1. Questions about AVR & PSS
Previous WECC Requirements versus NERC Requirements
Operating Practices Subcommittee
September 22-23, 2010
H. Deon Murphy, P.E.
Power Resources Office

2. NERC Registration Criteria
Generation
Individual generating unit > 20 MVA
Generating plant/facility > 75 MVA
Transmission
An integrated transmission element associated with the bulk power system 100 kV and above,
or lower voltage as defined by the Regional Entity necessary to provide for the reliable operation of the interconnected transmission grid.

3. WECC MORC Section 2 - Transmission Voltage and Reactive Control
Generating units 10 MVA and larger shall be equipped with automatic voltage control equipment. All generating units with automatic voltage control equipment shall normally be operated in voltage control mode. These generating units shall not be operated in other control modes (e.g., constant power factor control) unless authorized to do so by the host control area. The control mode of generating units shall be accurately represented in operating studies.

4. WECC POLICY STATEMENT ON POWER SYSTEM STABILIZERS
The following criteria shall be used to determine when a PSS shall be installed on a synchronous generator, regardless of ownership, that is connected to the transmission system (by generator step-up transformer to 60 kV or higher voltage):
A PSS shall be installed on every existing synchronous generator that is larger than 75 MVA and is equipped with a suitable excitation system …
A PSS shall be installed on every existing synchronous generator that is larger than 30 MVA, or is part of a complex that has an aggregate capacity larger than 75 MVA, if the excitation system is updated …
A PSS shall be installed on every synchronous generator that is larger than 30 MVA, or is part of a complex that has an aggregate capacity larger than 75 MVA, and is equipped with suitable excitation systems …

5. Concerns
AVR
WECC required AVR on all Machines ≥ 10MVA, regardless of the voltage at which it was connected or the aggregate plant size.
Has this change to unit size, and inclusion of an aggregate plant/facility requirement been studied to see if this has reduced reliability in certain local areas or has an impact to the Interconnection as a whole?
PSS
WECC previously required AVR on all Machines connected at ≥ 60-kV, not ≥ 100-kV.
The minimum size unit has changed from 30 MVA to 20 MVA, aggregate plant size has not changed.
Have these changes been studied to see if there is a discernable change in the reliability of the Interconnection?
Requirement to have PSS has gone where?