Comments from the report
Whilst pressurising the fire main for helicopter operations, a gasket failure occurred on the pipework valve under the engine room floor in front of transformers 690V/440V T3 and T4. The spray created a water fog and favourable atmosphere for an electric arc on T3 and T4 transformers, leading to a loss of 440v and 230v on vessel power plant. Upon depletion of the UPS batteries, the thrusters were lost.
A detailed investigation was undertaken with many findings including adding ingress protection at the transformers, adding isolation valves in the piping and modifying procedures. One supplementary finding related to the UPS systems, as both failed before 30 minutes. Investigation revealed that the load on the UPS’s was greater than when they were tested alongside during annual DP trials.
Considerations of the IMCA Marine DP Committee from the above event
- It was questioned whether the DP alarm should have been yellow rather than blue and it is assumed that, for some reason, the alarms generated at 0813 were not interpreted correctly.
- There was concern that a fire main was passing through a transformer space. It was considered that if the vessel had been equipment class 3, it would have been subject to an assessment of the space so the danger of such an occurrence happening would have been noted.
- UPS battery endurance tests (30min check) should be performed with all UPS consumers connected and in use.