Configuration Of Binary Signals; Operation Principle - Hitachi 670 Series Application Manual

1MRK505382-UEN Rev. K
Charging current compensation is achieved 100 ms after simulation start when the power line was
switched on to normal load. Under normal load conditions, approximately 92 A is subtracted, which
results in all fundamental frequency differential currents being close to zero. Since voltage profiles
are not known, the approximate method continues, even under fault conditions, to subtract the pre-
fault charging current of 92 A.
With low resistance faults, the 55 A difference of the approximate method in comparison to the exact
method, is relatively small when considering high fault currents. With high-resistance faults, the
charging current will not change much so it is acceptable to continue subtracting it.
4.8

Configuration of binary signals

4.8.1

Operation principle

In 64 kbit mode, communication takes place in standard ITU (CCITT) PCM digital 64 kbit/s channels.
Communication is two-way, and telegrams are sent every 5 ms (same in 50 Hz and 60 Hz) to
exchange information between two IEDs. The format used is C37.94, and one telegram consists of
start and stop flags, address, data to be transmitted, Cyclic Redundancy Check (CRC) and Yellow bit
(which is associated with C37.94).
Start
flag
8 bits
IEC01000134 V1 EN-US
Figure 45:
The start and stop flags are composed of 0111 1110 sequence (7E hexadecimal) as defined in the
HDLC standard. CRC is designed according to the standard CRC16 definition. The optional address
field in the HDLC frame is not used but, instead, separate addressing is included in the data field.
The address field is used for checking that the received message originates from the correct
equipment. There is always a risk that multiplexers occasionally mix up the messages. Each terminal
in the system is given a number. The terminal is then programmed to accept messages from a
specific terminal number. If the CRC function detects a faulty message, the message is thrown away
and not used in the evaluation.
If communication is used for line differential purposes, transmitted data consists of three currents,
clock information, trip, block and alarm signals and eight binary signals which can be used for any
purpose. The three currents are represented as sampled values.
If communication is used exclusively for binary signals, full data capacity of the communication
channel is used for the binary signal purpose which gives the capacity of 192 signals.
In 2 Mbit mode, telegrams are still sent using C37.94 but the HDLC part is not used. Instead, all 12
channels of the C37.94 frame are used, and a telegram is sent whenever a sample is available. The
address field is used in the same way as in 64 kbit mode but the CRC field is 32 bits. It carries 9
analog samples and 192 general purpose binary signals.
Communication set-up, 670/650 series
Application Guide
Information CRC
n x 16 bits 16 bits
Data message structure
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Analog and binary signal transfer for line differential protection
Stop
flag
8 bits
en01000134.vsd
Section 4
M12452-14 v6
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