KWH Metering Error with Ground Fault Resistor

Connect your VT neutral on the grounded side of the NGR (it should be called that - Neutral Grounding Resistor). The metered voltage is from phase TO GROUNDED NEUTRAL, which would encompass the NGR and the minimal votlage drop across it.

The resistor doesn't add any "errors." Under normal conditions there will be only a very minimal current flow in the neutral from any phase imbalance, meaning a small voltage drop in the NGR. That is part of the energy you are metering. If you leave the NGR out of the VT circuit, you will not be including that.

mynorac,

I would refer you to posts I made in 2009.

The posts attracted some interest, no one however made any constructive criticism.

See forum thread: Tariff Metering With Earthed Voltage Transformers

I believe you could have large voltage errors & it would be best if the VTs were changed to unearthed VF 1.2 types as per Table 1 of BS7729.

Hello, Just some thoughts...I can't think of any reason why installing a ground resistor would have any adverse affect on metering PT's. I'm not sure I understand correctly what your engineers are saying regarding tying the wye point to the line side of the GFR...the GFR should be installed on the ground conductor at your supply transformer. This would not have any affect on metering. The only concern with having a GFR is making sure your ground fault sensing relay is not set above the ground fault current available with the GFR. Hope this helps.

There is absolutely no error in power measurements when using a properly connected 3-element meter together with three Cts and three Vts. This applies to situations with or without grounding neutral impedance. See:

Oleh