GE Multilin EPM 2200 Instruction Manual page 16

REACTIVE ENERGY AND POWER FACTOR
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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 (IR) are combined to produce the
real power or watts. The voltage and the quadrature current (IX) are combined to
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 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
voltage 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.
CHAPTER 1: THREE-PHASE POWER MEASUREMENT
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EPM 2200 POWER METER – INSTRUCTION MANUAL
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