Author Topic: The skinny on Three Phase  (Read 8042 times)

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willib

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The skinny on Three Phase
« on: July 26, 2010, 01:00:11 PM »
To achieve Three phase one needs to have the correct number of poles and coils for an axial flux machine.

A pole is either a magnetic north or south.
 
Because most Axial flux machines have two rotors , thus two times the number of magnets , the term pole is sometimes used instead of magnets .

A Three Phase Machine in its most basic form has 3 coils and 4 poles evenly spaced around a circle.

A circle has 360 degrees .So in the above example, the coils are spaced or centered at 120 degrees apart , 360 divided 3, and the poles are spaced 90 degrees apart from each other , 360 divided by 4.

Since a useful Three Phase Axial Flux machine has more than just three coils and four poles , the number of poles and coils can be any multiple 4 and 3.

It can have 6 coils and 8 poles  or  9 coils and 12 poles  or  12 coils and 16 poles  ect .

The Three Phase setup extracts power evenly from the wind turbine blades .

Because as one phase is energized at a maximum , another phase is building up to a maximum , and the third is negative , looking at it from a sine wave point of view.

But when the three phases are rectified the phase that is negative is also producing power because the rectifier will flip the negative half positive  .

So all three phases are supplying power to the batteries , most of the time.

The Three Phase Axial Flux machine  is THE choice for wind turbines because it is able to extract power evenly from the wind turbine blades

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12AX7

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Re: The skinny on Three Phase
« Reply #1 on: July 26, 2010, 02:06:52 PM »
Hello!

Willib,  I think if one wants to tackle the subject of three phase it's important to mention what Delta and Wye are and their differences.
Some might "stumble" when trying to wrap their minds around "negative" without defining what or where the "zero/reference" points are.

Also, I'm uncomfortable with your comment of what a rectifier does..

 "But when the three phases are rectified the phase that is negative is also producing power because the rectifier will flip the negative half positive  .

If I was trying to explain converting three phase to DC to my wife this sentence would work fine, however this might confuse some newbies who chose to advance their solid state theory.

I hope someone will jump in and add their 2 cents

willib

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Re: The skinny on Three Phase
« Reply #2 on: July 26, 2010, 04:23:08 PM »
Ok good point..

A zero , for a particular phase , occurs when a pole is directly over the center of the coil for that phase.

Delta and wye connections need a diagram.



I got this diagram off the net and it is from a transformer page , thus the primary and secondary labels , just disregard them and consider the Star/Wye and Delta as two different diagrams. And the orange wires are coils .

A Wye or star connection is when the three ends of the three phases are connected to the three inputs of a three phase rectifier.In this case you would connect the L1 , l2 , and L3, to the inputs of the three phase rectifier.

A Delta connection is when the end of one phase is connected the start of the next phase , and the outputs from A three phase Axial flux machine , connected in Delta , are taken from the connections between phases , labled as load in the diagram..

Since the orange wires in the diagram are phases they can contain as few as one single coil or as many as two , three , four or five coils , in series , per phase.

In electronics there are Mathematical relationships between star and delta , and if you are interested in these relationships please try out the PDF below.

http://www.radioelectronicschool.net/files/downloads/3phase.pdf
« Last Edit: July 26, 2010, 04:32:21 PM by willib »
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klsmurf

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Re: The skinny on Three Phase
« Reply #3 on: July 26, 2010, 05:22:04 PM »
Thanks for the tutorial link! I'll have to read it a few times, but it still makes my head hurt. ;D
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12AX7

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Re: The skinny on Three Phase
« Reply #4 on: July 26, 2010, 05:30:47 PM »
It should be mentioned that with the WYE system, the center point (where the three legs are tied together) is often called "neutral".
Whether this neutral is tied to ground or not is another topic.

as an example,  if we're talking about 240 three phase.   The voltage between any two of the three legs would be 240vac.

L1 to L2 = 240vac
L1 to L3 = 240vac
L2 to L3 = 240vac
and
L1 OR L2 OR L3  to N (neutral) = 120vac

One can not directly get 120v from a 240 three phase DELTA system.

wooferhound

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Re: The skinny on Three Phase
« Reply #5 on: August 09, 2010, 01:04:04 PM »
More really good 3 phase information . . .
http://www.windstuffnow.com/main/3_phase_basics.htm