Voltage sag shows value of accurate wind forecasting.
Michael T. Burr is Fortnightly’s editor-in-chief. Email him at burr@pur.com.
Variability is a well-known characteristic of windpower, and system operators know they must plan for changes in wind generation over the course of a day. But when those plans fall short, voltage levels can drop quickly, forcing grid operators to dispatch resources to make up the difference—either by shedding load or bringing reserve generation online.
That’s exactly what happened in ERCOT on an evening in February, when a combination of events left the system operator short on power and long on demand (See Figure 1).
“On a macro level we forecasted load pretty close to what it turned out to be,” says Kent Saathoff, vice president of operations at ERCOT. “But there was a substantial difference between what we were getting from wind generators and what was reported to us in our look-ahead studies.”
Ultimately what happened in ERCOT was a non-event, in the sense that only interruptible load was affected and no involuntary outages occurred. Nevertheless, the episode illustrates the value of modern forecasting technology to provide accurate data for utilities and system operators who must keep the lights on.
Perfect Storm
While a rare combination of events created the February 26 emergency, none of the individual factors was unusual by itself.