P&B MR-REF, Technical Manual

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Page 20
MR-REF & MR-REF3 Technical Manual
Issue 3, November 2013
6.7.3. Restricted Earth Fault.
The MR-REF & MR-REF3 may be configured to trip, alarm and/or indicate as a result of an REF overcurrent
condition.
Generally it is desired that restricted earth fault protection be instantaneous although in some applications transient
earth fault currents may be seen, and requires a small delay to be imposed to prevent nuisance tripping. In most
cases the earth fault protection feature should be set to ensure appropriate coordination with other devices.
Depending on the type of system grounding (resistive or solidly earthed) an earth fault current has the potential to be
very large. The user must be aware of the maximum earth fault current the system can experience when using the
Restricted Earth Fault protection feature and that it is correctly rated and co-ordinated with the primary breaking
device.
Trip Level.
The earth fault level is set as a percentage of the EFCT Primary If the current rises and remains above the threshold
level action is taken after the trip time has elapsed.
Trip Time.
The trip time is set to determine how long an earth fault condition can persist before the configured action is taken.
6.7.6. Serial Timeout.
For a set period of inactivity on the rear communication port the unit can be configured to take some action in the
event.
It is worth noting that the MR-REF & MR-REF3 device is slave to any host system, the unit will not send information
via the serial port unless it has been requested by a master device.
6.7.7. Internal Error.
The MR-REF & MR-REF3 incorporates an internal software and hardware watchdog feature to monitor the integrity
of both on board hardware and software systems. This feature may be configured to indicate as a result of any
registered problems. If a problem with the hardware or software is located during the error check routines the MR-
REF & MR-REF3 will generate an error code (or diagnostic status).