ABB Relion 670 Series Technical Reference Manual page 797

1MRK505222-UUS C
13.1.2.3
13.1.2.4
Technical reference manual
zone to trip after the tCoord timer has elapsed. The tCoord in permissive
underreaching schemes is normally set to zero.
The logic for trip signal in permissive scheme is shown in figure 387.
PLTR-CRD
AND
CR
ANSI05000513 V1 EN
Figure 387: Logic for trip signal in permissive scheme
The permissive underreaching scheme has the same blocking possibilities as mentioned
for blocking scheme.
Permissive overreaching scheme
In a permissive overreaching scheme, a forward directed overreach measuring element
(normally zone2) 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 387.
The permissive overreaching scheme has the same blocking possibilities as mentioned
for blocking scheme.
Unblocking scheme
In unblocking scheme, the lower dependability in permissive scheme is overcome by
using the loss of guard signal from the communication equipment to locally create a
receive signal. It is common or suitable to use the function when older, less reliable,
power-line carrier (PLC) communication is used.
The unblocking function uses a guard signal CR_GUARD, which must always be
present, even when no CR signal is received. The absence of the CR_GUARD signal
for a time longer than the setting tSecurity time is used as a CR signal, see figure 388.
This also enables a permissive scheme to operate when the line fault blocks the 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.
0-tCoord
TRIP
0
en05000513_ansi.vsd
Section 13
Scheme communication
791