SASKPOWER OPEN ACCESS TRANSMISSION TARIFF

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SASKPOWER OPEN ACCESS TRANSMISSION TARIFFATTACHMENT CMethodology To Assess Available Transmission CapabilityBasis of AssessmentSaskPower will assess the Available Transfer Capability (ATC) for identified constrainedinterfaces. The assessment will be based on the lower of the individual interface facility limitsand SaskPower transmission system limits. The ATC will be posted, as required, on SaskPower’sOASIS site.Determination of ATCATC is a measure of the transfer capability remaining in the physical transmission network forfurther commercial activity over and above already committed uses. Mathematically, ATC isdefined as the Total Transfer Capability (TTC) less the Transmission Reliability Margin (TRM),less the sum of Existing Transmission Commitments (ETC) (which includes retail customerservice), less the Capacity Benefit Margin (CBM).Recallability is defined as the right of a transmission provider to interrupt all or part of atransmission service for any reason, including economic, that is consistent with the OATT orother contract provisions.For non-recallable 1 transmission service, ATC is calculated using the most severe (largest) TRMrequired for the period of time being considered.NON-RECALLABLE ATC = TTC – TRM – ETC – CBMFor recallable 2 transmission service, ATC is calculated by discounting the maximum TRM valueby means of a coefficient (TRM C ) when system operating conditions are better than for the worstcase.RECALLABLE ATC = TTC – (TRM C )TRM – ETC – CBMThe coefficient “TRM C ” is derived by doing a series of simulations for the interface to determinesensitivity due to variation in the pre-disturbance conditions. This range of values of transfercapability is compared to the original TTC for the interface to derive the value of “TRM C ” whichsatisfies the equation above that is used to post ATC values. The values of TRM C have a rangefrom 0 to 1.1 OASIS Non-recallable transmission service is equivalent to SaskPower OATT firm transmission service.2 OASIS Recallable transmission service is equivalent to SaskPower OATT non-firm transmission service.Page | 111
SASKPOWER OPEN ACCESS TRANSMISSION TARIFFUnder commercial use of an interface, the ATC at a particular point in time can be defined as:ATC = TTC – (TRM C )TRM – ETC – RES – SCHSaskPower’s software uses this equation to calculate the posted ATC for the interface.The two additional terms RES and SCH represent the ATC that has been, up to the point in timebeing considered, sold to a Transmission Customer(s). RES represents the sum of theunscheduled reservations on the interface and SCH represents the sum of the actual scheduledflow across the interface.Determination of TTCSaskPower determines the TTC of an interface based on the capability of the interface facilitiesand the first contingency transmission capability of the SaskPower system. To establish TTC forthe interfaces, the transfer level is increased in steps. At each step, the system is studied todetermine if the system meets the defined performance criteria for the critical contingenciesdefined. The maximum level of transfer, considering most likely load levels and probablegeneration patterns, becomes the TTC for the interface. The TTC for a particular interface isdetermined without simultaneous transfer on other interfaces.The TTC values are derived for power flow in both directions through the interfaces. The studiesare done in coordination with the respective interconnected Transmission Providers and facilityowners.Determination of TRMTRM represents a margin that is applied to account for uncertainties and variations in systemconditions and to allow for operating flexibility. The major components that are considered in thedetermination of TRM include:Probable variations in domestic load levels. SaskPower produces a high and low systempeak load forecast that represents an 80% confidence interval for load growth. These loadforecasts are used to account for load level and load distribution variations.Probable variation in SaskPower generation dispatch which is dependent on hydroconditions, fuel prices, and other applicable conditions.Simultaneous transfers on other interfaces. Currently, there is an interdependencybetween the Saskatchewan-Manitoba and the Saskatchewan-North Dakota interfaces.Parallel path flows. Parallel path flows, due to schedules, are not considered because allSaskPower interfaces are either directly or indirectly controlled.Interface control system deadbands.Page | 112
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SASKPOWER OPEN ACCESS TRANSMISSION TARIFF

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