Abstract
Benefiting from self-healing features, metallized film capacitors (MFCs) are widely employed to compensate reactive power (VAR) and thus improve the performance of AC systems. To ensure the aforementioned functions, self-healing testing is a compulsory quality inspection for every type of MFC. In 2014, the International Electrotechnical Commission (IEC) issued a standard that recommended a general and instructive test procedure based on audible noise or ultrasound signals. However, more details relevant to this high voltage (HV) test were not provided. In this paper, we focused on the ultrasonic detection technique to reveal the self-healing characteristics of two typical MFCs. By launching a series of HV tests with star and delta MFCs, the waveform features, discharge energy, and spectrum distributions were analyzed. It was observed that the partial discharge always occurs before self-healing discharge with the same spectrum features ranging above 40 kHz. To solve the entanglement of these two discharge processes, a relative amplitude difference method is proposed. Based on the experimental observations, a detection algorithm incorporated with the ultrasonic emission sensors, preamplifier, and high-speed A/D converter was developed to assist the self-healing performance test.
Highlights
Metallized film capacitors (MFCs) are widely used in reactive power compensation and the improvement of power factors
Dry-type MFCs with different inside reported in reference [17], the central frequency of the MFC self-healing signal is at around 60 kHz, which is located within the frequency band of the employed sensor (15–70 kHz)
We mainly focused on the ultrasound signals
Summary
Metallized film capacitors (MFCs) are widely used in reactive power compensation and the improvement of power factors. MFCs with poor self-healing characteristics can fail to heal and increase the danger of explosion in MFCs. As a result, self-healing measurement of MFCs is essential to eliminating poor-quality products and maintaining safety. The reliability of capacitors is important to the health of power electronic systems, so their degradation models and lifetime predictions have been investigated [2,3,4]. The contributing factors to self-healing, including the sheet resistance of electrodes; the interlayer air, pressure, and temperature dependence [6,7]; and other dynamic characteristics [8], were investigated to evaluate their effects. Models were built to describe the destruction [9,10,11] and Electronics 2020, 9, 1893; doi:10.3390/electronics9111893 www.mdpi.com/journal/electronics
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