Try -195? (-240? + 45?)
Calculation of neutral current
- Thread starter him76er
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kingpb
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This has been a good excercise to show how to obtain get an approximate neutral current. However, I was hoping someone might point out the fact that this is all based on the assumption that the voltages are 120deg apart.
Given the only information in the OP, some assumption had to be made, but lest not we forget that the line-to-neutral voltages in an unbalanced system will not be 120 degrees apart, therefore the 58.8 A is only accurate within some margin.
Given the only information in the OP, some assumption had to be made, but lest not we forget that the line-to-neutral voltages in an unbalanced system will not be 120 degrees apart, therefore the 58.8 A is only accurate within some margin.
-210 deg is wrong. Try again.
kingpb
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Mull982 edited his post within 3 minutes after realizing his error. You and Smart $ must have missed it
Mull982 edited his post within 3 minutes after realizing his error. You and Smart $ must have missed it
We would have posted anyway even if we had seen Mull's reply.
His post still has Ic = 40A @ -210deg...Mull982 edited his post within 3 minutes after realizing his error. You and Smart $ must have missed it
...what did I miss?In a wye system, how so if all loads are line-to-neutral...???
Some graphical representations of both the graphical and mathematical solutions...
Fig. 1
Fig. 2
Fig. 3
What is missing from the formulas in Fig. 2 that prevent solving for n?
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Pham Van Hung
Member
Dear Smart $,
I tried to use different method, that is using complex number operation under Ia = 1.41 * Ia rms * Sin (ωt + ψa). Adding phase current under complex number gets 53.65A (In = -53.642 - j 0.94). This is different to 58.86A calculated.
Where am I wrong?
Another question, can we calculate neutral current of 3 phase 4-wire system when only rms currents of phases are known? (power factor is not known).
Is the neutral current cause waste of energy under dissipated heat?
Hope your quick help.
glene77is
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where's "N" plug in...
Cad, I know you are making a joke, ha.
"N=" goes in front of the formula, and that makes an equation.
BUT, still no phase shift info.
What is the word I'm looking for . . . "Power Factor" !
Thats it! These electrician terms !
Have to learn two languages to get along, nowadays.
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How am I supposed to determine where you went wrong if you only provide the format of your vector math and your wrong answer. I would need to see the entire calculation. Otherwise all I can tell you is you went wrong somewhere in the middle
If you don't want to make your calculation public, PM it to me...Calculating with peak values (moduli) vs. rms values does not matter, as long as you are consistent throughout the calculations with the same type of values. As for calculating currents without knowing the power factor, you could assume all power factors are the same if all loads are of the same design. If not, it would be best to use approximate, typical power factors. As exemplified by this thread, accuracy of the resulting value can vary widely without knowing the power factor (or its equivalent).
Yes there will be the typical I?R losses associated with any neutral current. But if it is cold outside and the neutral conductor is inside a facility that relies on some type of space heating to keep it warmer than outside, then the energy is not wasted until it is warmer outside than it is inside.
Pham Van Hung
Member
Hi Smart $,
The link seems useful, but I have some questions for using the simulation.
1. As my understanding, the value on vertical axis is for percentage of phase current vs balance current. However, I don't know how to determine exactly the balance current.
In the OP, 50A, 40A and 40A, so the balance current should be 40A? and the phase 1 is 125% of the balance current?
Let's take another case of 175A, 190A and 210A so what is the balance current?
2. The other tabs in the simulation is Xc and XL, from that to give the phase angle shift, but how? as Xc and Xl are unknown in the OP.
In other words, which values of Xc and Xl to be put to represent PF of 0.707 lagging, 0.866 lagging and 0.707 leading?
thanks
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The phase angle shift (and Xc, Xl) are given by the power factor. Phase angle = arccosine(power factor.)
So the phase angles in the OP are .707 lagging = -45deg, .866 lagging = -30 deg, and .707 leading = +45deg.
In terms of the simulator, for an R value of 1, .707 lagging would require a value of Xl=1, .866 lagging would require a value of Xl=0.577 and a .707 leading would require a value of Xc=1.
I can't answer your questions. I have not downloaded or used the simulation.
Pham Van Hung
Member
When input the above parameters in your quote, the graphics show neutral current of about 1.2 time of phase current, about 48A ? It is not correct.
If we change the current of phase A to 125% (50A in phase A is 1.25 time of 40A), the neutral current is approximate 1.5 time of balance current, that is 1.5 x40A = 60A. This is near the right value 58.86A.
Anyway, this simulation has no room for actual current input and an approximation tool. Anyone has another tool of graphic representation?
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You are correct that this simulator doesn't accurately show the current magnitude when you add an Xl or Xc component. 0R and 1Xl still shows zero current.
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The answer is 58.86 Amps. One of your vectors is wrong.
45, 150, and 195 the last coming from 240-45
In is, as has been stated above a couple of times, 58.86A.
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