Current Differential Relay
GARD 8000 SYS RFL Electronics
June 20, 2014 13-70 973.334.3100
the element to become active and there must also be an active fault detector in the phase calculating the
trip and at least one additional fault detector.
Once tripped the CIF element will become inactive when the user specified time period has expired (if
the fault persists other elements should pick up).
13.5.1.6.4 Loss of load (LOL)
The loss of load algorithm is a multi-step algorithm that works only with the three phases. The only
potential involvement of the ground is that it can contribute a fault detector. The loss of load algorithm
is automatically disabled in single-pole configuration.
13.5.1.6.4.1 Prefault Condition
The system must start in a stable condition with all three phases seeing currents of at least 1.5A
RMS
(5A
CTs).
13.5.1.6.4.2 Loss Detector
A phase is considered lost when there is a phase imbalance and at least two fault detectors while
having been in a valid prefault condition within the past two cycles.
Phase imbalance is defined as at least one phase having greater than or equal to 3A
RMS
(5A CTs) and at
least one phase having less than 0.5A
RMS
(5A CTs).
13.5.1.6.4.3 Delay Timer and Action
Once the phase loss is detected the phase imbalance must continue for a user specified duration in
order to satisfy the algorithm (at which point the fault detectors will most likely be inactive as will the
prefault condition).
The user can specify if they want the open conductor algorithm to cause a trip, an alarm, or be ignored.
13.5.1.6.5 Stub bus protection
When the bus is configured with an 89 disconnect that may leave a bus stub energized and requiring
protection the 89B contact can be fed into the relay to enable the stub bus feature. The stub bus
functions may be disabled by the user.
The stub bus function basically isolates the local and remote relays. The local relay is switched into a
modified backup mode that provides only overcurrent and time overcurrent routines. The stub bus
overcurrent routines are identical to the backup overcurrent routines (section 13.5.1.6.2) but allow
independent configuration of the delay and phase and ground overcurrent thresholds.
The stub bus time overcurrent (TOC) routines use the same configuration settings as the backup TOC
routines (section 13.5.1.6.2) but have an independent enable/disable control.
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