Unexpected interruptions to the power supply can occur for many reasons including storms and lightning, trees or branches falling onto powerlines or car accidents.
However, sometimes it is also necessary for power companies to interrupt supply in a planned or co-ordinated way. This may occur because of routine maintenance or for safety reasons.
On rare occasions, planned or deliberate interruptions occur because electricity generators or transmission and distribution networks cannot safely supply the demand for power.
The occasions are known as rotating outages, load shedding or power sharing and often happen at very short notice at the direction of the Australian Energy Market Operator (AEMO). Although this is not common, all electricity networks operate in this way from time to time.