Generator fault.

For technical discussions about electricity, electrical equipment with particular emphasis on safe and compliant installations.
Off topic remarks are liable to be moved elsewhere, or in extreme cases to be deleted.
User avatar
BritDownUnder
Posts: 1037
Joined: Wed Sep 21, 2011 12:02 pm
Location: Hunter Valley, NSW, Australia

Re: Generator fault.

Post by BritDownUnder »

kenneal - lagger wrote: Sat Mar 13, 2021 11:44 pm Can anyone point me in the direction of an over frequency cutout switch to handle 30amps at 240 volts 50 Hz?
I would advise you to get some face-to-face professional advice on this as the sort of experience I have on this is with large power plants which have a suite of protection systems such as overcurrent to protect against a short circuit, over or under voltage, reverse power, loss of one phase and over or under frequency to name a few mishaps that can befall a generator.

Simply as an example, is a SEL generator protection relay. This comes in at USD2500 and you will also need a circuit breaker to go with it that will allow itself to be tripped by an external source (i.e. your generator protection relay).
The solutions are out there but in my experience of larger plant they will be costly to an individual.

Your first course of action is probably to ask your generator supplier what protection the governor/generator management system of the generator and what it can provide.

I hope the other members of the forum can help you better.
G'Day cobber!
User avatar
adam2
Site Admin
Posts: 8611
Joined: Mon Jul 02, 2007 5:49 pm
Location: North Somerset

Re: Generator fault.

Post by adam2 »

I am not aware of any ready made single unit that will do what you require.

There are however "mains monitoring relays" available that will detect voltage or frequency out of tolerance and "tell" a standby generator to start and take the load instead of the out of tolerance mains supply.
Such a mains monitoring relay could be used to open a contactor and disconnect an out of tolerance supply.

I appreciate that the problem in this case is a potentialy out of tolerance GENERATOR supply, not the mains, but the relay wont "know" that it is monitoring a generator supply rather than mains.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
User avatar
Potemkin Villager
Posts: 1415
Joined: Tue Mar 14, 2006 10:58 am
Location: Narnia

Re: Generator fault.

Post by Potemkin Villager »

kenneal - lagger wrote: Fri Feb 26, 2021 1:58 pm Speaking to my daughter this morning it would seem that the genny was over revving for about two minutes before the over frequency cut out activated.
I am wondering why you are looking for another over frequency cut out when the generator
already has one, albeit one that took far to long to operate considering the damage that can be caused to the generator windings
by extended over speeding. I wonder what the manufacturer had to say about
this and if they have conceded any liability for the incident! It is a well known fact that generators have some
degree of vibration in normal operation but this should not have caused the problem with the fuel solenoid if properly designed and installed. Diesel generators do not come cheap and it is reasonable to expect that they do what it says on the tin.
The Stone Age represents 99.99% of mankind's existence on this planet. Francis Pryor
kenneal - lagger
Site Admin
Posts: 12899
Joined: Wed Sep 20, 2006 2:35 am
Location: Newbury, Berkshire
Contact:

Re: Generator fault.

Post by kenneal - lagger »

I have been looked after quite well by Lister Petter but you can't switch off a diesel generator that is running away in the situation that I described above with a vapourized fuel supply entering the air filter. I have taken all the precautions that I can think of to avoid the same thing happening again but if there was a cheap way of protecting my downstream equipment with a switch which would disconnect the distribution infrastructure from the generator I would fit one on a belt and braces basis.

I will also have to look at ducting the air supply to the filter to the outside so that it's not vulnerable to fuel vapour in the Genny shed which will be a cheap thing to do.
Action is the antidote to despair - Joan Baez
User avatar
adam2
Site Admin
Posts: 8611
Joined: Mon Jul 02, 2007 5:49 pm
Location: North Somerset

Re: Generator fault.

Post by adam2 »

Failures of the type described, engine overspeed due to sucking in fuel with the combustion air are very rare. No engine governor can stop or slow the engine in such circumstances, it may well run away to destruction. If you are present when such an accident occurs the engine may be stopped by discharging a carbon dioxide fire extinguisher near the air filter. The will displace much of the air.
The electrical damage can be prevented by a suitable protection relay that opens a contactor.

In view of the rareity of such accidents it might be worth simply hoping that it wont happen again, rather than spending money on any elaborate precautions. Taking the combustion air from outdoors will reduce the risks.

BTW, I recal a demonstration years ago. A large diesel engine was running on load at a constant speed and generating electricity. A SMALL percentage of natural gas was introduced into the combustion air and the engined continued to run as normal, but the engine governor was observed to reduce the fuel supply. This demonstration was reasonably safe as a diesel engine wont run on natural gas alone.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
kenneal - lagger
Site Admin
Posts: 12899
Joined: Wed Sep 20, 2006 2:35 am
Location: Newbury, Berkshire
Contact:

Re: Generator fault.

Post by kenneal - lagger »

We recently got the genny back at a cost of just under £900 after it had a complete rebuild: new bores, pistons, rings etc. We are now having problems with it rattling itself to pieces. Various bits of peripheral brackets have failed, some twice even after we have bolted the machine down using new bolts in newly drilled holes. The latest problem is the mechanical fuel switch sticking and the solenoid actuator failing by burning out.

All I can put it down to is the fact that the new machine is on a sheet steel, bunded base whereas the virtually same machine, which we have had for eight years without any such problems, is on a welded, heavy steel base as were all the previous Lister gennies which we have owned over about 30 years.
Action is the antidote to despair - Joan Baez
kenneal - lagger
Site Admin
Posts: 12899
Joined: Wed Sep 20, 2006 2:35 am
Location: Newbury, Berkshire
Contact:

Re: Generator fault.

Post by kenneal - lagger »

adam2 wrote: Mon Mar 15, 2021 3:35 pm ................BTW, I recal a demonstration years ago. A large diesel engine was running on load at a constant speed and generating electricity. A SMALL percentage of natural gas was introduced into the combustion air and the engined continued to run as normal, but the engine governor was observed to reduce the fuel supply. This demonstration was reasonably safe as a diesel engine wont run on natural gas alone.
I looked at that a few years ago as we were contemplating generating our own biogas from sewage, food and garden waste. We didn't go ahead with it as we couldn't find any machine manufacturers which supplied anything that they would give a guarantee for.
Action is the antidote to despair - Joan Baez
User avatar
Catweazle
Posts: 2886
Joined: Sun Feb 17, 2008 12:04 pm
Location: Petite Bourgeois, over the hills

Re: Generator fault.

Post by Catweazle »

What about a centrifugal device that trips a flap to close the air intake ?
User avatar
adam2
Site Admin
Posts: 8611
Joined: Mon Jul 02, 2007 5:49 pm
Location: North Somerset

Re: Generator fault.

Post by adam2 »

Catweazle wrote: Wed Jun 16, 2021 2:08 pm What about a centrifugal device that trips a flap to close the air intake ?
That would work, but I am not aware of any ready made device to do this.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
kenneal - lagger
Site Admin
Posts: 12899
Joined: Wed Sep 20, 2006 2:35 am
Location: Newbury, Berkshire
Contact:

Re: Generator fault.

Post by kenneal - lagger »

The men from Lister came out and replaced the fuel solenoid and luckily they brought a new bracket with them as well because that had broken bits around the bolt holes. It was then running OK. They also fitted new anti vibration mounts which I presume are softer than the originals.

A few days later I got an inverter, the one that had been fried in the original incident, back from repair, a new power control board at nearly £600, and fitted that with an over voltage safety cut out between the generator and the inverter. The genny worked for a week or so and then the safety cut out cut out; it is set for 270V. On checking the genny it said it was producing 265V. Lister sent us, eventually, a new Automatic Voltage Regulator board which our supplier came and fitted for us the day it arrived. MechAlte whose alternator and controls are used have preset that and sealed the two pots which control the voltage and frequency so that they shouldn't be able to move.

The supplier, who we bought the genny through, Hendy Power Systems, have been pretty good throughout but not convinced that this is the end of our problems as there could still be a vibration problem. They would prefer, as we would, for Lister to take this unit back and supply us with a new one. To this end Hendy are paying for an independent engineer to come out and look at the installation. This could backfire on us but we have had the same model working in the same shed for about 12 years without any problems. We'll just have to wait and see.
Action is the antidote to despair - Joan Baez
User avatar
Potemkin Villager
Posts: 1415
Joined: Tue Mar 14, 2006 10:58 am
Location: Narnia

Re: Generator fault.

Post by Potemkin Villager »

Bad luck Ken you really seem to have been sold a lemon. It must be
very disheartening and frustrating. Hopefully they will replace with
something fit for purpose.

Many manufacturing firms have got in to trouble because the marketing people
have had their way and the company's reputation for reliable products gets shredded.
One place I worked in regularly had management in rows with engineers over falsifying MTBF calculations.
The Stone Age represents 99.99% of mankind's existence on this planet. Francis Pryor
Post Reply