Reactive Energy And Power Factor; Voltage And Complex Current - Electro Industries Shark 200 Installation & Operation Manual

1: Three-Phase Power Measurement

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 applications have an impact on reac-
tive power. Reactive power and power factor concepts relate to both load and genera-
tion 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 volt-
age. 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.
I
V
R
0
I
I
X
Figure 1.9: Voltage and Complex Current
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 ) are combined to produce the
R
real power or watts. The voltage and the quadrature current (I ) are combined to cal-
X
culate 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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Electro Industries/GaugeTech Doc E149701 1-12
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