(Adds background on previous request for usage curbs in paragraph 5, details of last year's wildfire in paragraphs 6-7)

April 15 (Reuters) - Hawaiian Electric urged Hawaii Island's residential and business customers to conserve electricity use on Monday due to several large generators being unavailable.

The Honolulu-based electric utility said 21,557 customers around the island experienced a 30-minute outage on Sunday night starting at 8:54 p.m (0654 GMT on Monday) and ending at 9:59 p.m.

"Hawaiian Electric's Hill 5 steam unit tripped offline yesterday. Puna steam unit and CT-1 combustion turbine unit also are under repair," the company said.

Hawaiian Electric did not immediately respond to a Reuters request for additional comment.

Last month, Hawaiian Electric asked its customers on Hawaii Island to reduce or shift their electricity use through April after the utility's largest generator went offline due to mechanical issues.

Hawaiian Electric is facing multiple lawsuits claiming it was to blame for a wildfire that tore through the island of Maui last year, killing at least 100 people. A spokesperson for the company said in September it does not comment on pending litigation.

In November, the company said it was unable to submit its quarterly filing with U.S. securities regulators on time due to financial contributions it made towards victims of the wildfire. (Reporting by Brijesh Patel in Bengaluru, Editing by Louise Heavens and Jan Harvey)