1. TPL-007-1 Voltage Guideline
Presented to TSS
Baj Agrawal
Arizona Public Service Co.
8/21/2017

2. TPL Requirement R3
Each responsible entity, as determined in Requirement R1, shall have criteria for acceptable System steady state voltage performance for its System during the benchmark GMD event described in Attachment 1.

3. Proposed Guideline
Steady-state voltages at all applicable Bulk-Electric System (BES) buses shall stay within the following limits for the benchmark GMD event:
A minimum of 85% of the of nominal for P0 events (All elements in service)
A maximum of 110% of the nominal for P0 events (All elements in service)
In the context of this document the word “nominal” carries its common definition and is the base (or operating) voltage used in the entity’s Planning Assessment. This voltage will vary from entity to entity.

4. Rational for low voltage Guideline
A minimum voltage of 85% is chosen based upon the same rational as used in NERC Standard PRC-023 where the protective relay settings are set for the 85% system voltage.
85% is also chosen based upon experience where it is seen that voltage collapse likelihood increases significantly for lower voltages.

5. Rational for High Voltage Guideline
The maximum voltage of 110% is based upon WECC-0100 criteria document where 110% of the nominal voltage is considered acceptable for contingency conditions (P1-P7). Since the GMD events are rare events, it is reasonable to use the performance criterion which is similar to those for contingency events (P1-P7).