Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 329)

Component Definition and Maintenance 6-39
7000 “B” Frame 7000-UM150I-EN-P – June 2013
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 (SCR or SGCT). The purpose of the snubber circuit is to
reduce the dv/dt stress 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 the resistance.
There is a snubber circuit test point located under the heatsink within
the PowerCage. There is one test point for each device. To verify
the resistance, follow the procedures outlined in Chapter 4 –
Commissioning.
Measure resistance between
heatsink and test point
Snubber resistor test point
Figure 6.26 – Testing the Snubber Resistor