Current Calc: 2 Phase 3 Wire

[mivey]

Your sign conventions suck...JMHSO.

I did not pick the directions. I used the conventions jghrist picked. But I have no problem with them either. Consistency is the key and I did not want to complicate the thread by picking a different set of direction arrows.

Please spare me any explanatory rhetoric you may consider in response. I'm well aware of how changing value signs amidst calculations can achieve the desired result... but that does not mean your application of sign changing is acceptable in all math circles.

Math is a universal language. To communicate broadly, you must be willing to use the complete language. You choose to live in a small universe.

 

[rattus]

Same same:

Same same:

What would be your calculations for the current in the leg #2 if we assume: V12=480V @ 90?, V23=480V @ -30?, V31=480V @ 210??

The current is unaffected by an arbitrary choice of phase angles as long as 120 degrees separation is maintained.

 

[jghrist]

Come on guy!! Simple two single phase loads. 3.125 amps!!! Y-delta makes no difference, SINGLE PHASE LOADS. Ah, but what would the VOLTAGE be?

Two single phase loads, but they are different phases.

 

[rattus]

Beg to differ:

Beg to differ:

Come on guy!! Simple two single phase loads. 3.125 amps!!! Y-delta makes no difference, SINGLE PHASE LOADS. Ah, but what would the VOLTAGE be?

These loads are connected line to line which is a DELTA configuration, and has been said, you can't simply add the magnitudes; the currents must be expressed with complex numbers in order to add them. That is, the phase angles must be taken into account.

 

[mivey]

These loads are connected line to line which is a DELTA configuration, and has been said, you can't simply add the magnitudes; the currents must be expressed with complex numbers in order to add them. That is, the phase angles must be taken into account.

I thought he was joking. Profile claims EE.

 

[Smart $]

Please ignore my Post #8. It confuses the issue.

I12* = 600/480@90? = 1.25@-90? = 0 - j1.25 => I12 = 0 + j1.25

I did not pick the directions. I used the conventions jghrist picked. But I have no problem with them either. Consistency is the key and I did not want to complicate the thread by picking a different set of direction arrows.Math is a universal language.

But you are continuing to use a negated current angle when jghrist said to ignore post #8.

To communicate broadly, you must be willing to use the complete language. You choose to live in a small universe.

Communicating broadly is not the same as communicating as one understands the concept he is trying to communicate. Have you ever watched the show NUMB3RS? Also, using a simple language analogy, I'm sure neither of us are wordsmiths, so I have to ask you if a wordsmith comprised a descriptive sentence which exhibited utmost precision yet used words not in your vocabulary, would he be communicating broadly?

My universe goes well beyond the math. To elaborate further puts me closer to having a disposition quite similar to yours... one which I don't care to have. While that could be taken as a derogatory implication, it should be taken solely on face value in my universe.

 

[skeshesh]

This thread has gone on for a longer duration and different direction than I expected. Both open and closed delta calculations are pretty straight forward. As far as the discussion on the "math", while I do see some merit in Smart $'s comments, I have to say phasors should be pretty basic math for an electrical engineer. I'm not sure about years ago, but when I was in college just recently much higher level math was required. I don't think arbitrary selection of coordinates and angles for a mathematical calculation should be considered as overly complicated. I guess at the end of the day it matters most who the audience is...

 

[jghrist]

But you are continuing to use a negated current angle when jghrist said to ignore post #8.

I said ignore post #8 precisely because I had not used a negated current angle in post #8. Note that when mivey (properly) used the complex conjugate to negate the current angle, he ended up with the same current angle that I had in my original post. The current angle is the same as the voltage angle.

The complex conjugate is needed when using both power and current in equations because the convention for reactive power is to use a positive angle while the convention for reactive current is to use a negative angle.

See http://en.wikibooks.org/wiki/Circuit_Theory/Complex_Power

 

[mivey]

But you are continuing to use a negated current angle when jghrist said to ignore post #8.

You missed the point.

Communicating broadly is not the same as communicating as one understands the concept he is trying to communicate. Have you ever watched the show NUMB3RS?

No. I don't put too much stock in Hollywood's perception of reality.

Also, using a simple language analogy, I'm sure neither of us are wordsmiths, so I have to ask you if a wordsmith comprised a descriptive sentence which exhibited utmost precision yet used words not in your vocabulary, would he be communicating broadly?

If there is something that is not understood or you have to phrase it differently so someone can understand, that would be revealed in further discussion. If there is part of my post you do not understand, please elaborate and I will attempt to clarify it.

My universe goes well beyond the math. To elaborate further puts me closer to having a disposition quite similar to yours... one which I don't care to have. While that could be taken as a derogatory implication, it should be taken solely on face value in my universe.

My disposition generally does not include spouting off in posts with boasts of superior knowledge and elite circles. While I am smarter than the average bear, I try to embrace other's ideas and try to see things from their perspective. I readily admit I don't know everything (I would say I know very little) and often make mistakes. But I usually know what I'm talking about and am pleased to find out when I don't because it means I've learned something.

As for my universe, I refuse to join circles of self-inflated wind-bags who trumpet their ignorance with loud boastings of exclusive memberships and refuse to use math they label as inferior. So let the pompous clowns carry on with their so-called elitist standards and attempts to denigrate those who refuse to do things their way, while the rest of the world enjoys the full use of the universal language of math.

Let's get back to reality. What "math circles" do not put negative signs in front of an angle indicator? Why would they label that as an inferior method? Can we not accept that a lot of math results are represented by vectors in just the 1st and 4th quadrant? Who has deemed this as inappropriate behavior?

 

[rattus]

Let's get back to reality. What "math circles" do not put negative signs in front of an angle indicator? Why would they label that as an inferior method? Can we not accept that a lot of math results are represented by vectors in just the 1st and 4th quadrant? Who has deemed this as inappropriate behavior?

Mivey, does this mean that the L1, L2 voltages in a 120/240V service are correctly expressed as:

V1n = 120V@90
V2n = 120V@-90?

Or is it the other way around?

 

[mivey]

Mivey, does this mean that the L1, L2 voltages in a 120/240V service are correctly expressed as:

V1n = 120V@90
V2n = 120V@-90?

Or is it the other way around?

I did not word that correctly. I was trying to say that you will often see a result with an angle between 270 and 360 degrees represented as a negative angle between 90 and 0 degrees in the 4th quadrant.

Similarly, you will often see a result with an angle between -270 and -360 degrees represented as a positive angle between 90 and 0 degrees in the 1st quadrant.

As for V1n and V2n, they can be represented in many valid ways. I usually use 0 and 180 but here are some ways for the values you gave:
V1n = 120V@90 = 120V@-270 = 0 + j120
V2n = 120V@-90 = 120V@270 = 0 - j120

Not sure if that is what you meant by "the other way around".

 

[Smart $]

You missed the point.

Perhaps I'm better off

As for a person's disposition, I often find in my universe that others betray their true disposition by thinking of others as they themselves are.

 

[skeshesh]

I often find in my universe that others betray their true disposition by thinking of others as they themselves are.

This is slowly turning into the Mike Holt's philosophy of life forums!

 

[mivey]

As for a person's disposition, I often find in my universe that others betray their true disposition by thinking of others as they themselves are.

I'm sure you will rise above it.

I like the pic. :grin:

 

[mivey]

This is slowly turning into the Mike Holt's philosophy of life forums!

Maybe they will start a new forum. :grin:

 

[rattus]

I did not word that correctly. I was trying to say that you will often see a result with an angle between 270 and 360 degrees represented as a negative angle between 90 and 0 degrees in the 4th quadrant.

Similarly, you will often see a result with an angle between -270 and -360 degrees represented as a positive angle between 90 and 0 degrees in the 1st quadrant.

As for V1n and V2n, they can be represented in many valid ways. I usually use 0 and 180 but here are some ways for the values you gave:
V1n = 120V@90 = 120V@-270 = 0 + j120
V2n = 120V@-90 = 120V@270 = 0 - j120

Not sure if that is what you meant by "the other way around".

I was referring to the big yow-yow we had a while ago regarding the phase relationships between V1n and V2n, and to the fact which you emphasize that there are many correct ways to express these voltages.

 

[Cold Fusion]

... does this mean that the L1, L2 voltages in a 120/240V service are correctly expressed as:

V1n = 120V@90
V2n = 120V@-90?

Or is it the other way around?

Depends on which elitist circle you are writing for - possibly neither one. In my crayon circle of show me on the whiteboard, sketching, non-elite, field engineers:grin:, it's:
V1n = 120V@90
Vn2 = 120V@90

cf

 

[Cold Fusion]

I was referring to the big yow-yow we had a while ago regarding the phase relationships between V1n and V2n,...

I had guessed that.

cf

 

[mivey]

Depends on which elitist circle you are writing for - possibly neither one. In my crayon circle of show me on the whiteboard, sketching, non-elite, field engineers:grin:, it's:
V1n = 120V@90
Vn2 = 120V@90

cf

I had forgotten about that one. That works good too.

Be careful changing the subscripts around willy-nilly. You might run afoul of Smart$'s bizzaro-universe of standards and be ostracized from the elite circles where only a subset of correct answers is socially acceptable. Of course it is hard to look down your nose at anyone when you are crunching numbers with crayons. :grin: Us big boys are using these: Color Sticks

 

[Cold Fusion]

... Be careful changing the subscripts around willy-nilly. ...

Not willy-nilly, it's Techno-Willie. I don't recall ever doing a symetrical components short circuit analysis on a single phase power system. So, I'm pretty unconcerned abut the direction or phase angle notation of single phase system voltage vectors. But the notation and derection I listed works well when the techs ask and I draw the system on the board showing the vectors nose to tail.

... Of course it is hard to look down your nose at anyone when you are crunching numbers with crayons.

That's true, but I have done some of my best work on white boards - with a handfull of colors.

Well, except I am partial to the back of restaurant place mats - but that work is never in color

... Us big boys are using these: Color Sticks

But I bet you don't have a circular slide rule

cf