Why is Neutral Grounding Resistor (NGR) used in Earthing?
NGR Neutral Grounding Resistors are used in generating stations, power transformers, and long-line shunt reactors. The NGR is made of a material with a high-temperature coefficient and its resistance remains fairly constant when large current flows through it.
Why is NGR used?
The neutral point’s earthing is done to ensure the upstream breaker’s tripping in case of an earth fault. This process of earthing the neutral point is called system grounding. System grounding can be done in three ways, solid grounding, resistance grounding, and reactance grounding. Each type of grounding system has its own pros and cons.
When solid grounding is used the enormous fault current flows through the equipment. However, the current transformer senses the current quickly and trips the circuit breaker to isolate the faulty section. The enormous current may cause damage to the electrical system and even it can cause catastrophic damage to the electrical system.
Here comes the role of the neutral grounding resistor. The enormous current flowing in the case of solid grounding can be limited if the impedance is created in the path of the fault current. The resistor resists the flow of electrons or current. Therefore, the resistance is added to the neutral grounding circuit. The value of the resistance is selected so that the earth fault current flowing through the equipment is not more than the full rated current.
The current transformer is mounted in the neutral grounding circuit to detect the earth fault current in order to trip the circuit to isolate the faulty section.
NGR Circuit Diagram
A neutral grounding resistor is connected between the neutral point of the electrical equipment and the earth point.
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