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Rotary Phase Converter ( I Know Prob Done To Death!)


JonAW

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Hi Guys,

 

I'm looking at building a rotary phase converter for my own use. I have a 100Amp 230v single phase supply available to me and I'm looking to convert to 400V 3 phase roughly about 12A variable load to supply my 3 phase equipment in my small workshop. I have the basic principles but I've heard that if done wrong can really mess up electronic components. My equipment is basic engineering tools with little electronics but I'd like to get it right anyway. Also looking to the future I might be looking at building and designing electrical control panels from my home (my current day job but not from home) and would need a simple low cost 3 phase supply for testing purposes.

 

My plan is to use a 230v to 400v step-up transformer wound to provide two phases at 120 degrees apart which then feed into a 7.5kw 400v idler motor. I will switch in capacitors to start and then use run capacitors to balance the load. This will be my basic setup but I need to know a little more:

 

1. How do I size the transformer? What calculation do I need to use to calculate the total load in the 230v line. I'm assuming that I would have to ask the transfomer manufacturer to wind it to suit AC3 loads.

2. Am I correct in having the output of the transformer wound to 120 degrees apart, if so will I lose efficiency?

3. When the idler motor is running, would there be any lag in the generated phase? If so how would I calculate the offset in the transformer to compensate for this? or do the capacitors take care of this?

4. To maximise efficiency in all load conditions is it feasible to use a simplified PF Correction monitioring device to switch in differing sizes of capacitors? This is probably not worth the extra expense but I would consider it just to be different! :rolleyes:

 

Its a little project I'd like to take on myself to see how pure a supply I can get from a diy converter. I have access to an osiliscope to meter the output on and off load. I'm in no hurry to get the equipment up and running.

Any help is much appreciated. I'm aware that this subjest has probably been done to death on this board already. :)

 

best regards

 

Jonny

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Hello Jonny

 

You can not wind a transformer to give a single phase input and two single phase outputs at 120 degrees.

If you have a single 400V winding, or two 230volt windings, they effect is still 180 degrees apart.

You would have to build in a "filter" circuit to provide the extra phase shift.

I would suggest that you couple a single phase motor to a three phase star connected motor. Connect the single phase supply to the single phase motor and also to one phase of the three phase motor. The spinning three phase motor which is energized on one phase wil generae the other two phases.

 

Best regards,

Mark.

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Hi Guys,

 

I'm looking at building a rotary phase converter for my own use. I have a 100Amp 230v single phase supply available to me and I'm looking to convert to 400V 3 phase roughly about 12A variable load to supply my 3 phase equipment in my small workshop. I have the basic principles but I've heard that if done wrong can really mess up electronic components. My equipment is basic engineering tools with little electronics but I'd like to get it right anyway. Also looking to the future I might be looking at building and designing electrical control panels from my home (my current day job but not from home) and would need a simple low cost 3 phase supply for testing purposes.

 

My plan is to use a 230v to 400v step-up transformer wound to provide two phases at 120 degrees apart which then feed into a 7.5kw 400v idler motor. I will switch in capacitors to start and then use run capacitors to balance the load. This will be my basic setup but I need to know a little more:

 

1. How do I size the transformer? What calculation do I need to use to calculate the total load in the 230v line. I'm assuming that I would have to ask the transfomer manufacturer to wind it to suit AC3 loads.

2. Am I correct in having the output of the transformer wound to 120 degrees apart, if so will I lose efficiency?

3. When the idler motor is running, would there be any lag in the generated phase? If so how would I calculate the offset in the transformer to compensate for this? or do the capacitors take care of this?

4. To maximise efficiency in all load conditions is it feasible to use a simplified PF Correction monitioring device to switch in differing sizes of capacitors? This is probably not worth the extra expense but I would consider it just to be different! :rolleyes:

 

Its a little project I'd like to take on myself to see how pure a supply I can get from a diy converter. I have access to an osiliscope to meter the output on and off load. I'm in no hurry to get the equipment up and running.

Any help is much appreciated. I'm aware that this subjest has probably been done to death on this board already. :)

 

best regards

 

Jonny

Hello.

 

I have learnt on this forum recently that some 3-phase frequency converters are able to work with one phase lacking. http://www.lmpforum.com/inforum/Lack-1-Pha...-Pro-t3939.html

 

If the need is practical : to power up, say, a 3-phase induction motor – in the absence of a 3 phase supply (when only one phase is at hands), maybe it is possible after stepping up the voltage to 400V, supply with it the motor through the converter.

 

(I may err, however, considering the rms of 400V, one pick per half-period, and the rms with two picks per half-period – the actual two phase voltage - to be the same thing from “the point of view” of the drive).

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