NGR full form is the Neutral Grounding Resistor, which is used in the electrical system to protect the transformer and generator. As the name suggests, the neutral ground resistor connects the neutral point of a transformer or generator to the ground.
After knowing the full form of NGR, let us discuss some points related to neutral ground resistors.
What Is NGR?
A Neutral Ground Resistor(NGR) is made using materials such as Stainless Steel and Nickel Chromium Alloy (NiCr). These materials have a stable resistance that does not change with temperature. Porcelain and ceramic are used to support the resistor elements.
Purpose of NGR
The primary purpose of an NGR (neutral ground resistor) is to limit the ground fault current that can flow in the event of a fault in the system. This helps prevent excessive currents and associated damage to equipment during a ground fault.
What is the NGR Panel?
The NGR panel is an outdoor enclosure that houses a neutral grounding resistor, current transformer, CT shorting terminals, insulators, terminals, and bus bar.
Installation of NGR
Neutral ground resistors are connected between the neutral point of a transformer or generator and the ground. The resistor is usually sized and rated based on the equipment’s voltage and its full load current.
The image below shows how to install NGR for transformer protection.
The image below shows how to install NGR for generator protection.
Resistance Value of NGR
To calculate the resistance value, we need two parameters – the rated voltage and current of the equipment. Let’s assume that the line voltage of the transformer is VL, and its full load current is IF. The resistance value can be calculated using the following mathematical formula.
NGR Monitoring
The NGR (Neutral Ground Resistance) plays a vital role in the protection of transformers and generators. It is essential to ensure that the NGR is healthy at all times. To monitor the condition of the NGR circuit, a neutral ground resistance monitoring relay is utilized, which provides a signal indicating any faults or issues with the NGR circuit.
This is all about the full form of NGR and its application in electrical circuits.