WECC-0071System Performance Criterion B. Vijayraghavan PG&E Company May 26, 2010 Columbia Grid Office
WECC Requirements-Existing • WRS1: In addition to NERC Table I, Planning Authorities or Transmission Planners shall comply with the WECC Disturbance-Performance Table (Table W-l) of Allowable Effects on Other Systems contained in this section when planning the Western Interconnection. Table W-l does not apply internal to a Transmission Operator Area. • WRS1.1. The NERC Category C5 initiating event of a non-three phase fault with normal clearing shall also apply to the 'common mode contingency of two Adjacent Transmission Circuits on separate towers unless the event frequency is determined to be less than one in thirty years.
Proposed Revisions to WRS1.1 • The WECC-0071 requests to revise WRS1.1 of the TPL System Performance Criterion. At the same time, it also proposes to replace WRS1.’s current language with: • “The NERC Category C.5 shall also apply to the common mode contingency of two Adjacent Transmission Circuits on separate towers unless the event frequency is determined to be less than one in 30 years. The fault to be used for this study shall be a single line-to-ground fault. The performance requirements of NERC Table 1 shall apply to this contingency and WECC Table W-1 shall not apply.”
Comments • The existing criterion does not prevent people from building within close proximity of the other lines, only that they study and mitigate the impact on other systems. • There is no restriction such that the entity cannot go with the NERC Standard instead of the existing WECC criterion. The only requirement is to let others impact it the same way. • Since most of the mitigation is usually to use RAS to drop enough load and generation so that the N-1 or N-0 performance requirement will become the most limiting. For areas that already uses RAS as a mitigation, getting rid of this standard may not provide much increase in transfer capability. • For areas that currently do not use RAS, they can increase transfer because this criterion is retired. However, since others can also make use of this relaxation, they can also increase transfer up to the point where N-1 or N-0 performance requirements becomes the most limiting for areas that do not currently use RAS. Will this increase transfer capability sufficiently? • Removing the existing WECC Criterion will default to NERC Category D, which allows instability and cascading. The existing criterion provides safety net against cascading event for multi circuit outages.