ABB RELION REX640 Technical Manual page 1243

1MRS759142 F
Z3
Bus A
~
Z2_START
Figure 708: 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.
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
time setting generates a logical CRL signal. A communication failure shorter than
the value of the
The unblocking function is configured with the
Unblock Mode = "Off": The unblocking function is disabled.
•
Unblock Mode = "Permanent": If the CRG signal disappears for a longer time
•
than defined in the
REX640
Technical Manual
Z1
3
Z2
Unblock Mode = "Time window" is not
The operation mode
recommended as the blocking is activated only for 150 ms after the
guard signal disappears. This results in an unwanted operation of the
protection.
Loss of carrier time setting is always ignored.
Loss of carrier time setting, the logical CRL signal is
Protection related functions
Z2
Z1
Z3_START
Unblock Mode setting.
Bus B
~
3
Z3
Loss of carrier
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