Rockwell Automation 1557 MEDIUM VOLTAGE AC DRIVE - Manual (Page 252)

10-10 TROUBLESHOOTING
1557-UM050F-EN-P – June 2013
Power Semiconductor Testing
If you suspect that a problem may exist with a power semiconductor follow the steps below to help identify
a suspicious device.
WARNING: Before attempting any work, verify the system has been
locked out and tested to have no potential.
1. Using an ohmmeter, measure the anode to cathode, anode to gate, and cathode to gate. The
resistance in circuit will differ from out of circuit where other assemblies provide a parallel path.
DEVICE TEST POINTS EXPECTED MEASUREMENT
GTO
ANODE TO CATHODE
ANODE TO GATE
CATHODE TO GATE
10.3K

10.3K

10

SCR
ANODE TO CATHODE
ANODE TO GATE
CATHODE TO GATE
23.5K

23.5K

12

DIODE ANODE TO CATHODE 10

Please note the actual resistance measurement will depend upon the device and the ohmmeter used. It is
not possible to accurately measure unclamped semiconductor devices.
2. If a short is found isolate the device on the stack and verify that indeed the device is faulty, only then
proceed with removing the stack from the drive.
3. If the semiconductor device is not suspected of being faulty, test other surrounding components, or
call your local RA/AB service representative for assistance.
Thyristor Clamps
Thyristor clamps are used to maintain the required contact force for the power semi-conductors. A pre-
calibrated force is exerted on the contact area of the semi-conductors, The force is exerted by a pre-set
load in the stack of disc springs at the head of the clamp. There are three different clamps used in each
1557 drive:
SNUBBER DIODE Quantity of clamps voltage dependent.
MACHINE SIDE CONVERTER STACK Quantity of clamps = 6
LINE SIDE CONVERTER STACK Quantity of clamps = 3