Electrical Power Systems Technology

58 Electrical Power Systems Technology

The power developed in an inductive circuit is dependent upon the power
factor (pf) of the circuit. Power factor is a ratio of apparent power (volt-am-
peres) and true power (watts) of a circuit, an expressed as:

true power
Pf = ———————
apparent power

Capacitance causes current to lead voltage in an AC circuit. The electro-
static field produced by a capacitor is responsible for this effect. The power
developed in a capacitive circuit is expressed as:

P = V × I × pf

just as in an inductive circuit.
The power relationships, as well as voltage and current relationships,
in AC circuits, may be simplified by using vector or phasor diagrams. These
diagrams allow us to examine, by a visual analysis, the effect of resistance,
inductance, or capacitance on a circuit.
Both single-phase and three-phase AC power systems are used exten-
sively. Electrical power systems involve:

1. Electrical power sources, such as generators.


2. Distribution of electrical power, mainly by specialized conductors.


3. Control of electrical power by various methods.


4. Electrical power conversion systems or loads, such as electrical lights
   and motors.


5. Measurement of electrical-power-related quantities with specialized
   equipment.

The units of this book discuss each of these five aspects of electrical-
power systems.