Public Service Co. of Colorado, a unit of Xcel Energy (NYSE: XEL), won’t need a synchronous condenser, which would provide local grid support, at its to-be-retired Arapahoe Unit 3 coal facility, after all.
Robin Kittel, employed by Xcel Energy Services as Director, Regulatory Administration, explained the change of plans in July 26 testimony filed at the Colorado Public Utilities Commission. The synchronous condenser had been approved by the commission under the utility’s plan to comply with the state’s 2010 Clean Air Clean Jobs Act (CACJA). That plan involved a number of coal unit retirements and coal-to-gas switching.
Even without the Arapahoe 3 synchronous condenser, the Denver metropolitan transmission system complies with the voltage stability and reactive resource adequacy metrics specified in the WECC System Performance Criteria, Kittel said. “At the time we filed our CACJA Plan we believed that re-using Arapahoe 3 as a synchronous condenser was necessary to maintain transmission voltage stability in the Denver metropolitan area, stability that was adversely impacted by the retirement of generation units in the Denver Metropolitan area,” Kittel noted.
A synchronous condenser is basically a synchronous motor that has had all mechanical load removed from the shaft. By adjusting the field excitation of this motor, the Volt-Amps-Reactive (VARs) produced by the machine can be controlled so that it behaves as a variable source of reactive power. This synchronous motor, referred to as a synchronous condenser, does not burn any fuel and has no emissions.
“Since the CACJA order was entered, the Company has completed the construction of the Cherokee 2 synchronous condenser,” said Kittel, referring to another coal unit on the shutdown list. “Through further study conducted while the Company was acquiring the necessary equipment for that project, the Company came to understand that the Arapahoe 3 synchronous condenser would not be needed. We foreshadowed this fact when we sought a [certificate of public convenience and necessity] for the Cherokee 2 synchronous condenser. In the settlement agreement approved as part of that docket, the Company agreed to seek Commission approval before abandoning the Arapahoe synchronous condenser project.”
Kittel added: “In addition, the construction of the synchronous condenser at Cherokee 2 is complete, we are able to produce more VARs than the approximately 80 MVARs originally estimated in the CACJA filing. The improved design of that project is able to produce up to 118 MVARs. As a result, we will not need to convert Arapahoe 3 to a synchronous condenser.”
In December 2010, the commission approved the following CACJA plan:
- Shutdown Cherokee Units 2 and 1 in 2011 and 2012, respectively, and Cherokee 3 (365 MW in total) by the end of 2015, after a new natural gas combined-cycle unit is built at Cherokee (569 MW);
- Fuel-switch Cherokee 4 (352 MW) to natural gas by 2017;
- Shutdown Arapahoe Unit 3 (45 MW) and fuel-switch Unit 4 (111 MW) in 2014 to natural gas;
- Shutdown Valmont Unit 5 (186 MW) in 2017;
- Install selective catalytic reduction (SCR) for controlling NOx and a scrubber for controlling SO2 on Pawnee in 2014;
- Install SCRs on Hayden Unit 1 in 2015 and Hayden Unit 2 in 2016; and
- Convert Cherokee Unit 2 and Arapahoe Unit 3 to synchronous condensers to support the transmission system.