Note: The Department of Energy, Mines, Indutsry Regulation and Safety’s investigation was ongoing. The information contained in this significant incident report is based on materials received, knowledge and understanding at the time of writing.
During normal operations at a gas processing facility, an early smoke detection and alarm system was activated in a substation’s switchroom. After workers confirmed the presence of fire, the electrical supply to the substation was manually isolated. The 6.6 kV upstream feeder protection (part of the power supply feeding the switchboard) did not activate.
Production was shut down and the emergency response team were unsuccessful in their attempts to manually fight the fire. The fire was finally extinguished when the switchroom was blanketed with an inert gas.
There had been a phase-to-phase arc fault on the line-side cables within a 185 kW 415 LV withdrawable motor starter in the switchboard’s motor control centre (MCC). The fault escalated to the main bus on the same switchboard, almost completely destroying the 415 V MCC in the switchroom, damaging adjacent equipment.
The subsequent investigation found that the switchboard’s MCC modules were heat damaged due to a high resistance connection to the main bus. These modules were used for both electrical and mechanical isolations over an extended timeframe. This is thought to have caused a high resistance connection which generated sufficient heat to escalate into an arc fault. The upstream 6.6 kV feeder protection failed due to a seized tripping mechanism in the contactor. The possibility for the latch roller to seize and fail was a known contactor vulnerability.
Further information
- Department of Energy, Mines, Industry Regulationa and Safety, Asset integrity management systems
- Standards Australia - AS 2067 Substations and high voltage installations exceeding 1 kV a.c.