COOLING FAN
COOLING FAN
ASf07037
COOLING FAN
Figure 7-37.--Internal cooling fans of a typical generator.
line. The vector sum of capacitor current and total
POWER AND POWER FACTOR
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
Introduction to Amplifiers.
current. The product of these two readings is called the
GROUNDED SYSTEMS
APPARENT POWER. Only when the ac circuit is made
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
Figure 7-38.--Grounded system.
the capacitor and inductive load and do not enter the
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