The Model 6 MCC high resistance ground unit is intended for systems where reliable service is a high priority. The assembly provides a path for ground current through a resistance, which limits the ground-fault current flow to a value equal to or slightly greater than the capacitive charging current of the system.
High resistance grounding offers many advantages of both solidly grounded and ungrounded systems, including partial suppression of transient overvoltage, reduction of equipment damage due to ground fault, and the ability to continue to operate the system with a ground fault present on one phase.
- Resistor bank limits overvoltages by grounding the system neutral through impedance.
- High resistance ground indication/control panel provides a user interface for the system.
- Grounding transformers are supplied when the customer’s installation does not have neutral connections available, and provide an artificial neutral for zero-sequence currents.
- Pulsing contactor provides a method for tracing a ground fault to its source – the contactor is used to bypass a portion of the grounding resistor, so the current, proportional to resistance in the circuit, will rise, and the resulting current pulse is detectable with a handheld, clamp-on ammeter.
- Voltmeter relay (single-setpoint meter/relay) with an adjustable voltage pickup to monitor current through grounding resistors.
The fundamental purpose of high resistance grounding is to provide sufficient system damping to overcome the negative effects of arcing ground faults, and at the same time retain all the advantages of an effectively ungrounded system. A Model 6 MCC high resistance ground unit is the ideal solution for industrial or commercial customers who need the capacity to:
- Continue operation of a facility during the first phase to ground fault
- Easily locate a fault
- Effectively plan for repairs
- Provide system stability
- Minimize overvoltage by damping high frequency system oscillations
- Detect and warn when the first ground fault occurs in the system
- Monitor the condition of the system voltage
- Pulse the ground fault current, so its path can be traced