ABB RELION REX640 Technical Manual page 1248

Protection related functions
signal. A security margin of at least 10 ms should be considered. The time delay
Carrier Min Dur for prolonging the CS_BLOCKING signal is set to "0".
Setting guidelines for the blocking scheme DCB
Scheme type = "Blocking"
•
Coordination Time = "0.1" s (10 ms + maximal transmission time)
•
Carrier Min Dur = "0" s
•
Directional comparison unblocking scheme DCUB
Metallic communication paths unfavorably affected by fault-generated noise or by
other electrical phenomena, such as lightning, are not suitable for conventional
permissive schemes that rely on the signal transmitted during a fault in the
protected feeder. Principally, the communication media must be properly shielded
or otherwise designed to provide an adequate performance during such conditions.
The unblocking scheme can be used to overcome the lower dependability of
permissive schemes. The function is used in older, less reliable communication,
where the signal has to be sent through the primary fault. The unblocking function
uses a carrier guard signal CRG which must always be present, even when no
CR_PRM signal is received. Due to the absence of the CRG signal during the security
time, the
permissive scheme to operate when the communication channel is temporarily lost
during an internal fault.
Setting guidelines for the unblocking scheme DCUB
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
is generated. The CRL signal remains active until the CRG signal is present. The
communication failure is not signalled by the LCG output. The
setting is set to "35" ms.
Unblock Mode = "Time window": If the CRG signal disappears for a longer time
•
period than the
signal remains active for 150 ms, after which a communication failure is signalled
by the LCG output. The value of the LCG output is reset 200 ms after the CRG
signal reappears. The
5.10.6 Signals
1248
Loss of carrier time setting is used as a CR_PRM signal. This also enables a
Loss of carrier time setting, a logical carrier received signal CRL
Loss of carrier time setting, a CRL signal is generated. The CRL
Loss of carrier time setting is set to "35" ms.
Unblock Mode setting.
Loss of carrier time
Technical Manual
1MRS759142 F
REX640