ABB RELION REX640 Technical Manual page 1244

Protection related functions
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
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
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.
5.10.5 Application
To achieve fast fault clearing on the part of the protected feeder not covered by the
instantaneous zone Z1, the stepped distance protection function can be used with
DSOCPSCH.
Applying DSOCPSCH requires a communication channel capable of transmitting an
"On" or "Off" signal in each direction. To enable fast tripping, the most important
requirement for the communication channel is the communication speed.
The performance of DSOCPSCH is directly related to the communication channel
speed, and to the security against false or lost signals. Therefore, dedicated
communication channels are recommended. With short distances of up to a few
kilometers, a typical communication media is a simple pilot wire based on auxiliary
power. With distances of up to 50 km with the integrated communication interface
or up to 150 km with external equipment, fibre-optic cables using digital data
transmission can be used. To avoid false signals causing unwanted operation,
the security of the communication channel should be emphasized. Also, the
dependability of the communication channel should be considered to ensure that
the signals are reliably transmitted during the power system faults.
DSOCPSCH supports five communication schemes.
• Direct underreaching transfer trip DUTT
• Permissive underreaching transfer trip PUTT
• Permissive overreaching transfer trip POTT
• Directional comparison blocking scheme DCB
• Directional comparison unblocking scheme DCUB
Depending on whether the communication channel is used for sending a block or a
trip signal, the communication schemes can be divided into blocking schemes and
permissive schemes.
In permissive schemes, the trip signals of the distance zones are interchanged
between the terminals to receive a permission to trip during an internal fault.
The tripping of the local terminal depends on both the starting of its own
forward-looking zone and on the received signal from the opposite terminal. In
the underreaching scheme, no signals are sent during an external fault. During an
external fault, a trip signal is also sent to the opposite terminal if the fault is seen
1244
Loss of carrier time setting, the CRL output signal
Unblock Mode = "Permanent" and Unblock Mode = "Time
1MRS759142 F
REX640
Technical Manual