[high_vacuum_house]

Last week we ran all of our gas and Diesel engines every day. The buy price for electricity went very high and on one of the days we ran them for 17 hours continuously. We certainly got through a lot of diesel!! (Approximately 100,000 litres!!) The grid frequency is the same all over the UK and all of the rotating alternators speed is governed by the grid frequency as they are all synchronous machines.

The national grid have to be very careful about the maximum and minimum frequency as well as the rate of change of frequency as all of our STOR power generation sites have protection relays called G59 which will trip the site offline should the frequency deviation go outside the prescribed limits. This is to prevent a situation called island mode where the power station can continue generating into the local grid when the power is cut to the local substation. This could cause a sudden voltage and frequency increase damaging equipment or making equipment being worked on live that should be dead.

The grid frequency is constantly changing slightly as demand and generation change throughout the day. The slightest increase in load slows it down whereas a slight increase in generation increases frequency. It is a fine balance to keep it as close to 50hz as possible.

Christopher Capener