As temperatures rose around southern Australia Loy Yang B's generators failed at around 4pm, instantly taking around 528 megawatts of energy out of the state’s grid.

The outage ahead of a major heatwave on Friday came despite assurances by its owner Alinta Energy that the ageing power station had the capability to continue providing power in the heat.

“There are no issues expected ahead with the forecast hot weather,” Alinta Energy chief executive Jeff Dimery told Fairfax Media on Monday.

He made his assurances after fellow Latrobe Valley brown coal-fired power stations, Loy Yang A and Yallourn, had also experienced a number of generator failures over this past month.

An Alinta spokeswoman confirmed the latest failure on Friday, explaining there was an unexpected failure of Loy Yang B's Unit 1 generator.

"The cause of the trip was identified and the unit returned to service" by  5:10 pm, she said. "Both units are operating and are expected to be fully available over the short term forecast Victorian hot spell, and into the summer period."

EARLIER, 3PM: Thousands of people have been left without power to the south of Ballarat.

As the temperature soars closer to 40 degrees, many residents in Mt Helen, Buninyong and beyond have been left without any power and therefore, without any air conditioning.

Powercor says it could take until 5pm for power to be restored.

It is believed the power went out about 2.40pm, at which time the mercury reached 39.3 degrees.

On its website, Powercor says the fault occurred in Learmonth Street, Buninyong, although the cause is listed as “under investigation”.

The following suburbs near Ballarat are currently without power:

BUNINYONG, 1350 (customers)

CLARENDON, 65

CORINDHAP, 78

DEREEL, 250

DURHAM LEAD, 132

ELAINE, 136

ENFIELD, 1

GARIBALDI, 48

LAL LAL, 116

MAGPIE, 92

MOUNT HELEN, 25

MOUNT MACEDON, 1

MOUNT MERCER, 60

NAPOLEONS, 27

ROKEWOOD, 28

SCOTCHMANS LEAD, 30 

SCOTSBURN, 121

SEBASTOPOL, 1

SMYTHES CREEK, 2