In order to not divert the “news” topic on this incident I would like to more deeply discuss or pull at the threads of various speculative statements and theories related to the Dali engineering plant over here in the Engineering section.
Fair warning - I think to keep this on topic will require a heavier moderation hand than normal, so if you are an engineer (or not) feel free to make technical comments but for example, unsolicited links to brochures without making a point will probably be judged off topic. We are old enough to find our own resources. I am hoping for application of actual experience, design knowledge and even educated guesses to what little technical evidence is before us at the moment. If you want to know how it should work (or share how you think it “should” work) please go read @Louisd75 post in the main topic first.
Let’s start here. I disagree with this analysis:.
Putting aside the “hydraulic lock” idea for a later discussion if anyone wants to - I certainly don’t dispute the contributors lived experience but I believe this scenario is mathematically impossible. Yes it’s true steering gear motors do not have thermal overload protection (but that condition is alarmed), the theory being better to run overloaded and afford the opportunity to start the standby then have it trip off. However, they do have overcurrent protection and if an overcurrent fault occurred at a motor it seems to me if it did not clear at the pump motor starter panel circuit breaker it certainly would at the main bus feeder circuit breaker. Additionally, and this is just an estimation on my part, the most extreme single steering motor fault would not generate enough power perturbation on the main buss of a plant with 2 each 4400 kW and 2 each 3840 kW to cause any SSDG circuit breaker safety relays/device to cause a trip. My guess is the plant would ride through even a severe short. Yes there would be damage at the motor starter but I just don’t see it taking all running DG’s off line.
I think we should look elsewhere for the cause of the blackout.
Hello KP
When I wrote that opinion, I did know about the generator capacity and numbers. Now that we know we have 4 of approx 4 MW, I agree that single phasing of a SG motor will not have enough juice to create a blackout. 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.
Thanks.
Hello KP
Kind of a long question. I am indeed suggesting that they managed to start the main engine few seconds after they restored power to the main switchboard (MSB) and the telltale indication is the heavy black smoke from the largest exhaust outlet in the funnel.
I am also of the opinion that the emergency diesel gen (EDG) started and continued to run powering the ESB right upto the point of impact. I think the running lights were only noticed when the main power came on about a minute after the initial blackout.
PS:
a. I am a new user and as such looks like I am restricted to only 3 replies … so I may not be able to reply again, and the suggested work around is to edit one of my posts … response will go into the proverbial black hole. Happened on the previous thread when I tried to respond to Mr 244.
b. By way of a short introduction as to my credentials, I am a mechanical engineer and a licensed Chief engineer. Have about 12 years of sailing experience in the 80’s with one of the largest shipping companies. Engine types are Sulzer RNDs, B&W GF and GB engines. Container and some tankers. Came ashore and management experience in the US includes container ships with Sulzer RTAs and MAN B&W MC engines. Left for different challenge to the O&G industry 15 years ago with one of the large companies who are designers and operators of FPSOs. Retired last year.
Thanks.
I’m glad you brought this up. That is what I would like to look at next. You said:
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.
This plant arrangement - if accurate - is interesting because the ME auxiliaries would be on the 440 side. If two HV DG’s were online at the time and they both faulted off does the switchboard logic or PMS automatically open the HV LV bus tie? Is the recovery shown in the video really a 440 DG coming online? I believe Chief Makoi considers that but discounts it. Other than a 3000 kW thruster I can’t imagine what else would come off the HV side, if that is true either automatic or manual intervention to split bus and get a 440 DG running would be a good response. But yet again we have no idea of the actual plant arrangement or status at that time.
Of course none of that would affect EDG coming on line and maintaining steering, unless that had an issue as well.
Gents,
A very interesting discussion and well above my technical experience so I will try to add as little as possible unless I think I can add some value to the discussion.
I can answer one question that KP asks.
Yes on an outward bound passage after the swing was completed, tugs let go and engine speed increasing that would generally be around the time that the BT would be stopped.
The usual protocol would be for the Captain to ask the Pilot if I was finished with the BT and I would reply in the affirmative , if I had not already stated I was finished with it.
The BT would have been of little use at that speed but of course you try anything in extremis.
Sorry just a little bit more.
If the ME was indeed running astern prior to the Allison then trying to use the BT would be a logical action and given more room/time may have made the consequences much less.
You see I would have thought they would have been directly fed from the 440 bus. Thinking the only motor with a voltage over 440 would be the bow thruster. Again this is assuming a lot without an electrical one line. But live and learn. Thanks.
Thanks for that. I guess what I was more concerned about is not necessarily WHEN that call would come but IF the thruster drive had a transformer say 6600 / 3000 V to supply the motor drive, was it normal to open a circuit breaker and denergize that upon being told the thruster could be secured. Or would the drive simply be turned off via a control input. We’ll have to see as plant details leak out or are discovered on line. Again thanks.
My suggestion on the HV feeding transformers occurred to me based on me being some distance from the road in a rural area. Our power supply is an 11KV line to a transformer (service is underground the last 180 metres. The transformer supplies 440 volts to the work shop plus single phase 240 volts and a single phase to two houses.
If HV is available it cuts down the size of wiring and the transformers are not that big.
It is all supposition on my part and I will learn more by reading the valuable contributions you engineers make.
Without knowledge of Dali arrangement or procedures, I think that a “finished with bow thruster” order in that location would entail no more than disarming the thruster controller on the bridge. There is another bridge not far ahead and a long passage before reaching the sea buoy so availability of the thruster might be desired. Who knows? It’s a captain and chief procedure thing. I would not completely isolate and secure the thruster until there was no possibility of needing it again.
Hello KP and 244
I think Mr. 2444 is correct in his assessment. The timing of the first blackout with the vessel on a straight track at 8 kts or so, seems to be about the time the Bridge would advise that they are done with the BT.
The lights flickering for a couple of seconds supports the theory that there seems to be a switchboard fault. Generally most blackout are immediate. In this case, again thinking out aloud, does the HV breaker ‘chatter’ while opening with one or more contacts stuck or fused? Is it the differential protection relays that monitors current deviation between the 3 phases activate? Possible.
On the SWBD arrangement, I think an educated guess is that the DGs are housed in 2 separate compartments feeding a HV SWBD. 2 on either side of this board with a bus-tie breaker that will be normally closed. (Slightly different than drilling rigs when a similar arrangement with many generators on either side are connected on a ring main. Bus tie as well as ring tie by connecting the other ends of the board. But this is not material for this conversation.)
This HV board will have the BT and the 8-10 6.6/440V transformers of about 1000KVA rating each located in the longt’l box girder (passage way P&S) fed directly via HV vacuum breakers on the HV board. 2 Feeder breakers on either side of the HV (for redundancy) to the 440V SWBD (MSB). The MSB will have a bus-tie (bus-tie are breakers connecting 2 SWBSs busses of the same voltage rating) to the ESB located in the same space as the EDG. On the face of it relatively simple to understand … but engineering and maintenance procedures for HV is a very complex dimension.
I think the BT motor is also 6.6kV. KP - Not sure about your thought there is a BT transformer. Typical arrangement will be the HV feeder to the motor controller located in the BT space. The motor controller will have step down transformers for operating the hydraulics/cooling water pumps. etc. When this feeder is energized, start sequence will be the hydraulics first to ensure blade pitch is zero and then the large motor starts - most likely a soft starter and not direct on line controller.
For BT stop and secure will be first to stop the motor and then the hydraulics and finally the HV feeder. All these HV feeders will be motor operated and controlled from the control room HMI.
If we are on right track, possibly the crew may suspect the BT feeder being defective. But if the Bridge asks for the BT, their job is not to reason why. Even if the Capt/Pilot had an inkling, they would not have ordered it unless it was a dire emergency.
Again these are somewhat educated guesses based on the info from this forum only. And I providing my thoughts as some you (such as Mr Pilot 244 and KP) are interested to brainstorm.
Thanks.
Have never see a circuit breaker this size and voltage chatter, air circuit breaker or vacuum, tripping by design near instantaneously. Hard to image where the re-closing force would come from once the springs are discharged. A magnetic contactor might chatter but I don’t think a circuit breaker would.
Your thoughts on the distribution system well received. My thoughts above were based on sailorsnipe89 post for what seems like a similar ship. I look forward to when the electrical one line diagram is posted to the NTSB docket.
My guesses at the bow thruster which is stated to be 3000 kW Was based on some assumptions that being built in 2015 they might have selected a variable speed drive installation rather than a CP unit with attendant hydraulics and increased complexity. So my thought was a transformer was fitted upstream of the drive up forward near the drive which would be near the motor. Of course they may have sized the drive and motor to have a drive input voltage of 6600 V so then a transformer would not be used. We have to wait and see about this. But for an example on a 5th gen drill ship (also made in Korea) 11 kV was transformed just upstream of the drive for 5500 kW motors. So my point above restated is - If some one opened a circuit breaker upstream of a transformer that size, that would have little affect on the bus BUT if they closed a breaker on a transformer of size that would have an affect on the bus depending what generating capacity was online at the time. Aside from the affect on the plant its not good for the transformer either but that is a different story. But it is also why I don’t think thruster control is routinely attempted by the HV, MV or LV circuit breaker.
Again I’m not sure it would be routine to open the HV breaker. Without a VFD for the BT and with a hydraulically controlled pitch type unit of this power what would the motor starter look like? At a minimum it would have to incorporate reduced voltage soft starter. These days and perhaps in 2015 these would be solid state devices and should not allow disastrous impacts on the main bus. A soft start of this type has control elements incorporated directly in to it and possibly via a contactor upstream of it so don’t see the need to open the HV breaker.
It may be that the bow thruster is somehow involved but the mechanism and sequence of events does not make sense to me yet.
When I look back on blackouts and brownouts of my own the causes are rather less dramatic than arc flashes, chattering circuit breakers etc. They do fit in the pie chart of causes posted in the other topic.
energizing propulsion transformer without sufficient generating capacity, brownout, load sheds etc.
fuel supply issues
switchboard control issues where Woodward load sharing devices lost comms
in my case number one was mechanical issues on the engine, improper reset of overspeed trip, improper reset of rig saver (not likely on this ship), fuel rack mechanical “issues”, speed pick up/governor issues. These mostly caused standby starts and not blackouts but there were a few mixed in there.
Very good thoughts. But I do think the main feeder breaker on the HV board to the BT will be secured for the long sea passage. Actually, even if the next port of call was a day or two away, this breaker will be secured.
Hello KP
Also, I think you are thinking about drillship/Semi’s thrusters that are usually azimuthing fixed pitch props with uni directional rotation. Motor inside and rotating unit external to the hull where a VFD is the way to go. BTs are tunnel thrusters with fixed speed and a CP prop to quickly change thrust direction. Thanks.
Starting to go off topic but - Well, a motor is a motor. You can mount it on a tunnel thruster as easily as on an azimuthing one. A VFD drive on a thruster will also change speed and direction quite easily without extra hydraulic package and more complex blades, linkages, actuation means in the gearbox outside the hull.
As far as the breaker being routinely used to secure the thruster again, my hypothesis is based on the idea of a transformer and drive being used if that is not the case then it could very well be used. As long as motor heater, starter heater etc had a separate source of power. Someday we will find out.
I’m not telling you what they had on the Dali or even what I think they had. I’m trying to pull at the threads of the technical issues you raise and see if they make sense, to me at least. In a limited, perhaps half-assed way I’m trying to shine a little realistic light on some of the dramatic and fantastical engineering claims being made. I’m happy to be disagreed with and even happier to learn things. But we should explain how things are happening not just that x, y or z happened.
Regarding the discussion of potentially overloading an insufficient number of generators by closing a large hv transformer incommer, is premag not common on newer ships these days?
Oooh tell me more. My last 11kV plant was DW Horizon and I got off that in 2006 so switchgear circuits not front of mind. I’ve seen drives pre-charge capacitor banks but what is pre-mag in this context?