Rockwell Automation 7000 PowerFlex Medium Voltage (B Frame) Commissioning - ForGe (PanelView 550) User Manual
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Rockwell Automation Publication 7000-IN006B-EN-P - May 2013
Chapter 5 Commissioning the Drive
Using an ohmmeter, measure the anode-to-cathode resistance of each SGCT in
the inverter bridge, looking for similar resistance values across each device. Easy
access from the anode-to-cathode is available by going from heatsink-to-heatsink
as shown in
Figure 33 - Anode-to-Cathode resistance test points
An SGCT when not gated on is an open circuit. A healthy device resistance value
should be close to the value of the sharing resistor, however due to parallel
resistances in the firing card, the resistance value will be slightly lower.
Example: The resistance across the anode-to-cathode of a 800 amp device may be
57 kΩ even though the sharing resistor is 80 kΩ.
You can detect SGCT failures by measuring a lower than normal resistance value;
one device in the converter may read 15 kΩ whereas the rest of the devices in the
converter measure close to 60 kΩ. This indicates a partially shorted device. A
fully shorted device will read closer to 0 Ω and is easily identified. If the SGCT is
out of tolerance, refer to the PowerFlex 7000 ‘B’ Frame User Manual’s
“Component Definition and Maintenance” section for detailed instructions on
how to replace the SGCT assembly.
Damage to a sharing resistor is detectable if the SGCT is replaced and the anode-
to-cathode resistance remains abnormal. If the resistor is found to be out of
tolerance, refer to the PowerFlex 7000 ‘B’ Frame User Manual’s “Component
Definition and Maintenance” section for detailed instructions on how to replace
the snubber/sharing resistor assembly.
Measure anode-to-cathode resistance
by testing from heatsink-to-heatsink.