Dali Engineering Aspects - various and sundry

[KPChief]

@retdmarineengineer

In one of my later posts, I theorized that the blackout could be when crew when to secure the power to the BT. High voltage switchgear. Please take a look at that post … the lights flickering before the first blackout may be an indication.

I’m glad you brought this up. That is what I would like to look at next. You said:

@retdmarineengineer

Blackout due to a fault (most likely electrical) and in turn this blackout resulted in the steering gear damage. The quick recovery from the blackout corroborates the electrical fault theory.

@retdmarineengineer

You see the timing of the first blackout also seems reasonable when the Bridge would announce they are done with the Thruster. And when they get the ME started and realize no steering they ask for the BT again as a last ditch effort. And the second blackout when they energize the BT breaker in the engine room.

So we are still looking for the cause of the original blackout. I certainly can’t comment on if that was a time to secure thruster or not.

@Sailorsnipe89 (his post) back on 26 March informs us that: their ship has a 6600 V and 440 V busses and there are DG’s on both busses. Also that the two are tied together by bus tie and transformers. Great I think we are on same page up to now.

So if these busses were united as normal operating procedures and the BT is on the HV bus. I am going to assume a typical installation of the HV bus breaker feeding a thruster transformer and then the motor drive - again assuming the thruster is directly powered by the drive and induction motor. Now if this is the case I would not control the BT by opening and closing the HV switchboard breaker. My longest experience is diesel electric in the drilling world and based on that when you close a breaker on a propulsion sized transformer you better have way extra generator capacity on line because the in rush could certainly cause bus voltage/frequency problems. Once you do it once you wouldn’t do it in a hasty manner again. So while what you say could cause a blackout under the right circumstances this is not a new ship and I would think the crew would know not to do that. But that’s what investigations are for.

There are better ways to secure the thruster, e-stop latched, or no doubt they have hard switch to call for the drive to be ready, or HMI buttons, etc. Energizing and energizing the transformer is not the way I would go but we are missing so much technical information to make better guesses that we are all pissing up a rope at this point.

Who knows that if in the effort to restore power this breaker was cycled and did pull down the HV bus enough to cause DG safety relays/devices to trigger a generator trip. But still we are looking for the cause of first blackout.