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1.3: Reactive Energy and Power Factor
The real power and energy measurements discussed in the previous section relate to
the quantities that are most used in electrical systems. But it is often not sufficient to
only measure real power and energy. Reactive power is a critical component of the
total power picture because almost all real-life
reactive power. Reactive power and power factor concepts relate to both load and
generation applications. However, this discussion will be limited to analysis of reactive
power and power factor as they relate to loads. To simplify the discussion, generation
will not be considered.
Real power (and energy) is the component of power that is the combination of the
voltage and the value of corresponding current that is directly in phase with the
voltage. However, in actual practice the total current is almost never in phase with the
voltage. Since the current is not in phase with the voltage, it is necessary to consider
both the inphase component and the component that is at quadrature (angularly
o
rotated 90
or perpendicular) to the voltage. Figure 1.9 shows a single-phase voltage
and current and breaks the current into its in-phase and quadrature components.
The voltage (V) and the total current (I) can be combined to calculate the apparent
power or VA. The voltage and the in-phase current (I
real power or watts. The voltage and the quadrature current (I
calculate the reactive power.
The quadrature current may be lagging the voltage (as shown in Figure 1.9) or it may
lead the voltage. When the quadrature current lags the voltage the load is requiring
both real power (watts) and reactive power (VARs). When the quadrature current
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0
I
X
Figure 1.9: Voltage and Complex Current
Doc
1: Three Phase Power Measurement
applications have an impact on
I
V
R
I
) are combined to produce the
R
) are combined to
X
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