Earthing neutral and frequency of 40 Kw generator.

I have a 4 cylinder Lister driven generator set for driving all the 3 phase devices in my workshop.

There is also a 2 to 3 phase converter that powers up to 3 HP but which has a problem starting a couple of my machines in the winter when the oil is v ery thick. I have been trying to rig up a phase comparison device to determ ine if the frequency of the set is correct, by connecting the alternator ou tput of one phase to the incoming mains supply via two 240 volt bulbs in se ries. this has worked on several generators over the years and the lights b eat against the mains voltage and when the speed is correct to give 50 Hert z the beating stops and the lights stay on or off. It works very well, how ever when I tried to connect one phase from the Lister to the mains through my two bulb box, the earth leakage trip tripped. I cannot see why this sh ould be unless there is a neutral to earth leak somewhere. A chase around with a meter did not reveal anything that I did not expect but I am wonderi ng if the neutral wire from the alternator should be strapped to the frame and / or run to an earth pole in the outside ground. The incoming mains is earthed by a copper rod below the electric meter.

A small portable single phase generator which is not earthed anywhere but w hich has an earth wire out just connected to it's chassis, performs perfect ly and as I can also test this against the Lister with no problem I have se t the little engine as accurately as I can to the mains frequency and then connect this to the Lister set and re-synchronized it. I want to mount the frequency setting facility permanently so I would rather fix the problem. Would it be better to run an earth wire across the workshop or bang a galva nized earth pole into the ground outside adjacent to the generator. set

What should I do about this tripping, is it an earthing problem or what? Any comments would be appreciated. By the way I have a very high quality 30 HP motor, (22Kw) that I am thinking of scrapping. It can be seen running and is really too good to scrap.

Thanks George.

Reply to
George
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se devices in my workshop.

as a problem starting a couple of my machines in the winter when the oil is very thick. I have been trying to rig up a phase comparison device to dete rmine if the frequency of the set is correct, by connecting the alternator output of one phase to the incoming mains supply via two 240 volt bulbs in series. this has worked on several generators over the years and the lights beat against the mains voltage and when the speed is correct to give 50 He rtz the beating stops and the lights stay on or off. It works very well, h owever when I tried to connect one phase from the Lister to the mains throu gh my two bulb box, the earth leakage trip tripped. I cannot see why this should be unless there is a neutral to earth leak somewhere. A chase aroun d with a meter did not reveal anything that I did not expect but I am wonde ring if the neutral wire from the alternator should be strapped to the fram e and / or run to an earth pole in the outside ground. The incoming mains is earthed by a copper rod below the electric meter.

which has an earth wire out just connected to it's chassis, performs perfe ctly and as I can also test this against the Lister with no problem I have set the little engine as accurately as I can to the mains frequency and the n connect this to the Lister set and re-synchronized it. I want to mount t he frequency setting facility permanently so I would rather fix the problem . Would it be better to run an earth wire across the workshop or bang a gal vanized earth pole into the ground outside adjacent to the generator. set

30 HP motor, (22Kw) that I am thinking of scrapping. It can be seen runnin g and is really too good to scrap.

The large genny frame & neutral ought to be earthed, but doing so won't sol ve the RCD tripping. To avoid a trip you'd need both neutrals connected, an d the bulbs live to live, and no earth leakage at the genny or anything con nected to it. However I doubt very much this would be legal, since the gen can then backfeed the mains supply in some situations.

FWIW indicator neons consume far less current than filament bulbs.

NT

Reply to
tabbypurr

Do you really mean Earth Leakage Breaker, or a new fangled RCD? And is this mains side or generator side?

Are the neutrals from your generator and mains commoned? Any unbalanced phase current will mean that the neutral from your generator will wander, and if there is any connection to earth, then an earth current will pass.

If commoned, then the sum of 3 phases + neutral should always be zero. Perhaps look out for an unintended connection between neutral and earth.

Reply to
Fredxxx

====snip====

Totally unsuited for use as a "Synchroscope", they require about 90v to strike and will extinguish at about 60 volts. Far better to use a couple of high efficiency panel lamp LEDs in antiparallel with a 5W 100K ballast resistor in series.

Since you need to accurately determine the extinguishing point of the light curve (minimal voltage difference across the sychronising breaker's contacts), you could add a 10 to 15K half watt resistor in series between the 5W resistor and the LEDs with a pair of 10v 400mW zenners in antiseries across the half watt resistor and LED part of the circuit to limit the maximum brightness and avoid dazzle to better facilitate detection of the minimum voltage difference point required to determine the least dramatic moment at which to close the synchronising breaker.

Reply to
Johnny B Good

I'm going to bite.

In my university days I was told that it was difficult to synchronise generators on what the article below calls the Three Dark Method. And that the Two Bright, One Dark Method illustrated in this article gave a reduced phase error as the eye could compare brightness and colour of two bulbs. Of course the bulbs had to be matched, but if they were from the same batch then they probably would be.

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I'm sure there are many ways. The issue here was to reduce any currents to well below any earth leakage threshold.

Reply to
Fredxxx

I'm amazed a normal tungsten filament bulb reacts quickly enough. Florries would, though.

Reply to
Dave Plowman (News)

For clarification do you mean the RCD on the mains supply tripped?

If so, that does not seem very surprising if I have understood the setup correctly.

If the genny output was truly floating, then I would expect it would just ride the mains waveform, but sink little or no current (hence the lamps would not light). However if the lamps are lighting, then you must be passing current in the mains live wire that is not also present in the mains neutral - hence the RCD trip. (it would also suggest that one side of the genny output (i.e. the neutral) is likely bonded to earth.

Reply to
John Rumm

se devices in my workshop.

as a problem starting a couple of my machines in the winter when the oil is very thick. I have been trying to rig up a phase comparison device to dete rmine if the frequency of the set is correct, by connecting the alternator output of one phase to the incoming mains supply via two 240 volt bulbs in series. this has worked on several generators over the years and the lights beat against the mains voltage and when the speed is correct to give 50 He rtz the beating stops and the lights stay on or off. It works very well, h owever when I tried to connect one phase from the Lister to the mains throu gh my two bulb box, the earth leakage trip tripped. I cannot see why this should be unless there is a neutral to earth leak somewhere. A chase aroun d with a meter did not reveal anything that I did not expect but I am wonde ring if the neutral wire from the alternator should be strapped to the fram e and / or run to an earth pole in the outside ground. The incoming mains is earthed by a copper rod below the electric meter.

which has an earth wire out just connected to it's chassis, performs perfe ctly and as I can also test this against the Lister with no problem I have set the little engine as accurately as I can to the mains frequency and the n connect this to the Lister set and re-synchronized it. I want to mount t he frequency setting facility permanently so I would rather fix the problem . Would it be better to run an earth wire across the workshop or bang a gal vanized earth pole into the ground outside adjacent to the generator. set

30 HP motor, (22Kw) that I am thinking of scrapping. It can be seen runnin g and is really too good to scrap.

How far from Stoke on Trent are you and can you tell me more about the moto r please?

Reply to
Weatherlawyer

Household filament lamps can be used for a useful chunk of the audio spectrum, so have no difficulty following a few Hz.

NT

Reply to
tabbypurr

trum, so have no difficulty following a few Hz.

Thanks for all the useful suggestions and advice, it will take a while to g o through then ,ut to clarify, I do not need very accurate frequency compar isons as the Lister engine will vary a bit according to the load anyway. I shall have a look this morning and identify exactly what is is that is tri pping and what it says on it.

The motor I mentioned came from a motor alternator set which was used to pr oduce 3 phase 415 supply for some industrial computer equipment that requir ed a frequency of 400 cycles/sec as it was then (Hertz now) The motor and alternator were mounted in line on a very heavy chassis and coupled togethe r by a big rubber cush drive. I still have all the kit but it is all separ ated and who would want a 400 Hz supply anyway. I also have a 65 Kw altern ator on a big frame, the same Computer quality, - this has been superseded by the Lister Genny. I can send pictures if I had emails to anyone or may be I shall post it on my website if I can find time : maribelecosystems,co, uk It was all made with cost not being an issue, I live in Norfolk, NE of Norwich, but the motor is fairly easy to transport.

Regards George.

Reply to
George

Most aircraft based power systems are 400Hz - perhaps this was computer kit originally intended to fly.

Reply to
John Rumm

If the windings got hot at any time or received mechanical damage of some sort,that would also trip things up wouldn't it?

I gather that can be cured to a certain extent by warming insulating resin and getting it to suffuse through the windings. I'm not sure how half baked that process or idea is.

Reply to
Weatherlawyer

Any particular reason for that frequency or is it just that it had to be something and with allied kit needing to co-opt/nationalcompanies merging etc.?

Reply to
Weatherlawyer

I'd also be a bit wary about inductive loads and the storage effects one can get as well. Most of the things I've seen done were back in the old days when we never had very sensitive trips like this. Goodness knows what abuse we did to equiipment and the mains supply! Brian

Reply to
Brian Gaff

Its mainly driven by size and weight requirements. You can make 400Hz gensets smaller and lighter (e.g. using less turns of copper) if you spin them faster. Transformers also get smaller and lighter. So 115V

400Hz 3 phase became the standard.

As with many things in aviation its a trade off. You get slight reductions in efficiency, and larger reactive losses in the wiring, but its still worthwhile since reduction in payload is more important.

Reply to
John Rumm

Higher frequency allows smaller transformers etc so weight saving - important in an aircraft. Where the cable runs ain't very long anyway.

Obviously, you'd have a standard. To make equipment easy to share.

400Hz was probably just chosen as a nice round figure compromise.
Reply to
Dave Plowman (News)

Could you run that by me again? ;-)

TV cameras in the 25 frame days were very sensitive to lighting running at a different speed. Because they used their own frequency standard which was far more stable than mains. Florries and some discharge types would cause flicker or hum bars on the picture. Tungsten not - I assume because of the persistence of the filament. Even with domestic GLS lamps.

If you wanted to use high efficiency florries, you'd normally used three phase with alternate phase tubes close together. Or the less efficient tubes with long persistent phosphors.

Reply to
Dave Plowman (News)

You could just get a frequency meter: either a digital one, like:

"AC 80-300V/30-70HZ 3in1 LCD Time Voltage Frequency Combo Meter For Generator

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" This does frequency, voltage, and runtime, for 10 quid.

Or get something a bit more fitting to a Lister, i.e. an analog "vibrating reed frequency meter", aka "resonant reed frequency meter". Or a mains fluorescent light, used as a strobe to illuminate an on an index mark on the generator?

Thomas Prufer

Reply to
Thomas Prufer

I think when broadcasters first changed over from locking the TV frequency to the mains frequency, when for the first time the mains lights could drift in frequency through the day but the TV frequency was accurately controlled, they used to use DC-powered lights or else power the tungsten lights from different phases.

When shooting high-speed film (for slow-motion sequences) it's still common to use DC lights. There's a boxing scene in the film The Krays where they didn't do this and in the slow-motion sequences you can see some variation in exposure (ie flicker) between different frames. However that affects the whole frame (being film) which is less noticeable than affecting parts of the frame, giving rise to rolling hum bars, as with TV cameras.

An additional problem with fluorescents is that the various phosphors have different decay times, so on fast-moving objects you see an orange "tail" where the redder phosphor in the fluorescent tube has a slightly longer decay time than the bluer phosphor.

When I was in America around the time of my nephew's birth, I shot some video with my sister's UK-standard camcorder. Tungsten lights, at 60 Hz, were fine, but the fluorescents in the "Birth Center" (maternity hospital) caused nasty strobing that varied in colour as well as brightness.

Reply to
NY

Don't think so. I started in TV in the early '60s. Pretty well all lights were AC. And the majority - fed from the grid - on one phase for safety reasons.

The standard grid lighting used for boxing matches being televised was three phase fluorescent. Ordinary TV lighting could give glare - so not allowed by the boxing authorities. All explained to me in some detail when we had a genuine pro boxing match in the studio.

You'd probably choose the tubes carefully for TV use - where you can. At one time they weren't used at all where there was a choice - but high frequency types changed that as they were more efficient for some types of location work, perhaps run from batteries. Before LEDs

Yes. As I said, tungsten doesn't normally give any problems. Hence my query about it being used as said. Same with a lathe, etc. Florries can make it look stationary. But tungsten not.

Reply to
Dave Plowman (News)

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