motor efficiency: single phase vs. 3 phase vfd

[MannyM]

You can run a fare amount of single phase motors on one three phase supplied VSD. With the VSD you can control the speed at start-up, if you have an intelligent system behind it, but this will be batch control for that set of motors. Soft starters, in my view, is an extension of a VSD, if you can control the individual drives without batch control.

 

[DickDV]

With the goal being energy savings without a major initial capital outlay, it seems to me that, since there are multiple fans in each greenhouse, why not keep the present single phase constant speed motors and control how many fans are operating, based in a temperature setpoint.

All this requires is a bit more brains in the temperature control system and the result would be significant energy savings, maybe not exactly equal to variable speed but much faster in payback and much simpler to troubleshoot.

The other options seem like so much front-loaded risk for the expected long-term return as to be not worth it.

 

[Gil47]

You can run a fare amount of single phase motors on one three phase supplied VSD.

Manny I Know of no way that a single phase motor will run on a three phase VSD , (or VFD to the Americans)

3 phase motors are required for a VSD / VFD.

 

[MannyM]

Still, the fundamental aspect stays the cost of running the manufacturing process. Doing it hard wired might be a solution, but cost effective, even compared to a small simple PLC controlled system, I don't think so.

With an intelligent system running the plant, with simple and fairly cheap products, the possibilities of controlling and measuring your product quality should be the main concern, because that is what keeps production going. And the money coming in.

 

[MannyM]

Gil47, sure it can be done.

I have said that a number of single phase motors can run of one three phase VSD. The load balance is important between the phases supplied via the VSD to the load. If you have three exact drives exerting, in a tolerane, the same load, then surely it can be driven from one three phase VSD. You need to make provision on the VSD kW rating to drive the required load connected.

The draw back is that the speeds of all those connected drives to the VSD, will be controlled by one single analogue from the PLC, at this stage.

The advantage is via a PLC, is to switch these drives according to the requirements and demand on each phase, thereby driving multiple single phase drives from one three phase VSD.

 

[leitmotif]

Gil47, sure it can be done.

I have said that a number of single phase motors can run of one three phase VSD. The load balance is important between the phases supplied via the VSD to the load. If you have three exact drives exerting, in a tolerane, the same load, then surely it can be driven from one three phase VSD. You need to make provision on the VSD kW rating to drive the required load connected.

The draw back is that the speeds of all those connected drives to the VSD, will be controlled by one single analogue from the PLC, at this stage.

The advantage is via a PLC, is to switch these drives according to the requirements and demand on each phase, thereby driving multiple single phase drives from one three phase VSD.

Whenever I say NEVER with anything electrical or I think I have if foolproof someone proves me wrong.

I will not say you cannot drive 3 single phase motors off a VFD but because they are often designed for a single frequency ie a match of inductance in windings vs the start / run capacitor I think you would have difficulty. Variable frequency wouldl throw these values off (impedance matching -- correct term?)and screw up the designed phase shift.

Try it out and let us know how well it works. Also let us know what kind of motors used.

Dan Bentler

 

[MannyM]

It works. From a mathematical, engineering & practical view point the VSD was designed to do this.

I have seen & tested this in industry, although it will suite lower load & closely matched equipment applications, preferably. Higher load applications tends to distort some measuring values by the VSD.

Tolerance will then play a greater factor. The frequency supplied should be exact between any phase. That is why you pay your utility company. Impedance changes with load and frequency. Impedance matching is done to have the maximum energey transfer between any one or more electrical systems.

 

[Stationmaster]

Manny,

I don't think the difficulty is expected in the VSD/VFD as long as the phases are load-balanced. I think the difficulty is expected with the single phase MOTORS being run at frequencies OTHER than the frequency for which they were designed.

Since you "have seen this tested in industry" could you please provide some more info?

What type and HP motors did you use?

Was there a frequency range limitation?

Stationmaster

 

[MannyM]

Stationmaster,

You select the drives designed for the process and application.

Seen & tested in a project. I have done this. Nine drives with the same functionality, and in a tolerance load wise, with closely the same frequency supplied per phase. That is what the VSD is supposed to supply, the same frequency to either phase in tolerance. It works and can be done.

Based in RSA, we don't talk about HP anymore. We use kW. Although we are in Africa, by the way the place to be, horse power is something of the past. We are in a new area. In Africa we still use HP, but only to cart vegies in the rural areas, using horses.

Frequency limitations are subject to your utility supplier's accuracy by generating the frequency required in the tolerance.

 

[Stationmaster]

Stationmaster,

You select the drives designed for the process and application.

Seen & tested in a project. I have done this. Nine drives with the same functionality, and in a tolerance load wise, with closely the same frequency supplied per phase. That is what the VSD is supposed to supply, the same frequency to either phase in tolerance. It works and can be done.

Based in RSA, we don't talk about HP anymore. We use kW. Although we are in Africa, by the way the place to be, horse power is something of the past. We are in a new area. In Africa we still use HP, but only to cart vegies in the rural areas, using horses.

Frequency limitations are subject to your utility supplier's accuracy by generating the frequency required in the tolerance.

Manny,

What KW motors did you use?

Exactly what kind of motors did you use?

How much were you able to lower the frequency output by the VFD below the frequency rating of the motor?

Stationmaster

 

[leitmotif]

Whenever I say NEVER with anything electrical or I think I have if foolproof someone proves me wrong.

I will not say you cannot drive 3 single phase motors off a VFD but because they are often designed for a single frequency ie a match of inductance in windings vs the start / run capacitor I think you would have difficulty. Variable frequency wouldl throw these values off (impedance matching -- correct term?)and screw up the designed phase shift.

Try it out and let us know how well it works. Also let us know what kind of motors used. Dan Bentler

I still would like to know what type motors were used
ALSO
If he merely saw a demo
OR if he has done it himself

Dan Bentler

 

[leitmotif]

One more thing I keep forgetting is the
centrifugal starting switches.
If you run the motor at low speed then you are running on starting winding or in "start mode" for extended periods.
Dont think this will give long motor life.

Dan Bentler

 

[Stationmaster]

One more thing I keep forgetting is the
centrifugal starting switches.
If you run the motor at low speed then you are running on starting winding or in "start mode" for extended periods.
Dont think this will give long motor life.

Dan Bentler

The motor start winding may be able to handle it, but the start capacitor is gonna go BOOM. They are engineered for short duration duty cycles. That's why I keep asking him how much he was able to vary the frequency. So far he has been elusive, pretending to think I'm asking about the "tolerance" of the supply from the utility company. Also, after mocking me for using the term "HP" instead of "KW", he ALSO avoided answering for KW. I realize there is some "language barrier" difficulty here, but I don't think that's the ONLY difficulty we're dealing with.

Stationmaster

 

[Steve Bailey]

Do a search for MannyM's posts and take a look at the recent ones. He certainly doesn't add much to the discussion in any of the threads he participates in. I'm beginning to think he just likes to stir things up.

 

[Stationmaster]

Do a search for MannyM's posts and take a look at the recent ones. He certainly doesn't add much to the discussion in any of the threads he participates in. I'm beginning to think he just likes to stir things up.

You're a-preachin' to choir there Steve-o.....

I was just trying to give him a chance to back up his "claims".

Stationmaster