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Demanding More from DR

Customer-specific demand-response strategies become more sophisticated.

Fortnightly Magazine - August 2010

of spinning reserves that can supplement or replace the governor response of generators and diminish the need for the under-frequency shed of feeders. DR systems often have been advertised as providing spinning reserves, but almost all of those systems don’t possess this under-frequency sensing capability. Without autonomous sensing and response, the DR systems can’t provide frequency responsive spinning reserves, because they otherwise would depend on the broadcast of a shed command from the DR head-end. The time it would take to sense under-frequency and send a shed command through the system would be too long to meet under-frequency response requirements.

The other type of reserves that are commonly supplied by DR often are referred to as supplemental reserves or daily operating reserves, which are typically dispatcher initiated and have response times in the order of 10 minutes, which easily can be met by existing DR systems. This type of DR application provides significantly more capacity response than regular DR events, because under these emergency conditions, the loads are shed and not duty cycled, so the available load reduction is the full value of the actual appliance diversified demand at the time of the event. This value easily could be two to three times the load reduction being delivered during normal load-reduction events.

When DR is used for under-frequency response, the customer loads that have been curtailed likely will have been off for an extended period of time ( i.e., 15 to 30 minutes is typical), which means that when they are turned back on, the duty cycle will be very close to 100 percent, creating a load that might be as high as four times the normal appliance diversified demand. Turning all the devices on at once and at the wrong time very likely would create its own secondary grid event. This risk can be totally avoided by designing the system to prevent unrestrained automatic load restoration after an under-frequency event. Automatic load restoration is allowed only after a significant ( i.e., configurable) time period and is only enabled as a precaution against operator failure to manually release these loads after the under-frequency event has passed.

DR Value

Full deployment of these technological advances within the DR systems can add significantly to the value and reliability of DR loads both in the DR marketplace and with the utility-owned programs. They specifically will improve customer acceptance, participation and their persistence over time—a critical component to the long-term success of any DR program.

There are three critical success factors with any DR program: customer participation, technology effectiveness, and the delivery of the required load reduction at the time it’s needed. Systematic technological approaches will contribute significantly toward each of those success factors.