Dungeness B, United Kingdom, 2007. Annex III. Description of Selected Open Phase Events

On 14 May 2007, the UK transmission system operator took the Super Grid Autotransformer 1 (SGT1) feeding the 275 kV substation out of service. At the time, Reactor 21 was shut down and Reactor 22 was operating at 490 MW. With SGT1 out of service, the two in-service Dungeness B station transformers, 21 and 23, were being supplied from SGT2. Over the following three days, the station electrical system suffered a series of apparently random voltage motor faults across various voltage levels: — 21A chiller tripped on thermal overload; — Cooling water pump 23 tripped on thermal overload; — Turbine 21 auxiliary lubricating oil pump tripped on thermal overload; — Active areas supply and extract fans tripped on thermal overload; — Cooling water pump 21 tripped on thermal overload