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

[Frank S]

Not to be splitting hairs here but the term for the US 2 120V lines coming into a house is called split phase and yes it is actually created from center tapping the transformer on the pole to create the neutral. I one looks up on the crossbar of the pole and sees only 2 wires for the transmission lines 1 is the ground and the other is the 13.2 KV high voltage the 3 out put lugs will be 120-0-120 or communally known as L1 N L2 when this enters the service panel the N or common is connected to the terminal strip on the side of the panel this is where all of the white wires are connected the bare ground wires are also connected to this terminal strip or may be connected to a desperate terminal strip but even so both terminal strips are connected together to the incoming neutral Plus the wire coming from the grounding rod driven in the ground near the main panel creating what is called a bonded ground
Now all 220v appliances receive their power from the L1 and the L2 and would be perfectly happy to have only 2 wires connected to them except for 2 things first would be the lack of safety without the ground . 2nd all controlling circuits are derived from either the L1+ the neutral/ground or the L2 + the neutral/ground in some rare instances where there happens to be more than 1 set of controlling circuits or the load of the controlling circuits and other 120v loads are enough to create an imbalance the loads may be split between both lines.
European 230v single phase equipment have only 1 power leg and 1 neutral leg+ ground
Now a 220v rotary phase converter in the US can actually be nothing more than a simple 3Ph motor with the 2 120v lines connected to the T1 and T1 terminals of the motor but this will not allow it to start up because as mentioned in previous posts the legs are actually 180° apart. Therefore some means to starting it to rotate is required this is accomplished by using either a pony motor to spin it up or a bank of capacitors connected to to the L1 or L2 at the T1 or T2 terminal and the neutral line to charge the capacitors the output terminal of the capacitors is connected to the T3 terminal. It is best to have a switch or a timed relay to charge the capacitors before switching on the converter motor but in the case of my 2 HP converter there is none this means the converter can take up to 15 seconds before reaching run Speed. on larger converters this would mean the inrush current would remain high for several seconds and possibly even a full minute which could cause a breaker to trip.
There was a discussion about single phase capacitor start single phase 220v motors in these there is a separate winding that is wound 1 tooth out of sync with the other winding's there is also a centrifugal switch that cuts the start winding from circuit after the motor reaches full speed. There are also motors with both start and run capacitors this is to assist in balancing the loads of the field winding's' when the motor is under load this arrangement is usually found in single phase motors that are started and ran constantly under heavy loads.
Some larger 3 phase motors are wired both in star and delta with 2 magnetic motor controllers these will be started with star then once up to speed will switch to delta or vice versa I forget which.
Then there is the DC start motors which are usually in the size range of or 1200 HP or more where the motor uses very high amperage 96 VDC to make it start rotating then as the RPMs increase it is switched to 4100 or 4300 Volts AC
1 last note if there are 3 wires on the pole it means that there are 2 13.2 KV lines and 1 ground all is needed there would be a 2nd transformer to get 3 ph by using the center tap method of the first and tying 1 leg to 1 of the input legs of the other then another connection is made from the grounds and one other lug I forget which it is but the output will be 120 198 120 which will give about 208 across any 2 legs
for true 220/240v 3 phase or 460V this requires there to be 4 wires on the pole and 3 transformers for the incoming line voltage
I hope I have not completely confused the issue

[old kodger]

Hi Dave,
These are precisely the considerations that have stopped me proceeding with experiments in that area to date.
I have seen commercial converters and I think that they use a lead and lag circuit based on inductors for one side and capacitors for the other leaving a primary circuit in the middle as the center phase, but they're very expensive.
Regards,
Rob.

[smithdoor]

All the parts for a static cost from Amazon is around $35.00 for 5HP FYI you need a potential relay I like APR5 works the best
Now if find a old use 3 phase motor star wound now you have rotary converter
You can add oil run cap make look better but that all

Dave

Hi Dave,
These are precisely the considerations that have stopped me proceeding with experiments in that area to date.
I have seen commercial converters and I think that they use a lead and lag circuit based on inductors for one side and capacitors for the other leaving a primary circuit in the middle as the center phase, but they're very expensive.
Regards,
Rob.

[old kodger]

Hi Dave,
I quite readily concede to not being an expert in anything, so, when I say that all of the info on potential relays that I have managed to locate on the net, seem to refer to "split phase" power supplies I can comprehend how the relay works. However, I'm in Australia and our 230 volt supply is ONE HOT LINE AND ONE EARTH BOUND NEUTRAL. there is ,L1 or L1 or L1, there is NO L2, so unless I'm missing something fundamental here (if so, I hope you will explain), I cannot see how a potential relay is going to help.
Regards,
Rob.

[Paul Alciatore]

Rob,

I feel your doubt. In fact, in spite of a background in physics and math, it took me some time to come to the realization that it is possible to get real three phase from a pair of Voltages that are 180 degrees out of phase with each other. It seems to be contradictory, I mean just how do two Voltages that are 180 degrees out of phase suddenly become 120 degrees out of phase? In most phase converters those original two phases are just passed through with no change. But when you do the vector math, it really does work. In fact, this is exactly what is happening when, here in the US, we take a 220V feed (call it single phase or two phase as you like, that's just terminology) and, using a rotary phase converter to convert it to three phase.

The "magic" lies in the vector math which shows a change in the ground reference. When a rotary phase converter is used to generate a third leg from the two existing phases of the power feed, although it does not actually generate an actual, new ground point, the third phase is generated in a manner so that the theoretical ground point is shifted in both Voltage and phase from the original ground point that is half way between the original two phases. And those original two phases are not changed in any way, but from the viewpoint of this new, theoretical ground point they REALLY are 120 degrees out of phase. This is at the same time that those original two legs are still 180 degrees out of phase when viewed from or referenced to the original, earth ground point. It sounds contradictory and I had to work out all the math before I was ready to believe it, but it does really work.

So, if you first convert the real single phase current which has one side grounded and the other at 220V to the 110V-G-110V configuration used in the US and then run it through a rotary phase converter, then you do get actual, true three phase. In fact, if you are using a rotary phase converter, you do not even have to use the transformers to convert it to 110V-G-110V, you can just use the 220V power from the wall outlet directly to the rotary phase converter and it will still work and produce true three phase.

This will also work for any other kind of phase converter that produces three phase from single/two phase. I talked about using the transformers because I do not have a copy of the plans being sold and I do not know if they require the center ground of the 110V-G-110V system or not. There are many schemes for producing three phase from 110V-G-110V and some of them may very well need that center ground.

Hi Paul,
I had been thinking about a 230-0-230 volt transformer arrangement such as is used in electronic circuit supplies (usually 25-0-25 for medium output amplifiers), however, as you point out, the phases are in fact 180 degrees out of phase not 120 and I did wonder how that would effect the performance of the motor, in that it would "confuse" the third phase orientation.

Regards,

Rob.

[Paul Alciatore]

Dave,

I am not sure that I understand your objection. First, there is an old, antiquated two phase system which had a second phase that was shifted by 90 degrees from the first phase, but that is no longer used anywhere that I know of and is completely irrelevant to this discussion. If you understand the vector math involved, you will see that two phases that are 180 degrees from each other can be viewed as being 120 degrees apart if the ground reference is shifted. This is what most, if not all, phase converters do. Please read my previous post, above.

It WILL work.

No this does not work this only 180 deg you need either 90 (2 phase) or 120 deg (3 phase)
Even single phase motors cap start has 2 phase winding for starting
I think most of wish that wood work too.

Dave

[smithdoor]

The relay turns the start cap off after the motor starts
The potential relay APR5 is adjustable for voltages (130-370Volts)
You find this type of relay use in AC and deep well water pumps
I replace centrifugal switch found in single phase motors
The first drawing below shows a typical single phase motor use a potential relay
Note the start winding is 90° to then main winding this give the motor the direction to turn
For three phase the winding are at 120° The second drawing shown how it is wired for three phase

Dave

Hi Dave,
I quite readily concede to not being an expert in anything, so, when I say that all of the info on potential relays that I have managed to locate on the net, seem to refer to "split phase" power supplies I can comprehend how the relay works. However, I'm in Australia and our 230 volt supply is ONE HOT LINE AND ONE EARTH BOUND NEUTRAL. there is ,L1 or L1 or L1, there is NO L2, so unless I'm missing something fundamental here (if so, I hope you will explain), I cannot see how a potential relay is going to help.
Regards,
Rob.

[Frank S]

To run a RPC (rotary phase converter in Australia, if you are in rule areas you could have what some call 2 ph 480 which would be to hots and neutral. but most areas without 3 ph or the rule areas with 2 ph there is only 1 240v line with a nuetral. to make a RPC run in those places a transformer would be required to make the 415v split phase L1 +N for input then tap at 175-0 240 +415 nominal for output. then connect the 2 output line to the PRC and the cap bank for starting and a module of thyristers for full balanced true sine wave 3p output.
Here is a commercial site selling their product but the information there will give you an idea of how to go about it
3 Three Phase Power Converter Australia converts single phase to three phase.
I think if it were me needing to do this I would buy MR nhengineer's plans then go from there adding what might be needed and contacting him for assistance

[smithdoor]

Look the Single to three phase converter in Australia converting single phase power into 3 phase power web site
It use a potential relay with a starting cap and run cap as shown in my drawing
They did add a step up transform to 415 volts
Odds are you can buy all parts from a AC supply or pump supply company for around usa $35.00 and add a transform if need.

Dave

To run a RPC (rotary phase converter in Australia, if you are in rule areas you could have what some call 2 ph 480 which would be to hots and neutral. but most areas without 3 ph or the rule areas with 2 ph there is only 1 240v line with a nuetral. to make a RPC run in those places a transformer would be required to make the 415v split phase L1 +N for input then tap at 175-0 240 +415 nominal for output. then connect the 2 output line to the PRC and the cap bank for starting and a module of thyristers for full balanced true sine wave 3p output.
Here is a commercial site selling their product but the information there will give you an idea of how to go about it
3 Three Phase Power Converter Australia converts single phase to three phase.
I think if it were me needing to do this I would buy MR nhengineer's plans then go from there adding what might be needed and contacting him for assistance

[nhengineer]

Yeah, I'm wondering how, with a 230V single phase; that is, one hot leg and earth ground the other, as in Australia, you could create an additional phase, whether it be 90° or 120° out of phase with the original simply by using a transformer.