Which phase in a 3 phase system does the PT monitor?

[mminehan]

I am having a small problem with identifying the correct phases in our '3 phase' system and GEM.

SHORT VERSION:
Which phase does the PT monitor?

LONG VERSION:
In New Zealand we have a 3 phase Y 230/400VAC system, color coded L1(A):red, L2(B):white, L3(C):blue & Neutral:black. Most houses have a single phase (230VAC) supply.
Our house is supplied with 2 of the 3 phases (L1 and L2) due to having an EV and an induction stove/hob. A single phase would not have been capable of safely supplying a peak load.

I set up the GEM quite some time and it has been working fine. Still is. Some of the circuits are on one phase and some on the other. During the setup I had to select the correct phase for each CT. No problem. I got it all sorted after some tinkering and am getting correct readings.

The problem is the naming of the phases. Our meter has:
Phase L1/A/Red connected
Phase L2/B/White connected
Phase L3/C/Blue not connected

I order to get the correct readings I had to set up the GEM as using phase L3/C and phase L1/A, NOT phase L1/A and phase L2/B. None of my settings in the GEM are phase B.

This is a little bit of a problem in that the meter reading for each phase do not correlate with the phases on the GEM.

I think what has happened is that meter phase L1/A is set up as phase C on the GEM, and meter phase L2/B is phase A on the GEM.

If I change any of the phase settings in the GEM the readings become inaccurate. I suspect the problem lies with the PT being connected to the wrong phase and hence effectively translocating the phases.

In the GEM manual Figure 3 (attached) it indicates that the PT is actually connected to L2 (phase B). But this does not make sense to me. If it is connected to phase B why do I get accurate readings with only phases A and C in the settings.

There is no phase angle setting (+/- 120 degrees) in the GEM that I can see.

I hope you can understand what I am trying to convey.

Thanks, Marty.

[ben]

I've forwarded this over to Paul as I don't quite remember how Phase B and Phase C are determined (other then using trial/error).

The GEM considers whatever phase the PT is connected to as "Phase A". If you have our 3-phase pen, you can set any wire that glows the same colour to phase A as the breaker the PT is connected to.

[ben]

Pauls response:

Marty,

You're correct in your observation that the reference in the diagram can be confusing. I believe the intention was to demonstrate that the PT can be connected to any phase however according to the GEM, the reference phase (which the PT is connected to) would be considered phase A. The other two phase voltages are "+/- 120 degrees" from the reference and used by the GEM to derive true power.


Your current setup should provide accurate results. Are you sure the PT is connected to phase A of your panelboard? If it is, then I'm not sure why the phase rotation is different.

[mminehan]

Hi Ben and Paul,
You are correct. I tested the phases with a multimeter and the PT is indeed on the grid phase B. That explains why the GEM is set up as having phase A (grid phase B) and phase C (grid phase A). The GEM has effectively been setup as being phase shifted one phase back.
Thanks for the explanation.

Marty

P.S. Might pay to mention that the PT should be on phase A in the next revision of the manual.

[ben]

Hi Ben and Paul,
You are correct. I tested the phases with a multimeter and the PT is indeed on the grid phase B. That explains why the GEM is set up as having phase A (grid phase B) and phase C (grid phase A). The GEM has effectively been setup as being phase shifted one phase back.
Thanks for the explanation.

Marty

P.S. Might pay to mention that the PT should be on phase A in the next revision of the manual.

The reason Paul made the diagram showing Phase B is because the PT can be on any phase. This is shown in case there's a convenient outlet that isn't on Phase A (120/208V installs don't necessarily require our special PT).

We'll have to revise the manual to make it clear that Phase A doesn't refer to panel phases and is just used as a general reference. That isn't stated in the current manual.

[GaryFunk]

Hi Ben and Paul,
You are correct. I tested the phases with a multimeter and the PT is indeed on the grid phase B. That explains why the GEM is set up as having phase A (grid phase B) and phase C (grid phase A). The GEM has effectively been setup as being phase shifted one phase back.
Thanks for the explanation.

Marty

P.S. Might pay to mention that the PT should be on phase A in the next revision of the manual.

The reason Paul made the diagram showing Phase B is because the PT can be on any phase. This is shown in case there's a convenient outlet that isn't on Phase A (120/208V installs don't necessarily require our special PT).

We'll have to revise the manual to make it clear that Phase A doesn't refer to panel phases and is just used as a general reference. That isn't stated in the current manual.

I think you just need to make a note the the PT must be plugged into the GEM that is on the same phase that the PT is powered on.

[mminehan]

think you just need to make a note the the PT must be plugged into the GEM that is on the same phase that the PT is powered on

Not sure what you mean by that. But if you are meaning the PT needs to be on the same phase as the GEM power supply then I'm not sure that is correct. The GEM is DC powered, so the phase of the power supply (transformer) is irrelevant as there is no such thing as a phase with a DC supply. You can even power it from the 5VDC USB connector. The phase that the AC PT is on determines what the GEM thinks is phase A.

The confusion for me was the phase labelling of the switchboard did not match the phases in the GEM setup as in my setup the PT is connected to phase B of the switchboard (grid). It would have been less confusing if I had connected the PT to switchboard phase A during the setup process but there was no phase A power socket close by.

M