Evaluation Of Sustainability Generator 3500 kVA Protection System Using Neutral Grounding Resistor

Generator Protection Using NGR

Abstract

A 3,500 kVA generator as a backup source in critical facilities requires reliable ground fault protection. This study evaluates the protection system of a Cummins QSK95G4 generator through analysis of Factory Acceptance Test (FAT) data on a Neutral Grounding Resistor (NGR) unit of 19 Ω, 200 A, 6.6 kV. The research methods include calculation of basic generator parameters, resistance analysis based on geometry and AISI 304 stainless steel material, thermal evaluation using lumped capacitance model, and protection coordination analysis between NGR, 200/1 A current transformer, 51G ground fault relay, and SE-330 monitoring relay. FAT results show actual resistance of 19.8 Ω with +4.21% deviation from design value, still within ±10% tolerance per IEEE Std C57.32-2015. Ground fault current is limited to 192.45 A, decreasing 93.7% compared to solid grounding condition (3,059 A). The 51G relay operating time is recorded at 0.30 seconds with high sensitivity (multiples M = 6.29), meeting generator protection speed criteria per IEEE Std C37.101-2006. Multi-scenario analysis indicates that 200 A NGR rating is the optimum choice balancing protection, thermal, and equipment coordination aspects. This research confirms that pre-installation FAT testing is a vital step to ensure protection system reliability and prevent field failure risks due to material deviation or relay coordination errors.

Keywords: NGR, FAT, generator protection system, reliability, pre-installation test