# How to have Wye-connected Potential Transformers(PTs) and Neutral Ground Resistor short circuit detection at my ground fault protection relay?

Detecting if the Neutral Ground Resistor (NGR) is shorted is something that must be checked at the Ground Fault Protecting Relay. The typical way to do this is to inject a DC component and to measure the voltage drop in the NGR. If no voltage drop is seen, it is assumed that the NGR is shorted and the relay trips. I would like to have Wye-connected PTs, used to monitor the quality of line to ground voltage and NGR monitoring with NGR short circuit condition detection at the same time on a 4160 V transformer secondary.

Having Wye-connected PTs may confuse the ground fault detection relay as for the DC component the PTs provide a low impedance parallel path which can be confused with a shorted NGR and this must be avoided.

Is adding a Potential transformers Ground resistor (PTGR) the only way to achieve both things? Wouldn't this affect the reading of the system monitoring the quality of line to ground voltage?

Update: There are also PTs that are build with a capacitor voltage divisor on their primary but I haven't found any operating at 5 kV

• What is the sensitivity of your ground-fault-detection-relay and what is the maximum current through your potential transformers? In my experience, a (sensitive) ground fault detection relay is set to about 5 amps primary, and the load current of the potential transformer would be about 0.1A. – Li-aung Yip Apr 7 at 8:44
• I have added more details to my question. The load current of the potential transformer for DC is very high. I would like to find what the typical impedance and load current of the potential transformer is for AC. Where can I find values like 0.1 A? Thank you very much – VMMF Apr 7 at 16:23
• A typical specification for a 11kV electromagnetic voltage transformer (no capacitor divider) has a rated output of 700 VA thermal on the secondary. Working backwards to 11kV amps, 700 VA / 11kV * sqrt(3) = 0.11 A. – Li-aung Yip Jun 12 at 14:11