COOLING FAN

COOLING FAN

ASf07037

COOLING FAN

line. The vector sum of capacitor current and total

inductive load current is equal to line current. The line

In a dc circuit, power is computed by the equation

current is now in phase with the applied voltage to the

P = EI (watts equal volts times amperes). If 1 ampere

parallel combination of the inductive load and

flows in a circuit at a pressure of 208 volts, the power is

capacitor. This reduction in line current reduces line

208 watts. The product of the volts and the amperes is

loss and increases the efficiency of transmission.

the TRUE POWER in the circuit.

Information on power factor and power factor

In an ac circuit, a voltmeter indicates the effective

correction may be found in NEETS, Module 8,

voltage, and an ammeter indicates the effective

current. The product of these two readings is called the

up of pure resistance is the apparent power equal to the

Almost all of the electrical and electronic circuits

true power. When the impedance of the circuit is either

you work with are grounded. This means that one leg of

inductive or capacitive, the current and voltage are not

the circuit is connected to a common conductor, such

exactly in phase. The true power is less than the

as a structural member (frame) of the power plant.

apparent power. The true power may be obtained by a

When the grounded leg of the circuit is connected to a

wattmeter reading. The ratio of the true power to the

good electrical conductor, this conductor may serve as

apparent power is called the *POWER FACTOR*, and is

one leg of the circuit. No separate conductor is needed

equal to true power divided by apparent power.

for this leg of the circuit.

It is desirable that equipments using ac power have

Figure 7-38 shows a simple grounded system.

as near a unity power factor load as practicable. This

Even though the grounds are shown at different points,

improves the efficiency of power distribution by

the potentials at these points are essentially the same

2

reducing the line current and I R losses. Most ac

since they are connected to a common conductor.

loads are somewhat inductive, resulting in a lagging

power factor. You may obtain power factor correction

A

by connecting a capacitor of the proper value in

parallel with the circuit. The connection should be

made as close to the inductance load as possible.

G

The nonenergy component of the current in the

inductive branch is 180 degrees out of phase with the

capacitive current. These currents circulate between

ASf07038

the capacitor and inductive load and do not enter the

7-29