Motor Regeneration Inverter Damage?

[tommytoop]

Hello,

Can anybody tell me the implications of turning on an already running inverter driven 3 phase ac induction motor i.e i'm designing a bypass system for the invertor and want to know the implications of switching it from bypass whilst it is running!
Can this cause damage to the Inverter?

My application is a large oven circulation fan 415v 4kw, 1750 rpm medium load.

 

[CJCPE]

Yes, this can cause damage to the inverter. Most inverters have regeneration protection, but the rotating field still in the motor and out of phase with the inverter can damage the inverter. Many inverters have a feature that will start a rotating motor "on the fly," but the field in a previously energized motor must be allowed to decay before connecting to the motor.

It is possible to synchronize an inverter with the power line and do a closed transition, but that is difficult to do and rarely considered to be worthwhile.

 

[cbarn24050]

For a tiny inverter like that its not worth trying. Breaking/making the output connections to a running inverter is not recomended.

 

[jraef]

Do a search on the term "VFD synchronous transfer" and you will see that it is possible, but very few VFD manufacturers offer it and it is very very tricky (which means expensive as well). Open transition is probably best for the VFD, but what is it about your application that makes you feel a closed transition is necessary on a fan?

JRaef.com
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[waross]

Do some Goodling on fast transition Automatic Transfer Switches. Some of the new ATSs transfer from generator to line so fast that they must wait until the standby power is in synchronism with the utility power to avoid damage to motors and current transients. If you can aquire or copy one of their synchronism check circuits, it may be able to identify safe windows of oppertunity to transfer from the invertor to the mains or vice versa.
The principal is to assume that the frequencys of both sources are not exactly equal and to wait until they are in sync. before making the transfer. It is a lot easier than trying to force the invertor frequency to sync. with the mains frequency.
Remember the story of the little boy shouting
"Shoo, Shoo, ##### off!" to a swarm of flies.
A passing clergyman took exception.
"Little boy. You shouldn't use such language. It is not nice and it is not nescessary. Just say 'Shoo, shoo!' The flies will #### off be themselves."
Don't try to force an invertor into sync. Just wait 20 or 30 seconds and it will go into sync. by itself.
respectfully

 

[LionelHutz]

Most VFD's have a catch on the fly feature so just cut the power to the motor and let it coast a few seconds so the field has decayed and the motor is generating little terminal voltage then connect the VFD and give it a start command.