High voltage breaker trip – DP observation

Comments:

Investigation started at the breaker for DG No. 5 in the port switchgear room. The breaker showed tripped and there was a fault present on the auto voltage regulator (AVR). DG No. 5 was locked out and investigation continued, the AVR breaker ‘S1’ was found tripped. Further investigating found that one of the wires from this breaker had chaffed on the inside of the box and resulted in a short and evidence of arcing to ground. The damaged wires were replaced and the rest of the wires in the junction box adjusted to avoid future problems.

After replacing the worn wires and test running the engine it was noticed that the load indicator on the PMS panel was showing a negative reading, which was incorrect. This signal was a feedback from the breaker module and was in fact sending a false milliamp signal to the PMS. Racked the breaker out to perform a hard reset, the kilowatt signal from the relay went to zero.
DG No. 5 was run, tested and connected to the 11kV bus, all in proper working order.

Considerations from the above event:

  • The investigation explained that the AVR breaker trip caused the DG No. 5 breaker to open presumably as a result of a reactive power (kVar) protection scheme. It seems from the investigation notes that there wasno connection between the original fault and the negative active power (kW) signal.
  • Similar wire checks should be made on all other engines.
  • Having four DGNSS enabled in the DP controller is not a good practice as the total ‘DGNSS weight’ is reducing the ‘acoustic weight’ to insignificant.
  • The DP alert status should be initiated in accordance with activity specific operating guidelines.