ABB RELION REX640 Technical Manual page 1152

Section 5
Protection related functions
1146
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.
• Unblock Mode = "Time window": If the CRG signal disappears for a longer time
than defined in the Loss of carrier time setting, the CRL output signal is generated.
The CRL output signal remains active for 150 ms, after which a communication
failure is signaled by the LCG output. The LCG output is reset 200 ms after the
CRG signal reappears. The purpose of this mode is to ensure tripping during a
fixed delay of 150 ms after the loss of communication due to possible
consequences of an internal fault. After this time, the accelerated tripping is
allowed only if the CR_PRM signal is received again.
With operation modes Unblock Mode = "Permanent" and Unblock Mode = "Time
window", the created CRL output signal is internally ORed with the CR_PRM input to
allow the permissive scheme to operate even when the communication channel has
been interrupted or lost. The CRL and LCG output signals are also available as outputs
for monitoring purposes. Activating the BLOCK input blocks the CRL and LCG
outputs.
1MRS759142 C
REX640
Technical Manual