Rotary Phase Converter (Create 3-phase power from a single phase source)

[nhengineer]

...and by the way, the pony motor need not very large regardless of the final load. It only needs to be large enough to overcome the 'at rest' inertia of the idler motor's armature and the friction of its bearings. Its only purpose is to get the idler motor turning under no load.

[old kodger]

Hi David,
Yeh, I'm with you on that one, the only way I could see of getting plus 230-0-minus 230 would be to get a big old 450volt output tranny with a center tap and use the center tap as the ground reference.
With two trannys working in tandem you'd still only get two lots of 230 IN phase.

I got this far and suddenly realized that if the two were tied in the middle and that junction grounded, you may very well get plus 230 and minus 230 at the other ends of the transformers, though whether they would be out of phase is still questionable.

Any thoughts on this?

Rob.

[Frank S]

I think there may be a very valuable point being missed here. All households in the USA have only 1 ph it is called split phase for a reason the 13.2 KV line on the pole needs onlu 1 hot and 1 earth to make the primary winding in the transformer function the secondary is tapped in the center or the (0) then tapped at the 120v stage on both ends this makes the 2 hot lines coming in the meter then to the main panel The only exception to this is the higher end larger homes that require 3 ph to run the HVAC equipment or on farms such as dairy which have lots of 3 ph equipment
Therefore Rorary phase converters used here in the US are receiving 2 hot lines at 180° once the Idler motor is running the output will be 3ph although without the use of tryristers it will not be true 120° ph to ph pure sine Most motors and some transformer induction equipment don't care it is only when the introduction of 3 ph CNC equipment to the system does the true sine 120°ph to ph matter.
In Australia the 1 hot could be considered to be just like the incoming pole line albeit at a much lower voltage.
so for a 10 HP idler motor one would need a simple multi tap transformer about 9KVA in size 1 hot 1 cold to the primary then tap the center for the neutral output and which ever voltage desired for the split phase output Normally in Au it would be around 415 across the to hot out lines but if you have 200/208, 220/240 3 ph equipment you are needing to run tap the transformer so you would have 120 -n-120 then to the idler. for the 3 ph output
Remember for 415v Single ph across the 2 lines you would want 230-n-175

[smithdoor]

Split phase is type of motor
Lower in cost over capacitor start motor
In the USA 120 volte to ground is used for safety

Dave

I think there may be a very valuable point being missed here. All households in the USA have only 1 ph it is called split phase for a reason the 13.2 KV line on the pole needs onlu 1 hot and 1 earth to make the primary winding in the transformer function the secondary is tapped in the center or the (0) then tapped at the 120v stage on both ends this makes the 2 hot lines coming in the meter then to the main panel The only exception to this is the higher end larger homes that require 3 ph to run the HVAC equipment or on farms such as dairy which have lots of 3 ph equipment
Therefore Rorary phase converters used here in the US are receiving 2 hot lines at 180° once the Idler motor is running the output will be 3ph although without the use of tryristers it will not be true 120° ph to ph pure sine Most motors and some transformer induction equipment don't care it is only when the introduction of 3 ph CNC equipment to the system does the true sine 120°ph to ph matter.
In Australia the 1 hot could be considered to be just like the incoming pole line albeit at a much lower voltage.
so for a 10 HP idler motor one would need a simple multi tap transformer about 9KVA in size 1 hot 1 cold to the primary then tap the center for the neutral output and which ever voltage desired for the split phase output Normally in Au it would be around 415 across the to hot out lines but if you have 200/208, 220/240 3 ph equipment you are needing to run tap the transformer so you would have 120 -n-120 then to the idler. for the 3 ph output
Remember for 415v Single ph across the 2 lines you would want 230-n-175

[Frank S]

Split phase is also the type of current here in the USA When talking about 220 v single phase
some mistakenly say there are 2 phases of 120v to get the 220 volt when actually it is only 1 phase split in the transformer to achieve 220v
Split phase is also used in rule Australia to get 480v

[smithdoor]

You can find on the internet split phase
If you split the phase it is now 2 or 3 phase this is used for starting motor
Even Wikipedia is not clear
If even send a center tap transform some will call this split phase. But it is still single phase
They have even made 6 phase for electronic work, this most I have seen

Dave

https://www.merriam-webster.com/dictionary/split-phase
http://3.bp.blogspot.com/-CuAIHuX75Q.../s1600/6.8.png
https://en.wikipedia.org/wiki/Split-...electric_power

Split phase is also the type of current here in the USA When talking about 220 v single phase
some mistakenly say there are 2 phases of 120v to get the 220 volt when actually it is only 1 phase split in the transformer to achieve 220v
Split phase is also used in rule Australia to get 480v

[smithdoor]

FYI
The most command types of motors use for Synchronous single phase today

1) Shaded pole
2) capacitor rum
3) split phase
4) capacitor start
5) capacitor start and rum

They made other types in past did list most where not made after the mid 50's
Three phase is just three phase motor they do not need a starting winding
Two phase I have not seen but is some time found in electrical books

A transform was made back the early 1900's from converting two phase to three phase or three to two phase. I do not know if this was true sync of wave or not

Dave

[nhengineer]

Gotta think on that one a bit.

[smithdoor]

Here we are taking about using a capacitor to delay the power for abut .006 seconds making a two or three phase wave. Given the motor the direction to turn. (this can be done with either a pony motor (using staring cap) or using staring cap in the main motor)
After the motor is turning at speed the start capacitor is turn off as this will shift the phase great than need.
At this point the main motor is turn into a generator. Generating the three phase power or if using static type converter the motor is running at 60% power.

Dave

[nhengineer]

I think there may be a very valuable point being missed here. All households in the USA have only 1 ph it is called split phase for a reason the 13.2 KV line on the pole needs onlu 1 hot and 1 earth to make the primary winding in the transformer function the secondary is tapped in the center or the (0) then tapped at the 120v stage on both ends this makes the 2 hot lines coming in the meter then to the main panel The only exception to this is the higher end larger homes that require 3 ph to run the HVAC equipment or on farms such as dairy which have lots of 3 ph equipment
Therefore Rorary phase converters used here in the US are receiving 2 hot lines at 180° once the Idler motor is running the output will be 3ph although without the use of tryristers it will not be true 120° ph to ph pure sine Most motors and some transformer induction equipment don't care it is only when the introduction of 3 ph CNC equipment to the system does the true sine 120°ph to ph matter.
In Australia the 1 hot could be considered to be just like the incoming pole line albeit at a much lower voltage.
so for a 10 HP idler motor one would need a simple multi tap transformer about 9KVA in size 1 hot 1 cold to the primary then tap the center for the neutral output and which ever voltage desired for the split phase output Normally in Au it would be around 415 across the to hot out lines but if you have 200/208, 220/240 3 ph equipment you are needing to run tap the transformer so you would have 120 -n-120 then to the idler. for the 3 ph output
Remember for 415v Single ph across the 2 lines you would want 230-n-175

Well Frank S, after further review, I believe you may be correct. See drawing below:


Image modified & copied from HERE

It appears that my design, slightly modified, will work for Australia and other former British Crown Colonies nations. All one would need is an appropriately sized transformer. I will work on that.

Reader comments welcome.