Generator transformers are often said to be the weakest part of a power station in terms of vulnerability. This was the case when we handled a failure of one 500 MVA unit at a three unit station. Bizarrely within a matter of eight days a second failure occurred to another unit, taking two thirds of the station off line.
Mitigation of the first loss was underway, with the installation of the company’s strategic spare, but when the second unit failed a global search ensued for a suitable spare – bringing with it its own problems. However an old unit was located and arrangements made with the owner for its purchase. Difficult logistics were overcome to transport the unit to site, by sea and road and it was successfully installed some 10 weeks after the failure.
Forensic strips were undertaken which showed the transformers failed for different reasons, just coincidentally at a similar time. Clearly there was some concern that a possible grid disturbance had caused the failures, questioning the survival of the remaining unit!