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Electric Reliability: How PJM Tripped on Gas-fired Plants

Fortnightly Magazine - May 1 1995

was the coal plants' performance, rolling blackouts would probably have been unnecessary.

Based on these numbers, the performance of PJM plants using gas as the primary or sole fuel on January 19 can only be judged unacceptable. The problem at these plants was not fuel handling or transportation; gas that was available for electric generation was handled and transported through pipelines without difficulty.

The operational problem began with the loss of gas supply at plants using gas as the primary or sole fuel. Many of these plants were served by interruptible transportation gas contracts. For the 1,154 MW of generation that relied solely on gas, interruption meant no generation of electricity. Since the four rolling blackouts on January 19 were four separate

500-MW load dumps (em never more than 1,500 MW at one time (em the gas-only plants by themselves nearly made up the entire difference between an electric system under great stress and one in crisis.

We cannot ignore the threat to reliability posed by plants that use only gas and are supplied with interruptible contracts, even though such plants amount to a small percentage of total capacity. When a system is stressed, reserve margins shrink precipitously, and the margin for reliable operation may be just a few percentage points of total capacity. Every megawatt counts in an emergency.

At gas-fired plants where gas was the primary fuel, interruption of gas supply should have meant switching to an alternate fuel. But attempts to switch to backup fuels frequently failed for a variety of reasons: The backup fuel gelled. Oil ran out, and transportation problems made it difficult or impossible to replenish supply. Mechanical problems cropped up when plants tried to switch from gas to an alternate fuel.

In fact, the mechanical problems at combustion turbine units were so pervasive, and the plants so unreliable, that PJM now assumes 50 percent of this installed capacity will not start when needed (em a remarkable planning concession to the realities of unreliable equipment.

All these problems merged in a compressed period and pushed the people and businesses within the areas served by the PJM power pool toward the precipice. Only decisive government action, the cooperation of the public, the work of electric utilities and other power producers, the National Guard and Coast Guard deliveries of oil through frozen rivers and roads, and a slight warming trend prevented a plunge over that precipice. t

John Hanger, a Commissioner with the Pennsylvania Public Utilities Commission, experienced the PJM emergency first-hand. This article incorporates the results of the PUC's investigation as well as his own research.

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