Introduction

Alternating current and voltage are having three parameters – magnitude, frequency and phase. We have to apply the rated constant magnitude and rated constant frequency voltage input to each and every electrical appliance for its proper functioning. The frequency and voltage value are specified on the label of the appliance. But for an electrical appliance there is generally no specification mentioned regarding the phase. Now the question is what is the phase of our supply voltage? Do we always use a single phase supply? We shall see that on AC generation is essentially polyphased. The optimum value of number of phase for the standard power system is three. We shall also see the load to this three phase system is also three phase. Though our domestic appliances are mostly single phase systems, we may have three phase load too. Though our domestic voltage supply is single phase, we need the three phase supply for industrial plants. In this chapter we shall focus on these different aspects of three phase system.

Concept of Three Phase Voltage

In the chapter 4, we have seen an AC voltage is sinusoidal in nature.

The AC voltage is having peak voltage Vm and frequency f = 1/T. This voltage is a simple single phase voltage we have chosen the reference point at 0 so the phase of the voltage is zero.