Monitoring NGR with Ground fault and ngr monitor RC48N.

NGR

The resistance grounded systems are created if the neutral is tied to ground via NGR (Neutral Grounding Resistor). The main advantage of resistance grounded system is that the resistor limits the amount of current flowing through earth fault. In short NGR is intended to reduce the maximum possible leakage current to a low pre-determined level. Typically NGRs are used to limit the maximum fault current to 750mA, 1A, 10A, 50A, 100A etc depending on local requirements. Thus the system becomes less hazardous (in fault conditions) as compared to solidly grounded system.

A ground fault current in a resistance grounded system will be limited in its magnitude. This is main difference when compared to the solidly grounded system where maximum fault current is limited by line impedance only which is very negligible. The ground fault magnitude depends on system voltage, the resistance ground of ground fault causing part and the resistance of NGR.

In a resistance grounded system what would happen if the current limiting resistor is destroyed or loses one of its connections? The answer is simple the resistance would become infinite and former resistance grounded system will become floating and there will not be any scope for ground return current to flow. Also in such a situation there an increased risk of transient over-voltages.

BENDER with its large amount of experience and R&D efforts over more than 70 years provide ingenious solution for earth fault monitoring and protection for various applications. Bender devices are known for successfully working in presence of various electrical noises without spurious operation and indications (EMI/EMC qualified) across the world. Thus for safe and efficient operation of NGR grounding system a Bender make NGR monitor RC48N should be used the details are discussed below.  

The RC48N ground-fault neutral-grounding-resistor monitor is used to monitor high-resistance grounded systems. It is designed to monitor the presence of the neutral-grounding resistor and sense the ground fault current.

The RC48N ground-fault and neutral-grounding-resistor monitor combines three functions in one device:

  1. Measures the residual current in the Neutral grounding resistor with BENDER residual current transformers. Thus monitoring the total leakage current of the supply/distribution system. In case the leakage current crossed a pre-determined limit RC48N will initiate an alarm and potential free contacts will changeover which can be used for remote alarm or tripping. Delay can be set according to the requirements.
  2. If the continuity of NGR breaks in a ground fault condition there will be a voltage available at the neutral point. Thus NGR monitor also monitors the voltage drop on the neutral grounding resistor via the coupling device. In case the voltage between the neutral point of transformer and the ground crossed a pre-determined level device RC48N will initiate an alarm and potential free contacts will changeover which can be used for remote alarm or tripping without any delay.