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
PT can be designed or built in two ways. Like classical two winding transformer (primary winding, which is high voltage side (10, 20, 35, 110 kV) and low voltage side (usually 100/V3, 100 V). Also standard PTs, have more secondary windings, for metering device, for RTUs, relay protection, etc. Second type pf PT is with capacitor divisor, or capacitor PT. On secondary side there is a winding with for creating a secondary voltage of 100/V3 or 100 V. Primary side of this winding is 10 or 15 kV for transmission types of PTs. Today PTs on secondary side gives you voltage for each phase. So it can be monitoring phase to ground voltage and can be used for relay protection and in connection with others phases you can have monitoring phase to phase voltage in relay device, and you can have open delta voltage to see what happened in isolated network.
Thank you very much for your answer Igor Ivankovic . Are you aware of any such capacitor divisor PT rated for 5kV?
Such detail I real don’t know. 5 kV divisor maybe it can be find in some high voltage laboratory or in some factory for PTs.
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