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Investigation of Electric Stress on the Insulation Systems of Inverter-driven Electric Machines

Xie, Yanyan
http://orcid.org/0000-0002-8420-518X
http://rave.ohiolink.edu/etdc/view?acc_num=osu1606869017169887

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
In AC electric machines, winding insulation breakdown is one of the most common reasons for machine failures. Many factors can contribute to the insulation degradation, such as thermal stress, electric stress, mechanical vibration, chemical aging, etc. This thesis focuses on the electric stress on the insulation of inverter-driven machine windings, including overshooting voltage and sharing currents in the windings. Fast switching power electronics with Pulse Width Modulation (PWM) techniques are increasingly applied to drive electric machines. These power electronic drives introduce high overshooting voltages at the machine winding terminals (130 % of VDC or higher). Those overshooting voltages are not evenly distributed in the machine windings, resulting in high voltage stress on the insulation. It has been reported that some inverter-driven machines demonstrated pre-mature winding insulation failures due to the voltage stress caused by power electronic switches. It is essential to have a clear understanding of how the voltage/current distributes in the winding to optimize the machine insulation and layout design. This work strives to simulate, analyze and test the electric stress distribution of the inverter-driven machine windings. Firstly, a high-fidelity finite element (FE) simulation approach was developed to simulate the voltage/current distribution on individual turn/strand of machine windings. This FE simulation approach considers all the parasitic parameters of each conductors of machine windings and provides the voltage/current of each conductor. The parasitic parameters (inductances and capacitances) were analyzed via FE computation and measured using a test fixture with precisely constrained wire locations. Secondly, tests were conducted with various types of machine windings built in a stator to verify the accuracy of the simulated voltage/current distributions in each wire of those windings. The studied winding structures include single-phase, three-phase, form-wound, random-wound, stranded and solid types. Clear voltage distribution patterns were observed in both tests and simulations. The effect of wire locations on the parasitic parameters and the voltage/current distributions were analyzed with simulations and tests. Subsequently, comprehensive sensitivity analysis for various types of factors was performed to investigate the root cause and the key parameters of the pulse voltage distribution patterns in machine windings. FE models were constructed considering various combinations of important factors in random-wound stranded machine windings, including various types of parasitic capacitances, parasitic inductances and random wire layouts in the slots. Moreover, to study the effect of other factors on the winding pulse voltage propagation (such as DC voltage, current, load and rotor speed), tests with a modified machine product were conducted at various machine operating conditions and the actual voltage stress were mapped for the machine. Finally, equivalent circuits for both single-phase and three-phase machine windings were constructed with coil-level parameters. Then, the expressions of the coil voltage were derived in Laplace domain based on the input voltage and the coil-level parameters. With frequency-denpendent inductances, these coil voltages varied depending on the frequencies. This analysis explained the pulse voltage propagation pattern observed in simulations and tests. The effect of the feeding cable length on the voltage propagation pattern was tested and investigated with three-phase machine windings.
Julia Zhang (Advisor)
Xu Longya (Committee Member)
Wang Jin (Committee Member)
Abhishek Gupta (Committee Member)
154 p.
Electrical Engineering

Recommended Citations

Citations

  • Xie, Y. (2020). Investigation of Electric Stress on the Insulation Systems of Inverter-driven Electric Machines [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1606869017169887

    APA Style (7th edition)

  • Xie, Yanyan. Investigation of Electric Stress on the Insulation Systems of Inverter-driven Electric Machines. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1606869017169887.

    MLA Style (8th edition)

  • Xie, Yanyan. "Investigation of Electric Stress on the Insulation Systems of Inverter-driven Electric Machines." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1606869017169887

    Chicago Manual of Style (17th edition)

osu1606869017169887
143
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This open access ETD is published by The Ohio State University and OhioLINK.