Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
When a terminal unit on the transmission line detects a reverse fault, a channel signal (channel start)
will be transmitted to avoid remote-end tripping by overreach elements (Zone 2 or Zone 3). Therefore,
overreach tripping will occur when no channel signal is received. The channel signal is transmitted to
the remote end by the terminal detecting the reverse direction fault.
Correct application of this scheme requires that the following conditions are satisfied:
1. The distance covered by the reverse element must be longer than the distance covered by the
forward overreach element of the remote end. This will avoid any Zone 2 (or Zone 3)
tripping for a fault outside the line.
2. Overreach elements must be provided with a time delay (DCB distance coordination time) to
allow the transmission of the channel signal between terminals.
Channel receive
Forward pilot zone
Power swing
blocking
Block pilot trip
Input channel stop
Zone 1 Fault
Enable Distance pilot
power swing block
Distance pilot
protection trip
Distance protection
channel start
50P-1 Phase A
Reverse pilot zone
(Z4)
50P-1 Phase B
50P-1 Phase C
50G-1 Ground
Fast carrier start
0
T
Distance extend
time
Distance protection
channel stop
T
0
DCB distance
coordination time
Figure 9-19. Directional Comparison Blocking
The DCB scheme can also use ‘Fast carrier start’. The ‘Fast carrier start’ uses non-directional
overcurrent elements to start carrier which enables faster trip (shorter DCB coordination time setting).
The ‘Fast carrier start’ scheme uses step 1 instantaneous overcurrent elements, 50P-1/50G-1 in the
diagram. For this scheme, the setting of these elements should be non-directional.
August 1, 2009
9-22
973.334.3100
