WHY THE LIGHTS WENT OUT

How could a power system that many people thought was made fail-safe after the Northeast's great 1965 blackout plunge New York City into helpless darkness once again? It may take months of investigation to get the complete answer. But at week's end, an outline of the falling-domino sequence of failures that led to the total collapse had begun to emerge.

Like other major utilities in the U.S. and Canada, New York's embattled Consolidated Edison Co. (see ECONOMY & BUSINESS) not only has its own electrical generating plants but is plugged into a larger regional pool of power producers. Depending on the electricity needs of its 9 million customers in New York City and neighboring Westchester County, Con Ed can either 1) rely largely on its own generators, or 2) buy power from neighboring utilities if the load--or demand from its users--is high, or 3) sell off surplus electricity to other companies. Yet those choices are complicated by another fact: electrical energy cannot economically be stored. Even a relatively small variation in load in one part of the system must be quickly compensated for elsewhere along the line. Indeed, the decisions of controllers to buy or sell electricity, or to switch in additional generators, require such split-second timing and are so complex that large utilities like Con Ed have increasingly computerized their operations.

On the night of the blackout, the New York metropolitan area was sweltering under a blanket of hot, humid air. With air conditioners whirring everywhere and electrical load high--though still far below the levels expected later this summer--Con Ed was importing from neighboring utilities about one-third of the electricity it was delivering to its customers. That in itself was not unusual. In the battle to keep its rates from soaring even higher. Con Ed has lately been buying more and more electricity from nearby companies that can provide cheaper power. Yet what made Con Ed especially vulnerable that soggy evening was a series of highly improbable natural events--"acts of God." as one spokesman called them.

A severe summer thunderstorm had just swept across the green suburban hills of northern Westchester in the vicinity of the Indian Point No. 3 nuclear power plant overlooking the Hudson River. At 8:37 p.m., according to Con Ed's preliminary analysis, flashes of lightning knocked out two 345-kilovolt lines. That immediately cut off all the electricity from the 900-megawatt Indian Point facility, and the nuclear plant was promptly and safely shut down. Then, while duty officers at Con Ed's main control center in Manhattan--a huge, display-filled room somewhat like Mission Control in Houston--scrambled to make up for the power loss, lightning struck again. At 8:56 p.m. bolts knocked out two more upstate 345-kilovolt lines in Westchester that bring in power from upstate New York and New England. Three minutes later, lightning knocked out yet another line. Worse still, circuit breakers designed to reset automatically after the enormous voltage surge caused by a lightning bolt apparently failed to close. By now the utility had suffered a massive loss of some 2,000 megawatts--more than a third of its electrical load that night.

In the past, this deficit might have kayoed the entire Con Ed system and blacked out nearby areas as well. But safety devices and procedures adopted after the 1965 blackout automatically went into action--at first reducing voltages supplied to customers by 5%, then by 8%. Lights flickered and television pictures shrank. Still, the maneuver temporarily staved off the complete shutdowns that the devices would otherwise have ordered to protect the generators and transformers from being burned out by dangerous overloads.

The voltage reduction also gave the control center time to call upon other power plants in the city to feed in more electricity. By revving up their turbines, they were quickly able to make up about 1,000 megawatts. Still, that was hardly enough. So the computers, acting on preprogrammed instructions, made a calculated tradeoff: to keep the city's vital subways, hospitals, elevators and other services running, they began ''shedding load"--reducing electrical demand--by blacking out several less populated suburban bedroom communities in West-Chester. Presumably, that would give Con Ed controllers time to call in more energy from elsewhere.

For a few minutes, the stratagem worked. But a new problem developed on the utility's eastern flank. Because Con Ed's great drain of power was overheating their connecting cables, the neighboring Long Island Lighting Co unplugged from the system. That left Con Ed with only three major sources of electricity: its often troublesome 1,000-megawatt "Big Allis" (for Allis-Chalmers) generator in the borough of Queens and two remaining out-of-state links--one to New Jersey's Public Service Gas & Electric Co., the other to upstate and New England utilities.

Incredibly, at about 9:27, still more lightning in Westchester cut off Con Ed's last remaining hookup to the north. Moments later, as they staggered under this additional demand, Big Allis was shut off by its automatic switches, and New Jersey also cut itself free. Thus the city was isolated from any outside sources of power because of the very safety arrangements made after the 1965 blackout. Only a handful of small local power stations were left to meet the overwhelming electrical load. By 9:41 even the last of these shut off.

The breakdown took little more than an hour, but the restoration of power was far more tedious. Though the equipment itself was undamaged, protective circuit breakers--many of them underground--automatically tripped and had to be individually examined and reset. In addition, since 1965, Con Ed has shut down several of its old local coal-fired plants. Thus it is forced to draw on generators far outside the city that are more difficult to reconnect into the system. Finally, no more than a single section of the city could be powered up at a time for fear of a new overload. In all, it was 25 hours before all the equipment could be brought back on line and the lights came on again.

Could the disaster have been averted? In the immediate post-mortems after the blackout, some critics suggested that Con Ed should have appealed to the public to shut off appliances, thus reducing load on the overburdened system. But could the message have got out quickly enough--and would the city have responded? Others wondered why the controllers did not react more vigorously by blacking out more areas sooner to save the overall system. Some even suspected that there might be an undiscovered yet crucial flaw in the network's design or equipment. As investigators explore these and other nagging questions about New York's calamity, every major utility in the country will be carefully listening to the answers.

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