ABB Circuit Breaker System GEK3 Problem

Our power station uses ABB circuit breaker system GEK 3 for both of our gas turbine generator.

In one of our previous start-up, we were unable to close the generator circuit breaker when we tried to synchronize the unit with the grid. The closing signal to GCB was given and the GCB reacted to the closing signal.

However, instead of closing, the GCB closed-opened upon receiving the signal. "GCB air pressure low" alarm appeared explained the release of pneumatic air to operate the GCB mechanism.

After the air pressure was charged up, "GCB air pressure low" alarm was reset and the operators did another attempt to close the GCB. However, similar situation occurred. A total of 3 attempts were carried out including the above.

At the 4^th attempt, the operators operated the GCB only after the GCB air pressure achieved 8.5 bars. GCB successfully closed and synchronize on the 4^th attempt.

I was actually suspecting the permissive from the adjusted value pressure switch F1. I am unable to determine the set point for F1 at the moment as that requires unit shutdown. However, frankly speaking, we do have many experience of closing the GCB with air pressure below 8.5 bars. Normally the air compressor will cuts in when the compressed air receiver reached 8 - 8.1 bars and above that set point we can comfortably operate the GCB without having much problem.

Did anyone encountered similar problem as we did before and any troubleshooting scheme to recommend?