Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
The timer ‘Distance extend time’ should be set to avoid overreach elements tripping in case of
transient reverse overcurrent after a fault has been cleared. The timer ‘DCB distance coordination time’
on the block diagram provides a coordination time delay to allow the transmission of the blocking
channel signal between terminals in case of faults outside the protected line. Channel tripping and
channel activation can be disabled using the status contact input ‘Block pilot trip.’ It can also be
disabled for power swing conditions by enabling the Power swing blocking setting.
9.2.7
DIRECTIONAL COMPARISON UNBLOCKING (DCUB)
The DCUB scheme was designed for Frequency Shift Power Line Carrier. The FSK carrier sends a
continuous blocking (guard) signal. When a forward distance element detects a fault, the transmitted
carrier frequency is shifted to a trip signal. The scheme is a permissive principle; forward operation
AND received permission are required for a trip. To accommodate for a risk of losing the carrier signal
in the fault on the line, an unblock trip window is provided. If the receiver does not detect any signal,
neither block frequency (GUARD), nor trip frequency, the relay is allowed to trip from its forward
distance element for a short period (150 ms) following loss-of-signal.
STATION “A” 21P (CARRIER KEY)
STATION “B” 21P (CARRIER KEY)
BKR
A
BKR
B
+
CARRIER
RX “A”
OR
150 ms
ONE-SHOT
LOSS OF CHANNEL
TRIP BKR A
+
T2A
“A” 21P
TRANSMIT
TRIP B
+
CARRIER
RX “B”
OR
150 ms
ONE-SHOT
LOSS OF CHANNEL
TRIP BKR B
+
T2B
“B” 21P
TRANSMIT
TRIP A
STATION “A” 21P (CARRIER KEY)
STATION “B” 21P (CARRIER KEY)
BKR
A
BKR
B
+
CARRIER
RX “A”
OR
150 ms
ONE-SHOT
LOSS OF CHANNEL
TRIP BKR A
+
T2A
“A” 21P
TRANSMIT
TRIP B
+
CARRIER
RX “B”
OR
150 ms
ONE-SHOT
LOSS OF CHANNEL
TRIP BKR B
+
T2B
“B” 21P
TRANSMIT
TRIP A
+
CARRIER
RX “B”
OR
150 ms
ONE-SHOT
LOSS OF CHANNEL
+
CARRIER
RX “B”
OR
150 ms
ONE-SHOT
LOSS OF CHANNEL
TRIP BKR B
+
T2B
“B” 21P
TRANSMIT
TRIP A
+
T2B
“B” 21P
TRANSMIT
TRIP A
Figure 9-20. Directional Comparison Unblocking
August 1, 2009
9-23
973.334.3100
