JERSEY CITY, N.J. (AP) _ A transformer exploded into a fireball at an electrical substation Wednesday, severely burning three utility workers and injuring two more.

Public Service Electric & Gas Co. workers were doing maintenance at the substation when a device at the top of the transformer ruptured, spewed oil and then ignited, said utility spokesman Frank Centore.

Substation mechanic Patrick Walker, 27, suffered second- and third-degree burns over 90 percent of his body. Mechanic Duane Doffont, 44, was severally burned over 60 percent of his body. Both were in critical condition after surgery, a hospital spokesman said.

Mechanic Edward Blatz, 63, had second- and third-degree burns over 40 percent of his body and was in stable condition.

The transformer, which steps down voltage from generating stations, was carrying the electrical load for the entire substation because the other transformer was out of service for maintenance, Centore said.

The explosion knocked out power for up to 50,000 customers for several hours.

The part of the transformer that exploded was to be analyzed at a lab, Centore said.