Scr anode-to-cathode resistance – Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - ForGe Control User Manual
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Rockwell Automation Publication 7000-UM202B-EN-P - June 2014
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Component Definition and Maintenance
Chapter 3
SCR Anode-to-Cathode Resistance
Performing an Anode-to-Cathode resistance test verifies the integrity of the
SCR. The SCR uses the snubber circuit to power the self-powered gate driver
boards. The resistance measurement taken across each SCR should be constant;
an inconsistent value may indicate a damaged sharing resistor, self-powered gate
driver board or SCR.
Using an ohmmeter, measure the anode-to-cathode resistance across each SCR in
the rectifier bridge, while looking for similar resistance values across each device.
Easy access from the anode-to-cathode is available by going from heat sink-to-
heat sink (
Figure 74 - Anode-to-cathode test
A good SCR and circuit should read between 22 and 24 kΩ.
An SCR that has failed from anode-to-cathode will commonly produce a
resistance value of 0 for a shorted device or
∞
Ω for an opened device. Unlike the
SGCT, it is highly irregular for an SCR to have a partially shorted device. If an
SCR is found to be out of tolerance, refer to
for detailed instructions on
how to replace the SCR assembly.
Resistance value
between two heat
sinks is Anode-to-
Cathode resistance