination of employment and any
notice of an intention to arbitrate) shall be in writing and shall be deemed to
have been duly given when delivered personally or received by certified or
registered mail, return receipt requested, postage prepaid, at the address of
the other party, as first written above (directed to the attention of the Board
of Directors and Corporate Secretary in the case of the Corporation). Either
party hereto may change its address for purposes of this Section 9 by giving 15
days' prior notice to the other party hereto.


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<PAGE>

     10. Severability. If any term or provision of this Agreement or the
application hereof to any person or circumstances shall to any extent be invalid
or unenforceable, the remainder of this Agreement or the application of such
term or provision to persons or circumstances other than those as to which it is
held invalid or unenforceable shall not be affected thereby, and each term and
provision of this Agreement shall be valid and enforceable to the fullest extent
permitted by law.

     11. Counterparts. This Agreement may be executed in several counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same instrument.

     12. Governing Law. This Agreement has been executed and delivered in the
State of Minnesota and shall, in all respects, be governed by, and construed and
enforced in accordance with, the laws of the State of Minnesota, including all
matters of construction, validity and performance.

     13. Effect of Agreement; Entire Agreement. The Corporation and Employee
understand and agree that this Agreement is intended to reflect their agreement
only with respect to payments and benefits upon termination in certain cases and
is not intended to create any obligation on the part of either party to continue
employment. This Agreement supersedes any and all other oral or written
agreements or policies made relating to the subject matter hereof and
constitutes the entire agreement of the parties relating to the subject matter
hereof; provided that this Agreement shall not supersede or limit in any way
Employee's rights under any benefit plan, program or arrangements in accordance
with their terms.

     14. ERISA. For purposes of the Employee Retirement Income Security Act of
1974, this Agreement is intended to be a severance pay employee welfare benefit
plan, and not an employee pension benefit plan, and shall be construed and
administered with that intention.

     IN WITNESS WHEREOF, the Corporation has caused this Agreement to be
executed in its name by a duly authorized director and officer, and Employee has
hereunto set his or her hand, all as of the date first written above.

                                         OTTER TAIL CORPORATION

                                         By    /s/ John Erickson
                                           -------------------------------------
                                             Its     President
                                                --------------------------------


                                         EMPLOYEE


                                          /s/ George A. Koeck
                                         ---------------------------------------
                                         George A. Koeck



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                                                                       EXHIBIT A



                                     NOTICE



The undersigned ("Employee") does hereby notify Otter Tail Corporation (the
"Corporation") pursuant to Section 4(i) of that certain Severance Agreement
dated as of the date hereof between the Corporation and Employee (the
"Agreement") that Employee has elected to be paid any amounts which become
payable under Section 4(i)(a) of the Agreement as follows:


check one)

_______ in a lump sum not later than one business day prior to the date that
the termination of Employee's employment becomes effective.

___X___ in 36 equal installments payable monthly, on the last business day
of the month, for 36 consecutive months following the date that the termination
of Employee's employment becomes effective.


Dated:    April 8, 2002
      ----------------------------------


                                         /s/ George A. Koeck
                                         --------------------------------------
                                         George A. Koeck



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