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
Loss of carrier time
setting is used as a CR_PRM signal. This also enables a
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
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, a logical carrier received signal CRL
is generated. The CRL signal remains active until the CRG signal is present. The
communication failure is not signalled by the LCG output. The
Loss of carrier time
setting is set to "35" ms.
•
Unblock Mode
= "Time window": If the CRG signal disappears for a longer time
period than the
Loss of carrier time
setting, a CRL signal is generated. The CRL
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
Loss of carrier time
setting is set to "35" ms.
5.10.6 Signals
Protection related functions
1MRS759142 F
1248 REX640
Technical Manual
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