- #1

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is it possible to sum at any given moment in time L1 + L2 + L3, algebrically speaking? If so, what would this value represent?

Thanks

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- Thread starter mariano54
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- #1

- 21

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is it possible to sum at any given moment in time L1 + L2 + L3, algebrically speaking? If so, what would this value represent?

Thanks

- #2

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If L1,L2,L3 are currents than their sum will represent neutral current (if there is a neutral conductor in 3- phase system, that current flows through it).

is it possible to sum at any given moment in time L1 + L2 + L3, algebrically speaking? If so, what would this value represent?

Thanks

Generally, one third of the phasors sum of all 3 phasors represent zero sequence phasor (in treatment by symmetrical system components)

- #3

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- #4

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Values must be taken at same instant of time, then the above holds.What if I sum L1 + L2 + L3, just the values?

- #5

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- #6

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current L1 * voltage L1 +. ... + currentL3 * voltageL3 (the formula is more complex, but I'm interested only on the phases)

so the currents in the single phases are relevant. Logically speaking, if I can use all three phases to calculate how much power the system is using, shouldn't I be able to add them up and say how much current is going into the system and thus used by the system?

Thanks

- #7

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OkI'm reading that in order to calculate how much power the system is using you actually use all three phases:

current L1 * voltage L1 +. ... + currentL3 * voltageL3 (the formula is more complex, but I'm interested only on the phases)

This sound very fishy/wrong to me. Show me calculation you have on mind on certain example.Logically speaking, if I can use all three phases to calculate how much power the system is using, shouldn't I be able to add them up and say how much current is going into the system and thus used by the system?

Thanks

- #8

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Ok

This sound very fishy/wrong to me. Show me calculation you have on mind on certain example.

P1 = V1 x I1

P2 = V2 x I2

P3 = V3 x I3

Total power = P1 + P2 + P3

is this formula/approach correct?

- #9

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P2 = V2 x I2 x cos φ

P3 = V3 x I3 x cos φ

Total power = P1 + P2 + P3

Now, it is correct

- #10

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Perfect, thanks.

- #11

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Values must be taken at same instant of time, then the above holds.

One more thing, regarding this point. What I meant was, what happens if I sum only the current values, without takng into account the phase shift, only the magnitudes.

I mean, even if th system is perfectly balances and the neutral is zero, there's still current going in, right?

- #12

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Why would you do that? For a balanced 3-phase system you'll get 3x higher line current and do what with it?One more thing, regarding this point. What I meant was, what happens if I sum only the current values, without takng into account the phase shift, only the magnitudes.

The phases have currents of equal magnitude. Phase shift between any two is 120I mean, even if th system is perfectly balances and the neutral is zero, there's still current going in, right?

- #13

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- #14

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I mean, if in the end you have kWh for each phase, then you must also have currents on each phase, this is common sense. By looking at the kWh consumption for each phase, L1 is increasing by 3 kWh at each reading, L2 by 1 and L3 by 2. Different kWh, different currents. From my ignorant perspective, this means I can actually monitor the different currents and voltages that are causing this.

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