Why Neutral Resistor Is Added Between Neutral And Earth Of An Alternator

A neutral resistor, also known as a neutral grounding resistor or neutral earthing resistor, is added between the neutral point and earth of an alternator for several reasons, primarily related to electrical safety and system protection. Here's why it's done:

1. Limiting Ground Fault Current: The primary purpose of adding a neutral resistor is to limit the magnitude of ground fault currents in the electrical system. In the event of an insulation breakdown or ground fault in the system, a direct connection between the neutral and earth would result in a high fault current flowing through the faulted phase(s) to ground. By inserting a resistor in the neutral path, the fault current is limited, reducing the risk of equipment damage and improving personnel safety.

2. Reducing Overvoltages: In ungrounded or high-resistance grounded systems, a neutral resistor helps reduce transient overvoltages that may occur during ground faults. By limiting the fault current, the neutral resistor helps mitigate the voltage rise on the unfaulted phases, minimizing the risk of insulation breakdown and equipment damage.

3. Improving System Stability: A neutral resistor can help improve the stability of the electrical system by reducing the likelihood of cascading faults or system-wide disruptions during ground faults. By limiting fault currents and overvoltages, the resistor helps contain fault conditions and maintain system integrity.

4. Facilitating Ground Fault Detection: In systems equipped with ground fault protection relays, a neutral resistor provides a measurable resistance value that can be used for fault detection and localization. The presence of a neutral resistor enables accurate measurement of ground fault currents, allowing for timely detection and isolation of faulted zones.

5. Complying with Standards and Regulations: Many electrical codes and standards require the installation of neutral grounding resistors in certain types of electrical systems, particularly in systems with high fault currents or where personnel safety is a concern. Adding a neutral resistor helps ensure compliance with applicable regulations and industry best practices.

Overall, the addition of a neutral resistor between the neutral and earth of an alternator plays a crucial role in mitigating the effects of ground faults, protecting equipment, enhancing system stability, and ensuring the safety and reliability of the electrical distribution system. The selection of the resistor's resistance value is typically based on factors such as system voltage, fault current levels, and regulatory requirements.