Unbalanced Systems
Practical systems rarely have perfectly balanced loads, currents, voltages or impedances in all three phases. The analysis of unbalanced cases is greatly simplified by the use of the techniques of symmetrical components. An unbalanced system is analysed as the superposition of three balanced systems, each with the positive, negative or zero sequence of balanced voltages.
When specifying wiring sizes in a three phase system, we only need to know the magnitude of the phase and neutral currents. The neutral current can be determined by adding the three phase currents together as complex numbers and then converting from rectangular to polar co-ordinates. If the three phase RMS (Root Mean Square) currents are, and, the neutral RMS current is:
which resolves to
The polar magnitude of this is the square root of the sum of the squares of the real and imaginary parts, which reduces to
Read more about this topic: Three-phase
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