Application Notes P54x/EN AP/La4
MiCOM P543, P544, P545 & P546
(AP) 6-61
AP
A
Z1A
B
C
Z1C
= area where no zone 1 overlap exists
Fault
A
Z1A
B
C
Z1B
No infeed
Fault seen by A & B in zone 2
A
B
C
Relay at C sees reverse fault until B opens
(i)
(ii)
(iii)
P1166ENa
P1134ENa
Figure 20 Teed feeder applications
Figure 20 (iii) illustrates a further difficulty for a PUR scheme. In this example current is
outfed from terminal 'C' for an internal fault. The relay at 'C' will therefore see the fault as
reverse and not operate until the breaker at 'B' has opened; i.e. sequential tripping will occur.
3.3.4 Blocking schemes
Blocki
ng schemes are particularly suited to the protection of teed feeders, since high speed
operation can be achieved where there is no current infeed from one or more terminals. The
scheme also has the advantage that only a common simplex channel or a triangulated
simplex channel is required.
The major disadvantage of blocking schemes is highlighted in Figure 20 (iii) where fault
current is outfed from a terminal for an internal fault condition. Relay 'C' sees a reverse fault
condition. This results in a blocking signal being sent to the two remote line ends, preventing
tripping until the normal zone 2 time delay has expired.
To Next Page
Loading...
