Image Credit: Martin Bodman
The UK power grid suffered a huge outage that affected almost one million people today. Customers in most network regions were hit, with Western Power Distribution reporting around 500,000 customers without power.
The issue began when Little Barford Gas fired power station in Bedford tripped off the network. The reason for the trip is currently unknown, but several large power stations can trip every day. Tripping is not an unusual occurrence in itself. Almost instantaneously, for seemingly unconnected reasons the Hornsea wind farm also tripped off the grid. Normally these events would be part of a daily routine, however the fact they tripped nearly instantaneously meant that there was insufficient time to balance supply and demand.
Electricity grids across the world need to be kept in balance, with supply matching needing to demand on a sub-second level. This is achieved by generators reducing and increasing their load to match the demand. When the supply is unable to keep up with the demand level, the frequency of the grid starts to fall. Normally as it falls the national grid will call on its demand response program to balance demand, either by requesting heavy users of energy reduce their demand, or with additional generation being brought on stream.
Due to the level of generation falling so rapidly, the grid frequency fell towards the lower limit of 49Hz and the grid protected itself by tripping off vast areas of load to keep its frequency stable.The frequency needs to be maintained because as the frequency falls, generation potential also declines further (a generator will produce less power if it runs slower), which can make the problem worse again, so protecting the grid by tripping load is an essential balancing mechanism in times of high grid stress but this is cold comfort to the customers who lost power.