J. Martinez’s research while affiliated with Aalto University and other places

This paper presents a coupled Finite Element Model in order to study the vibrations in induction motors under steady-state. The model utilizes a weak coupling strategy between both magnetic and elastodynamic fields on the structure. Firstly, the problem solves the magnetic vector potential in an axial cut and secondly the former solution is coupled to a three dimensional model of the stator. The coupling is performed using projection based algorithms between the computed magnetic solution and the three-dimensional mesh. The three-dimensional model of the stator includes both end-windings and end-shields in order to give a realistic picture of the motor. The present model is validated using two steps. Firstly, a modal analysis hammer test is used to validate the material characteristic of this complex structure and secondly an array of accelerometer sensors is used in order to study the rotating waves using multi-dimensional spectral techniques. The analysis of the radial vibrations presented in this paper firstly concludes that slot harmonic components are visible when the motor is loaded. Secondly, the multidimensional spectrum presents the most relevant mechanical waves on the stator such as the ones produced by the space harmonics or the saturation of the iron core. The direct retrieval of the wave-number in a multi-dimensional spectrum is able to show the internal current distribution in a non-intrusive way. Experimental results for healthy induction motors are showing mechanical imbalances in a multi-dimensional spectrum in a more straightforward form.

This paper presents the experimental study of induction motor broken rotor bars diagnostics. Fault tests are performed on a machine with 3 broken bars, driven through a frequency converter. Park's vector approach is used as an analyzing tool to detect the broken rotor bars. Park's vector patterns in case of stator current and voltage are investigated. Results of the tests and discussion are presented. Necessity for further study is pointed out.

This paper presents the experimental study of induction generator broken rotor bars diagnostics. As induction generators are often used in renewable energy applications, such as wind and hydro power plants where they are also equipped with frequency converters, diagnostics of such machines is becoming more important. Tests are performed with an induction machine with a healthy rotor and a rotor with three broken bars, supplied through a frequency converter. Park’s vector approach is used as an analyzing tool to detect the broken rotor bars. Park’s vector pattern using stator current and voltage is investigated. Results of the tests and discussion of the results are presented. The necessity for further study is pointed out.