Application - ABB RELION REX640 Technical Manual

1MRS759142 C
5.10.5
REX640
Technical Manual

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 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
because the signal is received but the fault is seen in the reverse direction. In either
case, the blocking is not dependent on the received signal so a lost communication
channel does not result in false operation.
In the blocking scheme, a blocking signal is sent to the opposite terminal if the fault
is locally seen in the reverse direction, that is, during an external fault. Thus, the
blocking is dependent on the received signal, and there is typically a need to delay the
tripping of the terminal receiving the blocking signal. This delay depends, for
Protection related functions
Section 5
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