ABB RED650 - Analog Signal Communication for Line Differential Protection

2 1 4 3
( ) ( )
2
d
T T T T
T
- + -
=
EQUATION1358 V1 EN-US (Equation 2)
1 4 2 3
( ) ( )
2
T T T T
t
+ - +
D =
EQUATION1359 V1 EN-US (Equation 3)
Δt is calculated every time a telegram is received, and the time difference is then
used to adjust and interpolate the current measurements from the remote end before
the current differential algorithm is executed.
The echo method can be used in telecommunications transmission networks with
varying signal propagation delay as long as there is delay symmetry, that is, the
send and receive delays are equal. The delay variation can depend on the signal
going different routes in the network from time to other.
When the delay symmetry is lost, the expression for Δt given above is no longer
valid..
6.1.7.3 Analog signal communication for line differential protection
SEMOD52424-1 v1
Communication principle
SEMOD52415-4 v3
For a two-terminal line, the current from the local CT needs to be communicated
over a 64 kbit/s channel to the remote line end, and the remote end current
communicated back on the same channel. If there is, for example, a three terminal
line another 64 kbit/s channel will be needed to exchange the same local current
with the third line end current.
In one-and-a-half breaker arrangements, there are two local currents meaning two
64 kbit/s channels to each remote substation. Alternatively, it is possible to add
together the two local currents before sending them and in that way reduce the
number of communication channels needed. This is achieved by selecting proper
setting for parameter TransmCurr (CT-SUM, CT-DIFF1 or CT-DIFF2). However,
information about bias currents is reduced if the alternative option is followed. For
further information and discussions on this matter, refer to the Application manual.
The communication can be arranged as a master-master system or a master-slave
system alternatively. Figure
30 shows a master-master system for a three-terminal
line. Here current samples are exchanged between all IEDs, and an evaluation is
made in each IED. This means that a 64 kbit/s communication channel is needed
between every IED included in the same line differential protection zone.
In the master-slave system, current samples are sent from all slave IEDs to one
master IED where the evaluation is made and trip signals are sent to the remote
ends when needed. In this system, a 64 kbit/s communication channel is only
needed between the master, and each one of the slave IEDs.
Section 6 1MRK 505 394-UEN A
Differential protection
102 Line differential protection RED650 2.2 IEC
Technical manual