Online neutral grounding resistor monitoring for unit-connected generators with hardware validation

Neutral grounding resistors are used to control transient overvoltages and overcurrents in power systems. Failure of these critical assets revives many disadvantages of ungrounded and solidly grounded traditional systems. Therefore, monitoring the neutral grounding resistors is necessary. A new continuous monitoring technique is proposed for such a resistor located at the neutral of unit-connected generators. It detects resistor failure by comparing the third harmonic of neutral and residual voltages. This proposed scheme demonstrates reliable operation under various conditions of the system and resistor as observed by PSCAD in conjunction with MATLAB. Further performance validation has been carried out using an industrial generator protection relay as well. In contrast to existing methods, this scheme does not require any additional measurement instruments. Thereby, it is easily retrofitted to installed unit-connected generator protection infrastructures. Moreover, this continuous monitoring technique prevents maloperation of the generator stator ground protection due to the neutral grounding resistor failure.