One of the nation's largest coal-fired power stations has had six failures of one of its units in the past three weeks, placing added strain on the power grid and prompting a call for fossil fuel plants to be set the same reliability standards being considered for renewable energy suppliers.

Loy Yang A station, owned by AGL, had its latest "trips" late on Tuesday evening and then two hours later at 1.10am on Wednesday, instantly shedding 230 megawatts and 161 megawatts of output respectively.

AGL said Unit One of the Latrobe Valley plant returned to service on 22 December following "a planned major maintenance outage", and had had difficulties since.

"Load may fluctuate due to minor maintenance issues that are addressed as part of normal plant operations," an AGL spokesman said. "Our key focus is on ensuring that Loy Yang continues to be a safe and reliable provider of generation to the National Electricity Market."