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Electric Reliability: How PJM Tripped on Gas-fired Plants

Fortnightly Magazine - May 1 1995

not enough power was available in the bulk-power markets, because many utilities in a very wide geographic area were coping with heavy demand and operational problems.

The real cause of the emergency was the incredibly high number of PJM units that were forced out of service. Of PJM's total installed capacity of 57,626 MW, 28 percent (16,248 MW) of PJM's capacity was unavailable on Monday, January 17. On January 18, the day of weekly peak demand, 30 percent (17,289 MW) of total capacity was unavailable. On January 19, the day of the rolling blackouts, unavailable capacity rose to and peaked at 37 percent of total capacity (21,223 MW). Of this figure, 16,248 MW had been forced out of service. The rolling blackouts coincided with the peak in the amount of capacity unavailable, not with the peak in demand.

At 37 percent of total capacity, unavailable capacity on January 19 rose a crucial 4,000 MW more than the day before, which meant that the daily peak could not be met without blackouts, even though it was less than that of the day before. Subsequently, on January 20 and 21, unavailable capacity amounted to 30 and 32 percent, respectively. No rolling blackouts were necessary on either day.

Why was so much capacity forced out of service?

Load Was Firm, Fuel Wasn't

It is too simple to say that cold weather caused the outages. This answer also begs the question of why electric generation could not operate under the severe conditions.

The forced outages stemmed from two main causes: 1) fuel supply and handling problems, and 2) mechanical failures. Plants were forced out of service because fuel either was not available or could not be handled efficiently in the cold weather. Fuel supply and handling problems occurred in oil, coal, as well as gas plants. During the rolling blackouts, coal plants generated 17,924 MW, about 33 percent of PJM's total capacity; yet coal plants accounted for 44 percent of the capacity forced out of service. Further, 60 percent of PJM's coal capacity was operational during the blackouts.

Obviously, performance at the coal plants was not adequate, though it was three times better than the performance of plants where gas was the primary or sole source of fuel. The fuel problem at coal plants was rarely no coal or too little coal. Plenty of coal was usually on site or being delivered by rail, but it sometimes froze, making handling and plant operation difficult. Steps to remedy these problems have been taken.

Plants where gas was the sole or the primary fuel provided about 8,642 MW of capacity, about 15 percent of PJM's total capacity; yet gas-fired capacity also accounted for about 44 percent of the capacity forced out of service. Consequently, although a proportionately small amount of PJM's total installed capacity, gas plants formed a disproportionately large amount of the capacity forced out of service. No more than 20 percent, and probably quite a bit less, of PJM's gas-fired capacity was operational during the blackouts. If 60 percent of gas-fired capacity had been operational, which