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62 Power systems engineering ± fundamental concepts
Fig. 2.33 Sampled voltage and current waveforms.
Fig. 2.34 Three-wattmeter connection.
which indicates that only two wattmeters are required, connected as shown in Figure
2.35. Since this is valid for instantaneous power, it is also valid for average power. It
is valid irrespective of the waveforms of voltage and current, requiring only that the
connection is three-wire.
Under sinusoidal AC conditions the two-wattmeter connection can be described
by the equations
P 1 hu ac i a i RefV ac I g V ac I a cos f 1
a
P 2 hu bc i b i RefV bc I g V bc I b cos f 2 (2:40)
b
