Distance Relay Setting Examples
GARD 8000 Distance Relay
RFL Electronics Inc.
8.2.11
67 DCB SCHEME
The 21L DCB Scheme can be complemented by a directional comparison blocking scheme for ground
and/or negative sequence overcurrent.
The directional ground DCB pilot logic uses directional ground and/or directional negative sequence
elements.
Both zero sequence and negative sequence elements can be used in the scheme, operating in parallel.
However, it is recommended that the operator use
either
zero sequence or negative sequence, and not
both. There are applications where zero sequence and negative sequence currents can have different
directions for the same fault. This would defeat the DCB logic and misoperations may occur. Also
make sure that the same elements are used at the two line ends.
This setting example will use zero sequence elements only.
Channel receive
50 G-2
Trip 67 pilot
67 channel stop
50 G-1
0
T
67 Coord Time
67 channel start
T
0
DCB 67 delay
time
Input block trip 67 pilot
50 Q-2
50 Q-1
50 G-3
50 Q-3
Input disable 67 pilot
67G reverse
67Q reverse
67G forward
67Q forward
Figure 8-4. Directional Comparison Blocking (DCB) Directional Overcurrent Scheme
Carrier start (blocking signal) is issued when the reverse 50G-3 (67G-3) and/or the reverse 50Q-3
(67Q-3) assert. The drop out of this signal is delayed by the time set on “67 Coord Time”
Trip is issued when the forward 50G-2 (67G-2) and/or the forward 50Q-2 (67Q-2) assert, after the set
pickup delay “DCB 67 delay time” AND no block signal (channel receive) is present. This indicates a
forward fault, within set 67 pilot reach.
Carrier stop is issued when the forward 50G-1 (67G-1) and/or the forward 50Q-1 (67Q-1) assert. This
indicates a forward fault.
Carrier stop is also issued by the forward 50G-2 (67G-2) and/or the forward 50Q-2 (67Q-2) elements,
but not until the DCB 67 delay time has timed out.
August 1, 2009
8-28
973.334.3100
