Yes, it applies to all large motor vessels, as all auxiliaries are electric motor driven. It is meant to be a feature that allows isolating a part of the switchboard for maintenance or repairs while the other could still be energized and power the ship.
I understand. That is why dis-connectable links are provided in the bus bars. Standard practice in dry docks is to check the torque of the bolts. Having a breaker in the LV board does not make sense if you only have 1 EDG and also all services must be made redundant - not just the pumps required to run the main engine.
BTW in the report they mention DG 3 tripped due to low fuel pressure. That is really strange. With 3 and 4 on the board at departure with a lot more load, wonder if this had something to do with stability of the HV board. ie knocking out the HR breaker (assuming either the under voltage coil tripped the breaker or the CT suddenly sensed a high current due to low voltage).
This is by rule, at least for ABS. It’s the difference between LVP and LVR. Steering is defined as essential vital service so gets LVR. If it was turned on before the blackout it should restart when power comes back.
If only the no 3 pump was on E-SWBD and was not running before the blackout, that could have required operator intervention to start it after the EDG was on E-SWBD. Then again loss of power is an alarm and HPU running are required indications on the bridge. So presumably one’s attention is drawn to the fact no 1 and 2 are not running and start no 3.
Then again we don’t know exact control scheme in this case. Perhaps number 3 starts automagically upon loss of any running main unit while in running mode.
What doesn’t make sense? It’s there to protect down stream cables and in a way the transformer as well. Why not clear the fault closest to the fault and limit what is exposed to excessive current? Also I believe class (at least ABS) requires coordination of protection between high and low voltage protective devices in their section on HV installations.
I am talking about the LVR tie breaker. Makes sense to operate open?
That’s my experience but don’t know for sure in this case.
Either way it’s not directly relevant because 0127:23 is when the SSDG came back online.
Given the choice I would rather have it than not have it. It may be required for all I know. But among benefits would be improved plant flexibility, possible advantages in recovery from serious damage / fire events, easier means to LOTO switchboard segments for M&R. Hard to evaluate without the one line. But for example heavy damage on / in a few cubicles of the LV SWBD could be isolated and presumably with proper distribution of vital loads, open bus tie and life goes on. As opposed to going dead ship to remove bolted links.
Whole heatedly concur. Very useful in any emergency situation such as the one you describe. As long as there is no UV coil or a shunt trip and even more preferable would be a rated disconnect switch without the hair trigger of a breaker (what would the trip setting be?)
So it looks like most (244. Aus, Texax T) if not all the Masters here are of the opinion that the SG was rendered inoperative and remained so until the contact. My question is what would be likely reason for the further steerage to the right now that we know the main engine was off and thus no prop walk.
Before we go any further I would just like to thank all the contributors for a very well informed discussion .
Learnt a lot these last few weeks
with the info we have so far - i don’t have a good guess. Sure will come out in the full report with the enviromentals, bridge team interviews, and data recorder info is out.
Actually I probably misled a lot of people insisting the main engine was re-started. I was thrown off by the size of the exhaust pipe on the video, but could not explain the other big mother on the stbd side – until we discovered the scrubber installation. Looks like aside from the main engine, possibly the aux boiler and at least a couple of the DGs are setup to discharge to the scrubber. The original main engine exhaust is used for this service and a separate new uptake (on the stbd side) for the main engine was installed along with the new superstructure.
The wait … painful … may have to wait couple of years!
It seems like it was running in a normal for a box ship configuration when the switchboard went haywire. We’ll be waiting a while for any real answers, “haywire switchboard” is one of those things that can intermittently haunt a box ship seemingly forever because of the lack of expertise and opportunity to do lengthy troubleshooting or repairs that might delay the ship.
Well there are circuit breakers and then there are circuit breakers no? Terms like UV trip and shunt trip I am used to associating with smaller molded case breakers or even bigger ACB’s being used as switchboard feeders to distribution panels or big control panels. Where you want to trip them remotely for say an emergency shutdown circuit or even a load shed command. In other words to open the breaker - using it as a “switch” so not clearing an overcurrent or overload fault.
Generator breakers, bus ties, power distribution transformer primary and secondary breakers are a whole different animal. Sure they can be opened and closed manually but tripping is via separately mounted protective devices. UV, OV, frequency, reverse power relays ( or software nowadays) etc. each of these usually throw a flag on the device (or message the monitoring system).
So I imagine this bus tie at least would be looking for overcurrent protection if for nothing else but to keep the transformer on line feeding the “good” half of the LV bus in case of a fault downstream of it on the “bad” side.
However, I’m not understanding why it is assumed that the breakers definitely “tripped” as in clearing a fault situation via a protective device. I know the NTSB said “unexpectedly opened (tripped)” but are they using tripped in a generic sense? If it was in reaction to a high current or other situation why wouldn’t NTSB know by now that it “tripped on overcurrent” or “tripped on undervoltage”? Like I said these things throw a flag that needs to be reset.
If there was say, a short big enough to generate a fault current, in my opinion there would be a trail right to it, whether tripped breakers closer to the problem or smoke or failure to reset the culprit after normal power was restored.
There could be a much more mundane explanation. Maybe truly an unexpected/ unintentional/not safety device related command. Like something in the breaker control circuit. A balky relay? Some misstep in troubleshooting the in port power issues left closing or opening circuits compromised?
Do they know and just didn’t include it in the prelim or is it in the realm of mystery still.
Each HV breaker is provided with a protection relay, you can see them in the report. These are digital devices specially designed to read the currents, voltages and tripping the breakers when the rated values are exceeded. If the breaker was tripped by the protection relay, then the history saved in the non volatile memory should have that event. The event and fault history can be downloaded to a PC or read on the device display.
AV2013,
Your line diagram reeks of redundancy as opposed to the diagram included in the preliminary report. It even states that the LV Bus tie closes automatically if one of the four stepped down feed breakers trips.
Exactly so why no detail on the “trip”?