United States

United States

Tighter rules for grid connection -- Everybody happy

Transmission operators in the US appear poised to fall in line with an agreement between the American Wind Energy Association (AWEA) and the North American Electric Reliability Council (NERC) on a tightening of the rules requiring wind turbines to ride through momentary drops in grid voltage rather than tripping off the network.


The agreement is for a more stringent standard than one approved by the Federal Energy Regulatory Commission (FERC) in May this year as part of its Order 2003, the nation's first grid code containing rules for wind power. NERC objected to Wind Interconnection Order 661. It requires wind generators of more than 20 MW to stay online when voltage drops to 15 percent of normal for a maximum of 0.625 seconds. That requirement will be in effect until December 31, 2007.

Under the AWEA and NERC agreement, the standard calls for wind generators to be able to stay online when voltage drops to zero and is recommended to take effect in January 2008. AWEA worked with NERC to reach the compromise so that the new FERC standard would meet NERC's own reliability standards.

AWEA's Mike Jacobs says that independent transmission operators and regional transmission operators have generally expressed favourable comments. They will be filing their own proposals with FERC. Based on early comments, says Jacobs, most appear to be in accord with the AWEA/NERC agreement.

"Our initial filing was something of a first step," says Jacobs. "With NERC's involvement we were able to get to the second step. Without NERC's involvement, we couldn't do that. When we put this [original] filing together, we had been seeking the involvement of NERC ... By the time we got through FERC's process, we had NERC's involvement." The jointly agreed revision was filed with FERC in late September.

New development

Grid codes which specifically include wind turbines and take account of their operational needs are a relatively new development in response to the rapid increase of wind power capacity in transmission networks (Windpower Monthly, September 2005). The revised US standard is similar to that operated in Germany and the United Kingdom, says Jacobs, so the ultimate result for wind turbine manufacturers is likely to be negligible. "Manufacturers do have to have a strategy besides one-size-fits-all," says Jacobs, but "they do have the technology." The phased in approach, he says, will give manufacturers time to accommodate the change.

Ironically, the Energy Policy Act of 2005 will reduce some of NERC's clout in such matters. The new federal legislation gives ultimate authority in such matters to FERC. Prior to the Energy Policy Act, it was not clear whether FERC or NERC was the ultimate authority for such reliability issues. Jacobs notes that the clear chain of command was good for the wind industry in that NERC's primary regulatory focus is on reliability, but FERC's standard is "no undue discrimination" towards generators.

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