Pump Load as Spinning Reserve David Lemmons Senior Manager, Market Operations August 21, 2012

Spinning Reserve From Load PSCo plans to use its Pumped Storage Hydro facility pump load as Operating Reserve – Spinning. Under the proposed BAL-003 at NERC, a single pump is approximately equal to the response required of PSCo for a.3 Hz dip in frequency. There are two pumps at the plant.

How it Works The load has a frequency relay installed to trip the pumps. Will turn off any pump online at the time. When triggered, a normal shutdown of the pump(s) will occur. If frequency trigger is not reached but event occurs in RMRG, PSCo dispatchers can initiate shutdown manually.

Response of Pumps Load starts to reduce within 8 seconds of trigger. Pump goes from full load to zero in about one minute.

Summary PSCo believes that the process as described clearly qualifies as Operating Reserve – Spinning. To the extent there are questions, PSCo is willing to listen and attempt to address issues.

Next Steps Take feedback from the OPS. PSCo will take process to WECC Compliance to get agreement on process for Standards Compliance. Begin utilizing pump load as Operating Reserve – Spinning once WECC Compliance is satisfied.