What is a Neutral Ground Resistor (NGR)?
A neutral ground resistor (NGR) is a component used in electrical systems, particularly in low-voltage distribution systems and in some medium-voltage systems. Its purpose is to limit the fault current that flows through the neutral point of a transformer or generator in the event of an earth fault.
Why a NGR for Fault Protection?
In electrical systems, the neutral point is typically grounded to provide a reference point and to facilitate the return path for the unbalanced currents in the system. However, during a ground fault, a large amount of current can flow through the neutral point, which can cause extensive damage to the equipment and pose safety risks.
The neutral ground resistor is connected between the neutral point and ground. It limits the fault current by introducing resistance into the circuit. By limiting the fault current to a safe level, the NGR helps protect equipment from damage and reduces the risk of electrical hazards, such as fires and electric shocks.
Neutral ground resistors come in various types and designs, depending on factors such as the system voltage, fault current magnitude, and specific requirements of the electrical installation. They are often specified based on parameters such as resistance value, continuous current rating, and withstand capability during short-circuit conditions.
In addition to providing protection, neutral grounding resistors also help in fault detection and localization within the electrical system by limiting the fault current magnitude and enabling the operation of protective relays and other monitoring devices.
Systems that Use NGRs
Neutral grounding resistors (NGRs) are commonly used in various types of electrical systems, particularly those involving transformers and generators. Here are some examples of systems where NGRs are frequently employed:
- Low-Voltage Distribution Systems: NGRs are commonly used in low-voltage distribution systems, typically with voltages up to 1000V. These systems are often found in industrial plants, commercial buildings, and residential areas.
- Medium-Voltage Distribution Systems: In some medium-voltage distribution systems, usually ranging from 1 kV to 36 kV, NGRs may be used to limit the fault current through the neutral point. These systems are often found in industrial facilities, power plants, and substations.
- Generator Neutral Grounding: Generators, especially those connected to isolated or ungrounded systems, use NGRs to limit the fault current during ground faults. This helps protect the generator and associated equipment from damage.
- Transformer Neutral Grounding: Transformers, particularly those in grounded wye configurations, utilize NGRs to limit fault currents and prevent damage to the transformer windings and connected equipment.
- Renewable Energy Systems: NGRs are increasingly being used in renewable energy systems such as wind farms and solar power plants to provide grounding and fault protection.
- Mining Applications: NGRs are commonly employed in mining applications where electrical systems are subjected to harsh environmental conditions and require reliable fault protection.
Overall, NGRs are essential components in various electrical systems where limiting fault currents and ensuring the safety and reliability of the electrical infrastructure are paramount.
Still don’t know what systems use a NGR? NGR Systems.