Posted: 15 December 2014
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Testing times
Testing times

Nigel Williams, Head of Electricity System Operation, on how National Grid's ‘proving tests’ on the three power stations are providing additional reserve this winter.

Balancing the system at National' Grid's National Control Centre.

"Testing is vital to ensuring the plant we have contracted can deliver when the electricity supply situation is tight."

Nigel Williams, National Grid's Head of Electricity System Operation.

As part of our response to tightening electricity margins, this winter we’ve taken the step of contracting three power stations to help us balance supply and demand. We refer to this arrangement as Supplemental Balancing Reserve (SBR), and we have contracts in place with Peterhead, Littlebrook and Rye House power stations. SBR is one of two new products that have made an additional 1.1GW of power available to our electricity control room this winter.

We need to be able to rely on these SBR units if and when we call on them. So included in these contracts is a requirement for a monthly “proving test”. Over the last week or so, we’ve been undertaking the first of these proving tests with the three generators. And so we can simulate a real-life scenario, we don’t tell them when they will be tested and give them only the notice that they would normally expect in a real life event.

Nigel Williams, National Grid's Head of Electricity System Operation.

Nigel Williams, National Grid’s Head of Electricity System Operation.

Before a test, we’ll give a generator notice of the need to warm-up, if the individual generator requires a period of warming. We’ll then give it a certain amount of time to reach the level of capacity it is contracted to provide. In our control room, we are able to see in real-time how the station ramps up and how long it stays at its required output.

We test the units by running them up to full output for one hour and comparing the volume of energy they should have delivered against what is actually delivered. We try to schedule these tests away from peak times to minimise their impact on other generators in the market.

Results are not a simple “pass” or “fail”. Results are based on all the tests undertaken over the contracted period so each test alone cannot be used to judge the performance of the plant. The individual generator’s reliability is taken into account in assessing how well it has performed across all tests. We have a “contracted reliability factor” against which we can compare a generator’s performance across the whole winter, not just for one test.

Because the cost of our new services to keep the lights on represents less than a pound a year on the average power bill, we have a duty to ensure we are getting value for money. That’s why non-delivery charges may apply if a generator fails to perform across these tests, or when called upon to provide reserve.

Testing is vital to ensuring the plant we have contracted can deliver when the electricity supply situation is tight. As a prudent System Operator, we undertake tests precisely so we know what to expect from these power stations. Testing is a rigorous process, and enables generators – and us – to learn valuable lessons. All three of our contracted units have now undergone their November tests and December tests are being planned in. We’re not complacent and will work closely with the generators to make sure plant is ready if and when we need it.

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