ECN Forum Forums General Topics of the Trade General Discussion Area VFD'S

A little more info would help, VFD make and model, distance between drive and motor, power supply configuration?

sparky*62,
In addition to the good advice already posted:
Check for possible ground faults with connected devices: motor, speed pot/input, switches or remote displays, etc.
Having said that, this sounds like an overvoltage problem on the DC bus. If you have a large overrunning load, (flywheel, large fan, etc) or anything driven with enough mass to pump too much emf back into the DC bus during decel this could be a problem. Most drives should be able to automatically handle this, by switching into a coast mode---the drive disconnects electrically from the motor and waits for the DC bus voltage level to drop before continuing the decel mode---or the drive should trip on a DC bus overvoltage. You might try changing the stop parameter to "coast to stop" if practical to see if the problem is linked to this.
Is this a fairly new "name brand" drive? I have had similar problems with some of the cheaper entries into the small hp drive market.

Len

To combine a few threads......

This thang aint one of them dang chiner speshuls is it?

I smell extended Overvoltage situations too!

This, plus the possibility of maybe the Caps are Polarized Electrolytics, would be sure to cause ruptures.

Are the Caps marked with any Polarity identifiers (aka "+" and / or "-", or listed as X00 VDC).

Polarized Caps continuously subjected to AC would fail (unless there's something I do not know of new Caps???). The higher the Hz, the easier to fail.

Scott35 S.E.T.

My first question would be distance from drive to motor. If the motor is not inverter duty rated and the distance is more than 50 ft. I would look at putting a line reactor or a motor terminator on the circuit. Allen Bradley has a good white paper to describe this: http://www.ab.com/drives/techpapers/InstallationConsiderations01.pdf. If it is a brake problem, most VFDs will give a DC bus overvoltage fault instead of blowing the cap. Also, another problem similar to this that I came across is how the motor control circuit stops the drive. I have seen many times a contactor used to disconnect power to the drive. If the contactor is on the ouptut of the drive, it creates problems and I have lost 7-8 drives that way. You must open the drive enable before disconnecting output power (at least on the AB and Mitsubishi drives I've worked on).

bchase,
The link you posted does not work.

Hey Nick try this link
http://www.ab.com/drives/techpapers/InstallationConsiderations01.pdf

Thanks for all the replies.The drive is a AB 160 series using xhhw cable.I did check the ground connections.My problem was the line side reactor it was sending a voltage spike and blowing the MOV's.How it was damaged is still a mystery.

I've seen a brand new one blow. We replaced it without any changes and it's working fine to this day! Probably made cheap.