ABB RELION REX640, Technical Manual, Page: 1257 / 1960

~ ~
DEFL_START
(Forward)
DEFL_START
(Reverse)
Bus A
Bus B
3 3
Figure 715: Simplified functional diagram of the blocking scheme, external fault
The unblocking function used with the blocking function provides a possibility to
supervise the communication channel. In this case, the
CRL
output signal is used as
a local blocking signal.
The operation mode
Unblock mode = "Time window" is not
recommended as the blocking is activated only for 150 ms after the
guard signal disappears. This results in an unwanted operation of the
protection.
Directional comparison unblocking scheme DCUB
The unblocking function is a complementary logic which can be used together
with the permissive communication schemes. In the unblocking scheme, the
dependability of the permissive schemes is improved by using the loss of guard
signal from the communication equipment to create a
CRL
output signal locally. This
enables the permissive scheme to operate even if the communication channel is
interrupted or lost.
The unblocking function uses a carrier guard signal which must always be present.
The absence of the
CRG
signal for a time longer than the value of the
Loss of carrier
time setting generates a logical
CRL
signal. A communication failure shorter than
the value of the
Loss of carrier time setting is always ignored.
The unblocking function is configured with the
Unblock mode setting.
•
Unblock mode = "Off": The unblocking function is disabled.
•
Unblock mode = "Permanent": If the
CRG
signal disappears for a longer time
than defined in the
Loss of carrier time setting, the logical
CRL
signal is
generated. The
CRL
output signal remains active until the
CRG
signal reappears.
The communication failure is not signaled by the
LCG
output.
1MRS759142 F Protection related functions
REX640
Technical Manual
1257