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DIFF
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Load
DTT
CS
CR
TRIP
TRIP
VT1
CT3
CT2
CT1
Power
Transformer
Line
X
source
Source
en03000120.vsd
IEC03000120 V1 EN-US
Figure 387:
Usually carrier receive (CR) signal trips the line circuit breaker directly in normal direct transfer
trip scheme (DTT) but in such cases security would be compromised, due to the risk of a false
communication signal. A false CR signal could unnecessarily trip the line. Therefore, a local
criterion is used, to provide an additional trip criterion, at the same location as the line circuit
breaker. The local criterion must detect the abnormal conditions at the end of the protected
line and transformer and permit the CR signal to trip the circuit breaker.
Another application is a line connected shunt reactor, where the reactor is solidly connected to
the line. Shunt reactors are generally protected by differential protection, which operates the
local line circuit breaker and sends a transfer trip command to the remote line end.
The line protection in the remote end is much less sensitive than the differential protection
and will only operate for low impedance reactor faults very close to the high voltage terminal.
To avoid frequent line trips at the local end due to false transfer trip signals, a local criterion
check is required to be added at the local end.
The trip signal from local criterion will ensure the fault at the remote end and release the trip
signal to the local side circuit breaker. The local criterion must detect the abnormal conditions
and permit the CR signal to trip the circuit breaker.
DTT scheme comprises following local criteria checks as shown in Figure
1MRK 505 343-UEN B
Section 15
Scheme communication
621
Application manual
Содержание Relion 670 series
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