A Case History of Shore Power Transformer Taps Arcing During a No-Load Condition: Understanding the Cause of Arcing

Shore Power Transformers are used to connect berthing ships at ports to use shore power from the port facilities. It has been established that using shore power instead of power from on-board generators can minimize air pollution as ships use low-grade fuel for power generation. The process of switching off the onboard generators of berthing ships and connecting to shore power is called shore-to-ship power supplies (STSPSs). To comply with mandatory air-pollution requirements, in 2014, the Port of Oakland installed STSPS projects at various berths. In 2015 at Berth 37, a 7.5-megavolt-A (MVA), cast-coil transformer within an outdoor enclosure experienced an arcing of the primary no-load tap connections at 12.47 kV. The installation and testing of Berth 37 complied with the International Electrical Testing Association. It is a normal practice to leave the transformer energized when the STSPS operation is finished. The taps arcing occurred when the transformer was energized without any load. There was no power system transient event when taps arcing occurred.