3 phase question

 

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?

 

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.

 



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.

 

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.

 

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!