Electro Industries Shark 200 Installation & Operation Manual page 25

1: Three-Phase Power Measurement
leads the voltage the load is requiring real power (watts) but is delivering reactive
power (VARs) back into the system; that is VARs are flowing in the opposite direction
of the real power flow.
Reactive power (VARs) is required in all power systems. Any equipment that uses
magnetization to operate requires VARs. Usually the magnitude of VARs is relatively
low compared to the real power quantities. Utilities have an interest in maintaining
VAR requirements at the customer to a low value in order to maximize the return on
plant invested to deliver energy. When lines are carrying VARs, they cannot carry as
many watts. So keeping the VAR content low allows a line to carry its full capacity of
watts. In order to encourage customers to keep VAR requirements low, some utilities
impose a penalty if the VAR content of the load rises above a specified value.
A common method of measuring reactive power requirements is power factor. Power
factor can be defined in two different ways. The more common method of calculating
power factor is the ratio of the real power to the apparent power. This relationship is
expressed in the following formula:
Total PF = real power / apparent power = watts/VA
This formula calculates a power factor quantity known as Total Power Factor. It is
called Total PF because it is based on the ratios of the power delivered. The delivered
power quantities will include the impacts of any existing harmonic content. If the volt-
age or current includes high levels of harmonic distortion the power values will be
affected. By calculating power factor from the power values, the power factor will
include the impact of harmonic distortion. In many cases this is the preferred method
of calculation because the entire impact of the actual voltage and current are
included.
A second type of power factor is Displacement Power Factor. Displacement PF is based
on the angular relationship between the voltage and current. Displacement power fac-
tor does not consider the magnitudes of voltage, current or power. It is solely based
on the phase angle differences. As a result, it does not include the impact of harmonic
distortion. Displacement power factor is calculated using the following equation:
Displacement PF = cos 
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Electro Industries/GaugeTech Doc E149701 1-13
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