TPU PhD student develops electrical insulation test bed

Veronika Gavrilenko, a PhD student of TPU and The Paris-Saclay University has developed an electrical insulation test bed for studying resistance of insulating materials. The test bed has been made using the SiC-based semiconductors of new generation. The research results are to be defended as a PhD-thesis.

The thesis “Characterization of winding insulation of electrical machines fed by voltage waves with high dV/dt” is devoted to studying partial discharges as well as mechanisms of insulation aging and destruction attributed to them when exposed to impulse voltage with nanosecond high-frequency impulse fronts specific to modern semiconductor equipment.

New generation semi-conductor devices based on the materials with wide band gap, for example, silicon carbide (SiC) are used in modern converters for transport facilities. Such materials are advantageous due to high working voltage, temperature, frequency and switching rate, which enables to gain 20-30% power waste reduction in converters and improve power electronics.

“High working temperature combined with impulse electric load trigger chemical reaction in insulating materials, accelerate their aging and reduce their reliability. Operational factors alteration necessitates the modification of the existing methods and mathematical models,”

Veronika Gavrilenko specifies.

To measure the voltage surge in the winding of the motors controlled by SiC-based inverters, the young researcher has proposed a high-frequency model of an electric drive. The model has enabled to identify the effect of a supply cable length and nanosecond surge fronts on switching surge voltages in the motor. These voltages determine the risk of partial discharge and insulation failure.

With the objective to develop the technique for determining electric insulating materials reliability, the scientists designed and constructed a high-frequency testing unit.

“The main unit module is a pulse generator with SiC MOSFET transistors. It was developed in the laboratory SATIE (France) and given to TPU. Our major task is to identify the factors influencing electric insulating materials. Our experiments have shown a rapid deterioration in the insulation properties and destruction on exposure to impulse voltage with nanosecond high-frequency impulse fronts. We have defined that the occuring partial discharges are of the filament barrier type and they cause the electroerosion of enamel insulation,” the PhD student says.

The study is under way within the framework of the agreement on international cooperative academic advising between TPU and The Paris-Saclay University (France). Part of the work is carried out on the basis of the laboratory SATIE (ENS Paris-Saclay) in collaboration with National Conservatory of Arts and Crafts (CNAM). Academic advising on the part of The Paris-Saclay University (France) is provided by the Professor Stephane Lefebvre and on the part of TPU – by Andrey Leonov, an Associate Professor of the Division for Power and Electrical Engineering.

“The topic “at interface of sciences” enables to integrate the knowledge and competences of the researchers from SATIE in the scope of power electronics and electric machinery and from TPU in the scope of electroinsulating and cable engineering,”

Veronika Gavrilenko explains.

The PhD-thesis will be defended on December 2, 2020 in France via videoconferencing with the participation of qualifying commission from Russia. Veronika Gavrilenko aims to continue the research with postdoctoral studies in the laboratory LAPLACE (Université Paul Sabatier) in collaboration with TPU.