Methodologies of Measuring Mechanical Power Delivered at the Shaft of an Induction Motor Driven by VFD

Abstract

Measuring precise power used by a load of an induction motor driven by a VFD implies a few facts that need to be considered. First, the real electric power. When dealing with waveforms of electric current that contain harmonics, traditional methods of power measuring could lead to inaccurate results. Therefore, further investigation needs to be performed in order to provide meaningful values. Then there is the efficiency. Motor losses are to be taken into account for finding out exactly how much power is being used for a specific application. This paper shows a method of measuring and calculating the electric real power of fundamental harmonic and of extracting an actual output value of mechanical power at the motor shaft. For this purpose we used a data acquisition system made of a basic power quality analyzer and data acquisition software. Harmonic analysis of the waveforms is considered, combined with the use of the true power factor.