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Rockwell Automation Publication 7000L-UM301F-EN-P - March 2020
Chapter 4
Commissioning
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 chill block to
chill block as shown in
:
Figure 186 - Anode-to-cathode Test
A good SCR and circuit should read between 22 kΩ 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
Maintenance on page 265 (Chapter 5)
for detailed instructions on how to
replace the SCR assembly.
SCR Sharing Resistance Test
To test the sharing resistor of an SCR module, disconnect the 2-pole plug of the
self-powered gate driver board labeled SHARING and SNUBBER on the circuit
board. The red wire of the plug is the sharing resistor. Measure the resistance
between the red wire of the plug and the chill block to the left. A value of 80
k-ohms indicates a healthy sharing resistor.
Anode Chill Block
Cathode Chill Block
SCR
