Current Differential Relay
GARD 8000 SYS RFL Electronics
June 20, 2014 13-72 973.334.3100
13.5.2.2.2 Exiting Test Mode
In order to exit test mode the user must turn off the test mode in the relay where it was originally set.
This local relay will then change the configuration message sent to the remote relay to indicate that it
should no longer be in test mode and the remote relay will also exit test mode.
If communications are lost while in test mode the remote relay will remain in test mode. If it is desired
to exit test mode while comms are down, the user may do so using the web pages, however, when
comms are restored the relay will again be commanded to enter test mode if the “local” relay is still
configured for test mode.
Note that the test mode is a volatile setting: it is cleared when power is removed. Thus, if power is
cycled at the remote relay the relay will power-up normally and return to test mode once it receives the
appropriate messages from the local relay. If the local relay (the one that the user initiated test mode
at) loses power it will power-up normally (not in test mode). This was done to prevent relays from
potentially powering-up (after an indeterminate period of time or even in different chassis) in test
mode.
13.5.2.3 PRIMARY GUARD BEFORE TRIP
Upon establishing communications (or reestablishing if comms had failed) the relay will require
100ms of communications with the remote relay without calculating or receiving any trips to satisfy
the GB4T criteria. While this provides a secure method of enabling protection under normal
conditions, it will prevent the relay from coming up with a faulted line.
To work around this the relay will also satisfy the GB4T criteria if a clear channel is detected. A clear
channel is defined as approximately 250ms without any detected communications errors.
13.5.2.4 MAJOR ALARM
The relay will go into major alarm when it detects a problem that prevents it from providing protection.
The alarm bit is sent out on the logic bus and is used in the system logic (in the GARD controller
module) to prevent trip signals from being issued.
13.5.2.5 MINOR ALARM
The minor alarm is a user alerting function that goes out as a bit on the logic bus. The system logic in
the GARD controller module has a timer that monitors the minor alarm signal. If this signal is
continuously active for a prolonged period (e.g. 10 seconds) they user can be notified.
The module minor alarm has no direct impact the protection functions of the relay; it is intended
strictly to alert the user to possible trouble conditions.
Current Differential Alarm
The current differential alarm is an indicator that the relay has calculated a current differential
trip; however, the trip has not been fully processed because there were not sufficient fault
detectors. See section 13.5.1.2.11 for further information.
Loss of Load / Open Conductor
The loss of load (section 13.5.1.6.4) and open conductor (section 13.5.1.5) algorithms may be
configured by the user to place the module in minor alarm.
Communications Alarm
When the communications alarm (section 13.5.2.6.2) is active the relay will be in minor alarm.
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