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## View Poll Results: Please select the best answer from these choices:

Voters
5. You may not vote on this poll
• Voltage A is in phase with voltage B.

3 60.00%
• Voltage A is out of phase with voltage B. (180 degrees out of phase)

1 20.00%
• It is meaningless to try to say whether those voltages are in phase or not.

1 20.00%
• No AC voltages powered by single core transformer are out of phase.

0 0%

# Thread: The poll -- Phasing of Voltages out of a Transformer

1. ## The poll -- Phasing of Voltages out of a Transformer

T1's primary is powered by 4000 VAC 60 Hz single phase power. The secondary of the transformer has 240 VAC between point A and point B. The transformer is shown with two secondary windings, but this is equivalent to a single center-tapped secondary in this case.

The voltage at GND, is our reference. Assume ideal circuits.

2. Being that the secondary as pictured is a single phase 240 volt winding there is no way that anything in that picture can be out of phase except for the primary to the secondary. As the picture shows at 1 on the primary is a dot and on the secondary the dot is 180 degrees displaced and is found at 7 and 5.

I order for the two 120 volt windings to be 180 degrees displaced then the dots would be at opposite ends or in the center together.

Considering one quarter of a football game where one team is trying to take the ball to one goal and the other team is trying to get the ball to the other goal both teams are running at 180 degrees against or out of phase if you please.

In a single winding or even the two windings you have posted the current will flow through the winding from one end to the other end and the laws of physics will not allow those electrons to oppose each other by being 180 degrees out of phase.

If you cannot grasp that what you are seeing on the scope is both ends of the sine wave looking toward the middle then there is not much hope of you ever making anything but a helper. Being able to figure the arc flash abilities of a panel would be totally out of the question.

Take a three phase 240 volt delta transformer and tap the center of one winding. From the corner of the tapped winding to the tap will be 120 volts. From the center tap to the odd winding will be the square root of the voltage from the center tap to the odd winding squared minus the square of the voltage from the center tap to the end of the winding that is tapped. 240 times 240 equals 57600. 120 times 120 equals 14400. 57600 minus 14400 equals 43200. The square root of 43200 equals 207.84.
A short cut one can take is to multiply the 120 by the square root of three which will be guess what, yep 207.84

Should we use this 240 volt three phase to power a 10 kw heater the amperage draw would be 24 amps. How one might ask. Multiply 240 by the square root of three to get the three phase voltage of 415.

I have been teaching electrical theory for a decade and a half, a lot more time than it takes to get a PHD.

3. I voted with JW before I read his post.....The secondary side is all in phase...

4. Originally Posted by Rich B
I voted with JW before I read his post.....The secondary side is all in phase...
Exactly but the entire secondary if 180 degrees out with the primary
in the diagram above there are two windings but they are connected just like it was one. As drawn it is like a broken magnet, two magnets that attract each other. If they were 180 degrees out with each other then the like poles would repel and all electron flow would stop. As the magnetic fields built up the two opposing fields would cancel each other out and there would be no electron flow.

5. JW I have no formal electrical training...just years of working on machines and trying to understand. I fix welders and generators. Some very complex stuff today. Makes my head spin and hurt but I learned to read prints and how to components on my own...

6. Originally Posted by Reach4

There is something wrong with that picture.

How can all of the current be flowing in the same direction ?

Carry on.

7. Originally Posted by DonL
There is something wrong with that picture.

How can all of the current be flowing in the same direction ?

Carry on.
It's AC. It's algebraic/vector math.
http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws
Kirchhoff's Current Law (KCL): At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node, or:
The algebraic sum of currents in a network of conductors meeting at a point is zero.
Those arrows are drawn fitting the sum of currents in a network of conductors meeting at a point is zero. If one of the arrows is drawn the other way, the phase will differ by 180 degrees, and we would use the other form of KCL.

8. Sounds like Jerkoff's law to me.

If you do not have a return current path, then you do not have any transformation of power. Your Transformer is bad.

Have fun.

9. Originally Posted by DonL
There is something wrong with that picture.

How can all of the current be flowing in the same direction ?

Carry on.
The way I see it, I agree with our moderator, and I think that Current path C is null as the current will all flow from A to B throught the equall resistive loads. then again, as Don said, Jerkoff's law applies here. We all seem to not have the Capacity or have Relcutance to seeing this clearly and are Impeding the resolution of this issue. As the Borg said; Resistance is Futile.

http://www.youtube.com/watch?v=AyenRCJ_4Ww

10. I think I figured out why that transformer has no current flowing.

Them 10 Watt resistors opened. lol

I have never seen a transformer that has a Exact 180 degree phase shift, Even from primary to secondary.

Even a vacuum can not make that transformer so precise. A degree or three off maybe.

Have Fun Everyone.

11. Originally Posted by DonL
I think I figured out why that transformer has no current flowing.

Them 10 Watt resistors opened. lol

I have never seen a transformer that has a Exact 180 degree phase shift, Even from primary to secondary.

Even a vacuum can not make that transformer so precise. A degree or three off maybe.

Have Fun Everyone.
Assume ideal circuits.

12. Delete... duplicate post.

13. Originally Posted by Reach4
Assume ideal circuits.

A ideal circuit would be to get rid of the transformer, and feed the load directly.

Any conversion is a loss of power.

Is it not ?

14. I was thinking of the circuit as being open ended and the resistors were there to represent 2 separate 120 volt loads.......

A 4 wire generators output is wired like this, well sort of but not exactly...........minus the resistors and there is no transformer....add a rotor to where the primary side is........

I work on them all the time.......Onan RV units......

15. Originally Posted by DonL
A ideal circuit would be to get rid of the transformer, and feed the load directly.

Any conversion is a loss of power.

Is it not ?
Are you saying that you suffer from hysteresis?

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