3 phase Rotary Converter Build questions

[robertl]

Hi All,
I am just about ready in my new workshop to buy and start using the 3 phase equipment i will need for my business. The biggest of which will be the press brake rated at 12.5kw max.
There will be a few other units but smaller - around the 1 to 3kw rating range, so with that i am looking at building a 18kw Rotary Converter.
The build isn't the issue and the parts can be come by cheap enough to make it.
The main issue is my incoming supply, i have a single phase 3 wire / split phase supply (no 3 phase on the poles) coming from a center tapped transformer.
Now, should i build the 3 phase converter using L1 and L2 (so power 2 coils of the motor and only have to generate the 3rd) or should i build it as a single phase machine with L1 and Neutral?
There are many designs in USA showing the 110v split phase using L1 and L2 and taking the neutral around the converter so to speak. Not sure which way is the sensible way to do this, or the best?
Thanks in advance for your help
Robert

 

[Pete999]

Hi All,
I am just about ready in my new workshop to buy and start using the 3 phase equipment i will need for my business. The biggest of which will be the press brake rated at 12.5kw max.
There will be a few other units but smaller - around the 1 to 3kw rating range, so with that i am looking at building a 18kw Rotary Converter.
The build isn't the issue and the parts can be come by cheap enough to make it.
The main issue is my incoming supply, i have a single phase 3 wire / split phase supply (no 3 phase on the poles) coming from a center tapped transformer.
Now, should i build the 3 phase converter using L1 and L2 (so power 2 coils of the motor and only have to generate the 3rd) or should i build it as a single phase machine with L1 and Neutral?
There are many designs in USA showing the 110v split phase using L1 and L2 and taking the neutral around the converter so to speak. Not sure which way is the sensible way to do this, or the best?
Thanks in advance for your help
Robert

Use a motor compatible to your supply parameters to drive a purpose built 3 phase alternator wound to give you the required frequency.

 

[robertl]

Use a motor compatible to your supply parameters to drive a purpose built 3 phase alternator wound to give you the required frequency.

Wouldnt that cost more to run than an induction motor used as a converter? and ultimately cost more (possibly a lot more) to buy?

 

[Pete999]

Wouldnt that cost more to run than an induction motor used as a converter? and ultimately cost more (possibly a lot more) to buy?

Yes probably, but how do you intend to get an output from an Induction motor?
[automerge]1588775418[/automerge]

Wouldnt that cost more to run than an induction motor used as a converter? and ultimately cost more (possibly a lot more) to buy?

I used to install Voltage stabilizers in areas where the supply voltage was erratic, not sure of how the manufacturers got over the frequency control, but I sure the Manufacturers of these stabilizer could build you something to meet your requirements, at a cost of course, but, you don't get much these days for free, everything has a cost, just depends on how urgent your needs are.

 

[robertl]

Yes probably, but how do you intend to get an output from an Induction motor?

Well, by using a design to turn it into a Rotary Converter, same as this type of thing.

Transwave Rotary phase convertor 15.0 hp

MSR rotary phase convertor 15hp - Our TRANSWAVE Converter provides an artificial means by which a 3 phase motor can be operated from a single-phase supply thereby offering a cost-effective solution to this dilemma. In most instances, no modification to the machine is necessary. The Rotary...

www.scosarg.com

 

[Pete999]

Well, by using a design to turn it into a Rotary Converter, same as this type of thing.

Transwave Rotary phase convertor 15.0 hp

MSR rotary phase convertor 15hp - Our TRANSWAVE Converter provides an artificial means by which a 3 phase motor can be operated from a single-phase supply thereby offering a cost-effective solution to this dilemma. In most instances, no modification to the machine is necessary. The Rotary...

www.scosarg.com

Yes probably, but how do you intend to get an output from an Induction motor?
[automerge]1588775418[/automerge]

I used to install Voltage stabilizers in areas where the supply voltage was erratic, not sure of how the manufacturers got over the frequency control, but I sure the Manufacturers of these stabilizer could build you something to meet your requirements, at a cost of course, but, you don't get much these days for free, everything has a cost, just depends on how urgent your needs are.

The company I bought my VS from is "Watford Controls" sorry have no more details google will be your friend on this

 

[pc1966]

The main issue is my incoming supply, i have a single phase 3 wire / split phase supply (no 3 phase on the poles) coming from a center tapped transformer.

What voltages do you have?
Is it 230-0-230 so in effect you have access to 460V single-phase?
What is the total current you have available?
18kVA is 78A at 230V (more if it is 18kW with a typical motor's phase angle) and you would have to have a soft-start arrangement on that to avoid causing problems on a 100A supply.

 

[Lucien Nunes]

Re the difference between USA and UK practice, on a standard 1-to-3 phase converter the output voltage line-line is the same as the single-phase input voltage. Therefore, if the input were 120V line-neutral, the output would be 120V line-line, which is not a standard 3-phase motor voltage. By using the 240V between the two lines of the split phase supply, the output is 240V line-line for which standard 3-phase motors are suitable. Also, input currents get quite unwieldy on 120V. For example at 0.8pf, 18kW would take 188 amps and leave next to nothing on that leg of a 200A 120-0-120V service. In contrast, 94A on each leg is much more practical.

It would also help you with your 18kW load to work between the two lines at 460V, taking only 49A, however all the motors and the converter would need to be 480V rated. These are standard in the US, but it would cause you a headache with UK motors. In a perfect world, you might stumble across a suitable single-phase autotransformer that would step your 460V down to 400.

should i build the 3 phase converter using L1 and L2 (so power 2 coils of the motor and only have to generate the 3rd) or should i build it as a single phase machine with L1 and Neutral?

This isn't quite how it works. If you take your power from two lines of a split-phase supply, or even two lines of a 3-phase supply ignoring the neutral, it's still single-phase. The circuit consists of two wires with a voltage between them and that is all, as the phase relationship w.r.t. neutral is not relevant. The working principle of the converter is exactly the same as when supplied from line-neutral; in either case it only has to produce the 'third wire' with the right phase relationship to make it 3-phase. What you cannot do is use two lines of a split-phase supply and the neutral to make a centre-grounded star output, since the phasing of the neutral will be wrong (it's correct for edge-grounded, which is a standard US power configuration.)