The Fogafale Power Station was commissioned in December 2005 consists of 3 x Daihatshu engines with medium speed of 750rpm, coupled with 750kVa Nishishiba 11kV alternators.
On the 1st April 2021, the Fool Day, “TE ASO FAKALOILOI”, the operator on duty reported that the Generator XNo 7 ac alternator is having problem. We thought that the report wasn’t correct because of TE ASO FAKALOILOI. But, later we learnt that the report was a genuine one.
The operator called the technicians to prepare #No 7 for starting up because the demand has increased. The operator started the generator and to his surprised that the two technicians signaled him to shutdown the set because they could see sparks from underneath the ac alternator.
The maintenance team dismantled the covers to get access to the coils. They found out that there are black marks (carbons) around the coils. The coils were tested and found the following:
- Red to Earth 624 M
- Yellow to Earth 130 K
- Blue to Earth 427 M
It can be found that the reading of the yellow phase has very low resistance compared to the red and blue phase. The readings seem ok because it wasn’t a dead short reading.
The fault is expected to be a flashover between the coils and had caused by the intruding of moistures in the windings. The alternators are fitted with space heaters and the level of moistures is really high which the heaters not able to clear it off in a short period of time. After cleaning and heating for several days the readings were significantly improved and as follows:
- Red to Earth 657 M
- Yellow to Earth 434 M
- Blue to Earth 449 M
The technical team unanimously agreed to give it a go and on Saturday 17th April 2021, the generator was started adn loaded and it works perfectly. So, on Sunday the 18th April 2021, the generator was putted on load for a longer period and it works without any difficulties.