Development of a test bench to investigate the impact of steep voltage slopes on the lifetime of insulation systems for coil windings

• Entwicklung eines Prüfstandes zur Untersuchung der Auswirkungen steiler Spannungsflanken auf die Lebensdauer von Isoliersystemen für Spulenwicklungen

Grau, Vivien Corinna; de Doncker, Rik W. (Thesis advisor); Franck, Christian (Thesis advisor)

Aachen : ISEA (2021)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge des ISEA 158
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

Wide-bandgap semiconductor power devices offer considerable advantages compared to the corresponding silicon-based devices. They feature a higher dielectric strength, a smaller size and low conduction losses. The key advantage, however, is their fast switching behavior resulting in low switching energies. This allows higher switching frequencies, which in turn enables a more compact design of the passive components and thus higher power densities. However, the highly dynamic switching transients increase the stress on insulation systems of electrical components such as coil windings. This stress often leads to accelerated aging and premature failure of the insulation systems. To fully exploit the potential of the fast-switching wide-bandgap semiconductor devices and to avoid a reduction in switching speed, it is crucial to investigate the causes of the stress inflicted by steep voltage slopes. However, there are no unified test setups or standards for measuring and characterizing the impact of wide-bandgap semiconductor devices on the insulation system of coil windings. For this purpose, a highly flexible test bench with multi-physical measurement diagnostics is developed and evaluated. The test bench enables the excitation of inductive and capacitive specimens with controllable voltage slopes. The steepness of the voltage slopes can be adjusted over a wide range. Moreover, a full-bridge topology is proposed for the test converter which allows unipolar and bipolar voltage waveforms. Hence, the test bench enables an in-depth measurement and investigation of the challenges associated with the high transients of steep voltage slopes. Steep voltage slopes demand a high bandwidth and immunity to interference of the measuring equipment. Conventional measuring equipment often reaches its limits at the critical steep voltage slopes. This is especially the case with partial-discharge measurements. To compensate for such limitations, the proposed test setup is designed to allow a multi-physical evaluation of effects. The precisely defined and quasi interference-free test environment ensures accurate measurements with high comparability. Furthermore, the use of test specimens conforming to standards is discussed and an adapted alternative is proposed. The identification of aging mechanisms in connection with steep voltage slopes provides an overview of the factors contributing to the accelerated aging of insulation materials. The statistical design of experiments enables the determination of correlations between decisive input parameters and provides an efficient experimental procedure to investigate the cross-coupling of diverse aging effects through multiple measurements. This thesis is an essential step toward the investigation and analysis of the effects of highly dynamic switching transients on the insulation material for coil windings.