You nailed it. Windings are rated in kVA or just amps!Isn't S known?

It is P and Q which are not, correct?

Does it really matter regarding winding phase current?

- Thread starter LongCircuit
- Start date

You nailed it. Windings are rated in kVA or just amps!Isn't S known?

It is P and Q which are not, correct?

Does it really matter regarding winding phase current?

- Location
- Boca Raton, Fl, USA

See, others are learning! Here's the rest!

Part 1, only V and A are known, so S (Apparent Power) = V x A = 126 x 56.3 = 7,150 VA!

Part 2, since P = 1,182 W (Real Power) is now known, then Q (Reactive Power) = Sqrt(S^2 - P^2) = 7,052 VAr!

I hate to ask the following of you, but since you didn't participate, how about revealing the load's power-factor... lagging or leading (decimal or %'s acceptable)!

Phil

Whoa! Whoa!

See, others are learning! Here's the rest!

Part 1, only V and A are known, so S (Apparent Power) = V x A = 126 x 56.3 = 7,150 VA!

Part 2, since P = 1,182 W (Real Power) is now known, then Q (Reactive Power) = Sqrt(S^2 - P^2) = 7,052 VAr!

I hate to ask the following of you, but since you didn't participate, how about revealing the load's power-factor... lagging or leading (decimal or %'s acceptable)!

Phil

We know S, and not P or Q, is what I said. How did we jump to knowing P in Part 2?

Ingenieur cannot tell you the load power factor because it has not been stated or otherwise established. For his calculations, he in effect stated the

- Location
- Placerville, CA, USA

As written, only the magnitude of S is known.Isn't S known?

It is P and Q which are not, correct?

Does it really matter regarding winding phase current?

If the phase offset on one L-L current is different than that of another connected to the same line it affects the magnitude of the corresponding L-N current and vice versa.

I am aware of that. Please keep the response simple. S* [scalar value; magnitude, if you will] is known, correct? P* and Q* are not, correct?As written, only the magnitude of S is known.

If the phase offset on one L-L current is different than that of another connected to the same line it affects the magnitude of the corresponding L-N current and vice versa.

*If we knew P or Q we could establish S vector.

How is knowing P and /or Q relevant?

What would knowing P and/or Q change?

- Location
- Placerville, CA, USA

It is not relevant as long as the phase angle of all three loads is the same.I am aware of that. Please keep the response simple. S* [scalar value; magnitude, if you will] is known, correct? P* and Q* are not, correct?

*If we knew P or Q we could establish S vector.

How is knowing P and /or Q relevant?

What would knowing P and/or Q change?

I assume you mean the sameIt is not relevant as long as the phase angle of all three loads is the same.

You do realize the probability of that being the case for unbalanced current magnitudes is quite, quite low, right there next to improbable, right?

- Location
- Boca Raton, Fl, USA

I'm not going to play your game of Obfuscation (typical of most engineers)! If anyone is interested in what I call "Vectors from Magnitudes" contact me off-forum!

Regards, Phil Corso

You want only phase current magnitudes. Kirchoff current law is applicable to both dc and ac circuits. So it should be applicable in an ac circuit with effective dc values only. So by considering line currents as dc values and replacing transformers by ideal dc sources (as a first approximation ) and by applying Kirchoff current law, equivalent dc phase current and so solution to your problem may be found.Good day, all.I require assistance in determining how tocalculatewhether one transformer in a three phase star/delta bank is overloaded based on the line current on the delta side (load side).I know that I can simply have a lineman take readings at the transformer at the X1 or X3 terminals, but I need to know how to calculate it.So for example, let's say that the bank consists of 50,75, 50 kVA transformers, and the line currents on the delta (load) side are taken to be 256A, 294A, 341A, how do I work out the phase currents in the delta side of the transformer?View attachment 15212Thank you in advance.

Sorry. I committed blunder: Kirchoff law cannot be appled that way..................Well another try. Suppose phase sequence of line currents is known. Then line currents can be represented in trigonometric form as functions of time. Each line current may also be represented as difference between respective phase currents also in trigonometric forms by applying kirchoff law. The resulting equations may be solved for an arbitrary instant of time to find intantaneous values of phase currents. From that it is easy to find RMS values.You want only phase current magnitudes. Kirchoff current law is applicable to both dc and ac circuits. So it should be applicable in an ac circuit with effective dc values only. So by considering line currents as dc values and replacing transformers by ideal dc sources (as a first approximation ) and by applying Kirchoff current law, equivalent dc phase current and so solution to your problem may be found.

If easy what are they?InJunEar...

Your wrong again! Both Q and S can be easily calculated! Knowledge of Xfmr %Z is unnecessary. The effect of %Z is already implicit in the OP's stated line-current values!

Phil

|V| 240

Iabc 256/294/341

no phase information known

You are correct

It is P and Q which are not, correct?

Does it really matter regarding winding phase current?

but with the given info P or Q can't be calculated

either one will give power factor

his example is easily calculated

1812 = 117 x 56.3 x pf

pf = 0.2751

ang = 74 deg

pf delta ang v - i

since v = 127 i = 53

Z = v/i = 2.08/74 Ohm

and

P 1812 given

Q 6332 j

S 6603/74

but the op NEVER gave P , Q or V phase, only V and I which yields a per ph kva

assume load is a ungnded wye

S/ph = 240/1.732 x Ix

frmm the kva a per phase |Z| can be calculated

|Z| = ph kva/V^2

op kva

35.5

40.7

47.25

Z

1.85

2.12

2.46

Iph

148

170

197

no phase info can be determined

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AHA! I traced his "example" back to post #75.Whoa! Whoa!

We know S, and not P or Q, is what I said. How did we jump to knowing P in Part 2?

...

Simple answers are best. It seems no one knows how to do that.

So it's just another "if" scenario that leads us nowhere, right?You are correct

but with the given info P or Q can't be calculated

either one will give power factor

his example is easily calculated...

I've often said people have a tendency to tell on themselves:

I'm not going to play your game of Obfuscation (typical of most engineers)! If anyone is interested in what I call "Vectors from Magnitudes" contact me off-forum!

Regards, Phil Corso

I'll buy anyone a beer (craft import to boot!) who can get mr phil to answer my questionAHA! I traced his "example" back to post #75.

Simple answers are best. It seems no one knows how to do that.

So it's just another "if" scenario that leads us nowhere, right?

I've often said people have a tendency to tell on themselves:

:roll:

If a tree falls in the forest what is the power factor?

You have to be in the forest when the tree falls to hear his answer. :happyyes:I'll buy anyone a beer (craft import to boot!) who can get mr phil to answer my question

:roll:

If a tree falls in the forest what is the power factor?

if that is the case I may jump into the trees fall pathYou have to be in the forest when the tree falls to hear his answer. :happyyes:

I could not bear another imaginary watt meter postulation

- Location
- Boca Raton, Fl, USA

InJunEar,

Just contact me off-forum!

Phil

Just contact me off-forum!

Phil

Hi folks! If each line current is known in trigonometric or vector form i.e if its intantaneous value as a function of time is known or if at least sufficient number of intantaneous values of each line current are known,then the phase currents may be found out.

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- Location
- Massachusetts

Phil this is lame.InJunEar,

Just contact me off-forum!

Phil

You keep telling posters they are wrong but you won't go into the reasons why or show how you feel it can be done.