PG&E 407-MW Helms Pump 2 in unplanned outage

LOS ANGELES, July 16 (Reuters) - PG&E Corp's (PCG.N) 404-megawatt Unit 2 at the Helms Pumped Storage hydropower station in California was off-line in an unplanned outage by Wednesday afternoon, the California Independent System Operator said in a report.

The other two units at the 1,212-MW, three-unit Helms power station were on-line on Wednesday, the report showed.

The 24-year-old station is in Fresno County.

One megawatt powers about 700 homes in the PG&E service territory in central and northern California.

Pumped storage plants store and produce electricity to supply peak power demands by moving water between reservoirs at different elevations.

At times of low demand and low power cost, the plant uses electricity from the grid to pump water into the higher reservoir. When demand and prices are higher, the station releases the water back into the lower reservoir through a turbine, generating energy.

PG&E's main subsidiary Pacific Gas and Electric Co owns and operates the station. (Reporting by Bernie Woodall; Editing by Andre Grenon)