# Three phase power meaurement questions

1. Aug 9, 2016

### TheRedDevil18

I have a few questions regarding three phase power measurement

Three Watt-meter method:

What would happen if the neutral where removed ?, my guess is that it wouldnt make a difference because the neutral doesnt carry any current

Same question as above

Two Watt-meter method:

What would happen if the neutral where removed for a balanced/unbalanced load ?

2. Aug 9, 2016

### cnh1995

Right.
For balanced load, removing the neutral should not make any difference. But without the neutral, phase difference between the currents for unbalanced load will no longer be 120°.

3. Aug 9, 2016

### TheRedDevil18

So for an unbalanced load, if the neutral where removed, would the wattmeter reading be higher than if it where not removed ?

Like, for the three wattmeter circuit if the neutral is removed, each wattmeter would have a different reading ?

4. Aug 9, 2016

### cnh1995

Yes, in case of unbalanced load.
I'm not sure about that. But since the currents are no longer 120° apart, the usual equations W1=VIcos(30+Φ) and W2=VIcos(30-Φ) are not applicable. So my guess is it's not possible to formulate the total power in terms of W1 and W2.

5. Aug 9, 2016

### TheRedDevil18

So basically if you have unbalanced loads, the correct way would be to measure with the neutral ?

Also, when the neutral is in place with an unbalanced load then the power and currents would be balanced for each load ?

6. Aug 12, 2016

### informatory

So,for the second picture it would be it,generally speaking neutral current is used for protecting electric circuits and taking the sufficient current also in this case when you remove neutral phase there is going to happen on some phases (b,y or r) higher or lower voltage ,in first case with neutral powers of each phase you can calculate seperately but it would be so called (in my language) literally phase voltages rhat counts for finding powers of each phase.(Also all of these volltages are "lined" because there is no neutral as you call it) Idk if have made the right discussion and satisfied you with answer,so ask again if you have a need
All the best

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7. Aug 12, 2016

### cnh1995

Three wattmeter method will work for both balanced and unbalanced load with or without the neutral.
No. The neutral maintains 120° phase difference between the currents in case of unbalanced load. The power consumption in each phase will be different.

8. Aug 12, 2016