Using a VFD to Power a Bus Duct

[jazer]

I had an engineer make a suggestion to solve a problem my facility is having. We want 120 volt, 50 hertz bus duct installed. He suggested instead of a typical motor powered MG set, that we use VFDs to change the frequency of standard 120 volt 60 hertz down to 50 hertz before it powers the new busway. I have never heard of this before. Was wondering if anyone has any experience with it?

Also, we would like these busways to be 3 phase 208 with a nuetral of course. Would the nuetral need to be run through the VFD as well? I have never seen or heard of anything like this, so any help is appreciated.

 

[iwire]

I think a VFD would be the same as a separately derived system so the supply side neutral has no relationship to the output conductors. I think the VFD would have to produce a neutral.

 

[Joethemechanic]

I had an engineer make a suggestion to solve a problem my facility is having. We want 120 volt, 50 hertz bus duct installed. He suggested instead of a typical motor powered MG set, that we use VFDs to change the frequency of standard 120 volt 60 hertz down to 50 hertz before it powers the new busway. I have never heard of this before. Was wondering if anyone has any experience with it?

Also, we would like these busways to be 3 phase 208 with a nuetral of course. Would the nuetral need to be run through the VFD as well? I have never seen or heard of anything like this, so any help is appreciated.

I would not see it being a problem, provided the waveform of the VFD's output was suitable for the loads that you intend to power off this bus. You may need to have a transformer on the load side of the VFD in order to establish a neutral.

 

[jim dungar]

A motor VFD will not have a neutral on it's output.

VFD's do not like having loads added to them once they are up and running (its called slamming), so special sizing might be required.

 

[rbalex]

Depending on the load size, rather than a conventional M-G set, I prefer a rotary frequency converter. They are generally more forgiving.

 

[jazer]

We are looking at a rough total of 750 amps when at full testing capacity. The idea was to have seperate 100 amp rated busways each with its own VFD. That way if one failed, it would be easily interchangeable while avoiding a single point of failure like an MG set.

 

[Jraef]

We are looking at a rough total of 750 amps when at full testing capacity. The idea was to have seperate 100 amp rated busways each with its own VFD. That way if one failed, it would be easily interchangeable while avoiding a single point of failure like an MG set.

No, as Jim Dungar said, a VFD is not suited for this kind of application. A VFD is designed to run one motor, or maybe even a group of motors, but all at exactly the same time with the VFD being the On-Off control point. Using it to feed a distribution system implies that you will have different points of use, all coming on and off at will. The VFD output transistors would die in short order, they are not designed for having loads turned on and off on their output.

This is a project for an M-G (Motor - Generator) set. But 750A at 120V, are you sure you have that much available? That's pretty extreme.

 

[jazer]

not sure what you mean by have that much available? The building has a 3000 amp service. We are at about 800 right now. We will probably have to put in two MGs.

If I have a 100 amp fused and rated busway with say a 60 amp steady load, adding or removing some of that load at say 2 amps at a time would be detrimental to a VFD?

 

[zbang]

If you don't want a rotating machine of some form, then look for a "solid state/static frequency converter". Not sure you'll find one that big. You could also inquire of the larger UPS manufacturers.

 

[jazer]

been looking at solid state freq converters from Visicomm. Seems to be the ticket. I only need to feed about 100 amps at a time, so a 40 KVA will cover it with a small footprint.

 

[rbalex]

Visicomm markets both solid state and rotary AND offers to help determine which is best for your application. At this point, I would take them up on their offer.

 

[jazer]

Thank you everyone for your help.

 

[Besoeker]

If you don't want a rotating machine of some form, then look for a "solid state/static frequency converter". Not sure you'll find one that big. You could also inquire of the larger UPS manufacturers.

That would be my preferred route.