Question About the Emergency Diesel Generator

Is there any way that the Emergency Diesel Generator (EDG) can be both in proper working condition and correctly configured to start and take the load and still fail?

Sure. It is a piece of machinery. So possible … but very unlikely.

In what scenario would an EDG fail to start in an actual emergency but still be able pass a routine test? Both before and after the actual failure?

For example say the EDG on the Dali was tested now and it started just fine.

Is there some possible explanation, maybe involving terms such as “3-phase” or "power factor’ (to pull a couple terms out of thin air) that might cause the EDG not to detect the power failure.

Internal combustion engines are not my strong suit. Back on the USS Ustafish, it wasn’t really uncommon to do an EDG load run and have it fail to start. There wasn’t anything really wrong, but it took some glaring from the diesel chief to get it started. This was a back up for a nuclear reactor, so maintenance was very routine.

I recall an instance of an emergency generator perfectly good in all respects not starting up after a power failure, because its air supply was blocked.

Its air supply was protected from spray by automatic louvers. When not in use the louvers sat closed, protecting the machinery from spray. If mains power failed a switch operated by battery would open the louvers and start the EDG. But for the EDG to start the louvers had to open, and they did not. The EDG was fine but the louver opening/start interlock system failed.


There is also the matter of the quick closing valve.

Not sure if this meets your definition of “correctly configured” but … during a typical Flag/PSC inspection for example the quick closing valve is tested using the remote closing mechanism located outside the space and then reset. If this is done after starting/testing the generator and everyone leaves it is possible the quick closing valve actually remains closed instead of open. The EDG would start in an emergency but would die out in less than a minute, probably a few seconds. It is probable that it would not run long enough to connect to the emergency bus.

As a best practice, the quick closing valve should always be tested BEFORE the generator so the running of the generator serves as evidence of the correct setting of the quick closing valve.


Not exactly what you are asking, but I have tested emergency generator where it auto started and ran, but breaker would not close due to under voltage condition. Generator governor had to be adjusted and re-tested to get emergency board on line.


I’m not familiar with the automation of their power management system but I don’t think they ever had to go to EDG power.

I’m Chief Eng of a modern Chinese built US flagged Tanker that was built for to class LR standards.

I have 4 AE’s on my ship. I had a very similar power failure a few months ago where I had went to put a second generator online in preparation for arrival and when the breaker for the oncoming generator attempted to close it failed to close. At the same time the inline generator tripped on high voltage we went over 490v on a 450v bus.

When this happened I had a total power failure and lost the plant just like the Dali did. My EDG started but I was able to manually close the breaker to the generator that I still had running that had failed to close. We had to go and close all of our under-voltage trips on the switchboard as well as through out the plant. Because we were making way and underway the engine was very easy to restart once we cleared the EOT alarms.

We never went on EDG power but it did start and idle, then started its cool down procedure and returned to standby status on its own.

Hope this helps.


Some ways the EDG could fail I’d never considered so perhaps my question is not relevant.

I don’t know what parameter causes the EDG to start and go on-line, I’d guess it’d be the voltage at the emergency switchboard going to zero.

Nothing too far-fetched but Is there any scenario such that there would be a power failure due to phase or frequency or some such that would cause electrical equipment to fail but would not be within the parameters required to have the EDG go on-line?

I’m not sure if you have some information that suggests that their emergency generator didn’t come online or you’re confused about what phase and frequency means.

There’s a required interlock for that switchboard. If there was power loss across any phase that interlock would open. So the scenario I think you’re considering where only one phase is lost and the EG fails to come on line doesn’t seem likely.

A scenario where the frequency falls to the point of failure of essential equipment but fails to start the EG is very implausible but I suppose technically possible. That would be a pretty temporary situation though.


Interesting incident escalation on failure of the emergency power. Late 90s one of our large post-panamax container vessels experienced really heavy weather and rolling with lashings giving way with containers overboard and stacks of containers dangerously tilted/slanted on deck.
Engine room personnel were on standby as the Master was trying his best on the Bridge. All of a sudden the emergency bus-tie breaker opens. And the EDG power does come on line. When they go upto the EDG space they see about a foot of water sloshing around. Location is main deck. Auto ventilation louvers for combustion air/cooling are required to be provided was open allowing green water ingress. (You also have ventilation louvers in front of the large radiator that opens during start up of the EDG). No drain in the space and the crew get to de-watering the space asap. So remember at this time, all the emergency services are inoperative. Back in the engine room, after about an hour or so out of the blue the essential generator stops. Totally dark. Somehow the engineers figured out it must be the 24V battery system that provides power to the safety system on the DGs must have drained out. With some temporary overrides, they manage to get the generator started and also provide temporary 220V to the battery charger. And the main engine as well. Couple of hours later, EDG room was dried out and switchboard restored. Quite a bit of the damage to the lashings/deck containers was during the blackout period.
Everybody onboard were really shaken up. The fallen containers damaged some of the fire hydrants on deck and thus no fire water fighting capability. The crew was so shaken up and it was a really a task to make them understand that it was a USCG requirement to get the integrity of fire main to be allowed to come in. Had to insert spade blanks on the fire main in the box girders and finally the vessel came to PNW.
On attending the vessel, turned out the bypass for the ventilation louvers of all places in the CCR was kept open since delivery as the space was getting too hot. We also corrected the battery charger issue by providing a secondary means from the main switchboard. Quite a bit of interviews and questioning of both the Chief and Master by the authorities. Both advised they had no desire to return to sea anytime soon.

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That sounds similar to one of the first blackouts I experienced. Each week we would swap over the 24v battery charger between banks, and also swap which battery bank was feeding 24v to the mains and generator controls system, including the electronic governors. But one week the Ch Elec swapped the charger but not the feeder breaker, so the charger was charging the offline battery bank, and the online battery bank slowly drained down over the course of a day. Error Chain: the 24v low-voltage alarm buzzer in the control room didn’t work and no one was aware. Mid next day we lost the plant as the governors lost power, generators slowed down and tripped on undervoltage. EDG started, and it fed the emergency bus, and the bus fed the battery charger, but that was feeding a battery bank that was offline. Someone had to run up six decks to the emergency generator room to swap the battery bank switch over. If we were heading for a bridge we would have hit it.

I’ve also been on a ship that was held in port after we did a regular black-start test of the EDG and it failed. We manually tripped the bus-tie, EDG started, but EDG breaker failed to close due to a mechanical piece in the spring mechanism failing. Worked every time prior, until it didn’t.

Different black out scenario, I’ve had one of those simple voltage sensing dead-bus relays fail on a standby generator. The relays were there so that if a generator started as a result of a blackout and the bus was dead it would just close the breaker immediately since there was no need to synchronize with another generator. We had two generators online and auto-started the third. Since that generator’s relay had failed it’s breaker logic system took that to mean the main bus was dead and it tried to close the breaker without synchronizing. It tried closing 180-deg out of phase, smoked the breaker, and tripped all generators off. I suppose something similar could happen to an EDG.


I wonder if it really could though. The bus tie at the main swbd normally closed. The bus tie at the E swbd closed but it is mechanically interlocked with the generator breaker -or- alternatively you have a bus transfer switch which accomplishes same thing, only one source at a time on the E swbd. I think you’d have to really do some unsavory things to get both sources closed at the same time. Then again could be designed for short term parallel ops for bumpless transfer back. Maybe it’s worth the extra automation for some operators.

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Also not exactly “correctly configured” - I was in a freighter bound for Desert Storm
when we lost the plant off the Gulf of Sidra, and were drifting toward Gaddafi’s “Line of Death”.
EDG did not start due to the exhaust valve being closed.

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Having read this thread I don’t think my question is relevant.

No need for highly convoluted explanations when there are many, more pedestrian ones that are far more likely, for example faulty breakers

Indeed bumpless transfer (both ways) arrangement is great during testing and especially under load as you can fix the load. Great feature for vessels without a UPS for bridge eqpt and no worries about gyro talking a walk.

This thread underscores the need for a global incident reporting system - at least for critical eqpt such as the EDG and SG. After all the primary objective of all regulations, rules and standards is safety in design and operation. Their job would be made much easier if data was provided to them. Of course, it has to be unfiltered and factual. (Many layers of owners, managers in between need to be considered)

I am a deck officer, early in my career aboard an ATB I was in the pilot house when the vessel lost power. After what seemed like an eternity the standby genset started and gave power.

On the same hitch it happened again. This time the standby genset failed to start. This was found to be dead 12v starting batteries. We were in open water and did not hit anything.

Later on I found out that these random power losses were due to faulty circuit breaker that was opening for no reason. It had been reported but the company was too cheap to buy a $1000 circuit breaker.

More recently I was on a wire boat when I lost the boat right next to an oil dock. This was later traced to the main fuel valve for the engine room. It was not a quick closing valve as has been mentioned. It was a regular ball valve. It had accidentally been left in the halfway position during a drydock.

Everything ran fine, but when I started working the main engines a bit to land the barge it starved the generator, causing it to shut down. When that happened I lose steering, nav lights, all electronics not on 12v battery backup and electronic engine controls. Miraculously we did not hit anything. After the incident I added a 24v battery backup to the controls, so I can at least maneuver the boat.

Both these incidents were caused by human error.


I must be old. In my day you wanted your emergency generator to fire up, you fired it up, yourself.

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The actual back up the nuc reactor was the battery back through the MG sets. The EDG was just there to charge batteries if you go to snorkel depth and could not get reactor stated again. MM (SS) nuc.