wye vs delta.

[Smart $]

Yes, but it should be noted that the Delta-source neutral is not at the same potential as the Wye-load neutral, nor should they be connected.

Considering the likelihood of someone actually doing this, I felt it was not necessary to note such

 

[LarryFine]

Considering the likelihood of someone actually doing this, I felt it was not necessary to note such

Actually, my comment is aimed toward those who consider re-supplying an existing Delta panel from a Wye source.

Actually.


"They mostly come out at night . . . mostly." ~ Newt in Aliens

 

[mivey]

I thought the shoe is where the flash mounts.

It is. It is also feet for the tripod (like rubber shoes, pivoting shoes, etc). There is also a shoe when the tripod has a quick-release plate/shoe adapter. See the features here:
http://www.bhphotovideo.com/c/product/133411-REG/Mamiya_211_571_Quick_Shoe_Model_3.html#features

 

[LarryFine]

Well, I guess the shoe is on the other foot now. :grin:

 

[zog]

I just finished 4 chapters of transformers at school and i am still very confused. I'm in a class where the much younger students and the teacher have the common interest of getting out of class 2 hours early which means asking questions in class is pretty much out. So i'm hoping to get some help here.

Sorry to hear that, I did training for 10 years and this seems to be the way a lot of training is done. 1st question was always what time will we be done? I never let them out early, in fact I would sometimes assign homework. They were not happy but by the end of the course they actually learned something.

 

[K2X]

Sorry to hear that, I did training for 10 years and this seems to be the way a lot of training is done. 1st question was always what time will we be done? I never let them out early, in fact I would sometimes assign homework. They were not happy but by the end of the course they actually learned something.

Well thanks, I'm tinking hard about going into 3rd year. I think i'm going to try to sit in on some third year classes this year and see if the instructors are actually trying to teach something.

Regarding Delta and Wye. Thanks for the replies, i'm still trying to digest.

This stuff is hard.

 

[Volta]

Actually, my comment is aimed toward those who consider re-supplying an existing Delta panel from a Wye source.

Actually.


"They mostly come out at night . . . mostly." ~ Newt in Aliens

Thanks- we'll be careful with that one! :roll: :grin:

 

[firealarmguy]

Well thanks, I'm tinking hard about going into 3rd year. I think i'm going to try to sit in on some third year classes this year and see if the instructors are actually trying to teach something.

Regarding Delta and Wye. Thanks for the replies, i'm still trying to digest.

This stuff is hard.

Delta and Wye can be a little tricky....still trying to master delta-wye transformations.

Remember the following for delta & wye:

Wye:

1. Voltage line to line = 1.73 x Phase voltage (line to neutral)
2. Line current = Phase Current

Delta (standard, not high leg):

1. Voltage line to line = Phase Voltage
2. Line Current = 1.73 x Phase Current

The Wye is easier to implement 120/208 3 phase than the Delta. However, the delta does have 240 volt 3 phase which can be an advantage for certain motors.

 

[Smart $]

...

Delta (standard, not high leg):

1. Voltage line to line = Phase Voltage
2. Line Current = 1.73 x Phase Current

...

Need to note your #2 is only true of balanced loads.

 

[WDeanN]

New mental image for a wye system:

Let's compare a 120/240v winding like the pedals of a bicycle, with the two pedals at the usual 180 degrees apart, with the axle of the crank as the center tap. Let's say the length of each pedal's arm is 120v long, so the pedal-to-pedal distance is 240v.

Okay, here 'tis:

We still have three legs, but instead of a three-armed pedal crank setup, let's say our bike is a velocipede (and no, it's not a dinosaur) with three pedals bolted to the front wheel.

So what would a zig-zag transformer for grounding a delta system look like?

Would this be a tandem tri-pedal bicycle?
Who sits in front and steers?

 

[Smart $]

So what would a zig-zag transformer for grounding a delta system look like?

Would this be a tandem tri-pedal bicycle?
Who sits in front and steers?

Nah! Same bicycle with planetary geared hub

 

[KP2]

K2X, I recently took a Mike Holt free quiz and a question that I had no idea how to answer was, "what is the neutral load on a 3phase 208/120 volt wye transformer with a balenced load on two phases and no load on the third phase?
A 70%
B 80%
C 90%
D 100%

I had to guess 70%. And after looking into the books I have, and google I still had no idea. I found a post in the forum archives, "unbalenced neutral currents in three phase systems. It was a great thread. Mostly over my head but I learned the answer was 100%. Good luck with school. I'm starting my journey to be an engineer in Sept.
Kevin

 

[LarryFine]

Kevin, here's how to visualize why it's 100%, or equal to the other two lines (if they're equal.) Start with a balanced load; zero neutral current, right?

Now, reduce one line by one amp, and the neutral current will jump up that same one amp. Keep going until that line has zero current. See it now?

 

[KP2]

Kevin, here's how to visualize why it's 100%, or equal to the other two lines (if they're equal.) Start with a balanced load; zero neutral current, right?

Now, reduce one line by one amp, and the neutral current will jump up that same one amp. Keep going until that line has zero current. See it now?

Larry, I referring to a 3 phase 208 / 120 volt transformer. Your rationale is true to a single phase 240 / 120 volt transformer. Here is the answer to your example for a 3 phase system.

phase currents
A B C N (grounded point)
0 10 10 10
0 10 9 9.539
0 10 8 9.165
0 10 7 8.888
0 10 6 8.718
0 10 5 8.66
0 10 4 8.718
0 10 3 8.888
0 10 2 9.165
0 10 1 9.539
0 10 0 10

Use the 3 phase neutral formula and omit the A phase. N=sqrt B^2 + C^2 - BC.

 

[KP2]

That did not post how I typed it, but I think it makes sense.

 

[Smart $]

Larry, I referring to a 3 phase 208 / 120 volt transformer. Your rationale is true to a single phase 240 / 120 volt transformer. Here is the answer to your example for a 3 phase system.
...
Use the 3 phase neutral formula and omit the A phase. N=sqrt B^2 + C^2 - BC.

Your calculation is not what Larry said, which was start with a balance load... i.e. A phase would also be 10.

 

[KP2]

Your calculation is not what Larry said, which was start with a balance load... i.e. A phase would also be 10.

I see what you mean.
A = 10
B = 10
C = 9
N = 1

or

A = 10
B = 10
C = 5
N = 5
I didn't realize the neutral would change like that. Thanks for helping me out.
And thanks to Larry as well.

 

[LarryFine]

Larry, I referring to a 3 phase 208 / 120 volt transformer.

As was I. My example was to explain why you have what you used as the starting point:

phase currents
A B C N (grounded point)
0 10 10 10

In other words, why the neutral of two lines is a CCC when the source is a 3ph Y.

 

[KP2]

I see that now. Thanks for the example. After doing it out it makes sense.
Thanks again
Kevin