Dormant VFD Drive 2

[artgodfrey]

We have an A-B 1336 Plus II VFD that we have stored for about 2-3 years. Drive is rated at 150HP and has never been powered up. I have been cautioned about applying full line voltage to the drive, rather to apply a lower voltage and slowly increase the value. A Yaskawa FAQ article refers to this as "reforming." Anyone have details what to do for the A-B drive?

 

[Skogsgurra]

If you have no A-B information, a safe way of doing it is to hook up a Variac and a bridge rectifier (the 26 A types are good for this, make sure it can take the voltage). Use an isolation transformer to avoid problems. Increase the voltage in 20 percent steps over an extended time until full DC link voltage is reached. You can use a 100 - 200 W resistor at 50 or 100 ohms in series with the rectifier. Monitor the voltage drop over the resistor to see that leakage current does not increase. Be prepared to shut off if things get nasty. They seldom do. And - IMPORTANT - do not stand in front of the capacitors when doing this. I have seen one guy being hit by an exploding capacitor. The 450 V 10 000 uF bombs are no toys. Best thing is to keep the cabinet doors closed and bolted.

Regarding time: There used to be a graph with hours vs months, where hours indicated time required to go from zero to full voltage and months told how long the inverter had been out of service. Cannot find it any more. Take your time and use most of the day for it. Increase 20 percent every hour (five hours in all). That should be a safe procedure.

 

[jraef]

In case you couldn't figure it out from skog's reply, the problem is the capacitors. IF the electrolytic compond has degraded over time, it's inability to separate the conductive films in the caps will cause them to instantly short and vaporize with explosive force. He is absolutely right, I have personally witnessed the caps of a 40HP ABB VFD blow up with enough force to sent the enclosure cover flying about 50 yards. That happened when the VFD was energized at 0 degrees F, which causes a similar condition as age in the capacitors.

"Venditori de oleum-vipera non vigere excordis populi"

 

[artgodfrey]

We have continuous DC power supplies in our test area, where the drive will be used. Do we just apply the DC voltage to the DC buss, and if so, should we disconnect any components or pull any fuses?

 

[Marke]

Hello artgodfrey

If you connect across the DC bus, you will still be connecting across the capacitor bank. As recommended by others, it is best to form the capacitors first.

From the DC bus, you could use a large resistor in series so that there is a very slow charge up time.
When the capacitors have been formed, the slow charge should still be applied every time you power up, but can be a fraction of the time required when forming the capacitors.

There is a soft charge circuit built into the drive that operates when the AC is first applied.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[artgodfrey]

The inputs we received were helpful. Along the way I made another stab at finding the topic on the A-B website (their "knowledgebase") and got an exact match. I must have been lucky! I found an advisory that contained a good description of the re-forming process and why it is necessary. I also found that the drive is over 4 years old, never been used. Anyway, I think the problem is now solved. Thanks to all for the help.