~ ~
Z1
Z2
Z1
Z2
Z3
Z3
Z2_START
Z3_START
Bus A Bus B
3
3
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.
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
1MRS759142 F
Protection related functions
REX640
Technical Manual
1243
To Next Page
Loading...
