A West Coast View: The Case for Flow-Based Access Fees
of power (MW)where:
D Generator injection of power is some fraction of a generator's power output.
12The Sacramento Municipal Utility District used a 3-percent cut-off value in a power-flow study that modeled eight bilateral contracts to discern the transactional use of California transmission facilities. The North American Electric Reliability Council (May 1995) has suggested a 2-3 percent value as a reasonable level of significance for distribution factors when evaluating transmission line ratings. The General Agreement on Parallel Paths experiment for pricing loop flow uses 5 percent of a transaction to determine the "prime path." See, Allegheny Power Srv. Corp., et al., (Order Accepting for Filing GAPP Experiment Participation Agreement), FERC Docket No. ER-97-697-000, March 25, 1997, 78 FERC ¶ 61,314.
13As the ISO examines the functional use of the 230-kV system, pursuant to the California legislation (AB 1890), one can expect the ISO will find many or all 230-kV lines running parallel to 500-kV lines provide the same regional function as the 500-kV system.
14Using a cut-off value of less than 1 percent is pushing the accuracy and credibility limits of the input data in the power flow model. For example, information concerning transmission lines may only have Å5 percent accuracy concerning knowledge of actual length, height and weather conditions. Similar variations can exist with load, generator and transformer characteristics.
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