NERC Generation Standards Drafting Team September 15 17

NERC Generation Standards Drafting Team September 15 -17, 2008 Dallas, TX NERC PRC-024 -2 Drafting Team Voltage Ride-Through (VRT) Curve Genesis Craig Quist, PE Pacifi. Corp, Transmission Planning Salt Lake City, Utah

– Based on an earlier request from the WECC Voltage Ride-Through (VRT) Standard Task Force, the WGTF has been working on a VRT white paper that would be used as the justification for a new VRT Standard. – This white paper discusses the low voltage, low voltage recovery and high voltage period, immediately following a system event. – The white paper was approved by the Technical Studies Subcommittee (TSS) on 5 -22 -07 and distributed on 6 -13 -07. – When reviewing the paper, references to generator, wind plant or wind farm should be considered synonymous with each other. © 2007 PACIFICORP | PAGE 2 Voltage Ride – Through Standard

– Disturbance voltages traces (at POI) fit within the defined WECC VRT Curve (SLG Faults added to during NERC evaluation) – Issues were raised by the PRC 024 -2 drafting team concerning voltage duration at specific locations on the curve. – As PRC-024 -2 is a generator protection system standard (vs. generator performance standard), questions surfaced concerning how such a curve can be applied? – Generator protection relays typically utilize voltage duration © 2007 PACIFICORP | PAGE 3 WECC VRT Curve vs. Voltage Traces

– The approach of the PRC-024 -2 drafting team shifted to defining time duration for generator protection – To develop a time duration VRT boundary it was determined that the voltage traces provided in the WECC white paper could be converted to time duration format – Additional SLG fault voltage traces and Southern Company voltage traces were also added © 2007 PACIFICORP | PAGE 4 Time Duration - Voltage Traces & WECC VRT Std

Time Duration - Voltage Traces & New NERC Std HVRT Reduction Relay Failure FERC 9 Cycle Limit © 2007 PACIFICORP | PAGE 5 – Initially, a “zero margin” boundary was defined as an envelope for the time duration curves – However, it was determined that margin would be added along with SLG voltage traces to develop the new time duration boundary – Additionally, voltage traces from Southern Company were entered to form the Pink curve. – The new time duration boundary reshaped both the low voltage and high voltage boundaries from those proposed by WECC white paper.

© 2007 PACIFICORP | PAGE 6 Proposed PRC-24 -02 VRT Standard

Other PRC-24 -02 VRT Participant Inputs – Areva 4 4 Provided the European LVRT voltage performance standard Suggest sticking with a regular scale for criteria. Mixing criteria between this and the log scale gets confusing. The voltage prior to the fault should be clarified Previous curves stopped at 4 seconds. This curve goes out to 10 seconds 4 4 When fed from a unit-connected transformer or a delta-wye wound transmission-connected transformer, most low voltage AC contactors will probably ride through close-in SLG faults on the transmission system. However, if fed from a wye-wye wound transmission-connected transformer, many will probably drop out, even with fast clearing. © 2007 PACIFICORP | PAGE 7 – Excel Energy SLG feedback

NERC Time Duration Curve vs. WECC VRT Std © 2007 PACIFICORP | PAGE 8

– On 9 -10 -08, WECC distributed the PRC-024 -WECC-1 -CR Generator Low Voltage Ride. Through Criterion. – In developing the criterion, the WECC Reliability Subcommittee (RS) decided to let the NERC PRC-024 -2 drafting team do the “heavy lifting” in developing a new standard. – Effectively, changes were made to bring the WECC standard inline with the current FERC LVRT standard. – Comments are due 10 -10 -08. Chart Source: Brendan Kirby (AWEA) © 2007 PACIFICORP | PAGE 9 PRC-024 -WECC-1 -CR - Generator Low Voltage Ride. Through Criterion