•
Unblock mode = "Time window": If the
CRG
signal disappears for a longer
time than defined in the
Loss of carrier time setting, the
CRL
output signal
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 is present again. 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
Unblock mode = "Permanent" and Unblock mode = "Time
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 values of
CRL
and
LCG
output signals are also available
through the Monitored data view. Activating the
BLOCK
input blocks the
CRL
and
LCG
outputs.
5.11.5
Application
To achieve fast fault clearing on the part of the protected feeder not covered by the
instantaneous step of the residual overcurrent protection, the directional residual
overcurrent protection can be used with RESCPSCH.
Applying RESCPSCH requires a communication channel capable of transmitting an
"On" or "Off" signal in each direction. To enable fast tripping, the most important
requirement for communication is the communication speed.
The performance of RESCPSCH 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 150 km, fibre-optic cables using digital
data transmission can be used. To avoid false signals that could cause 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 power system faults.
RESCPSCH 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 directional residual overcurrent
protection 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 function and the received signal from the
opposite terminal. In the underreaching scheme, no signals are sent during an
external fault. A trip signal is sent to the opposite terminal during an external
fault if the fault is seen in the forward direction and the overreaching scheme is
used. However, in case of external faults, tripping is always blocked because either
no signal is received as the opposite terminal sees a reverse fault or the signal
Protection related functions
1MRS759142 F
1258
REX640
Technical Manual