IMCA - Near Miss - High voltage ace inside tether termination manifold

Description of Incident

A high voltage arc occurred inside a ROV tether termination manifold. The ROV

HPU Breaker tripped during the return of the ROV to the TMS. Initial investigation

into the trip was conducted and findings indicated no hard fault was present. The

ROV crew performed a reset of the breakers and restarted the ROV HPU to recover

it to the TMS.

Approximately 3 hours later, it was noted that the line insulation monitoring system

for the ROV HPU was reading 12 M/Ohms, which under normal operation would

read >60 M/Ohms. Upon investigation after recovery to deck, the crew found there

was approx. 80mm of gas at the top of the tether termination manifold.

The system was isolated; the gas was vented out and the oil was drained out of the

manifold. Inside the manifold it was noticed that one of the ROV HPU conductors

had dislodged from its crimp which had in turn caused electrical arcing in the

manifold.

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