Rockwell Automation 7763 Medium Voltage OneGear SMC Flex Motor Controller (10-15 kV) - Manual (Page 41)

Rockwell Automation Publication 7760-UM001D-EN-P - October 2014 41
Product Overview Chapter 1
Power Module
The three-phase AC line controller consists of three removable power modules,
one for each phase. Each power module includes series connected PowerBricks
(5 for 12 kV, and 6 for 13.8 kV applications), an isolated current loop power
system, a set of fiber optic cables for SCR control, and line and load connections.
Each PowerBrick includes two inverse parallel connected SCRs plus snubbers
and self-powered gate driver circuits.
Each PowerBrick includes a snubber circuit to limit the rate of rise in voltage
across each SCR pair. The module also includes patented current loop gate driver
circuits which derive their power primarily from the snubber circuit.
Voltage sharing resistors are connected across each SCR pair to provide static
voltage balance for series-connected SCRs. These resistors are tapped to provide
a reference for overvoltage protection circuitry on the gate driver board.
A voltage sensing board is used to reduce the line-side and load-side voltages to
lower levels that can be measured by the SMC Flex control module.
Current Loop Gate Driver (CLGD) Board
This board provides the turn-on capability for SCR devices. The board also
provides optical fibre isolation between itself and the gating source logic. It is
primarily powered by recovering energy from the snubber circuit, so it is fully
isolated from the control and logic circuits. The board also receives short-term
power from the current loop power supply.
The MV SMC Flex has three heatsinks fitted with a thermistor to monitor
temperature rise. The circuitry on the gate driver board accepts the thermistor,
and drives a fibre-optic cable if the temperature is below the setpoint (85 °C). If
the temperature rises above the setpoint, the driver is turned off, and the MV
SMC Flex is signaled to stop gating and initiate a temperature fault. For a detailed
layout of this circuit board, refer to
Figure 28 in Chapter 2 .
Interface Board
This circuit board takes current transformer signals plus line-side and load-side
voltage feedback signals from the voltage sensing board and passes them to the
SMC Flex for processing. The control module produces gating signals for the
SCRs, which are received on the interface board, and used to drive fibre-optic
transmitters. The gating signals are sent to the gate-driver circuit board via fibre-
optic cables. The interface board also receives temperature feedback from the
gate-driver board via fibre-optic cable(s). If the heatsink temperature rises above a
set value, a signal is sent to the SMC Flex to stop gating the SCRs and initiate a
temperature fault. For a detailed layout of this circuit board, refer to
Figure 27 in
Chapter 2 .