Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C-Frame) - ForGe Control - Manual (Page 291)

Rockwell Automation Publication 7000L-UM301D-EN-P - June 2014 291
Component Definition and Maintenance Chapter 5
SGCT and Snubber Circuit Similar to all power-conductors or thyristors, the SGCT must have a snubber
circuit. The snubber circuit for the SGCT is comprised of a snubber resistor in
series with a snubber capacitor.
Figure 240 - SGCT and Snubber Circuit
In addition to the snubber circuit, a sharing resistor is connected in parallel with
the SGCT. The function of the sharing resistor is to ensure the voltage is shared
equally among the SGCTs when connected in series. SGCTs are connected in
series to increase the total reverse voltage blocking (PIV) capacity as seen by the
electrical circuit. A single SGCT has a PIV rating of 6.5 kV. At 4.16 kV, 2 SGCTs
must be connected in series to provide a net PIV of 13 kV to achieve the necessary
design margin. Similarly, three SGCTs must be connected in series at 6.6 kV.
The cooling requirements of the SGCT are achieved by placing the SGCT
between two liquid cooled chill blocks – one chill block on the anode and the
other chill block on the cathode. The force placed on the SGCTs differs with the
size of the device. A 63-mm device (1500A) requires 20 kN. The clamp assembly
on the right hand side of the inverter module generates these forces.
Sharing
Resistor
Snubber
Resistor
Snubber
Capacitor
Test
Point
SGCT
Chill
Block
Chill
Block