Hurricane Harvey knocked out service at power plants and across giant transmission lines — but the ERCOT electric grid weathered the storm.

All told, power stopped flowing across six of the state’s massive 345 kilovolt lines as well as across 91 138 kV lines and 138 69 kV lines, according to a report from a top ERCOT official.

But ERCOT’s Chad Seely also said that more than 60 percent of the 345 kV lines were already back in service, as well as 52 percent of the 138 kV lines and 34 percent of the 69 kV lines.

ERCOT, also known as the Electric Reliability Council of Texas, oversees the state’s principal transmission system. Seely, a vice president there, confirmed that the storm had caused significant problems around the Coastal Bend area, including the loss of 8,000 megawatts of generating capacity.

A single megawatt is enough power for about 200 homes during a hot summer day.

“The outages are generally attributable to rain or floodwaters affecting fuel supplies, outages of transmission facilities at the generator’s point of intersection, or the inability of plant personnel to reach the generating facility,” Seely wrote in a memo Wednesday to the Texas Public Utility Commission.

“The amount of outages has been dropping, down from a maximum of over 10,000 MW,” he continued. “(And) despite the foregoing storm-related outages, ERCOT has had plenty of generation to meet total system demand and expects to have sufficient generation for the foreseeable future.”

Seely also reported that cooler than normal temperatures combined with storm-related forced outages had significantly reduced electricity demand on the system — and therefore was easing the strain. “The demand is approximately 15,000-20,000 MW lower than what is typically observed during this time of year,” he said.

PUC staff also confirmed on Thursday the complete loss of a substation serving the Holiday Beach community in Aransas County. In response, PUC Commissioners Ken Anderson and Brandy Marquez authorized the waiver of certain parts of the utility code to facilitate quick reconstruction. The commissioners also waived certain other PUC rules in support of the governor’s recent disaster proclamation.

The PUC on Thursday also directed utilities, when appropriate, to use their best efforts to account for reduced consumption when estimating bills corresponding to the storm period. The regulators also signaled that they may direct retail electric providers to offer deferred payment plants to customers in disaster areas, upon those customers’ request.

— R.A. Dyer