High Horse Power Drives IGBT Fault

1500 KW, 1580 Amps, VFD Tripped, THE Pressure is ON!

When big Drives are gone, every second is important, the production line is stopped and nobody can do anything in whole Cement factory.

In this article I’m going to share an experience about a variable frequency drive for ID fan application in Cement industry and probable cause inside the VFD.

The unit was MX multi-pro 6C1200/1500, 690V, 1580A liquid cooled,12 pulse, from Schneider Electric

Trip was an IGBT fault in 5 Hz during acceleration time. (first photo)

Where will you start?

First step is to make sure the problem is inside the VFD, or something after UVW (Motor, Motor Cables)

Possibilities inside the VFD:

1-?????IGBT

2-?????CT (current transformers)

3-?????Gate Drivers

4-?????Measuring Board

*After disconnecting the unit from the main power and waiting for all capacitors to fully discharged (there is a LED on the unit to show the approximate level of DC voltage, it must be completely off, or if there is external +24V, the keypad monitors the DC level), first start with Ohmic Resistance test, between UVW and DC busbar.

If all IGBTs are the same, it shows they are good. If not, follow the Phase with problem and do more accurate test on those specific IGBTs.

*Current Transformers, might be the cause as well. Normally accessible from the back of VFD. If one CT is defected, it will send either nothing or wrong dc level to Measuring Board.

*Gate drivers are triggering the IGBTs and if defected there would be unbalance in PWM output and might cause IGBT fault.

*If measuring board sends wrong data to Power board, it will cause the fault, even all number 1-3 is fine, conductive pollution or high operating temperature may defect the MB, there are LEDs on that board to indicate more data.

In this case measuring board was defected, and with replacing that, the unit was ready again (last photo) you can find much more data about 1.5 MW VFD, in the photos and IGBT model, used in this unit.

Please feel free to add your ideas and experiences in comments and this article/photos are free for everyone to use or share.

Good Luck