POWERFLEX 70 QUESTION

[oldnerd 3]

Maintenance called me to look at a PowerFlex 70 drive they said was on but was giving a ground error fault. When I arrived I found they had connected the drive backwards, 480 volt on the load side and motor leads on the line side. The drive was on, how? Had them to reverse the wiring and the drive ran normal much to my surprise why no damage?

I have never seen this before so I'm curious as to why there was no harm and why the drive was on.

[VFD Guy 16]

This is because of drive hardware. Not on purpose for this. But because it has flyback diodes on the output. This is how a drive handles regeneration. Think of when a motor is decelerating. It is a power source. The drive takes this ac waveform and then converts back to dc. This is when a brake resistor could be used to bleed the bus back down through the 7th igbt

https://images.app.goo.gl/mJVRktTy7REPpmj48

see if you can see this image  the right side  see the black diodes

 

Edited 6 August by VFD Guy

[ElectronGuru 84]

@VFD Guy is spot-on but I'm amazed the drive didn't burn up. The last time I saw this mis-wire on a PF525, it sounded like a canon blast when they closed the disconnect. PF70 must be a bit more robust, lol.