Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 243)

4-38 Commissioning
7000L-UM300I-EN-P – June 2013 7000 “C” Frame
Gate to Cathode Resistance
One test that can be performed on SCRs that cannot be performed on
SGCTs is a Gate to Cathode Resistance Test. Performing a Gate to
Cathode resistance measurement will identify damage to a SCR by
revealing either an open or shorted gate to cathode connection. To
test an SCR from gate to cathode, disconnect the SCR gate leads from
the self powered gate driver board and measure the gate to cathode
resistance on the SCR firing card Phoenix connector as shown below:
Disconnect SCR 2-pole
connector from board
Test points for gate to cathode
resistance on 2-pole connector
Disconnect SCR 2-pole
connector from board
Test points for gate to cathode
resistance on 2-pole connector
Figure 4.10 – SCR Gate to Cathode Test
The resistance value from gate to cathode should be between 10 Ω to
20 Ω. A value close to 0 Ω indicates that there is an internal short in
the SCR. An extremely high value indicates that the gate connection
in the device has broken.
If a Gate to Cathode test reveals a damaged SCR, a detailed
replacement procedure is located in Chapter 6 – Component
Definition and Maintenance.