Ross Hill VFD voltage waveform

[schell44]

We have an 8000 HP Ross Hill 12 pulse drive at one of our sites and recorded the attached waveform at a 120 volt receptacle. There is a 1000 kVA xfmr stepping down to 480 volt and a 30 kVA stepping down to 120/208 volt before the receptacle. With the thyristor front-end, notching is expected but I notice that there are no notches at 120 and 240 degrees. Is this normal?

 

[davidbeach]

Looks like commutation notching from the drive is showing up on the 120V.