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Session Chair: Dr. Aleksandr Khazanov, National Electric Coil, United States of America
Location:Egret
Session Topics:
Manufacturing (RM), Life Management & In-service Experiences (RM), Failures Cases, Investigations and Repair Procedures (RM)
Presentations
9:00am - 9:30am
Inverter voltage endurance testing of twisted pairs according IEC 60851 with a self-developed, adjustable generator
C. Staubach1, B. Sahan1, A. Litinsky2
1University of Applied Sciene Hannover, Germany; 2Axalta Coating Systems, Germany
E-mobility is a key component nowadays to fulfil the goal of overall reduction of greenhouse gas emissions. An important step is to switch to regenerative energies and another is to make the vehicles as efficient as possible and feasible, technology wise.
Key components are installed in electric vehicles are the charging system, the battery and the electric motor. With regards to these components new developments and trends are introduced in recent times, such as an increase of the voltage level from 400 to 800 V and implementation of new materials for the multi-level inverter used in the drivetrain. By increasing the voltage level, the ohmic losses and charging times are reduced, whereas the usage of advanced materials, i.e. SiC-MOSFETs, the slew rate is increased to minimize the switching losses. In addition, a trend is to increase the switching frequency. These developments lead to higher electric and thermal stress especially in the enameled copper wires used in electric motors and will limit the resulting lifetime.
For investigation and qualification of new insulation system an inverter voltage generator was developed and comprehensive measurements were conducted to quantify the effects of temperature, switching frequency, voltage-level and rise time.
Depending on the capacitive load the inverter voltage generator is able to generate bipolar square-wave voltages in the range of 1-20 kHz with a rise time down to 50 ns and a voltage level up to 20 kVpk/pk. A big advantage of the generator is, that the rise time can be adjusted and the overshoot is quite low (<5 %).
The inverter generator is presented and basic results of the conducted lab testing are presented and discussed in this paper. During the testing we recognized that in some cases a high scattering of the lifetime results especially under inverter stresses is obtained, which is not consistent with the results under sinusoidal stress. Even if the guideline acc. IEC 60851 to manufacture the twisted pairs is tightly followed, we noticed a strong scattering in the PDIV, which can´t be explained by the test setup itself.
Therefore, we also did some investigation on a modified test setup acc. IEC 60851 and discuss these results.
9:30am - 10:00am
On-line Partial Discharge Diagnosis on Stator Winding Insulation: Impacts of Voltage Distortion and Winding Temperature
S. Nakamura, T. Kuraishi, S. Miyazaki
Central Research Institute of Electric Power Industry, Japan
Partial discharge (PD) magnitude and phase-resolved PD (PRPD) patterns are key indicators for on-line PD diagnosis for stator windings. These indicators can be influenced by generator operating conditions because generators are subjected to high temperatures and voltage distortion. This study investigates the impacts of voltage distortion and winding temperature on on-line PD diagnosis. We measure PDs in stator windings of a hydrogenerator. The voltage waveform and winding temperature varied with the load condition. Harmonic voltages of about 2-4 kHz are superimposed on the generator voltage. The temperature ranges from 27°C to 70°C. Although the superimposition of the harmonic voltages altered the PRPD pattern, its effect on PD magnitude remains negligible. In contrast, the shape of the PRPD pattern is independent of the temperature, whereas the PD magnitude decreases with the temperature. Based on these findings, we state notes for conducting on-line PD diagnosis under varying generator conditions.
