Chapter 3 - Device Overview
54 3BHS335648 E82 UNITROL 1020 User Manual
number of machines inside a segment is not limited. Only the maximum number of total
machines is limited to 31.
The status of the breakers must be wired to digital input (Secondary Net 1 and
Secondary Net 2) of the AVR.
Where Secondary Net 2 is used for the left side (decreasing) breaker and Secondary Net
1 is used for the right side (increasing) breaker.
Ring segment, terminated by left and right side breaker
SM SM
AVR 1 AVR 2
Note that the net IDs are equal to the bus segment where the AVR is connected to. The
AVR status gives an indication of two different island operations.
Primary Net One of the section breakers is open
Secondary Net Both section breakers are closed
A ring structure is built with up to 8 segments; see the example for 3 segments below.
Segment 2
Ring segment, terminated by left
and right side breaker
SM
SM
Segment 3
Ring segment, terminated by left
and right side breaker
SM
SM
Segment 1
Ring segment, terminated by left
and right side breaker
SM
SM
The auxiliary contact of the breaker must be wired only inside the segment. In order to
select the correct machines regarding the load sharing, all AVRs give the information of
the segment breaker and their own position (segment number) over the RS485 bus to all
other AVRs. This enables the system to detect wrong configuration which is indicated as
“VDC Ring Error”.
In addition the user can select the common section breaker, where a combination of two
breakers in series is routed to neighboring sections. This will ensure correct load sharing
even if one segment is completely powered off.
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