Clock Notation of Star-Delta 3-phase transformer

[jaus tail]

Homework Statement

Homework Equations

Dot is A2.
A1-A2 of star is in phase with A1-A2 of delta

The Attempt at a Solution

I'm getting answer as Y-Delta - 1. Assuming Y is HV.
How is C right answer?

 

[jaus tail]

I think for Yd-7, the dots on L.V (Delta connected) winding should be on right side of each winding.

 

[Baluncore]

That is the first time I have seen the terminals drawn against the magnetic laminations, with a greater separation between the primary and secondary.
But here are some others without the laminations.
https://www.kullabs.com/classes/subjects/units/lessons/notes/note-detail/3507
Notice the polarity of the secondary is reversed which puts a 180° shift in all phases.
That may convert 1 o'clock to 7 o'clock.

 

[jaus tail]

I practiced from this website and was able to draw clock correctly for all phasors. But I still think the question in post one isn't YD-7.
The polarity aren't reversed in secondary. In primary current is from Terminal R to winding, whereas in secondary it's from R winding toward terminal. So the flux of both are in phase.

From what I know:
1) Mark A2 of winding that is closest to input connection/source.
2) Mark other end of winding as A1.
3) A1-A2 is in phase with a1-a2 or out of phase with a1-a2. Same for B1 - B2 ---> b1 -- b2 as well as for C1--C2 and c1---c2
4) In star A1 is neutral.
In delta, A1 and A2 is also B1 or B2 or C1 or C2 so from there start phasor of other winding. Like in above clock, right side, a2 is also c1, so start c1 -c2 from a2.
5) Use Dots for
----Now if in primary current is entering winding from A2 terminal and in secondary current is leaving winding from a2 (figure out from dots), then A1-A2 and a1-a2 are in phase.
----But if in primary current is entering winding from A2 terminal and in secondary also current is entering winding from a2, then A1-A2 and a1-a2 are 180 degree out of phase.

 

[jaus tail]

I got this phasor diagram

Left is from google:
http://electrical-engineering-portal.com/understanding-vector-group-transformer-1

Right is the one in practice test. I don't think right one is YD-7. Please help me. Exam is in 10 feb. Thanks.

 

[jim hardy]

I've never encountered that kind of notation before. Do the odd numbers 1 5 7 11 refer to phase shift somehow?

From that link you posted, Star-Delta is either YD₁ or YD₁₁
https://www.kullabs.com/classes/subjects/units/lessons/notes/note-detail/3507
..............................

....................................

So, drawing yours i get (pardon my awkwardness with Paint)

Looks to me like YD1 per that KULLABS reference.

Aha ! found another reference...

http://electrical-engineering-portal.com/understanding-vector-group-transformer-1
....................................

..................................

Starting from the very basics i get same phase shift as you got, thirty degrees behind.
/Begin Rant
Is this the same book that's so fraught with other errors?
Point them out to your department head. What kind of example is that to set for engineering students?

Please correct me if I've made an error. This is my first experience with that labeling scheme, and i think it's an unnecessary embellishment.
Just figure it out from the basics it's not difficult and as your textbook example shows these "mental shortcuts to avoid thinking" lead to mistakes..
The added confusion that you order the letters not by direction of normal power flow but by voltage-- well how "cute" - i don't know why it aggravates me so, perhaps "Old Dog New Trick" ...
/End Rant.

Satire III
By John Donne
Kind pity chokes my spleen; brave scorn forbids
Those tears to issue which swell my eyelids;
I must not laugh, nor weep sins and be wise;
Can railing, then, cure these worn maladies?...

old jim

 

[Baluncore]

I've never encountered that kind of notation before. Do the odd numbers 1 5 7 11 refer to phase shift somehow?

Yes. The 1, 5, 7 and 11 refer to the hour hand on a clock. 6 and 0, or should that be 12, also happen. There are 12 hours on the clock face so each hour is 30° degrees. And so here I am trying to forget that the sun appears to move 15° per hour in the sky. I have been trying to sort out the convention but I get phasor angles that are the opposite of what I need.

My logic at the moment is ...
Phasors rotate counter-clockwise mathematically. A2 is the reference pointer so it points upwards at 12 hours. It will be followed by B2 at 4 hours and then C2 at 8 hours. The phasors are lettered or named clockwise because they are rotating anticlockwise.

Swapping the end connections to all primary or secondary windings, introduces a 180° shift which would be called Yy6. Reversing both will cancel back to Yy0.

The secondary voltage is in phase with the primary, so phasor positions at time zero may be rearranged, but not the orientation of the phasors, when for example the connections are changed to make the y secondary into a delta. That is neglected by many references and leads to major confusion. You got it right in your paint, the diagram you cut and posted got it wrong. Why is that so difficult?
I float the neutral in the middle of the delta as my phase origin.

There are two ways of doing that transformation.
1. You can connect a2 to c1 etc, which makes a Yd1 group, secondary leads primary by 30°.
2. You can connect a2 to b1 etc, which makes a Yd11 group, secondary lags primary by 30°.

It just does not seem to make sense yet, I am always out by two hours.

 

[jim hardy]

You got it right in your paint, the diagram you cut and posted got it wrong. Why is that so difficult?

All i did was pay close attention to labeling and add them head to tail , as we were taught decades ago.
Hmmm

He sure did get it wrong, didn't he ? That's ahead. Thanks, i missed it.
i was taught if you're rigorous in labeling you'll come out okay. That's what i did in that Paint sketch.
I was taught like you, N goes in the center. My professor always drew V_NA horizontal though .
I don't think it is difficult, in fact it's way easier than trying to memorize all that stuff.
Mixing CCW rotating phasors with CW rotating clock faces is in my opinion a disservice to students. Even the KULLABS guy got confused.
My old mentor often said "Just watch how people will work their butts off to avoid thinking."

Have you followed Jaus's adventures with this textbook? It seems to me fraught with errors.

LATE ENTRY -- the 1 and 2 suffixes weren't shown, just the dots. Jaus assigned 2 to the dotted ends. I stuck with that on both primary and secondary. Kullabs didn't show dots. So both Jaus' textbook and Kullabs' tutorial were less than rigorous in labeling. And rigor in labeling is key to working three phase. old jim

 

[jaus tail]

What is the labelling way to draw clock?

Is this answer YD1 or YD7? It's always difficult to think that book may be wrong.

 

[jim hardy]

It's always difficult to think that book may be wrong.

Where does book put A1 and A2 on primary and secondary ? Same place you did, or A1 on left both primary and secondary ? That'd reverse the secondary connections as @Baluncore suggested.

Gotta be rigorous in labeling. If textbook didn't label with rigor it's student's choice and a textbook error

Stick with the basics.

 

[jaus tail]

I tried a hand at YD5

Is this right?

 

[jaus tail]

Where does book put A1 and A2 on primary and secondary ? Same place you did, or A1 on left both primary and secondary ? That'd reverse the secondary connections as @Baluncore suggested.

Gotta be rigorous in labeling. If textbook didn't label with rigor it's student's choice and a textbook error

Stick with the basics.

Book has only drawn YD1 and YD11 and not labelled anything. just dots. I found labels on google.

 

[jaus tail]

@Jim

When would you draw delta red phasor in phase with HV phase and out of phase with HV phase?
For which dot connection would you draw R phasor of delta from right to left.
Here you have drawn R phasor of Star from left to right and R phasor of Delta from left to right?

How did you achieve this conclusion from the dots on winding?

 

[Baluncore]

Is this answer YD1 or YD7?

I am not yet sure of the correct process to follow when reading the clock.
When I am convinced I understand it, I will be happier.

Then there are slippery things like this.
The "UPPER" case labels refer to HV terminals, not to the primary.
The "lower" case labels refer to LV terminals, not to the secondary.
Does that affect the hour?

 

[jaus tail]

Upper case is HV and lower case is LV. Yeah I know that. It will change hour form 1 to 11 and 5 to 7 if one employs with reverse nomenclature.

 

[jaus tail]

I think the question in post#1 is wrong. I tried all clocks here
http://electrical-engineering-portal.com/understanding-vector-group-transformer-1
with rules in post#4 and got right clocks.

Can somebody please explain with?

When will the other winding phasor be upwards and when will it be downwards? As in where should dot be?

 

[jim hardy]

Is this right?

Add your numbers to the windings ? Then its labelled with rigor.

Vab is shifted ahead 210 degrees ? On a clock face, advancing from 12 by 210 degrees would put the hand at 7 o'clock.. (unless it's 24 hour clock).

Whoever invented that notation probably had a digital watch. Makes me want a sundial.

old jim

 

[jaus tail]

Yeah a2 is actually c1. I named wrong at delta triangle. This gives 7'o clock now.

 

[jim hardy]

I was taught to label voltage From - To , ie voltage from Neutral to A is Vna .
Voltage from A to Neutral is Van.
Draw your phasor with tail at FROM and head at TO.
So Van points one way. Vna points opposite.

When will the other winding phasor be upwards and when will it be downwards? As in where should dot be?

Direction of phasor is determined by dot and which ends of the winding you assigned as FROM & TO... that is, where you wrote your a1 and a2

i'll have to digest your post 4. It's kinda long.

 

[jaus tail]

@jim hardy
As per your rules will the two diagrams below have different clocks / phase shifts?

 

[jaus tail]

As per what I've studied till now, there must not be any difference in clocks of above two connections. But I need to be sure.

 

[Baluncore]

They are the same because the dots are consistent, the dots show the arrow head end of each phasor. BUT there is still one unknown. You must be consistent, because you do not know if the windings should be labelled A,B,C, from the top to the bottom, or from the bottom to the top. That means the rotation could be forwards or backwards. It is not possible to know the direction of rotation from the dots alone.

Without a specification of the order of the winding's phasors, the question of Yd1 or Yd11 becomes impossible to answer, because there are two ways to wire a delta, or to label the diagram, forwards or backwards.

 

[jim hardy]

@jim hardy
As per your rules will the two diagrams below have different clocks / phase shifts?
View attachment 218935

Great question .
Clearly they'll behave the same when measured at their dotted ends. But -- As "Author In Charge of the drawing" you're free to assign your labels this way, Not that you would but somebody else might.

Left one, secondary Vab is voltage across A winding. Right one, it's voltage across B winding..
Label carefully. .

 

[jaus tail]

Great question .
Clearly they'll behave the same when measured at their dotted ends. But -- As "Author In Charge of the drawing" you're free to assign your labels this way, Not that you would but somebody else might.
View attachment 218946
Left one, secondary Vab is voltage across A winding. Right one, it's voltage across B winding..
Label carefully.
.

Just to clarify:

I intended this. The labels on secondary right side are at terminals, and not near to the core. So I guess book is wrong in post#1. My rules in post#4 are correct. Thanks.

 

[jim hardy]

I think you have it now.
This worries me somewhat

5) Use Dots for
----Now if in primary current is entering winding from A2 terminal and in secondary current is leaving winding from a2 (figure out from dots), then A1-A2 and a1-a2 are in phase.
----But if in primary current is entering winding from A2 terminal and in secondary also current is entering winding from a2, then A1-A2 and a1-a2 are 180 degree out of phase.

Dots are simpler than that.
The dots tell you which ends of a winding pair go positive (with respect to other end of that winding) at any instant.
In your most recent drawing, when A end on the primary winding goes positive, A end on the secondary winding also goes positive. With respect to other end of same winding .
Same for the B's, and the C's.
In both your One and Two .

The dots guide you in assigning your labels so that your phasor diagram will work out nicely.

 

[Baluncore]

Here is a phasor diagram showing a primary star with the two possible secondary delta configurations.
The Neutral is on the zero volts line. Winding ratio is 1:1

 

[jaus tail]

There are actually 4 possible combinations. The delta r line can face downwards as well.