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Snubber resistors – Rockwell Automation 7000A PowerFlex Medium Voltage Drive (A-Frame) - Classic Control User Manual

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Component Definition and Maintenance

7000A-UM150F-EN-P –June 2013

7000 “A” Frame

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.
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 6.25 – Testing the Snubber Resistor