Why load shedding happens
Supply and demand on the grid have to match every second. If a large generator or transmission line trips on a very hot day, there may not be enough supply left. Rather than let the whole system collapse, AEMO directs networks to cut demand in a controlled way. United Energy lists extreme heat, power station faults and transmission incidents as the usual triggers.
AEMO describes controlled load shedding as an absolute last resort to protect the system and prevent long-term damage to infrastructure. Without it, protection systems could trip large parts of the grid, a far worse outcome known as a system black.
Whose power goes off
Networks keep a priority list. Areas with major hospitals, water and sewage pumping and major public transport are kept on as long as possible. United Energy says the first areas switched off are mainly residential, and power is typically off for one to two hours before being restored and another area switched off.
Life support and load shedding
Load shedding comes at very short notice, so there is no time for the usual planned outage warnings. If someone relies on powered medical equipment, have a backup plan ready.
Recent events
- 13 Feb 2024
Victoria
Storms brought down six transmission towers near Geelong. AEMO directed AusNet to shed load, affecting about 90,000 customers, while storm damage separately cut power to a peak of 530,000 customers across Victoria's networks.
- 28 Sep 2016
South Australia
Not load shedding but a statewide black system. Tornadoes damaged transmission lines and a chain of faults disconnected the state from the grid. AEMO's final report set out the causes.
Common questions
AEMO, the Australian Energy Market Operator. It tells the networks how much demand to reduce, and the networks switch off supply to particular areas in rotation.
Each area is usually off for one to two hours before power is restored and another area is switched off. The event continues until AEMO directs networks to restore everyone.
Usually very little or none. Networks receive the instruction at short notice. Check your network's outage map during hot weather or major events.
Sources
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