Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive - Air-Cooled (A Frame) - Manual (Page 271)

Component Definition and Maintenance 5-29
7000 “A” Frame 7000A-RM001A-EN-P – January 2011
Snubber Resistors Snubber resistors are connected in series with the snubber capacitors.
Together they form a simple RC snubber that is connected across each
thyristor (SGCT). The purpose of the snubber circuit is to reduce the
voltage stress (dv/dt and peak) on the thyristors and to reduce the
switching losses. The snubber resistors are connected as sets of various
wire-wound resistors connected in parallel. The number of resistors in
parallel depends on the type of the thyristor and the configuration and
frame size of the drive.
Testing Snubber Resistors
Access to the snubber resistor is not required to test its resistance.
Located within the PowerCage under the heatsink is a snubber circuit test
point. For each device, there is one test point. To verify the resistance,
follow the procedures outlined in Chapter 4 – Commissioning.
Measure resistance between
heatsink and test point.
Snubber resistor test point
Figure 5.22 – Testing the Snubber Resistor