The A.C. distribution calculations and d.c. distribution calculations are different in the following respects :
1. In case of d.c. system, the voltage drop is due to resistance only which in a.c. system it is due to combined effect of resistance, inductance and capacitance.
2. The voltages or currents are added or subtracted arithmetically in case of d.c. system whereas they are added or subtracted vectorially in case of a.c. system.
3. It is required to take into account the power factor while making calculations in a.c. system which is absent in d.c. system. The distributors are normally tapped at different points with the loads having different power factors.
There are two ways of referring the power factor.
a) The p.f. may be referred to receiving end voltage which is reference vector.
b) The p.f. may be referred to the voltage at load point itself.
By different methods the a.c. distribution problems can be solved.
The most convenient method is the symbolic notation method wherein voltages, currents and impedances are expressed in the complex notation and the calculations are similar to those in case of d.c. distribution. In a.c. calculations, addition and subtraction must be done by expressing various quantities in the rectangular form while the multiplication and the division must be done by expressing the various quantities in the polar from.