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  <xs:element id="ottr_MinnesotaPublicUtilitiesCommissionMember" abstract="true" name="MinnesotaPublicUtilitiesCommissionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ottr_ShelfRegistrationShares" abstract="false" name="ShelfRegistrationShares" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ottr_EquityToTotalCapitalizationRatio" abstract="false" name="EquityToTotalCapitalizationRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ottr_NetAssetsRestrictedFromDistribution" abstract="false" name="NetAssetsRestrictedFromDistribution" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ottr_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardCliffVestingPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardCliffVestingPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ottr_PercentageOfTargetAmountAsActualPayment" abstract="false" name="PercentageOfTargetAmountAsActualPayment" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ottr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPerformanceMeasures" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPerformanceMeasures" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
</xs:schema>
