why the two out of phases is called single phase ??

[keithkyll]

... the basics for the electrical power in general are not clear to me !!

That is the problem. That is why we are spinning in circles. If you start a new subject about Generators, I will help you. So will everyone else.
We share knowledge here. It is not free. We expect a contribution from those that are helped. If you try, we will help.

Many do not understand 3 phase. Many would benefit from a discussion about how a generator works. This information isn't just for you. We want to help many people. That is why we ask that you do it here, not in PM's.
You ask us, you ask engineers in Egypt, but you still do not understand, and you know why. So do what I ask - study about generators, then post a drawing and ask some questions.

 

[magdyfayad]

thanks , i will begin and start studying about generators !!


i will search at google about how generator works

then i can open new forum


i thank you again as you want to continue with me

 

[keithkyll]

English lesson: The area of this site is called a 'forum'. The 'Forum' contains many 'Threads'.
You will not 'open new forum'.
You will 'start a new thread'.

 

[leitmotif]

Maddy,

I too am growning irritated.

I gave you two assignments
1 do calculations in Excel and graph out 3 phase and dervive single phase from two of the three phases.
You did NOT do it.
2. Take two batteries and see what happens with the common
You did NOT do it.

In my class you flunk, fail, get an F

You say you are not lazy and want to learn -
DO YOUR HOMEWORK

Dan Bentler

 

[magdyfayad]

first thanks keithkyll for this english lesson


second thanks lietmotif

i repeat i am not lazy and i want to learn

1- first i do not understand exactly what do you want to do for the first assignment as you said :

" do a sine function for 0 to 360 degrees in 10 degree increments and label it A
Do another stagger it by 120 and label B

Do another stagger by another 120 and label C
Now subtract the difference betweeen A and B.
Do again for B and C and for A and C

NOw draw graphs for all calculations. Kinda hard to visualize it until you do the math and do the graphs. That is what I had to do to really understand what is going on."

as i do not understand what do you want !! and i have not a scope

2- for the center tapped i can say i understand it a little as you can read post 90 for me as i said :

" also i want to be sure for this information which if we applied at the primary of a transformer two hot wires ( as R , S either come from delta connection or star connection ) the output ( the secondary ) of the center tapped transformer are also two hot wires , then we can call about the output is
in- phase as there is no lead or lag in angle between them but there is a difference between the voltage amplitude as if a hot wire at maxinum positive value , then the another must be at the maximun neagative value at the same time , so the current pass through the nuteral is always zero , is not right ?? "



as i noted the direction of the current for the above half is reversed to the direction of the current for the down half of center tapped transformer and the both are equal in value , so i think the current at the nuetral is always zero !!

thanks all

 

[leitmotif]

first thanks keithkyll for this english lesson


second thanks lietmotif

i repeat i am not lazy and i want to learn

1- first i do not understand exactly what do you want to do for the first assignment as you said :

" do a sine function for 0 to 360 degrees in 10 degree increments and label it A
Do another stagger it by 120 and label B

Do another stagger by another 120 and label C
Now subtract the difference betweeen A and B.
Do again for B and C and for A and C

NOw draw graphs for all calculations. Kinda hard to visualize it until you do the math and do the graphs. That is what I had to do to really understand what is going on."

as i do not understand what do you want !! and i have not a scope

REPLY you do not need a scope. I DID forget to say do this on a computer and use Excel or other spreadsheet program that has trig functions in it.

2- for the center tapped i can say i understand it a little as you can read post 90 for me as i said :

" also i want to be sure for this information which if we applied at the primary of a transformer two hot wires ( as R , S either come from delta connection or star connection ) the output ( the secondary ) of the center tapped transformer are also two hot wires , then we can call about the output is
in- phase as there is no lead or lag in angle between them but there is a difference between the voltage amplitude as if a hot wire at maxinum positive value , then the another must be at the maximun neagative value at the same time , so the current pass through the nuteral is always zero , is not right ?? "

as i noted the direction of the current for the above half is reversed to the direction of the current for the down half of center tapped transformer and the both are equal in value , so i think the current at the nuetral is always zero !!

thanks all

REPLY well you have the concept of the neutral understood very well so there may be no need to do the battery drill. Current in neutral is zero with equal loads and will be the difference between the two if not equal resistance.

 

[keithkyll]

Maddy is in School

I gave him some lessons to study at this site .

We'll wait for the reply or new thread.

 

[milmat1]

The 220 VAC entering your house is actually SPLIT PHASE !! Does that make more sense ??

 

[Jim Dungar]

The 220 VAC entering your house is actually SPLIT PHASE !! Does that make more sense ??

Split phase is not a universally recognised term. I do not believe I have ever seen it used in any published industry standard.

What comes into most houses in the US is 120/240V 3-wire, 220V has not been a nominal voltage since the 1950's

 

[Stationmaster]

I admire the patience of the many posters trying to help Maddy with this thread, and I thought long and hard about whether my 2 cents would do more good or more harm. But I noticed something that may help a little with the original concept.

Maddy was asking about U.S., household, "single phase" power.

Perhaps it would be of value to explain that in the U.S., the final transformer, serving every house, is selected, by the power company, because it is wound to convert 2 conductors of WHATEVER primary voltage is available, into a 2 conductor, 240vac, single phase, secondary.

Since the available primary voltage can vary widely from area to area, and may be single phase OR 3 phase, WYE or Delta, the power companies use a variety of transformers to accomplish this "transformation" to 240vac single phase.

Once the proper transformer is selected, the final result (for household) is ALWAYS: 240vac, 2 wires, single phase.

The neutral (third wire) is created by the secondary center tap, also engineered into the secondary of the selected final transformer. Only because there IS a center tap can you develop 120vac. The neutral is connected to earth ground.

As measured from the center tap (neutral, earth, ground ), the 2 "line" conductors will show up on a scope as being 180 degrees out of phase with respect to each other.

I know you've moved on to 3 phase generators, but I'm not sure 3 phase generator theory will answer that particular question of Maddy's.

Stationmaster

 

[keithkyll]

Maddy viewed the 2 hots from a 3 phase source as '2 phase'. Next, he tried to compare this '2 phase' with single phase 240 US house power.
The concept of neutral and phases went over his head. I'm hoping that he will first learn how a generator works, so he will understand how a sine wave is generated. After that is absorbed, we can show 3 generators ganged together, 120 degrees apart. If you don't know how a generator works in the first place, you will never understand 3 phase.
After all this is absorbed, it will be an easy task to explain how 3 phases runs a motor, then how a VFD generates 3 phases to do the same thing. We might drift a little OT from time to time, but I'm trying to keep the subject focused on our industry. Contributions from others is always appreciated!

 

[keithkyll]

REPLY well you have the concept of the neutral understood very well ...

Obviously not, judging by his current thread.
magdyfayed: Did you study how a generator works? Please post your answer. I am still waiting.

Neutral is connected to Earth. A copper rod 1 to 3 Meters long, driven into the ground. Ground and Neutral are connected to this rod. The Hot is connected to the transformer. It switches between +170 to -170. Both the Neutral and Ground are zero. Because we are drawing current on the Neutral, you may see several volts on it in reference to Ground.
If you touch the Hot wire, you might die. If you touch the Neutral or Ground, you will not die.

Now, tell us how a generator works!

 

[Roy Matson]

Skipfast's sketch shows a single phase setup (both hot wires are in phase)
Even if the primary were connected across 2 phases the voltage applied is still single phase. To be 2 phase there has to be 2 hots 120° out of phase with each other.
Roy

 

[Jim Dungar]

Do not count phase/line CONDUCTORS as PHASES. Two phase power is 2 sets of line-line voltages that are 90° degrees apart.

 

[keithkyll]

Using the term 'Phase' means the voltage has a lead or lag with respect to the other, but does not dictate that they must be 90 or 120 degrees apart. I could have 18 phases 20 degrees apart. Each would still be a phase.