Scr anode-to-cathode resistance – Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) Commissioning - ForGe Control User Manual
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Rockwell Automation Publication 7000-IN012B-EN-P - June 2014
Chapter 4 Commissioning the Drive
SCR Anode-to-Cathode Resistance
Performing an Anode-to-Cathode resistance test verifies the integrity of the
SCR. Unlike the SGCT, 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 39
).
Figure 39 - Anode-to-cathode test
A good SCR and circuit should read between 22...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 publication
for detailed instructions on how to replace the SCR assembly.
Resistance value
between two heat
sinks is Anode-to-
Cathode resistance