Pole mounted utility transformer

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Re: Pole mounted utility transformer

In your diagram it shows a simple triangle that has three 60 degree angles that totals 180 degees. That is not a sine wave. Its a triangle!
Click to expand...
You have recited a few of the basic principles, but it appears that you're not familiar with phasor diagrams or vector addition.

With regard to the phase voltages being 60 degrees out-of-phase, are you aware that they are actually generated 60 degrees out-of-phase in the utility's alternators.
It is the "center phase reversal" that converts the phase displacement to 120 degrees for transmission and distribution.

Ed
 
Re: Pole mounted utility transformer

Ed,
That's your opinion, I'm talking about a three phase circuit here. Take a look at instruction #4 in your diagram you forgot to make a 120 degree left turn. Try this, connect a scope meter to your three phase circuit and see it for yourself in real time!
The phase angles are 120 degrees apart!
I think you need to sit down and go over your vector math again with the utility engineer.
 
Re: Pole mounted utility transformer

Try this, connect a scope meter to your three phase circuit and see it for yourself in real time!
The phase angles are 120 degrees apart!
Click to expand...
I believe you are referring to the phase angles between the three voltages in a three phase transmission or distribution system.
Of course they are. That is well understood by most everyone in the industry.

:)

Until the three windings are connected together into either a wye or a delta connection, we just have three voltages that happen to be generated at different points in time, because the rotating alternator rotor (magnet) cannot be in three positions at the same time.

The sketch below represents a basic two-pole alternator which produces one cycle per revolution in each of the phase windings. Each winding has two poles connected in series, and each winding's leads are identified Start and Finish.

If we accept the standard definition of one cycle as being 360 electrical degrees, it follows that in a two-pole alternator, electrical degrees are equal to mechanical degrees.

You can see that the voltages are generated 60 degrees out-of-phase with each other, and the phase sequence is a, b, c.

Wave1.gif


However, to transmit the three currents over a distance to a load, it would require six wires, two for each phase, if the voltages remained 60 degrees out-of-phase.

In order to create either a wye or delta connection so that three wires will get the job done, the three voltages have to be displaced in time so that at any instant, the total positive voltage is equal to the total negative voltage.

This is accomplished by interchanging the leads of the "center" phase winding, and re-identifying them. It is done by the machine manufacturer, not the electrician. The phase displacement is now 120 degrees, and the phase sequence is now a, c, b.

Wave2.gif


The practical result is that, at any instant, the current flowing in one direction in the circuit is equal to the current flowing in the other direction.

3Ph%20Motor3.gif


Thats enough for now. Comments are welcome.

Ed

[ January 30, 2005, 01:56 PM: Message edited by: Ed MacLaren ]
 
Re: Pole mounted utility transformer

Ed, your the man!
appl.gif


Roger
 
Re: Pole mounted utility transformer

By Ed,

I was responding to a question by Physis in his post of January 26, 2005 04:47 PM, where he said - "So now I'm wondering, how can they be 120? from each other in delta?"
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But I was ζΦהּ₣ب?ε?, :D
 
Re: Pole mounted utility transformer

Jan 26,2005
Quote:
"Physis,
I'm a three phase rookie, so help me out here. I was thinking the same thing,120 degrees out of phase. But I'm all better now. They are only
120 degrees out in relation to there neutral".

January 27,2005
Quote:
"Physis,
So now I'm wondering, how can they be 120
degrees from each other in a Delta".

January 27, 2005
Quote: Ed's response
"The Phase voltages are 60 degrees out of phase
with each other in a Delta connection".

Ed,
The post that we are decussing here is about transformers not utility alternators. I was trying to help explain Delta to the three phase rookie.
 
Re: Pole mounted utility transformer

Ed, your diagrams are BEAUTIFUL. It illustrates another point about three-phase generation that I never considered. The more I hang around here, the more I find out just how much I DON'T know about electricity.

The scary thing is, around my work place, I am considered to be one of the smart ones :eek:

Thanks for the diagram!
 
Re: Pole mounted utility transformer

The more I hang around here, the more I find out just how much I DON'T know about electricity.
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Me too. Every day I see something posted here that makes me think and I usually end up changing my ideas of what I thought I knew.

The post that we are decussing here is about transformers not utility alternators. I was trying to help explain Delta to the three phase rookie.
Click to expand...
Yes, isn't it great that this forum exists so that we can all contribute to each other's learning. :)

I didn't get a chance yet to finish explaining what I meant when I said "The phase voltages are 60 degrees out of phase with each other in a Delta connection", in answer to the "three phase rookie's" question.
I had to start with the generation of the voltages in order for it to make sense.
Maybe later this evening.

Ed
 
Re: Pole mounted utility transformer

Might as well conclude my response, begun on Jan 30, to the question regarding the phase relationship between the phase voltages in a delta connection.

The separate coil symbols in the sketches below represent the three windings of a three phase alternator (or transformer secondary), before they have been connected either wye or delta.
The terminals of each winding have been identified S and F, meaning Start and Finish. The three voltages are 120 degrees out-of-phase with each other and we will assume the winding voltage is 120 volts.

I think it makes more sense if we look at a wye connection first.

Ed

3ph-conn2.gif


3ph-conn3.gif
 
Re: Pole mounted utility transformer

In conclusion to this post discussion on, "Pole mounted utility transformers".

"Yes, isn't it great that this forum exists so that we can all contribute to each others learning".

Ed,
The post only contributes to ones learning if the topic is kept in the correct context! :p
 
Re: Pole mounted utility transformer

Actually Sparks1, I don't think Ed's far out of context at all. Looking at delta, it's phase angles and their vectors, Ed's brought up some things I wouldn't have thought of.

It's a given that an alternator would be wired with the coil orientation being F-S, F-S, F-S (refering to Ed's diagrams) but because it's so axiomatic I hadn't given it any thought.

I plotted the functions of the three phases 60? apart and found enough room in a cycle to put another set 180? away from the first. Implying you might want to build an alternator with six phase coils, just like the one Ed was talking about. (I must of have done it right, when I looked back at the diagram it says the same thing)

And 60? is certainly relevant in three phase vector calculations.

Three phase is a weird animal. I don't think I've dealt with anything analogous to it.

Tesla was a groovy cat man :cool:

Edit: Actually I plotted the three phases based on the coil polarities. It confirmed the 60? phase relationship. There, that's more accurate.

And some grammar/typo repair

[ February 02, 2005, 12:25 AM: Message edited by: physis ]
 
Re: Pole mounted utility transformer

Sparks1, you said this:

January 27, 2005
Quote: Ed's response
"The Phase voltages are 60 degrees out of phase
with each other in a Delta connection".

Ed,
The post that we are decussing here is about transformers not utility alternators. I was trying to help explain Delta to the three phase rookie.
Click to expand...
Well, you're a teacher.

I've got this vector problem:

the hypotanuse = 120, the verticle side = 103.92, the angle at the intersection of the verticle side and hypotenuse is 30?, the angle at the verticle side and the horizontal side is 90?.

The missing values are:

[A] The length of the horizontal side.

the angle at the horizontal side and the hypotenuse.

And [A] = (the numeric values)

This triangle was always around while I was considering what Ed was talking about.

Do you know what the angle of is?
 
Re: Pole mounted utility transformer

And I thought you wouldn't answer. :D

Edit: If the angle is 60? and the hypotenuse 120 then cos 60 = .5 and .5 x 120 = 60.

[ February 04, 2005, 11:03 PM: Message edited by: physis ]
 
Re: Pole mounted utility transformer

Physis,
0.5 is the cosine of the angle!
The cosine of 60 degrees is 0.5
What is the point you are trying to make here?
 
Re: Pole mounted utility transformer

Ax = A cos Ө

Ax = horizontal side
A = hypotenuse
Ө = angle of intersection
 
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