Voltage Transients Tripping VFDs 1

[bytebyte]

I have a customer that's been complaining that their VFD's been tripping offline due to voltage spikes, and it was determined that the spikes or transients were from the switching online of a nearby capacitor bank. What are the different options the customer have to protect his VFD's from voltage transients? I know customers should install a UPS to protect their computers, so should they install a UPS to protect their VFDs? Thanks.

 

[ScottyUK]

Have a read of thread237-244719 then if there are any further questions post 'em here.


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If we learn from our mistakes I'm getting a great education!

 

[bytebyte]

Thanks, ScottyUK... the thread was very informative. However, will installing a UPS upstream of the motors protect the motors from tripping on voltage spikes?

 

[LionelHutz]

It has to be a 3-phase UPS sized to run the motors connected to these VFDs which could become very pricy.

But then, a UPS of this type is more or less a VFD running at a fixed 60Hz output so the over-voltage transients could just begin to trip the UPS instead....

 

[ScottyUK]

If you have major power quality problems then normally the utility would be expected to take reasonable steps to reduce the disturbance they are causing to the system. On the other hand if you are causing them yourself with your own PFC caps then the utility probably won't care too much unless the transient is causing a disturbance at the point of common coupling. If the origin is your own PFC system then the chances are the transients are relatively low energy and could probably be controlled using a line reactor and MOVs to reduce both the amplitude and total energy which gets through to the drive. If something happening out on the transmission system is causing this then the energy levels involved could be several orders of magnitude larger and much more difficult to suppress.

You really need to find out more about the switching transients so you can design a solution - a storage 'scope with a decent single-shot bandwidth allied with a reasonably high bandwidth isolation probe would allow you to see what is happening safely.

A UPS seems excessive to me.


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If we learn from our mistakes I'm getting a great education!