ABB RELION REX640 Technical Manual page 1260

Protection related functions
Coordination time = "0.050" s (10 ms + maximal transmission time)
•
Carrier Min Dur = "0.1" s
•
Permissive underreaching transfer trip PUTT
In the permissive underreach scheme, a permission to trip is obtained locally from
the underreaching function and sent to the remote end. The received signal is then
combined with the local fault indication from the overreaching function resulting in
a trip command after a settable pick-up delay
The protection relay of either feeder end sends a permissive signal to trip the
other end. The communication channel must be able to receive and transmit at
the same time. In permissive schemes, the communication channel must be fast
and secure, but also dependable. Inadequate security causes unwanted tripping
for external faults. Inadequate speed or dependability causes delayed tripping for
internal faults.
The CS_PRM signal is issued based on the underreaching residual overcurrent
protection function.
The permissive scheme is not applicable on short feeder lengths because the
residual overcurrent protection cannot easily distinguish between the internal and
external faults in such cases.
The residual overcurrent function may start only at one end due to the system
conditions such as weak zero-sequence source at one end, or high fault resistance.
However, fast tripping from both ends can be achieved by connecting a general
forward start signal to CACC. So, even if the local overreaching residual overcurrent
function has not picked up, the local OPERATE output is activated. The function also
generates a CS_PRM signal by combining the carrier received CR_PRM signal from a
remote end and also the local activation of CACC, giving the permission to a remote
function to trip instantaneously.
The CR_PRM signal must be received when the overreaching residual overcurrent
protection is still active to achieve an instantaneous trip. In some cases, due to the
fault current distribution, the overreaching protection can operate only after the
fault has been cleared by the remote terminal. In this case, there is a risk that if the
remote terminal is tripped directly by the instantaneous underreaching function,
the CS_PRM signal that it issues resets before the overreaching function of the local
end terminal is operated. To ensure a sufficient duration of the CR_PRM signal, the
CS_PRM signal can be prolonged by time
the
The received communication signal is combined with the output from the local
overreaching function. Therefore, there is less concern about a false signal causing
an incorrect trip. Therefore, the timer
communication channel failure does not affect the selectivity, but delays the
tripping at the other end for certain fault locations.
Setting guidelines for the permissive underreach scheme PUTT
Scheme type = "Permissive Underreach"
•
Coordination time = "0" s
•
Carrier Min Dur = "0.1" s
•
Permissive overreaching transfer trip POTT
In the permissive overreach scheme, the permission to trip is obtained locally from
an overreaching function and sent to the remote end. The received signal is then
1260
Carrier Min Dur setting is "0.1" s.
Coordination time .
Carrier Min Dur . The recommended value of
Coordination time can be set to "0". A
1MRS759142 F
REX640
Technical Manual