Smart 1-Line
TM
Page 38
AC-PRO and AC-PRO-II trip units use Modbus RTU serial communications. Communications
performance and speed depends on several items. Some of the major items that can affect
communications performance and speed are:
•
Smart 1-Line settings
•
Trip unit settings
•
Baud Rate (of the trip units and Smart 1-Line)
•
Power state of trip units
In general, the best speed performance will be achieved with AC-PRO-II with VDM (Voltage Divider
Module). This is because the AC-PRO-II offers faster baud rate setting options, and the VDM
provides continuous trip unit power, for uninterrupted communications.
The Smart 1-
Line “Timing Settings” affect the speed performance. “Scan Period” is one Timing
setting, which determines how often the Smart 1-Line requests data from each trip unit. For
example, if the “Scan Period” setting is set to 10 seconds, then the information from each breaker will
be requested (and should be updated) every 10 seconds. See Section 3 for additional information
about the Smart 1-Line settings.
The Baud Rate is the rate at which information is transferred. The Smart 1-Line and all connected
trip units need to be set to the same Baud Rate. AC-PRO can operate at a Baud Rate of 9600.
AC-PRO-II can operate at Baud Rates of 9600, 19200, 38400, 57600, and 115200, depending on
the firmware version.
Due to the nature of RS-485 network serial communications, the system communications
performance is best if all trip units are powered continuously. Standard AC-PRO-II and AC-PRO trip
units derive their power from the CTs (sensors) if current is flowing. The AC-PRO-II with VDM
(Voltage Divider Module) option can also derive trip unit power from the energized line-side stabs of
a racked-in breaker, even if the breaker is open and/or zero current is flowing.
Therefore, AC-PRO-II with VDM (Voltage Divider Module) trip units are recommended, because the
system voltage (from the line-side stabs of a racked-in breaker) will power the AC-PRO-II
continuously, even if the breaker is open and/or zero current is flowing.
Example if trip units are not powered up: If the Smart 1-Line is making data requests to trip units that
aren’t responding (because no current is flowing and/or they aren’t powered up), then the
communications system will become backed up. Communications
to the trip units that aren’t
powered up will be interrupted, and communications to other trip units will be slowed down.
If AC-PRO-II or AC-PRO trip units (breakers) are known to be racked out or out of service for an
extended period, URC recommends modifying the Smart 1-Line in Designer Mode. Specifically, the
‘Address’ and ‘Depends’ fields that have the particular out of service trip units’ address(es) should be
temporarily blank, or the breaker should be removed from the Smart 1-Line drawing until the breaker
is placed back into service.
The Smart 1-Line is factory-configured for easy and simple operation without the need to customize
the PC or Windows. The following sections provide some additional information.
6.0
System performance & speed
6.1
Smart 1-Line Settings
6.2
Baud Rate
6.3
Power state of AC-PRO-II and/or AC-PRO trip units
7.0
General and PC Items
