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.
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On Monday, 15 August 2016 16:10:24 UTC+1, George wrote:

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
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On Mon, 15 Aug 2016 08:20:14 -0700, tabbypurr wrote:
====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.
--
Johnny B Good

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On 15/08/2016 21:52, Johnny B Good wrote:

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.
http://www.industrial-electronics.com/elecy3_13.html

I'm sure there are many ways. The issue here was to reduce any currents to well below any earth leakage threshold.
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On Mon, 15 Aug 2016 22:14:07 +0100, Fredxxx wrote:

I was addressing the issue of using neons in place of incandescent lamps to determine synchronisation between two generators (in this case, every generator connected to the national grid and your lister driven 3 phase genset).
As I understand it, you're not trying to parallel up your 3 phase genset to the public mains supply, just using a single phase incandescent lamp synchroscope to use the mains frequency as a reference by which to set the speed of your 3 phase genset the use of which now seems to be causing the earth leakage breaker to trip.
I suspect that the mistake you've made is to plug into a 13A wall socket that's protected by an ELCB or equivilent to access the mains supply as your frequency reference.
If, otoh, the consumer unit is protected by a whole house ELCB, then your simple incandescent lamps synchroscope just isn't "Going to 'cut it'" and, contrary to good sense, your cheapest option may prove to be tabbypurr's suggested use of neon lamps (but only because you're not going to be relying on it to *actually* parallel up *one* of the three phases of your genset to the mains supply, merely use it to ascertain when your genset is frequency, but not phase, matched to the mains supply).
Incidentally, I'd crossbond the genset frame to your local earth point and, for good measure, crossbond the genset's neutral to your consumer unit's incoming neutral. Protection against 'earthing faults' demands such crossbonding of the neutrals and (frame) 'earths in order to function properly (fuses and elcbs).
Good luck % HTH
--
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On Thursday, 18 August 2016 00:05:54 UTC+1, Johnny B Good wrote:

Neons won't get you in sync, but they will compare the frequencies without tripping anything. Filaments have much more brightness change around peak voltage, so are good to sync, but also trip RCDs.
NT
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On 18/08/2016 00:05, Johnny B Good wrote:

If the OP has a RCD, then the neutrals should be bonded after they have passed their respective RCDs, so that any current in the live phase is matched in the neutral conductor.
I do agree the use of neons with their very low current draw should be ideal in determining frequency errors.
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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
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On 15/08/2016 16:10, George wrote:

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.
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On Mon, 15 Aug 2016 19:32:19 +0100, Fredxxx wrote:

As I understand the OP, George isn't trying to synch up to the mains, just use the mains frequency as a reference by which to set the speed of his 3 phase genset. I suspect his incandescent lamps 'synchroscope' is being fed via an elcb protected supply (13A socket in his workshop). Normally, the uneconomic consumption of such a lamps based synchroscope is not an issue but, in this particular (peculiar?) case, it's now creating an elcb issue.
If he doesn't care for tabbypurr's idea of using neon lamps, he could use a one to one isolating transformer between his synchroscope box and the 13A mains socket so that the 'neutral' connection of the secondary winding is to the genset's neutral instead of the consumer unit's neutral. The potential 180 degree phase reversal won't be an issue when the synchroscope is being used simply to match frequency (however, the transformer secondary could be wired for phase coherence if phase matching is required - in this instance it isn't).
As a matter of fact, there are plenty of alternative ways by which to compare two different source frequencies, it's just a pity that George's tried and trusted incandescent lamps based synchroscope method is incompatable with ELBS. :-)
--
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On Thursday, 18 August 2016 00:24:08 UTC+1, Johnny B Good wrote:

The usual voltage ELCBs usually don't care about a lightbulb's worth of earth leakge. RCDs do, sometimes aka current ELCBs. Nothing cares about neons.
NT
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On Wed, 17 Aug 2016 16:51:25 -0700, tabbypurr wrote:

====snip===
In a sense, neons are like 'stupidity', not a problem in small quantities but a major force to be reckoned with in very large numbers as most politicians are only too well aware. :-)
BTW, thanks for the heads up on ELCBs and RCDs. I can never remember the differences between what would seem, on the face of it, to be devices with essentially the same function. We don't have a single one of either of those devices in this house, hence my lack of motivation to learn the distinction between them. :-)
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On 18/08/2016 01:42, Johnny B Good wrote:

A reasonable description here for those who are interested:
http://wiki.diyfaq.org.uk/index.php/RCD http://wiki.diyfaq.org.uk/index.php/ELCB
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Cheers,

John.
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I'm amazed a normal tungsten filament bulb reacts quickly enough. Florries would, though.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Tuesday, 16 August 2016 00:53:00 UTC+1, Dave Plowman (News) wrote:

Household filament lamps can be used for a useful chunk of the audio spectrum, so have no difficulty following a few Hz.
NT
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On Tuesday, 16 August 2016 09:25:50 UTC+1, snipped-for-privacy@gmail.com wrote:

if

lbs

the

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ies

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.
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On 16/08/2016 10:19, George wrote:

Most aircraft based power systems are 400Hz - perhaps this was computer kit originally intended to fly.
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John.
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On Tuesday, 16 August 2016 10:37:54 UTC+1, John Rumm wrote:

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.?
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On 16/08/2016 11:05, Weatherlawyer wrote:

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.
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John.
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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.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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