Optimal Design and Efficiency Test Method of Induction Motors Fed by Frequency Converters

Abstract

The different international energy policies recommend the use of electrical drives with variable speed. With these variable speed drives (e.g. centrifugal pumps, fans, etc.) a higher efficiency of the process is achieved, thus allowing for energy saving.

Efficiency of electrical motors has been improved for normal sinusoidal supply, without taking into account the negative effects when feeding the motors by means of frequency converter.

The frequency converters produce first a high amount of hysteresis and eddy losses in both stator and rotor iron and secondly a temperature increases of the rotor because of the current distribution in its rotor slots.

The conventional calculation using analytical tools could not calculate precisely the required parameters in order to obtain an optimal model to build a prototype that its properties confirm the calculated values with the model.

With a finite element method (FEM) application for magnetic field and heat transfer could be elaborated very precisely the required elements to design a new prototype and it is also a tool to prove the already existing motors for this application.

The presently applied standards to determine efficiency are not suitable to recognise this improvement. Applying high-tech tools we can define test method to measure the actual efficiency of this type of motors. This allows us also to create energy efficient electrical drives according to the recommendations of the last EEMODS conference held in London in 1999 with the support of the European Committee for Energy Saving.