App.5-2
IM CW240E
Appendix 5 Reactive Power Method
●
When using the reactive power method (reactive power 1)
The calculation shifts the current phase 90°, in the same manner as a common
wattmeter, and measures the reactive power directly. With this operation,
imbalance in the object of measurement, and the influence of harmonic
elements, can be removed, and the result is a measurement value for only
frequency elements that are the same as the voltage and current.
Q
= v(t)
⫻
i(t
+
)dt
Q
=
Reactive power
v(t),
i(t)
=
Input signal
T
=
1 cycle of input signal
T
0
T
1
4
T
In this case, the power factor is obtained from the active power and the reactive
power, and this power factor is called the power ratio power factor.
If the voltage and current are both sine waves (the state excluding harmonic
elements) and are balanced, the value obtained from the above two types of
calculation will be the same result. If either voltage or current are unbalanced, or
harmonic elements are included, the result will differ, so it is necessary to select
the measurement method according to the state of the object of measurement
and the content of analysis.
Also, when comparing with other measuring devices, etc., make the selection
after confirming the measurement principles of that measuring device.