# 3 phase theory help please...

Discussion in 'Homework Help' started by ElecNerd, Feb 6, 2011.

1. ### ElecNerd Thread Starter New Member

Jan 2, 2011
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0

Hi

Please could someone assist me on an assignement which I am completing on 3 phase theory. I have to calculate the current in the neutral. To do this I understand that I have to know the current per phase prior to me being able to proceed however I am struggling with the formula to do this. Each phase is connected with a 20ohm resistor in the red phase, 50 in the blue phase and 25 in the yellow phase. I have a phase voltage of 100V.

Any assistance greatly appreciated.
ElecNerd

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
Are you familiar with complex numbers or operations such as phasor addition?

3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Analyse the circuit just like a DC circuit but use complex numbers to represent voltages and currents as t_n_k mentioned.

4. ### renotenz New Member

Oct 25, 2010
11
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It's a Y-three phase system right?

Just as mik3 said, use simple DC analysis (I = V/R) to the phase/line current (it is the same in Y) on each phase. Given the phase voltage already, it should be quite easy to calculate that. Just keep in mind that each phase voltage has 120 degrees phase angle difference.
Since the loads are resistors, no further phase angle calculations are needed to find the current on each phase.
Then use the complex number addition to sum up the phase currents.