4 ms·

Breakers are usually tripped when too much power is used. Because the ship was traveling slowly in the harbor using lower power, we need to understand other rea

Breakers are usually tripped when too much power is used. Because the ship was traveling slowly in the harbor using lower power, we need to understand other reasons why a breaker would open.

toomuchtodo 2y ago
Failing breakers commonly trip below current limits. Hopefully they will comprehensively test the circuit path and its components in scope. Someone will have to explain why they weren’t replaced prior to failure if root cause.
- raverbashing 2y ago
  True. But to have both fail at the same time usually means an actual overcurrent for some reason Hopefully they get an actual current measure somehow
  - caf 2y ago
    It would not be unusual for the protection design to have the LV and HV breakers on either side of the transformer linked, so that if one trips the other does too. So you can't necessarily read anything in to the fact that both tripped.
    - londons_explore 2y ago
      Why link them? Any failure opening one or other breaker is sufficient to stop fault current. The only reason to even have both breakers is so the transformer can be taken out for maintenance.
      - caf 2y ago
        The idea is to fully disconnect the faulted element from the power system. In particular with transformers, you don't want it backfed from the low voltage side if the high voltage side is isolated.
        raverbashing 2y ago
        Interesting, makes sense. And yes I think the backfeeding is the problem, you don't want the other generator to start automatically while the other side is still connected
    - jcalvinowens 2y ago
      I don't know anything about marine regulations, but on land you generally only have a breaker or fuse on one side of a transformer (usually the "powered" side). If you're in US, the mains transformer feeding your residential service almost certainly has no overcurrent protection on the secondary, it has a fuse on the primary.
ok_dad 2y ago
Traveling slowly in a harbor is when the most load is required due to having a bunch of stuff happening during transit. You’re going to have every generator and engine on, all the anchor equipment, line handling equipment, the steering and auxiliary motors will be working overtime, etc.
tmm 2y ago
Engine speed has nothing to do with power generation, these are totally separate systems. It's not like a diesel train with electric motors; on this ship (and most others) the engine is directly coupled to the prop. The engine requires one of the HV generators to remain online so that oil and cooling pumps operate (and also to bring fresh air in to the engine room for the crew, but those fans can probably run off the emergency genset). Once the HV generators were disconnected, the pumps shut down and the engine stopped. Restarting the engine is a process. Here's how it's done for a small engine (5500hp)[1]. And for something similar to the Dali (55,626hp)[2]. The circuit breakers are a little different than common magnetic household breakers. They will trip in over-current scenarios of course, but also for over- or under-voltage, over- or under-frequency, or if triggered by the ship's SCADA system(s). Breakers tripping on the HV and LV side of the transformer makes me think that they tripped because of something other than over-current. Three things in the report caught my attention: 1) The crew initially tried resetting the tripped breakers (HR1 and LR1) instead of energizing the alternate set (HR2 and LR2) which they had been operating on for months. 2) The second blackout was caused by the diesel generator breakers (DGR3 and DGR4) tripping. The report doesn't specify whether they began startup procedures for generators 1 and 2 when HR1 and LR1 tripped (probably not, because at this point gensets 1 and 2 were still operating), but it does say that genset 2 was in standby and connected automatically after the second loss of power. With #3 and #4 online, adding #2 to the mix isn't as easy as throwing a switch, it has be to be synchronized to the frequency of the other two first and this takes some time. But once DGR3 and DGR4 opened, DGR2 could be closed immediately and DGR1 wouldn't be far behind (i.e. as soon as generator #1 was synced to generator #2). I expect the state of the generators will be fleshed out more fully in later reports. 3) The report makes no mention of the state of the compressed air tanks. There should have been sufficient compressed air available to attempt several restarts (up to a dozen per regs), so running the compressors wouldn't be necessary. But if there wasn't enough stored compressed air, then no matter what the crew did with the electrical system wouldn't have mattered; they wouldn't have had time to fill the tanks enough to restart the engine. Again, I expect this to be covered in later reports. My guess is that there was some fault with transformer #1, which caused HR1 and LR1 to trip off. When it was brought back online and they attempted to restart the engine, the combined load of normal ship operations, additional startup equipment (combustion air blowers, etc) along with whatever (possibly intermittent) fault TR1 had overloaded the generators, which then tripped offline. Perhaps instead they should have closed HR2 and LR2, and started an additional generator before attempting an engine start. But that's just a guess. The report doesn't mention any restart attempts, so there may have been other electrical faults that needed to be sorted out first. Also, having used up some compressed air to start the engine at the dock, they may have been running the compressors to bring the tanks up to the required stored capacity which would have contributed to the load on the electrical system (but only up to the first blackout, as they wouldn't have restarted automatically). 1: https://www.youtube.com/watch?v=J-D9Ka3TM1I https://www.youtube.com/watch?v=J-D9Ka3TM1I 2: https://www.youtube.com/watch?v=5mFmCxOjY_A https://www.youtube.com/watch?v=5mFmCxOjY_A

Breakers are usually tripped when too much power is used. Because the ship was traveling slowly in the harbor using lower power, we need to understand other reasons why a breaker would open.

toomuchtodo 2y ago

Failing breakers commonly trip below current limits. Hopefully they will comprehensively test the circuit path and its components in scope. Someone will have to explain why they weren’t replaced prior to failure if root cause.

raverbashing 2y ago
True. But to have both fail at the same time usually means an actual overcurrent for some reason Hopefully they get an actual current measure somehow
- caf 2y ago
  It would not be unusual for the protection design to have the LV and HV breakers on either side of the transformer linked, so that if one trips the other does too. So you can't necessarily read anything in to the fact that both tripped.
  - londons_explore 2y ago
    Why link them? Any failure opening one or other breaker is sufficient to stop fault current. The only reason to even have both breakers is so the transformer can be taken out for maintenance.
    - caf 2y ago
      The idea is to fully disconnect the faulted element from the power system. In particular with transformers, you don't want it backfed from the low voltage side if the high voltage side is isolated.
      - raverbashing 2y ago
        Interesting, makes sense. And yes I think the backfeeding is the problem, you don't want the other generator to start automatically while the other side is still connected
  - jcalvinowens 2y ago
    I don't know anything about marine regulations, but on land you generally only have a breaker or fuse on one side of a transformer (usually the "powered" side). If you're in US, the mains transformer feeding your residential service almost certainly has no overcurrent protection on the secondary, it has a fuse on the primary.

ok_dad 2y ago

Traveling slowly in a harbor is when the most load is required due to having a bunch of stuff happening during transit. You’re going to have every generator and engine on, all the anchor equipment, line handling equipment, the steering and auxiliary motors will be working overtime, etc.

tmm 2y ago

Engine speed has nothing to do with power generation, these are totally separate systems. It's not like a diesel train with electric motors; on this ship (and most others) the engine is directly coupled to the prop. The engine requires one of the HV generators to remain online so that oil and cooling pumps operate (and also to bring fresh air in to the engine room for the crew, but those fans can probably run off the emergency genset). Once the HV generators were disconnected, the pumps shut down and the engine stopped. Restarting the engine is a process. Here's how it's done for a small engine (5500hp)[1]. And for something similar to the Dali (55,626hp)[2]. The circuit breakers are a little different than common magnetic household breakers. They will trip in over-current scenarios of course, but also for over- or under-voltage, over- or under-frequency, or if triggered by the ship's SCADA system(s). Breakers tripping on the HV and LV side of the transformer makes me think that they tripped because of something other than over-current. Three things in the report caught my attention: 1) The crew initially tried resetting the tripped breakers (HR1 and LR1) instead of energizing the alternate set (HR2 and LR2) which they had been operating on for months. 2) The second blackout was caused by the diesel generator breakers (DGR3 and DGR4) tripping. The report doesn't specify whether they began startup procedures for generators 1 and 2 when HR1 and LR1 tripped (probably not, because at this point gensets 1 and 2 were still operating), but it does say that genset 2 was in standby and connected automatically after the second loss of power. With #3 and #4 online, adding #2 to the mix isn't as easy as throwing a switch, it has be to be synchronized to the frequency of the other two first and this takes some time. But once DGR3 and DGR4 opened, DGR2 could be closed immediately and DGR1 wouldn't be far behind (i.e. as soon as generator #1 was synced to generator #2). I expect the state of the generators will be fleshed out more fully in later reports. 3) The report makes no mention of the state of the compressed air tanks. There should have been sufficient compressed air available to attempt several restarts (up to a dozen per regs), so running the compressors wouldn't be necessary. But if there wasn't enough stored compressed air, then no matter what the crew did with the electrical system wouldn't have mattered; they wouldn't have had time to fill the tanks enough to restart the engine. Again, I expect this to be covered in later reports. My guess is that there was some fault with transformer #1, which caused HR1 and LR1 to trip off. When it was brought back online and they attempted to restart the engine, the combined load of normal ship operations, additional startup equipment (combustion air blowers, etc) along with whatever (possibly intermittent) fault TR1 had overloaded the generators, which then tripped offline. Perhaps instead they should have closed HR2 and LR2, and started an additional generator before attempting an engine start. But that's just a guess. The report doesn't mention any restart attempts, so there may have been other electrical faults that needed to be sorted out first. Also, having used up some compressed air to start the engine at the dock, they may have been running the compressors to bring the tanks up to the required stored capacity which would have contributed to the load on the electrical system (but only up to the first blackout, as they wouldn't have restarted automatically). 1: https://www.youtube.com/watch?v=J-D9Ka3TM1I https://www.youtube.com/watch?v=J-D9Ka3TM1I 2: https://www.youtube.com/watch?v=5mFmCxOjY_A https://www.youtube.com/watch?v=5mFmCxOjY_A