single vs. 3 phase

[coulter]

Brings up another issue of the delta 3-wire vectors. You can draw it with arrows going clockwise. Or counterclockwise.

True. For me that comes up when syncing generator to utility. I've only worked a few, so could be that "Coulter's Law of Stastical Samples of One" are getting me. For some reason, the utility PTs and the bus PTs are Wye. Generator PTs open Delta. Really improtant to pay attention to the scope connections when verifying phasing and rotation for the synchronizer.

carl

 

[coulter]

rattus refering to rotation:

Hoping someone would become non-silentio on the subject!

I really don't think I have anything more to add that will help.

A couple of threads ago we had a similar discussion. No matter what I said, or references I gave, your responses translated to, "Not so - I'm right." And you kept asking for more. Eventually I got to thinking that repeating myself would not help. You didn't read it the first or the second time - no reason to think you would read it the third.

We are in a similar suituation. However you have added an additional response, "That's pointless - it has nothing to do with this discussion."

My only suggestion is to read jon's post 260.

carl

 

[mivey]

...I can even redefine a Scott Tee." (Yes, you did that, see post 253...

I think you are confusing a phasor diagram with a circuit diagram. Get that straight, then go back and read post 253 so you can understand what I am saying.

Then I would suggest you go read winnie's post #260 and answer his question

For example, if you operate on the principal that the phasors used to describe the two sides of a 120/240V single phase system should both be 120V 0 degrees, what phasors are used to describe the _three_ outputs of a 240/120 high leg single phase system?

I have already said you could show these with three phasors in a "T" orientation with the phasors Van, & Vbn, & Vcn. I did not suggest using Van, Vnb, & Vcn. In the general case, when neutral loads are present, I don't think I would use Vab, Vbc, Vca.

I you try to represent the shape of a circuit diagram by using phasors, you are limiting yourself on which phasors you can use. Again, a phasor diagram and circuit diagram are two different things.

This significance of this statement completely eludes me.

Simply stated, you can meter a 3 phase 3-wire with two stators but should use 3 stators for a 3 phase 4-wire. What you may decide to do for a 3-wire may be different than what you decide to do for a 4-wire.

...And, I don't ever remember doing a fault current analysis...Fault current analysis doesn't have much to do with the neutral...

Carl, when I first started playing when these circuits, I did not even know there was such a thing as fault current analysis. I was a child experimenting with circuits on my bedroom floor.

Fault current analysis doesn't have much to do with the neutral.

Did you just say that a neutral does not play a significant role during a fault?

[edit: typo]

 

[jim dungar]

Any phasor arrow can be drawn in either of two directions whether it makes sense or not.

And I am still waiting for additional reasons why you would choose a direction that is: opposite that of the current in the winding when looking at 2-wire loops; opposite that of the transformer polarity marks enumerated by IEEE/ANSI; and ignores the physical laws of transformers.

To use a previous analogy.
If I pick myself as a reference point I can say that a plane is coming towards me or going away from me but the plane never changes its actual direction. Now if you are standing on the North pole the plane is still moving in its original direction but you can say it is coming North and then going South. At the same time If Mivey stands at the equator and watches the same plane fly over the North pole he can say the plane is going North and then it is going South.

Moving the point of reference does not change the real/actual direction of the plane (which hopefully is always forward as dictated by its engines). The only thing that changes is how the movement appears to each one of us and therefore how we describe that movement.

 

[coulter]

I think you are confusing a phasor diagram with a circuit diagram. ...

I think you are right:-?

... Get that straight, ...

I'm trying - but truly I'm having difficulity in separating the two. When tmy fingers grab the picture out of my head, that's sort of the way I want to hook them up.

... then go back and read post 253 so you can understand what I am saying. ...

I did several times I did again I promise I really tried. I get stalled somewhere around, "but some of the secondary phasors could be in a "T" or "X" or "L" or box or triangular shape..." An 'X' or an "L", that just doesn't make any sense to me at all 'Box" leaves me blank - triangular I could see.

Ususally I'm not too dumb about this stuff. I can generally figure out where someone is headed. You guys are making me feel bad. (This is humorous, not adversarial - but true) Sigh

carl

 

[coulter]

...Simply stated, you can meter a 3 phase 3-wire with two stators but should use 3 stators for a 3 phase 4-wire. ...

Okay - got that, true.

carl

 

[coulter]

... when I first started playing when these circuits, I did not even know there was such a thing as fault current analysis. I was a child experimenting with circuits on my bedroom floor. ...

Me as well. But I did move on.

carl

 

[coulter]

...Did you just say that a neutral does not play a significant role during a fault? ...

I hope not. I'm going back to look.

"Fault current analysis doesn't have much to do with the neutral.

Okay, you would have had to translate that. Try this:

For 240/120 4WD, the neutral has little to do with calculating the 3ph bolted fault current - which is what one would use for selecting panels and CBs.

Hopefully that reads a little better.

carl

 

[mivey]

Ususally I'm not too dumb about this stuff. I can generally figure out where someone is headed. You guys are making me feel bad. (This is humorous, not adversarial - but true) Sigh

carl

Just a quick example. I can draw a phasor for the voltage across the coil of a transformer, say the A-B coil. I can also draw a phasor from the A-B center tap "N" point to the C terminal. The A-B phasor can be used to draw a phasor that has the same orientation as the actual coil (i.e. it can look like the actual circuit component). It can also represent the voltage from A to B.

The C-N phasor can represent the voltage from C to N but when drawn, will not resemble a circuit component (unless you connect a load between C and N.

The phasors are used to represent referenced voltages (or currents) in the circuit but are not actually a circuit diagram. A subset of available phasors can be used to show certain voltages that have reference points that lie along the circuit path.

[edit: I forgot you asked about the box. For a 5 wire Scott-Tee with 1-2 connected to 3-4 in an "X" shape (1 on right, 2 on left, 3 at top, 4 at bottom), I can draw a "box" using the phasors 1-3, 3-2, 2-4, 4-1. I guess there would be no reason I could not connect resistors from 1-3, 3-2, 2-4, and 4-1 and these phasors would show the current/voltage for these resistors]

 

[mivey]

I hope not. I'm going back to look.


Okay, you would have had to translate that. Try this:

For 240/120 4WD, the neutral has little to do with calculating the 3ph bolted fault current - which is what one would use for selecting panels and CBs.

Hopefully that reads a little better.

carl

Whew! The earth is back on its axis. :smile:

 

[coulter]

...[edit: I forgot you asked about the box. For a 5 wire Scott-Tee with 1-2 connected to 3-4 in an "X" shape (1 on right, 2 on left, 3 at top, 4 at bottom), I can draw a "box" using the phasors 1-3, 3-2, 2-4, 4-1. I guess there would be no reason I could not connect resistors from 1-3, 3-2, 2-4, and 4-1 and these phasors would show the current/voltage for these resistors]

I've never seen or heard of a 5W Scott Tee. Can you buy one? What would you do with it? Power up a 2ph system? Haven't ever seen one of those either.

carl

 

[crossman]

If I pick myself as a reference point I can say that a plane is coming towards me or going away from me but the plane never changes its actual direction.

Moving the point of reference does not change the real/actual direction of the plane

There is no "real" or "actual" direction of that plane. The direction and speed of that plane is totally dependent on the choice of reference.

sorry if this leads the thread astray

 

[mivey]

I've never seen or heard of a 5W Scott Tee. Can you buy one? What would you do with it? Power up a 2ph system? Haven't ever seen one of those either.

carl

It was before my time but here you go, from my GE distribution transformer manual diagram #31:

 

[mivey]

There is no "real" or "actual" direction of that plane. The direction and speed of that plane is totally dependent on the choice of reference.

sorry if this leads the thread astray

I think it is one of the main themes of the current discussion

 

[mivey]

As for the 240 and 208 discussion read
http://forums.mikeholt.com/showthread.php?t=97747
so why don't we just call 120/240 "single phase service" and 120/208 "network service". EEI uses the term network in their metering handbook to describe 3-wire 120/208.

[edit: they actually have a section titled "How to distinguish between three-wire network and three-wire, single-phase services"]

 

[coulter]

It was before my time but here you go, from my GE distribution transformer manual diagram #31:...

So 5W Scott was common in 1938 for powering up 2ph systems. I can't say I ever had to do analysis on one of these.:smile:

carl

 

[mivey]

...If I pick myself as a reference point I can say that a plane is coming towards me or going away from me but the plane never changes its actual direction. Now if you are standing on the North pole the plane is still moving in its original direction but you can say it is coming North and then going South. At the same time If Mivey stands at the equator and watches the same plane fly over the North pole he can say the plane is going North and then it is going South...

I agree with this direction description. Now, who says we have to use the North pole as a reference instead of using where Jim Dungar is standing? Does IEEE/ANSI say that we have to use the polarity dots to define our reference or do they say the dots are there so we know how the transformer is wired? If we must use the current coming out of the polarity dot, why would metering ct's be wired to measure the current flowing at X1 and X3 instead of X1 and X2?

 

[jim dungar]

There is no "real" or "actual" direction of that plane. The direction and speed of that plane is totally dependent on the choice of reference.

sorry if this leads the thread astray

Foward, opposite the engine thrust, is not a direction?

 

[jim dungar]

I've never seen or heard of a 5W Scott Tee. Can you buy one? What would you do with it? Power up a 2ph system? Haven't ever seen one of those either.

carl

Be careful.

There are T connected transfromers and Scott "Tee" connected units.

T-connected are the normal run of the mill 3-phase dry type units we see every day, they are usually limited to max 15kVA.

Scott units were designed specifically to convert a 3-phase system into a 2-phase system.

 

[jim dungar]

I agree with this direction description. Now, who says we have to use the North pole as a reference instead of using where Jim Dungar is standing? Does IEEE/ANSI say that we have to use the polarity dots to define our reference or do they say the dots are there so we know how the transformer is wired? If we must use the current coming out of the polarity dot, why would metering ct's be wired to measure the current flowing at X1 and X3 instead of X1 and X2?

I have not said you have to pick a specific reference point. I have been asking for more than one reason why you chose your method voltages when it ignores the real world construction of a transformer.

I don't know which metering cts you are talking about with your "X" references. A standard utility KWH meter for use on 120/240V 3-wire circuits has a single potential coil wired Line-Line, and the current coils facing different directions (it does not reference the neutral at all). They have the currents in different directions for the ease of manufacture (see it is possible to have a reason for different directions). A two-element wattmeter for 4-wire WYE loads has two current coils, call them A & B facing in the same direction and two current coils, call them C and D that face in opposite directions.