Mithun_K_Das
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I do not need to calculate 100% preciously. As with the DMM, near value is enough. Using a DMM, I can measure the Line-Line voltage. But I need the equation so that I can calculate the line-line voltage measuring the Neutral-Phase voltage.Hi,
If you want it to be exact, you need the phase angles information of the three line voltages. Treat them as vectors. Then subtract the vectors as you like.
For a raw estimation maybe averaging the two line voltages before multiplying with sqrt(3l is sufficient.
I don't know how you get the values of L1, L2, L3.
* It may be a DVM: Then you don't have the chance to get the angle, but you have tha chance to connect the DVM directly to L1 and L2 fir example.
Mind that a DVM is slow, it does not see fast variation, nor noise. And the voltage will vary!
So the values you see are valid only for a short time. Let's say you measured L1 first, then L2 .... can you be sure that L1 did't change?
What I want to say: if the measured voltages are not reliable and stable, then there is no need for an overly complicated calculation, because the result will not be more reliable than the inputs.
* if it is a scope: use the add/subtract function
* if it is an ADC: use synchronous sampling then subtract two input channels v1(t) - v2(t)
Klaus
But that we also find using DMM while measuring voltage Line to Line. How can we find the equation of that reading? Yes we know that taking average will not give actual value. But what equation we should use?Please review the simulation in previous post. It clarifies why the average attempt (or any similar approach) doesn't work. You get actual phase-phase voltages between 350 and 406 V for a similar situation due to phase shift.
If they calculate phase-to-phase voltage instead of measuring directly, they are adding/substracting instantaneous values, not rms values.In common 3 phase panel meters (volt) the lines and the neutral are connected to the meter. The GND of the internal circuit is common with Neutral. Or with a series resistor. And the other 3 phase lines are connected through some resistors. Simple voltage divider circuit.
But how do they calculate the phase to phase voltage just by measuring Phase to Neutral voltage? Of course, they use some kind of equation. Maybe that is not accurate enough but they measure it. And no negative cycle is measured there. If the N-Ph voltage is different, line-line voltage is also different.
No, it's your misunderstanding. I know the basic math and physics of 3phase. But you are misunderstanding me. Yes, it's complex to calculate. But I found many 3phase meters at extremely low cost. Inside the MCUs are also lower level which is not suitable for the basic math of calculating vectors, phase angles, and so on. But they are measuring. That is what I explained in my previous post. Also explained what I'm practically getting.Hi,
You ignore our answers.
You ignore rules for physics and math.
How can we help?
Klaus
Does that mean at a certain moment, they are comparing the difference between two voltage signals and then calculating from that difference? As physically the MCU is not capable of measuring the negative half.If they calculate phase-to-phase voltage instead of measuring directly, they are adding/substracting instantaneous values, not rms values.
I just want to know how they are calculating the line-line voltage measuring the line-neutral voltage while the individual phase is not equal in voltage. Nothing else. Also, it doesn't need to be 100% accurate.I notice that you didn't mention the project your are working on, used measurement hardware etc. Respectively it's not clear which kind of measurements is available and which calculations are feasible for you.
Maybe it´s a misunderstanding. Maybe because we still don´t know your situation. Sometimes you talk about DMM sometimes microcontroller. It is different as already written. All is already written.No, it's your misunderstanding. I know the basic math and physics of 3phase. But you are misunderstanding me. Yes, it's complex to calculate. But I found many 3phase meters at extremely low cost. Inside the MCUs are also lower level which is not suitable for the basic math of calculating vectors, phase angles, and so on. But they are measuring. That is what I explained in my previous post. Also explained what I'm practically getting.
If they can measure, that means they are using a suitable equation to calculate. If so, then what is that?
I just want to know how they are calculating the line-line voltage measuring the line-neutral voltage while the individual phase is not equal in voltage. Nothing else. Also, it doesn't need to be 100% accurate.
You get 381 V for line voltages of 230 and 210 V, it's the correct result for phase angle of 120°. In contrast the simulation shows 350 V with the assumed unbalanced load and a resulting phase angle of 105°.I don't know if it is right but as I measured with DMM, I found an equation that is exactly what we measure using DMM.
Say,
V1, V2, V3 are the Neutral to Line voltages.
Then,
Line to Line voltage:
V[1][/2] = Root([V[1]][/2] + V[2]][/2] +V[1]V[2])
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