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382
Galvanic data communication module
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These interface modules are intended for connection to commercially available com-
munication equipments or multiplexers and can be used both with 56 and 64 kbit/s data
transmission.
Since the protection communicates continuously, a permanent communication circuit
is required. Consequently, the call control and handshaking features specified for some
interfacing recommendations are not provided.
Even if the standard claims that the reach for these interfaces are up to 1 km at 64 kbit/
s it is not recommended to use that distance for protection purposes where the commu-
nication has to be reliable also under primary power system faults. This is due to the
low level of the communication signals which gives low margin between signal and
noise. If the protection terminal is in the same building as the multiplexing equipment
and the environment is relatively free from noise, the protection terminal may be con-
nected directly to the multiplexer via shielded and properly earthed cables with twisted
pairs for distances less than 100 m.
Modules are available for the following interface recommendations, specifying the in-
terconnection of the digital equipment to a PCM multiplexer:
•
V.35/36 co-directional galvanic interface
•
V.35/36 contra-directional galvanic interface
•
X.21 galvanic interface
•
RS530/422 co-directional galvanic interface
•
RS530/422 contra-directional galvanic interface
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