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.
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