October Magnox North News

The mystery of Turbine 4 moves closer to being solved following the arrival of a specialist team from E.ON on site last month (September).

Since August 2007 there has been an intermittent fault on the turbine when momentary voltage control loss results in a loss of excitation, tripping the generator. The fault has tripped the generator three times – the last time it happened was just after Reactor 2 had been returned to service. As the generator trips steam, which would otherwise have powered the generator, is released through the boiler safety relief valves and into the air, making significant amount of noise as it does so.

Conventional Plant System Section Head Steve Webber explained: “The fault itself lasts for perhaps just 510 milliseconds but the results look and sound very dramatic. The release of steam is a designed safety feature and even though the noise as the steam vents blow has been heard as far as Cemaes Bay, there is no danger to anyone and it is only steam that is being vented.

“The generator trip does lead to a loss of generation and during the past year we have done a huge amount of work in attempts to isolate the cause of the problem. System Engineers Wil Jones and Fon Williams from Conventional Plant Systems and Power & Safety Systems as well as our Senior Engineering Consultant Ted Allsop and Magnox staff from Oldbury are amongst the key people to have been involved. “We believe it could be an issue with the microprocessors which operate the circuitry and which were fitted in the early 1990s, and we have contacted other users of similar systems to see whether they have had any similar experiences we can learn from.

“One of the biggest challenges in understanding the problem is that it is such an intermittent fault that when we have, in the past, thought we have found and eliminated what could be the cause, we have been proved wrong when it happens again. The E.ON team, which is now working on site, has been called in because of their expertise in working with British Energy Generators. With their help we expect to establish a solution to finally resolve this and allow Turbine 4 to reliably return to service”