Development of Resonance-Based Test System to Measure Lifetime Curves of Dielectric Materials
A.C. Patil (TU Delft - Electrical Engineering, Mathematics and Computer Science)
M. Ghaffarian Niasar – Mentor (TU Delft - DC systems, Energy conversion & Storage)
Peter Vaessen – Graduation committee member (TU Delft - DC systems, Energy conversion & Storage)
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Abstract
With the increasing growth and penetration of power electronic devices in the power system, it is essential to understand the behaviour of insulation materials and systems under the varied signals that are produced with power electronic systems. These signals could be square pulses, sinusoidal or even superimposed. The high-frequency sinusoidal excitation in the range of 50-100kHz is the focus, of this project. The project aims to design a resonance-based test system to measure the lifetime curves of dielectric materials such as oil-impregnated paper and epoxy under high frequencies.
The major components of this project are the H-Bridge Circuitry found on the low voltage side and the resonant transformer which is tuned with the test sample to be in resonance. The design techniques and critical factors for the design of gate driver circuits have been provided. Moreover, through simulations in COMSOL Multiphysics and MATLAB along with practical measurements using vector network analyzers the behaviour of the transformer equivalent circuit parameters with changes in geometry is discussed. Through this understanding, the critical parameters to design a test system to obtain the highest gain while in resonance have been highlighted.
The final test setup is designed and is used to perform lifetime tests on oil-paper and epoxy samples, both materials exhibited different behaviour during the tests. Due to the high gain of the system, it is very sensitive to changes in the capacitance of the test object and hence a constant voltage is not applied to the oil-paper sample. Therefore the breakdown times cannot be considered for the lifetime curve. Recommendations are provided to improve the test setup. Epoxy showcased a different behaviour, it is observed that the linear voltage gain of the resonance system is lost once partial discharges are initiated, and the voltage across the test sample becomes constant even upon a further increase in the input voltage. Based on these observations recommendations are provided to improve the test setup along with further topics that need to be studied.