Rockwell Automation 1560E SMC Flex Smart Motor Controller - Manual (Page 32)

1-22 Product Overview
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Hardware Description The following sections contain descriptions of system components and
system operation. Each section will be described to give the user an
understanding of the MV SMC-Flex to facilitate operation and maintenance
of the system. Refer to Figures 1.18 through 1.21, Typical MV SMC-Flex
Power System.
Power Module
The controller consists of three power modules, one for each phase. Each
power module consists of incoming and outgoing terminals for cables, SCRs,
heatsink and clamp assembly. The SCRs are connected in inverse parallel
(and in series for 12- or 18-SCR assemblies) to form a three-phase, AC
line controller configuration.
Each power module includes a snubber circuit to limit the rate of rise in
voltage across each SCR pair. The module also includes patented gate
driver circuits which derive their power 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.
Self-Powered Silicon-Controlled Rectifier Gate Driver 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 powered by recovering energy from the snubber circuit, so it is
fully isolated from the control and logic circuits; it is self-economizing
when the unit is not running, or is in bypass mode.
Note: If pump control or stop control are used, the gate driver boards are
powered continuously using separate power supply boards. (Refer to
Chapter 8 for additional details.)
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 signalled to stop gating and initiate a
temperature fault.
Due to the self-powered nature of the circuits, this function is active only
while the SMC is active. While the starter is off, or in bypass, no power is
dissipated in the SCRs and the temperature of the SCRs can only decrease.