Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
Frequency is a reliable indicator of unbalance between generation and load. Any decrease in frequency
is caused by excess loads. Under frequency relays are used for load shed in order to adjust the load to
available generation to avoid a system collapse. When the frequency is restored to normal and the
system has stabilized, the loads are reconnected. The restoration is made by using over frequency
relays. Sufficient time delay should be employed to assure that the power system is stable prior to
initiating load restoration. In areas where isolation of a large surplus of generation relative to
connected load can be anticipated, automatic over frequency tripping of generation may be considered
to prevent excessive high frequency and resultant uncontrolled generator tripping and equipment
damage.
9.19
BREAKER FAILURE RELAY UNIT
The breaker failure unit is used to detect failure of the breaker to open following a trip command and
to give a trip signal to other circuit breakers to isolate the fault.
The breaker failure unit incorporates a retrip function whose objective is to send a new tripping
command to the failed breaker.
The breaker failure unit uses six current detectors; two for each phase. One set is for the 1 Pole pickup
setting and the other for the 3 Pole pickup. The breaker failure relay is capable of performing on a per
phase basis in single pole trip applications. When applying GARD to three pole tripping, single phase
pickup and three phase pickup should be set on the same value, as well as 1 Pole 50BF delay and 3
Pole 50BF delay.
The current measuring elements are designed with a fast reset (<5 ms) in order to minimize the breaker
failure timer setting.
Breaker failure relay initiation is made by all GARD 8000 trips, but external initiation can also be
made via an input. Both re-trip and breaker failure trip outputs are provided. Each of these has their
individual time delay setting.
August 1, 2009
9-70
973.334.3100
