High Resistance Grounding
High Resistance Ground (HRG) systems are available for both 480V and 5kV systems and provide a high resistance path to ground. Most commonly used for testing distribution systems and locating ground faults for corrective action. These units can be constructed as stand alone cubicles or installed integrally into low voltage or medium voltage switchgear.
High resistance grounding system grounds the neutral through a resistance which limits the ground fault current to a value equal to or slightly greater than the capacitive charging current of that system.
Ground-Gard high resistance grounding equipment consists of a group of devices coordinated and connected to provide a high resistance ground and ground fault detection for a power system. Major components of this system include:
- UL Labeled Enclosures
- Bank of Three Grounding Transformers (Delta Connected Systems)
- Single Grounding Transformer (Wye Connected Systems)
- Grounding Resistor
- Device to Disconnect the Ground-Gard from the Power System
- Metering and Control Devices
- Pulsing System
A ground fault is detected by a contact-making voltmeter (MR). The meter-relay actuates a timer set for about five (5) seconds. This timer prevents alarming faults of a transient nature. If it times out, an auxiliary relay picks up and seals in through a reset button. Contacts of the auxiliary relay then energize whatever alarm or annunciator system desired by the user. Another auxiliary relay is connected to alarm if the control voltage fails or the ground is disconnected from the system.
A normal operating sequence would be for an operator to acknowledge the alarm, find and clear the ground fault, and then reset the high resistance grounding system.
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