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2.36.1 Data communication interface
Communication interface is relevant to the property and capacity of channels; hence, IEEE
C37.94 (either N=1 or N=3) is provided in the DIF_COMM function. Securing clock recovery,
jitter tolerance, physical connection, and spuriousness are specified by the international
standard.
(i) IEEE C37.94 (N=1)
The C37.94 (N=1) link provides transmission format. Thereby, the DIF_COMM function uses
the transmission format for sending. The data which is sent for the remote-terminal is current
values, command signals and others:
• Current data in phase–a, –b, and –c at sampling time
• Residual current data at sampling time
• Output signals in phase-a, -b, and –c from the differential protection function
• Statuses of breaker and disconnector in phase–a, –b, and –c
• Statuses of scheme switches such as test and others
• Blocking commands for reclosing
• Sampling synchronization control signals
• Synchronized test trigger signals
• User configurable data
The current data are represented in instantaneous values; the values are sampled every
30-electrical degree. For instance, provided the power system frequency is 60 Hz, the 30-
electrical degree means that the sampling interval is 1.38 milliseconds (=1/720Hz). Twelve bits
(11 data bits plus a sign bit) are used to present a current data. The IED determines the current
data in the every 30-electrical degree; hence the DIF_COMM function can send the data in the
every 30-electrical degree. The DIF_COMM function also sends commands and other data; the
data are made of several signals: a signal of the differential current function, a signal of the
direct transfer trip function, a test signal, and a sync signal. Note that the DIF_COMM
function sends a signal per the 30-electrical degree with regard to the differential current
function the direct the transfer trip function. On the other hand, the DIF_COMM function
sends the other signals per 360-electrcal degree (=a cycle of the power system frequency)
The transmission format includes cyclic redundancy check (CRC) bits and check bit solid.
In case of communication failure, the DIF_COMM function set zero data for the format so as
not to operate the differential and other protection functions. Consequently, the protection
function corresponding to the DIF_COMM function can halt.
When the user wishes to use a communication module for the protection in the IEEE
C37.94 (N=1) at the channel#1, set Normal for the scheme switch [CH1_COM_WIDTH], for
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