Permissive Overreaching Scheme - ABB REL650 series Technical Manual

Section 12
Scheme communication
12.1.6.4
12.1.6.5
500

Permissive overreaching scheme

In a permissive overreaching scheme, a forward directed overreach measuring element
(normally zone2) through the input CSOR sends a permissive signal CS to the remote end
if a fault is detected in forward direction. The received signal CR is used to allow an
overreaching zone to trip after the settable tCoord timer has elapsed. The tCoord in
permissive overreaching schemes is normally set to zero.
The logic for trip signal is the same as for permissive underreaching, as in figure 231.
The permissive overreaching scheme has the same blocking possibilities as mentioned for
blocking scheme.
Unblocking scheme
Unblocking schemes were designed to operate with power-line carrier (PLC)
communication using frequency shift keying between a trip and guard frequency.
The unblocking function uses a guard signal CR_GUARD, must be present, when no CR
(trip permission) signal is received so that the channel can always be monitored. The loss
the CR_GUARD signal for a longer than the setting tSecurity time is used as a CR signal,
see figure 232 and 233. This enables the unblock (permissive) scheme to trip when the line
fault interrupts the unblock signal transmission.
The received signal created by the unblocking function is reset 150 ms after the security
timer has elapsed. When that occurs an output signal LCG is activated for signalling
purpose. The unblocking function is reset 200 ms after that the guard signal is present
again.
CR
NOT
CR_GUARD
200 ms
0
ANSI05000746 V1 EN
Figure 232: Guard singal logic with unblocking scheme and with setting Unblock =
Restart
0-tSecurity
0
150 ms
OR
AND
0
1MRK 506 335-UUS A
CRL
OR
AND
LCG
en05000746_ansi.vsd
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