HOUSTON, March 19 (Reuters) - The hydrocracking unit at Chevron Corp's 279,000 barrel per day (bpd) Los Angeles-area refinery in El Segundo, California, was shut on Friday after a fire in an electrical substation, according to a notice filed with California pollution regulators.

Chevron calls the hydrocracker an Isomax unit and, according to a company website, the unit is designed to crack heavy crude oil into jet fuel.

Chevron's El Segundo refinery provides about 40 percent of the jet fuel to Los Angeles International Airport, according to a Chevron website about the refinery.

(Reporting by Erwin Seba; Editing by Gary Hill)

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