Operation Principle - ABB RED650 Technical Manual

1MRK 505 394-UEN A
19.1.6
Line differential protection RED650 2.2 IEC
Technical manual

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
Information
flag
8 bits n x 16 bits
IEC01000134 V1 EN-US
Figure 353: Data message structure
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.
Remote communication
Stop
CRC
flag
16 bits 8 bits
en01000134.vsd
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