| 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
2: https://www.youtube.com/watch?v=5mFmCxOjY_A |
Mildly interesting: to reverse propulsion, the engine is stopped and restarted rotating the opposite direction.