ABB RELION REX640, Техническое руководство, Страница: 1262 / 1960

To secure that the blocking signal arrives before the local overreaching function
trips, the trip is delayed by the
Coordination time setting. This setting must be
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
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
•
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 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.
5.11.6 Signals
Protection related functions 1MRS759142 F
1262 REX640
Technical Manual