An underground mine in New South Wales mine was evacuated last week after a fault occurred involving the three-phase and ground on the 33kV overhead line on the mine surface.
While the initial fault cleared quickly, it appears to have led to a ‘cross country fault’ in the 33kV reticulation system. Over the next six minutes a failure occurred on a 33kV pole-mounted circuit breaker and a 33kV cable splice underground.
Monitoring systems logged significant disturbances on the high voltage (HV) network throughout this period, leading to the HV protection system shutting down power to the site.
The failure of the underground splice caused a fire at the splice and after an unsuccessful attempt to extinguish the fire, the mine was evacuated.
The initial fault may have been caused by a fallen branch or wildlife coming into contact with the 33kV overhead line resulting in a phase-to-phase and phase-to-ground fault that was cleared within 50 milliseconds.