Basic AC Power
POWER TRIANGLE
POWER TRIANGLE
While direct current has one form of power, alternating current has three different
forms of power that are related in a unique relationship. In this chapter, you will
learn that power in AC circuits cannot be calculated in the same manner as in DC
circuits.
EO 1.1
DESCRIBE the relationship between apparent, true, and
reactive power by definition or by using a power
triangle.
EO 1.2
DEFINE power factor as it relates to true power and
apparent power.
EO 1.3
Given the necessary values for voltage (E), resistance
(R), reactance (X), impedance (Z), and/or current (I),
CALCULATE the following power components for an
AC circuit:
a.
True power (P)
b.
Apparent power (S)
c.
Reactive power (Q)
d.
Power factor (pf)
EO 1.4
DEFINE the following terms:
a.
Leading power factor
b.
Lagging power factor
Power Triangle
In AC circuits, current and voltage are normally out of phase and, as a result, not all the power
produced by the generator can be used to accomplish work. By the same token, power cannot
be calculated in AC circuits in the same manner as in DC circuits. The power triangle, shown
in Figure 1, equates AC power to DC power by showing the relationship between generator
output (apparent power - S) in volt-amperes (VA), usable power (true power - P) in watts, and
wasted or stored power (reactive power - Q) in volt-amperes-reactive (VAR). The phase angle
(q) represents the inefficiency of the AC circuit and corresponds to the total reactive impedance
(Z) to the current flow in the circuit.
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