ABB RELION REX640 Technical Manual page 1262

Protection related functions
To secure that the blocking signal arrives before the local overreaching function
trips, the trip is delayed by the
set longer than the sum of the maximal transmission time of the channel and the
start and response times of the protection relays sending and receiving the CS_PRM
signal. A security margin of at least 10 ms should be considered. The time delay
Carrier Min Dur for prolonging the CS_PRM signal is set to "0".
Setting guidelines for the blocking scheme
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 adversely affected by fault-generated noise or by
other electrical phenomena, such as lightning, are not suitable for conventional
permissive schemes that rely on signal transmission 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
Unblock mode = "Off": The unblocking function is disabled.
•
Unblock mode = "Permanent": If the CRG signal disappears for a longer time
•
period 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
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
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
5.11.6 Signals
1262
Loss of carrier time setting is used as a CR_PRM signal. This also enables a
Loss of carrier time setting, a CRL signal is generated. The CRL
Loss of carrier time setting is set to "35" ms.
Coordination time setting. This setting must be
1MRS759142 F
Loss
REX640
Technical Manual