ABB Rellon 620 Series, Руководство по протоколу связи

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Section 2
IEC 60870-5 overview
RER620 11
Communication Protocol Manual
2.3.2 Event acquisition
Events occur spontaneously at the controlled outstation's application level. The events are
buffered in the controlled outstation because the events may appear faster than the
communication link is able to transfer them.
When unbalanced transmission is used on the link layer, the buffered events must be polled
by the controlling station. The controlled outstation must always wait for a request for
transmission from the controlling station.
When balanced transmission is used on the link layer, the buffered events are sequentially,
without a delay, transmitted by the controlled outstation to the controlling station.
2.3.3 Interrogation
The controlled outstation's interrogation function is used for updating the controlling
station after an internal station initialization, or when the controlling station detects loss of
information.
When the function is used, the controlling station requests the controlled outstations to
transmit the actual values of all their process variables. Normally, the amount of
information is known by the application functions in both the controlling stations and
controlled outstations. The interrogation can be done either by an interrogation group
(1…16) at a time or all groups at once (general).
2.3.4 Clock synchronization
The clock of the controlled outstation has to be synchronized with the clock of the
controlling station. Synchronizing of the clocks provides a correct chronological sequence
of time-tagged events or information objects that are transmitted to the controlling station,
or that are logged locally.
After system initialization, the clocks are initially synchronized by the controlling station.
Then, the clocks are periodically resynchronized by transmission of a clock
synchronization command (C_CS ACT).
The time information must always be corrected either by the controlling station before
sending or by the outstation when an ASDU with time tag is received. A delay acquisition
command can be used to define the measured or estimated transmission delay in the
outstation. The command corrects the time on the outstation side when sending.
2.3.5 Command transmission
A command is used in telecontrol systems to change the state of operational equipment,
for example, a circuit breaker. A command may be initiated by an operator or by automatic
supervisory procedures in the controlling station. Provision against unauthorized access or
against unwanted actions are system- or process-dependent.
The two standard procedures for command transmission are a Direct command or a Select
and execute command.
Direct commands are used by the controlling station to immediately control operations in
the controlled outstations. For safety reasons, the controlled outstation's application