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#129830 - 09/19/05 01:03 AM odd numbered polyphase  
PEdoubleNIZZLE  Offline
Member
Joined: Jun 2004
Posts: 176
McKeesport, PA, USA
Ok, It seems like most polyphase systems are odd numbers (3 phase for commercial dist, 5 phase in wind powered generators.), with the esxpetion of 2 phase, where 1 phase is 90 degrees out of phase from the other. Is there a reason for an odd number of phases, or is it because i've just never come accross even number phase systems. Can any number of phases be connected in series (such as 3 phase delta) and/or parallel (such as 3 phase star)?


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#129831 - 09/19/05 07:32 AM Re: odd numbered polyphase  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
For 'high phase order power' distribution, multiples of three phases are always used because the phases are derived from ordinary three phase power using various transformer arrangements. You could get other phase counts, but the transformers are more symmetrical if you stick with multiples of three.

In motors, you actually almost always have an _even_ phase count; the most common is _six_ phases. However three of these phases are derived internally as the 'back side' of the three phase supply. If you look at the phase bands in the stator, they are 60 electrical degrees apart, generated by the 'supply' side of phase A, then the 'return' side of phase C, then 'supply' B, then 'return' A, then 'supply' C, then 'return' B, and then back to 'supply' A.

Most of the work done on HPO motors has been with supplies that are multiples of three phases. This is simply because the available transformers, stator lamination stacks, and inverter electronics, are all focused on three phase systems. Usually (though not always) the HPO motor will be arranged so that you have twice as many 'half phases' in the motor as you have 'supply phases'.

HPO machines can be connected 'mesh'; this is the high phase version of the delta connection. You are not limited to connecting the phases in adjacent series; you can make any of a number of symmetric connections; for example in a 7 phase machine the motor coils could be connected between phases 1 and 2, then 2 and 3, then 3 and 4.... or they could be connected 1 and 3, 2 and 4, 3 and 5... or 1 and 4, 2 and 5, 3 and 6....

This particular field is my baby; I've been doing research on high phase order motors for about 10 years, and high phase order mesh connected machines for about 5 years. One nifty aspect of HPO machines is that you can intentionally run harmonics into them in order to _improve_ efficiency, and HPO mesh connected machines respond differently to different harmonics, so you can use harmonics to get some very interesting control capabilities.

I guess that I'm pretty severely tooting my own horn here; I'll edit out the following link if Bill thinks that it is not appropriate, but my company has lots of information on HPO machines on this tutorial page: http://www.chorusmotors.gi/technology/index.shtml

-Jon

P.S. I'd appreciate it if you could send me a link to the 5 phase wind generators that you mention.


#129832 - 09/21/05 02:00 PM Re: odd numbered polyphase  
Tesla  Offline
Member
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
Your 5 phase wind generator sounds like a 3 phase machine with a variable DC excitation circuit.

Tell me more.


Tesla

#129833 - 10/06/05 12:24 AM Re: odd numbered polyphase  
PEdoubleNIZZLE  Offline
Member
Joined: Jun 2004
Posts: 176
McKeesport, PA, USA
I don't have the plans. You have to buy them, but I'm assuming it's a symmetrical 5 phase circuit, where the phases are 72° apart. I kinda like these projects, because they have helped me understand polyphase a bit more. But the site for it is http://www.scoraigwind.com/ . I don't think it's an excitation circuit, because it uses permanent magnets. they are small scale, and to use electromagnetic exciting fields would be inefficient, as you would be draining your battery on windless days. (this guy lives on Scoraig Peninsula, Scotland, miles away from civilization. (I'm assuming he would be the AHJ in his area?)


#129834 - 11/08/05 09:45 AM Re: odd numbered polyphase  
Wolfgang  Offline
Member
Joined: Sep 2005
Posts: 153
the very West of Germany
As far a I Know quite a lot of modern European locomotives use 4 phase (90°) motors. 4 phase is generated onboard out of what is available outside. This might differ from country to country (AC 16,7HZ or 50 Hz or 3kV DC or else).

The reason is supposedly a better torque in the moment of starting.


#129835 - 11/11/05 11:43 PM Re: odd numbered polyphase  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Wolfgang:

Quote

As far a I Know quite a lot of modern European locomotives use 4 phase (90°) motors.


The 4 Phase System you mentioned sounds quite like an antiquated U.S. Polyphase AC System
2 Phase

[Linked Image]

[Linked Image]

[Linked Image]

Are any of these Schematics similar to the 4 Phase System?

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!


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