Chapter 3 - Device Overview
52 3BHS335648 E82 UNITROL 1020 User Manual
Load sharing will only be accurate in case of matched PTs. Voltage
must be matched to a single reference with 0.1% accuracy
Voltage droop compensation can be used for two different bus configurations.
a) Busbar configuration with 2 breakers
b) Ring structure with up to 8 segments
The load sharing takes place only in machines that are connected directly and
automatically controlled by digital inputs that give information about the breaker.
Common parameters for VDC:
Network Connection Type Busbar or Ring
RS485 error forces to AUTO mode False / True
VDC Ramp Time 0.1 – 60.0 sec
Baud Rate 59.7k / 57.6k
Calc ref from AVRs in VDC mode only False / True
Communication over RS485 between the parallel units:
Each AVR has to be configured with a unique AVR-ID number which identifies itself
among the others on the bus.
The VDC communication refers to the data transmitted over the RS485 bus whereas the
VDC operating mode refers to whether this data is used for compensation of the reactive
power or not. The AVR enables the VDC communication (i.e. transmit data over the bus)
as soon as the "Gen CB Closed status" input is active (logical one) in case bus bar
configuration is selected and VDC software is available in the device except during
Standby or when Remote Access via the RS485 is active. When Ring structure is
selected all AVRs will transmit their information on the bus. As long as the AVR is in
Standby or as long as Remote Access via RS485 is active, the VDC communication is
disabled and will not be transmitted over the bus. Once the VDC communication is
enabled, the data available on the bus is taken and used for the regulation. This is only
possible when the AVR is switched to VDC operating mode (i.e. by VDC Enable digital
input).
The availability of the VDC communication disregarding the operation mode (even during
Excitation Off) allows the cabling connections and communication quality to be easily
tested. The testing is performed by forcing the "Gen CB Closed status" input signal and
by monitoring the status of the communication using the VDC Monitor tool included in the
CMT1000. For more information about VDC Monitor refer to Chapter 6.4.7
Communication Menu.
The wiring connections of the RS485 bus are explained in Chapter 3.3.9.3 RS485
Interface.
3.4.3.2 Voltage Droop Compensation for busbar configuration
The VDC software allows the network to be divided into smaller entities. Each AVR can
operate in one of three pre-determined island grids called Primary and Secondary Nets.
The Primary Net (open breaker) is selected by default if the Secondary is not configured.
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