Oliver Magdun

Investigation of influence of bearing load and bearing temperature on EDM bearing currents

To detect the worst case and the best case of the bearing operating conditions concerning the magnitude of the high frequency discharge bearing currents (“EDM currents”) and the frequency of electric discharges in the bearings of the small power inverter-fed AC motors, systematic investigations have been performed for three, 4-pole, 1.5 kW squirrel cage induction motors at different speeds, bearing loads and bearing temperatures.

High-Frequency Induction Machine Modeling for Common Mode Current and Bearing Voltage Calculation

In this paper, several inverter-fed induction machines with rated powers between 1.5 and 240 kW are modeled for calculating the common mode (CM) stator ground current and the capacitive bearing voltage. Simple methods to extract the parameters of the high-frequency machine model from the measured CM and differential mode impedances are presented. Furthermore, the most significant parameters are given for five different machine sizes between 1.5 and 240 kW rated power. Calculation examples are provided in comparison to the experimental results.

Prediction of common mode ground current in motors of inverter-based drive systems

A ladder parameter model to predict the common mode ground current in motors of inverter-based drive systems is analyzed. The comparison of the calculated and measured common mode current at IGBT inverter supply shows a good agreement for a 110 kW induction motor. The parameter calculus for the winding has been done with analytical methods and was checked with FEM.

Prevention of harmful EDM currents in inverter-fed AC machines by use of electrostatic shields in the stator winding overhang

In this paper, an inexpensive mitigation technique is used for prevention of harmful EDM currents in small power inverter-fed AC machines. An electrostatic shield is mounted close to the stator winding overhang to eliminate the capacitive coupling between the stator end winding and the rotor surface. The bearing voltage that is caused by the common mode voltage at the motor terminals via the machine capacitances is reduced and the harmful EDM currents are eliminated. A 3D finite element method (FEM) is proposed for the calculation of the machine capacitances. The results are verified by analytical calculation, 2D FEM calculation and measurements.

Calculation of bearing and common-mode voltages for the prediction of bearing failures caused by EDM currents

The paper deals with the calculation of the common-mode (CM) voltage and the electrostatic induced voltage across the bearings in the small power inverter-fed AC machines with wound round wire windings. A method for the calculation of the bearing voltage directly from the CM voltage at the neutral point has been previously proposed in the literature. In this paper, a new representation of the stator winding, which is verified experimentally, is proposed to be easily implemented in a simulation software tool for the calculation of the CM voltage. Moreover, an accurate calculation of the bearing voltage from the integral of the CM current, via the bearing voltage ratio, is proposed. The EDM currents and the bearing threshold voltages, which are responsible for the occurrence of the fusion craters, electrical pitting or fluting of the lubricated bearing surfaces, are also calculated.

Representation of iron core and dielectric losses for calculation of common mode stator ground currents in inverter-fed AC machines

A time-domain high frequency model of an induction machine, which is based on the design parameters, is proposed for calculation of common mode (CM) stator ground currents in inverter-fed AC machines. Basically, the model is an extension of the measured frequency response models and considers an adequate representation of the iron core and dielectric losses over a wide frequency range, e.g. 1 kHz–10 MHz. The proposed model eliminates the disadvantages of the transmission line models, when they are used in the design stage to calculate the CM currents.

Modeling of asymmetrical cables for an accurate calculation of common mode ground currents

The paper deals with modeling methods for asymmetrical cables of speed variable AC motor drives to calculate precisely the common mode ground stator currents. The analytical and numerical calculation of the cable parameters is presented and the results are compared to measurements. An impulse run-time method for the cable parameter evaluation by measurements is proposed.

A stator coil model for studying high-frequency effects in induction motors

For studying parasitic effects in inverter-fed drives high-frequency effects in induction motors have to be examined. A transmission-line model for the stator coil system in induction motors is presented. The capacitances between the coil wires are considered as well as the capacitance between coil and yoke.

Calculation of stator winding parameters to predict the voltage distributions in inverter fed AC machines

Transmission line models are commonly used to calculate and predict the voltage distributions along the inverter-fed electrical machine windings. In this paper, frequency-dependent parameters of the stator windings are calculated via finite element and analytical methods. They are implemented in a transmission line model to predict the voltage distribution in a round wire stator winding induction machine. As a difference from the existent models, the laminated iron core effects are taken into account by an eddy current loss resistance. A metal-oxide varistor model is implemented in the cable-machine winding simulation model, and the voltage distribution is calculated. Comparisons with the measurements are given.

An iron core impedance model for calculating high frequency common mode currents and shaft voltages in inverter-fed AC machines

In order to calculate the common mode currents and induced shaft voltages in the inverter fed AC machines, a 2D finite element (FE) common mode impedance model of the laminated iron core, assuming the rotational symmetry and the uniform radial current distribution in the lamination sheets, has been proposed in the literature. In this paper, as an alternative to the existent 2D FEM models, a 3D FEM model of the iron laminated core is proposed to calculate the iron core impedance per phase. The proposed 3D FEM model considers better the radial distribution of the common mode current in the stator lamination sheets. The iron core impedance per phase is used to calculate the peak values of the most significant harmonics of the common mode current and of the induced shaft voltage.