Alternative Power sources - 3 phase question

Author

3 phase question

William

2005-11-02, 6:21 pm

I recently hosted a music even on my farm. (They needed 3phase which I have.
240 v per phase.)

When I read the meters the following day, they all worked out at 53 Kw.
That's 3 separate meters.

I thought that kinda strange, as all the equipment (lights, sound stuff) was
single phase. Further investigation showed that the sound guy had a problem
with the EL (GFI) tripping, so what he did was use the safety earth as a
neutral!
Ok, I understand that the neutral is bonded to the safety earth at the
service entrance, but I've got a couple of concerns and queries:
1) Why did this stop the GFI tripping?? (Surely this should have guaranteed
that it tripped?)
2) Doesn't this indicate there is something wrong with the connection setup?
Everything works fine though.
3) Why did every meter show an identical load?
4) Should I be worried?

Solar Flare

2005-11-02, 7:21 pm

Most detail would be needed to determine what is going on.
Why do you have three meters? What kind. Elements? ratings? types?
How did the meters read 53KW when there was no load the next day?
What is an even?
What is the source configuration? Wye or delta supply? I assume wye because of
your comments.

"William" <someone@microsoft.com> wrote in message
news:dkbc9m$bp4$1@ctb-nnrp2.saix.net...
> I recently hosted a music even on my farm. (They needed 3phase which I have.
> 240 v per phase.)
>
> When I read the meters the following day, they all worked out at 53 Kw.
> That's 3 separate meters.
>
> I thought that kinda strange, as all the equipment (lights, sound stuff) was
> single phase. Further investigation showed that the sound guy had a problem
> with the EL (GFI) tripping, so what he did was use the safety earth as a
> neutral!
> Ok, I understand that the neutral is bonded to the safety earth at the
> service entrance, but I've got a couple of concerns and queries:
> 1) Why did this stop the GFI tripping?? (Surely this should have guaranteed
> that it tripped?)
> 2) Doesn't this indicate there is something wrong with the connection setup?
> Everything works fine though.
> 3) Why did every meter show an identical load?
> 4) Should I be worried?
>
>

JoeSixPack

2005-11-03, 12:21 am

"William" <someone@microsoft.com> wrote in message
news:dkbc9m$bp4$1@ctb-nnrp2.saix.net...
>I recently hosted a music even on my farm. (They needed 3phase which I
>have. 240 v per phase.)
>
> When I read the meters the following day, they all worked out at 53 Kw.
> That's 3 separate meters.
>
> I thought that kinda strange, as all the equipment (lights, sound stuff)
> was single phase. Further investigation showed that the sound guy had a
> problem with the EL (GFI) tripping, so what he did was use the safety
> earth as a neutral!
> Ok, I understand that the neutral is bonded to the safety earth at the
> service entrance, but I've got a couple of concerns and queries:
> 1) Why did this stop the GFI tripping?? (Surely this should have
> guaranteed that it tripped?)
> 2) Doesn't this indicate there is something wrong with the connection
> setup? Everything works fine though.
> 3) Why did every meter show an identical load?
> 4) Should I be worried?
>

More than likely they were using a wye transformer to balance the load,
therefore all 3 phases were being used equally at all times, thus the
identical readings on all meters. The output from such a setup is
single-phase for each output circuit used.

Since all circuits in such a setup use a common neutral, it's likely that
harmonic distortion anywhere in the setup would carry through to all
circuits on the system, thus the tripping. Isolating to a safety ground is
what probably eliminated that problem.

Solar Flare

2005-11-03, 12:21 am

I think it just clicked here.

The load was a transformer with a wye primary and a delta secondary possibly .
The primary wye of a transformer with a delta secondary should never be
connected to the system neutral. Any volatge unbalance or faults on the supply
system will be attempted to balance in your wye delta tramsformer windings. The
delta secondary forces the wye winding neitral to be exactly in the centre of
the supply voltages. Any source system unbalance will be carried by your
transformer and blow fuses etc. The wye winding tap should have been floated and
not connected to ground or anything at all.

I still don't understand 3 meters in use.

"William" <someone@microsoft.com> wrote in message
news:dkbc9m$bp4$1@ctb-nnrp2.saix.net...
> I recently hosted a music even on my farm. (They needed 3phase which I have.
> 240 v per phase.)
>
> When I read the meters the following day, they all worked out at 53 Kw.
> That's 3 separate meters.
>
> I thought that kinda strange, as all the equipment (lights, sound stuff) was
> single phase. Further investigation showed that the sound guy had a problem
> with the EL (GFI) tripping, so what he did was use the safety earth as a
> neutral!
> Ok, I understand that the neutral is bonded to the safety earth at the
> service entrance, but I've got a couple of concerns and queries:
> 1) Why did this stop the GFI tripping?? (Surely this should have guaranteed
> that it tripped?)
> 2) Doesn't this indicate there is something wrong with the connection setup?
> Everything works fine though.
> 3) Why did every meter show an identical load?
> 4) Should I be worried?
>
>

William

2005-11-04, 5:21 am

Ok...after some reading, (mostly on www.cbi.co.za they have some good
papers/info there.) A few things clicked.
I don't know what type of transformer it is, I think Wye secondary. ( not at
all sure) the 3 meters are single phase Kw/H meters, instead of using one 3
phase meter. Common practice around here; less stock to carry, etc etc.
1) Everything IS wired correctly.
2) When the guy wired up his systems normally, the GFI tripped because there
was a "normal" small earth leak somewhere. When he used the safety earth as
a neutral, (at the same potential, but the safety earth doesn't go thru the
GFI.) the GFI simply didn't detect a differential, and didn't trip. Purely a
side effect of GFI design. I'll write the GFI vendor to confirm theory.
As to why the meters measured the exact same consumption, it's either a
coincidence (all the loads were directly connected to one of the phases) or
somehow, the loads 'floated' some being slightly overvoltage and some under,
but not enough to be out of limits, and the loads automatically balanced. I
don't pretend to know exactly how that happens, but I did come across
literature about this.

In short, I'm not worried!

"Solar Flare" <s.flare@hotmail.com> wrote in message
news:xqGdnROvFZF0E_TenZ2dnUVZ_tqdnZ2d@golden.net...
>I think it just clicked here.
>
> The load was a transformer with a wye primary and a delta secondary
> possibly .
> The primary wye of a transformer with a delta secondary should never be
> connected to the system neutral. Any volatge unbalance or faults on the
> supply
> system will be attempted to balance in your wye delta tramsformer
> windings. The
> delta secondary forces the wye winding neitral to be exactly in the centre
> of
> the supply voltages. Any source system unbalance will be carried by your
> transformer and blow fuses etc. The wye winding tap should have been
> floated and
> not connected to ground or anything at all.
>
> I still don't understand 3 meters in use.
>
>
> "William" <someone@microsoft.com> wrote in message
> news:dkbc9m$bp4$1@ctb-nnrp2.saix.net...
>
>

Dale Farmer

2005-11-04, 12:21 pm

William wrote:

> Ok...after some reading, (mostly on www.cbi.co.za they have some good
> papers/info there.) A few things clicked.
> I don't know what type of transformer it is, I think Wye secondary. ( not at
> all sure) the 3 meters are single phase Kw/H meters, instead of using one 3
> phase meter. Common practice around here; less stock to carry, etc etc.
> 1) Everything IS wired correctly.
> 2) When the guy wired up his systems normally, the GFI tripped because there
> was a "normal" small earth leak somewhere. When he used the safety earth as
> a neutral, (at the same potential, but the safety earth doesn't go thru the
> GFI.) the GFI simply didn't detect a differential, and didn't trip. Purely a
> side effect of GFI design. I'll write the GFI vendor to confirm theory.
> As to why the meters measured the exact same consumption, it's either a
> coincidence (all the loads were directly connected to one of the phases) or
> somehow, the loads 'floated' some being slightly overvoltage and some under,
> but not enough to be out of limits, and the loads automatically balanced. I
> don't pretend to know exactly how that happens, but I did come across
> literature about this.
>
> In short, I'm not worried!

The GFI should have tripped out. They work by sensing how much
current is flowing through the hot and neutral wires, and comparing
the difference. If the difference is large enough, they trip. Many
poorly maintained sound systems will trip GFIs, as they are, in fact,
dangerous in various ways. ( the most common is the so-called
death diode in older guitar amplifiers. If it failed closed, it put mains
AC power on the chassis of the amplifier, raising the entire guitar
to line voltage. Guitarist is playing, current runs up the guitar cord,
energizing the metal of the guitar and the guitarist, then grabs the
microphone to sing or speak, which completes the circuit to
ground through the guitarist. )
I suspect that the sound guy either bypassed the GFI entirely,
or had a ground/nuetral swap someplace that he inadvertently
corrected by his ground/nuetral swap. There shouldn't be a
"normal" earth leak large enough to trip a GFI in a system. That
leakage is enough to kill someone, and needs to be repaired.

What is the name of the sound system company? I'd like to
know who are the more dangerous ones out there.

--Dale

Dale Farmer

2005-11-04, 10:21 pm

Dale Farmer wrote:

> William wrote:
>
>
> The GFI should have tripped out. They work by sensing how much
> current is flowing through the hot and neutral wires, and comparing
> the difference. If the difference is large enough, they trip. Many
> poorly maintained sound systems will trip GFIs, as they are, in fact,
> dangerous in various ways. ( the most common is the so-called
> death diode in older guitar amplifiers. If it failed closed, it put mains

Capacitor not diode. *thwaps self on forehead* Must remember to
type when fully awake.

>
> AC power on the chassis of the amplifier, raising the entire guitar
> to line voltage. Guitarist is playing, current runs up the guitar cord,
> energizing the metal of the guitar and the guitarist, then grabs the
> microphone to sing or speak, which completes the circuit to
> ground through the guitarist. )
> I suspect that the sound guy either bypassed the GFI entirely,
> or had a ground/nuetral swap someplace that he inadvertently
> corrected by his ground/nuetral swap. There shouldn't be a
> "normal" earth leak large enough to trip a GFI in a system. That
> leakage is enough to kill someone, and needs to be repaired.
>
> What is the name of the sound system company? I'd like to
> know who are the more dangerous ones out there.
>
> --Dale

Steve Thomas

2005-11-07, 4:21 pm

Dale,
Your description of the operation of GFI devices matches what I
have heard elsewhere.
I have also read or heard that these devices do not depend on the
existence of a separate earth ground to operate. Because of this, they could
be used to improve the safety of outlets on older 2 wire house hold outlets.
It makes sense to me that the devices could be designed that way.
I was suprised therefore to find that the installation instructions for
the one I purchased, was explicit in that it was only for use on circuits
that have an independent safety ground. I doesn't say so in so many words,
but there seems to be a strong implication that it won't work.

I can see that all else being equal, a seperate ground would be better.

The question is, do all, some, or none of these devices work on the
older 2 wire wiring?

Steve Thomas

Dale Farmer

2005-11-07, 6:21 pm

Steve Thomas wrote:

> Dale,
> Your description of the operation of GFI devices matches what I
> have heard elsewhere.
> I have also read or heard that these devices do not depend on the
> existence of a separate earth ground to operate. Because of this, they could
> be used to improve the safety of outlets on older 2 wire house hold outlets.
> It makes sense to me that the devices could be designed that way.
> I was suprised therefore to find that the installation instructions for
> the one I purchased, was explicit in that it was only for use on circuits
> that have an independent safety ground. I doesn't say so in so many words,
> but there seems to be a strong implication that it won't work.
>
> I can see that all else being equal, a seperate ground would be better.
>
> The question is, do all, some, or none of these devices work on the
> older 2 wire wiring?
>
> Steve Thomas

They work for certain values of work.
They are allowed for retrofit work only without a ground connection
under the US National Electrical Code. They do not create a ground
where one did not exist before. So anything that actually depends on
a good ground connection, such as AV systems and surge protectors,
to name two of the most common, will not work correctly, and may
make your gear more susceptible to damage.
They are there pretty much only for life safety purposes when you
retrofit them onto a two wire power circuit. They will give you a
false sense of security, when you plug in a three wire power cord,
thinking that there is actually a protective electrical ground present.
As for the manufacturers instructions, unfortunately this is one of
those things that qualified people only should be installing, but lots of
unqualified people install. So they put in a lot of weasel words into
the instructions. Damn lawyers and the pathetic lawsuits they bring.

--Dale

Daniel Armstrong

2005-11-25, 11:21 pm

GFCIs consist of line and neutral conductors passing side by side or
coaxially through the center of a toroidal transformer. Any current
imbalance in the two conductors causes a small voltage to be produced in the
secondary and a circuit board amplifies this voltage and uses it to energize
a solenoid thus tripping the internal circuit breaker and cutting off the
power to the outlet. The circuit safety ground is not used by the device but
it should be present for added safety.

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