Detect Ground Fault

[Humble2000]

How can we detect the ground fault location in HRG or floating ground sytem.
XFMR is Delta -Wye
XO is not grounded or HRG is installed.

Thanks

 

[dpc]

With HRG, the customary method is detect voltage across the grounding resistor with a voltage relay. Current sensing can also be used, but current is very low - 1 to 5 amps, so voltage detection is much more reliable. There can be a fair amount of harmonic voltage present, so the voltage relays generally have 3rd harmonic filtering - at least in olden times. Probably not an issue for any microprocessor-based relay.

 

[davidbeach]

To expand on dpc's post - The presence of a ground fault in an ungrounded (high impedance capacitively grounded) or HRG system is best detected using voltage and there are several ways of doing so. Current through the resistor of an HRG system can also detect the presence of a ground fault.

Locating the fault is not nearly as easy. Some HRG systems allow the ground resistance to be alternated between two values, producing two current levels, such as 10A and 5A. With proper instrumentation it is possible to trace this pulsing current to the ground fault. Other than that turning circuits off one at a time is a good means of isolating the fault.

Unless an element specifically states otherwise, you will find that numeric relays operate on fundamental current or voltage, ignoring harmonics. Some times harmonics are used for blocking, and third harmonic voltage is used in generator protection, but for the most part it will be only the fundamental that is considered by the relay.