Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 196)

Commissioning 4-37
7000 “B” Frame 7000-UM150I-EN-P – June 2013
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:
Test points for gate to cathode
resistance on Phoenix connector.
Disconnect SCR Phoenix
connector from board.
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.