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.
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.
On Mon, 15 Aug 2016 08:20:14 -0700, tabbypurr wrote:
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.
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.
I'm sure there are many ways. The issue here was to reduce any currents
to well below any earth leakage threshold.
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
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
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
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.
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.
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!
This newsgroup posting comes to you directly from...
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
If commoned, then the sum of 3 phases + neutral should always be zero.
Perhaps look out for an unintended connection between neutral and earth.
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. :-)
On Wed, 17 Aug 2016 16:51:25 -0700, tabbypurr wrote:
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. :-)
On Tuesday, 16 August 2016 09:25:50 UTC+1, email@example.com wrote:
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.
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.
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.
*Why do they put Braille on the drive-through bank machines?
Dave Plowman firstname.lastname@example.org London SW
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