Insulation resistance (R) monitoring
In ungrounded power system, the installation must either be ungrounded or must be grounded using a sufficiently high level of impedance.
In the event of only one ground or earth fault, the fault current is very low and interruption is unnecessary. However, given that a second fault could potentially cause the circuit breaker to trip, an IMD has to be installed to indicate an initial fault. The device installed along with IMD detects the initial fault on the particular channel where the fault occurred. This device triggers an audible and/or a visual signal.
By constantly monitoring the insulation resistance, you can keep track of the system quality, which is a form of preventive maintenance. Further, monitoring the insulation resistance of individual channels, you can keep track of the individual channel quality.