VFD Input Overload

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bdogu

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How to protect vfd input bridge from overload ? it has built-in overload and short circuit protection for the motor at the load side. Manufacturer recommends fuses in the manuals to place ahead of vfd. Is there anyone who knows if the fuses-breakers are just for line side short-circuit protection or includes overload for vfd input as well.
Thanks.
 
The VFD is generally protected from overloads the same way a motor starter is. Often the choice of input fuses and or circuit breakers is mostly about getting an appropriate sccr.
 
bdogu said:
How to protect vfd input bridge from overload ? it has built-in overload and short circuit protection for the motor at the load side. Manufacturer recommends fuses in the manuals to place ahead of vfd. Is there anyone who knows if the fuses-breakers are just for line side short-circuit protection or includes overload for vfd input as well.
Thanks.
Click to expand...
If it's any help we used semiconductor fuses. Mostly Ferraz.
 
petersonra said:
Hard to know what is common in Turkey. Best bet is to just follow the instructions in the manual.
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Actually I went to Turkey for a few months on a drives project. Part of it was a zinc mill in Kayseri. It was a bit of a challenge.
 
Unless you lost an incoming line it shouldn't overload if the output has overload protection.

Lose an incoming line and it still runs as single phase in three phase out - but with increased current on the remaining two lines and is a reason you need to oversize a drive if you are using it as a single to three phase converter.

How fast you want it to respond, assuming it is operating near full rating, would be a factor in determining how to select an overcurrent device.

If a portion of the front end rectifier fails it is toast anyway. All the fuses they suggest you use do is possibly change how spectacular that failure may be to witness.

Cheap lower output rating drives, probably not worth the extra $$ for such fuses, unless maybe available fault current is high enough you want lessen the significance of the arc flash that might occur.
 
kwired said:
Unless you lost an incoming line it shouldn't overload if the output has overload protection.

Lose an incoming line and it still runs as single phase in three phase out - but with increased current on the remaining two lines and is a reason you need to oversize a drive if you are using it as a single to three phase converter.

How fast you want it to respond, assuming it is operating near full rating, would be a factor in determining how to select an overcurrent device.

If a portion of the front end rectifier fails it is toast anyway. All the fuses they suggest you use do is possibly change how spectacular that failure may be to witness.

Cheap lower output rating drives, probably not worth the extra $$ for such fuses, unless maybe available fault current is high enough you want lessen the significance of the arc flash that might occur.
Click to expand...
Most drives will shutdown on input overload as well. the fuses or circuit breakers are just for short circuit protection. Most of the cheaper foreign drives seem to require fast blow type T fuses for use in the USA, while the better ones can usually use some kind of circuit breaker.
 
petersonra said:
Most drives will shutdown on input overload as well. the fuses or circuit breakers are just for short circuit protection. Most of the cheaper foreign drives seem to require fast blow type T fuses for use in the USA, while the better ones can usually use some kind of circuit breaker.
Click to expand...
I'd guess most small cheap drives won't trip if input is overloaded. If DC bus drops too low if you lost an incoming line might get a low bus voltage fault being about the next best thing that would protect it. If you lost part of the rectifier it is toast anyway.
 
You fuse/breaker according to what the manufacturer recommends. In the event of a short on the output side this protects the VFD throughout.

The big problem is available short circuit current. Generally if the transformer kVA is more than about 10 times the VFD kVA, watch out. This is just a rule of thumb though. The obvious solution is increase %Z. So line reactors of about 3% work good over a wide range with only a 3% voltage drop. Otherwise check AIC and if that can’t be fixed semiconductor fuses are the only option. Avoid this if you can. Delivery times are ridiculous, they tend to be non-interchangeable among brands, and thus they are very expensive. Recently since UL started testing AIC has greatly improved.
 
Some drives used to be built so you could repair and maintain them.

IMHO diodes/rectifiers fail because the caps need to be replaced and/or lightening strikes/power surges. Used to be easy to buy a higher voltage/amperage diode and a higher temperature rated/better quality capacitor. These days they expect you to trash the drive and buy a new one. If it was up to me I'd pay the extra money for a drive that used film caps. But I have only seen that in new chillers.

Fuses and MOV's might help with lightening and surges but they won't with caps. Some drives do have inrush limiting protection but I believe it is "out of the circuit"once the drive is up and running. Most of my drives run 24/7/365.
 
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