YOKOGAWA CW140, User Manual, Page: 278 / 292

IM CW140-E
App 5-2
●
Calculation Using Reactive Power Method (Reactive Power 1)
The CW140 directly calculates reactive power by shifting current phases by
90 degrees, as with common reactive power meters. This method can
eliminate the effects of the unbalanced element and harmonic content on the
measured object, gaining measurement values for the voltage and current
with the same frequency element.
Q =
T
T
1
∫
0
v( t ) × i ( t + ) dt
4
T
Q = Reactive power
v( t )
C
i ( t )
= Input signals
T = One period input signal
With reactive power 1, the power factor is calculated as the ratio of the active
power to the reactive power, and is called a power-ratio power factor.
Reactive power values calculated by the two methods above are the same if
both the voltage and current are sine waves (excluding harmonic content) and
balanced. However, if either the voltage or current is unbalanced or includes
the harmonic content, the reactive power values are different. Therefore,
select the method best suited to the state of the measured object and analysis
details.
In addition, if you want to compare the reactive power values with those of
another instrument, be sure to understand the measurement principles before
selecting the instrument.
Appendix 5. Explanation of Reactive Power Method