Power Metering with HV PT's and LV CT's on a WYE-DELTA Transformer

[JeffM123]

Hi there, I am a little bit of a dillema, I am tring to set up an Ion 7350 power meter (from Schnieder Electric), and not haveing any luck. I have verified that all of the connections and settings are correct, and I am running it in the delta configuration. Now comes the problem: When I am metering the line I am getting strange readings, both the voltage readings and the current readings are bang on, but the power factor is out to lunch. There are 2 - 1500HP 5Kv motors connected as the load to this circuit, when they are running with no load on them they are running at a PF of approx in the range of 0.2 to0.3 and when they are under load they will run with a PF in the range of -0.2 to -0.3. I have come up with what I think to be the solution: The PT's that I am using are on the HV side of a 13.8Kv/4160V Wye-Delta Transformer, and the CT's are on the LV sid eof the transformer, and there is a phase shift of 30 degrees across the transformer. If I were to put in a 3 phase delta-Wye 1:1 120v transformer, it should restore the proper phasing, hence fixing my problem. Please let me know if any of you have heard of anyone metering like this, or if you have an more suggestions, or if you think my plan will work. Im all ears.

 

[dpc]

I suspect the kW readings are incorrect as well.

You're correct that the delta-wye phase shift is throwing off the metered data.

You may be able to configure the Ion meter to compensate for this internally, but it probably won't be fun. I would contact the Ion folks to see if it is possible. I have found these meters to be somewhat complicated to configure.

The aux PTs would also solve the problem.

 

[Skogsgurra]

Hello,

Connecting like this is like connecting to the LV side, but chosing the wrong configuration.

I suppose that you can select different configurations, like wye or delta. The one you have now corresponds to a wye connection (delta plus 30 degrees for voltage, and wye for currents = wye for both). Have you tried that setting? You may need to re-orient your CT:s to get a decent PF.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[stevenal]

Your method sounds reasonable for monitoring purposes if the right ratios are entered into the meter. If for revenue, your transformer losses are not fully included or excluded using this method.

 

[slavag]

Hi JeffM123.
Please contact to ION support, as DPC saied.
I worked with this support several times, good team and good company.
Regards.
Slava.

 

[scottf]

Why not just put VTs on the low side or CTs on the high side?

 

[slavag]

Hi Scottf.
Is not so intresting )))
I try answer instead JeffM123:
It's unpossible or it's expensive.
JeffM123, sorry, it's joke.
Slava

 

[scottf]

Slavaq-

5 kV class VTs cost about $350/each. That's not so much more than a 120 V Aux VT, and would make the metering much better. The ION meter can handle xfmr loss correction if the metering needs to be converted to the high-side equivalent.

 

[slavag]

Hi Scottf.
For me it's clear add VT on LV side or CT on HV side.
My joke is only 50% joke. In many cases we are electrical Eng. locking for some "cheaper solution" instead right technical solution. ( I'm sure lot of them have same problem
, problem is $).
BTW, I'm not sure that ION7350 have xfrm losses correction.
I think are 8400-8600 or 7500-7600.
BTW, this correction work with good accuracy.

I think split toroid CT on HV side ,more or less have same price.
Regards.
Slava

 

[JeffM123]

For information purposes, we have to do this on a hot circuit, and it is not possible to move either the PT's or the CT's, without an outgae. As an outage is not a possiblility at this point in time I am looking for alternative methods of correcting this problem, and the aux PT's seem to be the best solution thus far. I thank all of you for your help and sugestions.

 

[Skogsgurra]

Isn't it possible to do what I said? Configure for wye instead of delta. That takes care of the 30 degree problem introduced by the D/Y transformer.

Or didn't it work?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[slavag]

O.K.
JeffM123:
1. Try recommendation of Gunnar.
2. If it's not help and you need only meterig option (not kWh and kVarh), use
math option of ION7350 for visualization on dispaly.
For this you need ION Setup SW ( free of charge) and comm cable.
If you put today aux PT as temp. solution, you don't change
this connection in future.
Regards.
Slava