Main Purpose of Using Neutral Grounding Resistor

Neutral Grounding Resistor(NGR)

The main purpose of using Neutral Grounding Resistor(NGR) in the Power system is to limit the high current which flowing due to Line to Earth fault.

In the substation, the Neutral point of the secondary winding of the Transformer is connected to the earth through a Resistor. This resistor is called Neutral Grounding Resistor. In generating station the neutral point of the Alternator also connected to the earth.

We already discussed why we need Earthing and Grounding, What is the Difference between Earthing and Grounding. You can read can read that article. Today we are going to know why we need the Neutral Grounding Resistor.

The main purpose of Neutral grounding Resistor:

As you see in the above figure, the neutral point of the alternator is connected to the ground. Now if by chance Line to Earth fault occurs then a huge amount of current will flow. According to the above figure, a huge amount of current will flow through the 'B' phase and Earth. This huge amount of current will damage the winding of the Alternator. That is why we connect the neutral point to the earth through a resistor which limits the high current during fault and protects the alternator from damage. 

The value of the resistor is selected according to the system. This Resistor does not affect the line or phase voltage. But it causes to show lower voltage when we measuring the voltage between line and earth.

Again you can see in the above figure, the neutral point of the secondary winding of the transformer is connected to earth through a resistor. Here also the same reason for using Neutral Grounding Resistor as previous. Here the resistor protects the Transformer from damage. 

This resistor also helps to generate a voltage drop across it. A voltage drop also occurs accross the resistor if there is any leakage current flowing through the NGR. By measuring this voltage drop across the NGR, we can easily aware about the leakage current.

Other importance of Neutral Grounding Resistor:

(1) The current flowing through the Neutral Grounding Resistor can be monitored and measured. This can be used to operate the Earth Fault Relay. Earth fault Realy will trip the circuit when the earth fault occurs.

(2) The Neutral Grounding Resistor provides the protection against Transient Over voltage. 

(3) It helps to connect other protective equipment(like Relay) which cannot operate with high current, so to reduces the current, this resistor is also used. It helps to increase the range of the protective device connected to that.

Read Also:

• The List of Faults RCCB can Protect and Can't Protect
• Short Circuit Fault Causes, Effects, Protection
• Neutral Fault Causes, Effects, Example, Explanation
• ELCB and RCCB Difference, Advantages, Limitations, Diagram
• Main Purpose of Using Neutral Grounding Resistor

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