ABB A43

Measurement Methods
A43/A44 86 2CMC48001M0201
User Manual Revision: C
Illustration The type of load can be represented geometrically by 4 power
quadrants, see figure below.

Export of
reactive
power
Export of
active power
S
Q
P
1
43
2
Import of
reactive
power
-
+
+
-
Import of
active power
7.1.1 Single Phase, 1-Element Metering
1- element metering in a 2-wire system
Calculating
active power
In a 2 -wire installation a single phase meter is used. Normally the 2 wires are
a phase voltage and the neutral.
The active energy consumed by the load is the product of momentary voltage
and current integrated over the desired measuring time period.
In the case where no harmonics is present and the rms value of the voltage
and current is constant, the active power can be expressed as:
P = U
rms
* I
rms
* cos 
Where  is the phase angle between the voltage and the current.