NGR(neutral grounding resistor)

●● NGR(neutral grounding resistor): 

A neutral grounding resistor (NGR) limits dangerous fault currents in an electrical system by providing a controlled resistance path between the system's neutral point and the ground. When a fault occurs, the NGR prevents the current from becoming excessively high, protecting personnel and equipment by reducing damage, electrical fires, and shock hazards. It converts the fault energy into heat, allowing the limited current to be detected by protective relays for fault clearing.  

● How an NGR Works: 

• Connection: 

The NGR is connected to the neutral point of a transformer or generator. 

• Fault Condition: During a single line-to-ground fault, a high fault current would normally flow if the system were solidly grounded. 

• Controlled Path: The NGR introduces a specific resistance into the path of this fault current. 

• Current Limiting: According to Ohm's Law (I = V/R), the added resistance limits the magnitude of the fault current. 

• Energy Dissipation: This limited current flows through the NGR, where the resistor converts the energy of the fault current into heat. 

• Protection: The NGR's resistance level is carefully chosen to be low enough for protective relays to detect the fault but high enough to prevent equipment damage and maintain system stability. 

● Benefits of Using an NGR

• Personnel Safety: Reduces the risk of electrical shock hazards. 

• Equipment Protection: Prevents severe damage to transformers, cables, and other electrical equipment from overcurrents. 

• Fire Prevention: Mitigates the risk of electrical fires by controlling fault current magnitudes. 

• Arc Flash Reduction: Lowers the energy released during a fault, reducing arc flash hazards. 

• System Stability: Helps maintain stable voltages and minimizes voltage imbalances during a fault. 

• Fault Detection: The limited current allows for easy detection and clearing of the fault by protective relays.