Sources of Intermittency On The UK National Grid
The largest source of intermittency on the UK National Grid is the power stations; in fact, the single largest source is Sizewell B nuclear power station. Whenever Sizewell B is operating the entire 1.3 GW output is liable to stop at any time without warning. Its capacity is 2.16% of the national grid maximum demand, making it the single largest power source and therefore the largest source of intermittency. Despite this issue, NG readily copes with it using the methods outlined above including the use of diesel engines. An industry-wide rate of unplanned scrams (shutdowns) of 0.6 per 7000 hours critical means that such a shut-down without warning is expected to happen about once every year and a half. However, no matter how low the rate of unplanned scrams, this is largely irrelevant - what matters is the fact that it can and does happen, and measures have to be in place to deal with it.
In 2008 both Sizewell and Longannet power stations both stopped unexpectedly within minutes of each other, causing widespread power failures, as substations were tripped off using prearranged under-frequency relays.
Read more about this topic: Control Of The National Grid
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