Riddle me this drive gurus...

[OkiePC]

Why can't I walk up to brand x VFD, punch a few keys on the keypad and perform a megohmeter test? Doesn't the VFD contain the necessary hardware to pull this off with modest accuracy?

I know of some old Telemechanique drives we had that do a test when you enable them whether you want them to or not. There was no parameter to disable/enable this feature which lead to faults at times.

By why can't I get a meghohms test at up to 600V and a readout plus or minus a few k?

 

[RussB]

And I guess you would want parameters to tell the drive how far it was from the motor and what kind of wire was used to connect the two, and throw in there how many connections there are too.

 

[bce123]

By why can't I get a meghohms test at up to 600V and a readout plus or minus a few k?

I put this on my list for Santa!!! Merry Christmas!!!

 

[DickDV]

While that is an interesting question, Okie, my first reaction is that a 600VDC megger test is about worthless on a 460VAC motor. As far as I am concerned, meggering an inverter duty motor at anything less than 1000VDC is not going to tell you much.

In some ways, you could say that a 460V VFD is CONTINUOUSLY meggering the motor since the ground fault and short circuit fault is super fast and is being conducted with every string of PWM pulses.

I suppose it is for that reason that occasionally you encounter motors that megger ok but the drive keeps faulting on them. Eventually, the drive is proven correct and the motor fails the rest of the way so a megger can see it.

 

[JRW]

A cheap plug for siemens

I can't speak for some other brands but Siemens S 120 will do this

It's called a motor ground test. It will also do encoder direction tests etc

Merry Christmas bce123

Call it a stocking stuffer

 

[Gene Bond]

<snip>

In some ways, you could say that a 460V VFD is CONTINUOUSLY meggering the motor since the ground fault and short circuit fault is super fast and is being conducted with every string of PWM pulses.

I suppose it is for that reason that occasionally you encounter motors that megger ok but the drive keeps faulting on them. Eventually, the drive is proven correct and the motor fails the rest of the way so a megger can see it.

Amen, Brother!

Fighting one right now

300hp pump works fine for 2 hours or so @ Full Load. Then trips on Over Current. Old Drive tripped on Ground Fault. Had me check out drive #3, 'since it has to be another bad drive' ... tripped in 1.5 hours. I threw up my hands and said 'bad motor'. They called in the motor experts, and I warned them to heat the motor up to test... They couldn't find a problem (probably didn't heat it up). So, drive #4 gets connected... guess what? yep, it tripped

I'm waiting for the 'experts' to pull the motor and find the problem now!