NGR Neutral Grounding / Earth Resistor

Neutral Grounding / Earth Resistor

Neutral Ground Rezistor Germany Europe

Neutral Grounding Resistor (NGR) and Neutral Earth Resistor (NER) solutions are manufactured in Germany and Europe for advanced transformer and power system protection applications. Designed to provide reliable fault current limitation and enhanced electrical safety, our grounding resistor systems help protect transformer centers, switchgear and industrial power networks against damaging earth fault conditions.

Neutral grounding resistor systems are engineered to reduce technical problems such as insulation breakdown caused by transient overvoltages and arcing ground faults in ungrounded systems. They also help prevent damage to motors, transformers and switchgear in solidly grounded systems by limiting excessive fault currents to controlled levels.

​The two primary grounding methods used in electrical systems are low resistance grounding and high resistance grounding. 

NGR / NER systems are designed to trip protection systems safely in the event of a line-to-ground fault while limiting ground fault currents typically between 100 A and 1000 A. Zero-sequence grounding resistor systems used with transformers and protection relays allow reliable fault monitoring and fast system response, with relays commonly detecting and tripping faults at 5–20% of the maximum ground fault current. Germarel GmbH is a Germany-based manufacturer and producer of industrial Neutral Grounding Resistor (NGR) and Neutral Earth Resistor (NER) systems for medium and high voltage applications worldwide.

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Germarel GmbH is a producer and manufacturer of Neutral Grounding Resistor (NGR) and Neutral Earth Resistor (NER) systems in Germany and Europe for medium and high voltage power applications. Our grounding resistor systems are engineered to provide reliable earth fault current limitation, enhanced equipment protection and improved operational safety in transformer and industrial power systems. Neutral grounding resistors are commonly rated for 10-second duty with a maximum temperature rise up to 800°C, depending on the application requirements and grounding method. The maximum ground fault current permitted by the resistor must be high enough to reliably actuate the applied ground fault relay system. NGR / NER systems rated between 200 A and 400 A are widely used for transformers operating in 6.9 kV to 34.5 kV systems, while 100 A to 400 A rated grounding resistors are commonly applied in 2.4 kV to 4.16 kV systems. Once the required current rating is determined, the resistance value is calculated by dividing the line-to-neutral voltage by the selected current rating. For example, in a 4.16 kV system with a Neutral Grounding Resistor rated at 400 A, the line-to-neutral voltage is approximately 2400 V. The required grounding resistance value is therefore calculated as 2400 V divided by 400 A, resulting in a 6 Ohm high resistance grounding resistor. High resistance grounding systems are recommended for applications where uninterrupted operation is critical and where tripping during a single line-to-ground fault would negatively affect the industrial process. In these systems, the transformer network may generate an alarm condition without immediate trip operation. High resistance Neutral Grounding Resistor systems typically limit ground fault currents between 5 A and 10 A. Zero-sequence current transformers and protection relays continuously monitor the system and can detect fault conditions at approximately 5% to 25% of the maximum ground fault current occurring on the transformer side. Continuous-duty NGR / NER systems are generally designed with maximum temperature rise limits up to 400°C. The selected resistor current rating must exceed the total system capacitance-to-ground charging current, while the vector sum of the charging current and resistor current should not exceed 8 A for stable system operation. For example, in a 480 V system with a Neutral Grounding Resistor rated at 5 A, the line-to-neutral voltage is approximately 277 V. The grounding resistance value is then determined according to the required current limitation level and protection philosophy of the electrical system.​

Neutral Ground / Earth Resistor Technical Datasheet

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Basic need as a required resistance will be 277 volt / 5amper = 55.4 Ohms. In medium voltage line power systems low resistance is generally used with a Neutral Grounding Resistor (NGR) / Neutral Earth Resistor (NER) that will limit the ground fault to a maximum of 25 amper to 50 amper. This is necessary to limit the touch voltage to 100 Volt or less volt.

Zero sequence current transformers and ground fault relays detect the fault and will trip at less than one third of the resistor rating to secure the protection.

​The Neutral Grounding Resistor (NGR) / Neutral Earth Resistor (NER) is rated for continuous duty with a maximum temperature rise of 375 celcious. Modern mine power systems can have a significant amount of distributed system capacitance and as will all neutral grounding resistors the maximum ground fault current allowed by the resistor must exceed the total capacitance to ground charging current of the system and the vector sum of the system charging current plus the resistor current shall not exceed 8 Amper. The references industrial power systems system neutral resistance grounding. Germarel GmbH is a supplier and manufacturer of Neutral Grounding Resistor (NGR) / Neutral Earth Resistor (NER) systems with high quality materials from Germany and Europe.

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