LONDON The U.S. power industry survived its toughest test in years in January when lights and heaters stayed on even as the polar vortex swept over the country. But it was a close run thing, as regulators revealed in a new report published on Tuesday.
According to the North American Electric Reliability Corporation (NERC), power system operators “successfully maintained reliability” during the coldest winter temperatures since 1997 through a combination of training, preparation and emergency tools to manage generation and demand. (“Polar Vortex Review” Sep 30)
On Jan. 7, as average temperatures across the eastern United States fell to 20-30 degrees below the seasonal norm, demand on the Eastern and Texas Interconnections hit a record 559,000 megawatts, exceeding the previous peak by almost 3 percent.
But while grid operators appealed to their customers to reduce non-essential demand, only 300 MW of firm load was actually lost, amounting to less than 0.1 percent of the total load served on the Eastern and Texas Interconnections, according to NERC.
Only two grid areas were forced to reduce demand to ensure that the power grid remained within safe operating limits and could withstand a worsening of the emergency.
PJM and some providers in South Carolina cut voltage in their areas by 5 percent, while South Carolina Electric & Gas was forced to disconnect a small number of customers to protect the rest of the network.
The report could not completely disguise the concerns about the strain on the grid, however. Around 35,000 MW of generating capacity was unexpectedly unavailable during the crisis owing to equipment breakdowns and fuel shortages.
Planned and forced generation losses in some regions exceeded the worst-case assumptions used by the industry in its seasonal assessments.
“Of the 19,500 MW of capacity lost due to cold weather conditions, over 17,700 MW was due to frozen equipment,” NERC concluded.
Equipment failures were particularly severe in Texas and the Southeast, crippling almost 10,000 MW of generating capacity so that it was unable to start when instructed by the grid.
NERC catalog more than 60 different equipment failures, including iced up transformers, frozen valves and cooling systems, and lubricating oils and diesel that became gelled because of the extreme cold.
In the Midwest and on the East Coast, where equipment is designed to cope with lower temperatures, lack of fuel was more of a problem.
Since the late 1990s, most new power generating units have been built to burn natural gas. Unlike coal or oil, gas is not usually stored on site, so generators rely on real-time deliveries from the gas pipeline network.
In many cases, generators relied on purchasing extra gas in the spot market to meet peaking electricity demand. But with gas consumption also hitting record levels, generators were unable to contract for sufficient volumes and arrange for delivery through an already congested pipeline network.
The increase in gas-fired generation has introduced an unanticipated and dangerous link between the gas and electricity systems - with the risk of common failure.
According to NERC, gas supply problems led to losses of 620 MW of generation in the Midwest, 3,300 MW in the Northeast, 11,000 MW in the Middle Atlantic states, 2,000 MW in the Southeast and around 2,000 MW in Texas.
On the East Coast, in a bid to cope with the problem, grid operator PJM asked generation units that were unable to secure enough gas and had dual-fuel capability to burn diesel and fuel oil instead.
But oil burning generates more pollution, and some generators apparently felt constrained from running too long on oil in case it breached their emissions targets. Concerns about emissions limited the availability of as much as 1,000 MW of capacity.
Further up the coast in the Northeast, oil supplies began to run low because power plants could not get enough tanker deliveries. “Generation owners found it difficult to keep oil tanks full ... and had to limit run hours for their units. There were approximately 2,000-3,000 MW of generation affected by oil supply and delivery issues,” according to NERC.
Grid operators were able to cope with all these outages by lowering the voltage by as much as 5 percent, instructing generators to postpone routine maintenance, ordering available power plants to run flat out, calling on demand response, and appealing to customers to use less power by issuing “energy emergency alerts”.
Normally, grid operators would also expect to be able to call on mutual aid from neighboring areas to meet demand. Some were able to do so even this winter. But with eight of the 10 balancing areas in the eastern part of the country recording all-time record power demand on Jan. 6 or 7, the entire eastern network was stretched to the limit.
Given the severity of the conditions, NERC concluded that the grid performed well during the crisis. Lessons had been successfully learned since the last period of extreme cold in February 2011, which resulted in power cuts.
But more work needs to be done to ensure gas deliveries to power plants, weatherize generators so they start reliably even in extreme cold, and alert plant operators to the possibility of seeking waivers from emissions limits during a crisis so they can switch to diesel and fuel oil without worrying about being penalized.
The Federal Energy Regulatory Commission (FERC) is already working alongside NERC and the gas and power industries to ensure closer coordination between pipeline operators and power plants on scheduling deliveries. The aim is to ensure more gas reaches the generators in future and to make outages due to fuel supply issues less likely.
But regulators are not taking any chances. On Tuesday, FERC and NERC announced a joint study into how utilities plan to restore power after a mass blackout (a “blackstart”) caused by terrorism, operational failure or weather-driven events.
(editing by Jane Baird)