Reactor category
Generator Neutral Grounding Resistor
Generator Neutral Grounding Resistor
If you operate generators, transformers, or auxiliary equipment in a power system, chances are you have a neutral grounding resistor (NGR).generator neutral grounding resistor This important component limits fault current and protects the integrity of your circuits during a ground fault event. Adding this component to your wye-connected systems helps reduce overvoltages, arc flash hazards, and equipment damage and enhances power system reliability.
A generator neutral grounding resistor is a large resistor that is connected between the neutral point of a transformer or generator and ground.generator neutral grounding resistor It is used in low-voltage distribution systems and some medium-voltage distribution systems to limit the current that flows through the neutral star point during a fault event. The NGR lowers the current enough to prevent equipment damage but not so much that protective relays cannot operate, thereby enabling system monitoring and protection.
The NGR is designed to withstand the heat generated by the flow of current through it during a ground fault event. It is rated based on the line-to-neutral voltage of your system and how long you want the NGR to continue carrying fault current after the protection devices have isolated the fault. NGRs are available in a wide range of resistance values and thermal duty ratings to meet your specific requirements.
In addition to lowering the fault current, an NGR can also limit the amount of energy that is transferred through the system during a ground fault. This is because increasing the resistance in a grounding path increases the amount of current it takes to travel through that path and causes the voltage across that resistor to decrease. This is a simple application of Ohm’s Law.
When a neutral grounding resistor is sized correctly for your system, it will prevent equipment damage and provide reliable operation of your generators and auxiliary equipment during a ground fault event. This is because the NGR limits fault current to a predetermined value, which makes it easier for protective relays and other monitoring devices to detect the ground fault and initiate an appropriate response.
NGRs are an integral part of most MV feeder protection schemes and are commonly included in a high-level grounding design. When selecting an NGR, be sure to consider your source voltage, grounding point (transformer or generator neutral), frequency, short-circuit levels, and cable lengths and types. Also, share your site ambient data with the NGR vendor so they can set the correct temperature rise for your application.
A continuous neutral grounding resistor monitor, like the LOGIC3 from Powerohm, is an excellent way to ensure your NGRs are always functioning properly and protecting your assets. By continuously measuring the temperature of a neutral grounding resistor, this technique is capable of detecting any degradation in the NGR and isolating any malfunctioning protection relays. You can then take the necessary steps to rectify the condition before it leads to any potential equipment damage or system interruptions. For more information, click here. Powerohm’s LOGIC3 is easy to install and provides a cost-effective way to continuously monitor the neutral grounding resistor of your unit-connected power systems.
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