What's new
What's new

Two phase to three phase conversion in New Zealand

neilharr

Plastic
Joined
Apr 2, 2021
I'm the author of the hand drawn sketch. I left the polarity dots off it because some transformers might not be so marked. Fundamentally, there are two possible 'phasing' connections of the transformers - one will yield a third phase (Line C) which is 120 degrees away from both Line A and Line B, exactly as we'd want. The other will yield a third phase (Line C) which is 60 degrees apart from A and B, which is exactly what we don't want.

When the phasing connections of the transformers is correct, there will be equal line-to-line voltages all around. Build it. Check it. Flip the polarity of one of the transformers if it isn't right...
 

neilharr

Plastic
Joined
Apr 2, 2021
i have just checked the voltages on my transformer set up and phase to neutral voltages are 243 251 and 248 volts phase to phase voltages are 423 424 and 432 volts does this look right ?
 

Dag S K

Aluminum
Joined
Aug 22, 2007
Location
Norway
The voltage looks right.
The job by turning single phase to 3 phase is to make it a rotating magnetic field. The very first simple generators was just a permanent magnet on a spindle turning around and making magnet fields. With 3 coils you could make the field move in one direction, did they reverse the generator the field reversed. They actually started with 2 wires for each field (6 wires) Then they dicovered to let 3 of them be a common neutral, and it was even possible to skip the neutral if the lower voltage was not needed. Here you have only 2 of the wires. If we call the 3 wires A,B and C and each is a corner in a triangle. You have A and B and may draw a line between those, but you have no idea if the C is ower or under your line.
Of-course we may solve that :-) We could buy a frequency converter for 3 phase, and it will work with only 2 wires in. Some electronics helps to do that... It may even not be extremely expensive. How did they solve it before the electronics became available? A rotating motor-generator,
It is described better in this forum than anywhere else in the internet :D Or you could just use a capacitor, but that is not good enough when the load varies.
If we compare it whit something much more common, a diesel motor: It does not rotate...or does it? The pistons is moving forth and back as the drawing of the line A-B but have a flywheel that rotates, you probably know how :) That i s what you have to do with the magnetic field.
 

neilharr

Plastic
Joined
Apr 2, 2021
i only wish i had known about these two phase to three phase conversions 30 years ago when we first had the second phase installed me and my brother use to make bulk conveyor bodies powered by 3 phase 3 hp motors we use to have to take them down to the local potatoe processing factory to try out the electrics and true up the conveyor belt our mig welders use to run on just the two phases but we could not run any equipment with 3 phase motors we did buy a static converter but it was not much good we also looked at buying a diesel generator but they were very costly certainly alot more expensive than a couple of transformers or the parts required to make a rotary phase converter i asked quite a few firms in the uk who build rotary phase converters if it was an advantage to be starting off with two phases all but one of them said it was not so i got that one firm to build me one then i made my own
 

neilharr

Plastic
Joined
Apr 2, 2021
I have a 63a fuse on each of the phases coming in. One minute a RPC for this setup sounds like a walk in the park the next minute very complicated.

I could also just use one phase and copy the uk version on you tube but thought being 2/3 the way to three phase would make it easier. Scraping a whole factory I will be able to get almost all the parts for scrap value, the electrical workshop and spares are also being binned.
 

neilharr

Plastic
Joined
Apr 2, 2021
there is a firm in india called beta power control who build both single phase to three phase and two phase to three phase converters to power up to 75hp motors i don.t know how they work but it says it produces 3 perfect sine waves ig you google them their website comes up
 








 
Top