Metallized Film Capacitors Research Articles

Metallized polymer film capacitors ageing law based on capacitance degradation

Passive components, particularly capacitors, are very used devices in power electronics applications providing key function on board. Nevertheless, capacitors breakdowns can have catastrophic consequences on the financial and human scale; a good acquaintance of their deterioration over time would contribute in the improvement of the availability of the whole system by performing a predictive maintenance on the component. This operation requires the knowledge of the capacitor ageing law and their failure mechanisms associated to the application. Capacitance loss can be mainly attributed to the self-healing process occurring in metallized film capacitors when used under high steady electrical and thermal stresses. In this paper, a capacitance ageing law is proposed based on the identification of voltage and temperature degradation kinetics from three experimental floating ageing tests performed at different voltage and temperature constraints. A total of 34 capacitors provided from different manufacturers using polyester film as dielectric have been studied and compared to validate the proposed law.

Capacitive energy storage and recovery for synchrotron magnets.

Feasibility studies on capacitive energy storage and recovery in the main-ring synchrotron of the Japan Proton Accelerator Research Complex were conducted by circuit simulation. The estimated load fluctuation was 96 MVA in total for dipole magnets, which is likely to induce a serious disturbance in the main grid. It was found that the energy stored in the magnets after the excitation period can be recovered to the storage capacitor by controlling the voltage across the energy-storage capacitor using a pulse-width-modulation converter and reused in the next operational cycle. It was also found that the power fluctuation in the main grid can be reduced to 12 MVA. An experimental evaluation of an aluminum metalized film capacitor revealed that capacitance loss was induced by a fluctuating voltage applied to the storage capacitor when applying the proposed method. The capacitance loss was induced by corona discharge around the edges of segmented electrodes of a self-healing capacitor. The use of aluminum-zinc alloy was evaluated as a countermeasure to mitigate the effect induced by the corona discharge. For a zinc content of 8%, which was optimized experimentally, a capacitor with a sufficient life time expectancy of 20 years and a working potential gradient of 250 V/μm was developed.

Improved model of metalized film capacitors

Metalized film capacitors are commonly used components in power electronics applications and their characteristics are drastically dependent on their operating frequency. Parasitic parameters could appear at low and high frequencies and disturb substantially the behavior of the component. Proper design of metalized film capacitors requires an understanding of all parasitic parameters' sources and their impacts on the circuit operation. This paper presents a modeling approach based on the complex form of the capacitor impedance to build its equivalent electrical circuit. This approach proved to be more accurate than the traditional modeling technique of identifying the electrical parameters using the modulus of the component impedance. Two different types of capacitors were tested; experimental results allowed to validate our model from 10 kHz to 35 MHz.

通过电容器层间压强的增强提高电容器寿命

通过电容器层间压强的增强提高电容器寿命

Lifetime Improvement of Metallized Film Capacitors by Inner Pressure Strengthening

Metallized polypropylene film capacitors (MPPFCs) are widely used in pulse power systems for their characteristics of high reliabilities, high energy densities, and excellent pulse power handling capabilities. The teardown showed that the capacitance loss decreased gradually from the outer layers to the inner layers in a cylindrical MPPFC winding. This paper concentrates on the inner pressure in the MPPFC winding. First, the effects of the inner pressure on the self-healing and the lifetime are investigated. The lifetime can be extended by the inner pressure strengthening. Second, an inner pressure calculation formula is presented. The effects of the heat treatment and wrapped film on the pressure are considered. In addition, the heat treatment and wrapped films are chosen to strengthen the pressure. Finally, the experiments are designed to validate the effect of the lifetime improvement by the methods of the inner pressure strengthening. Results show that the lifetime can be extended by 30% with rational heat treatment and by 38% with rational design of the wrapped film.

Lifetime Prediction of Metallized Film Capacitors Based on Capacitance Loss

Metallized film capacitors possess characteristics of self-healing, high reliability, and long lifetime. Lifetime and reliability of capacitors are the key factors that ensure the stability of the electromagnetic launch system. In the capacitor lifetime test, it is a time-consuming work to get enough capacitance loss (CL) data to characterize the performance of the capacitor. Thus, it is necessary to analyze experimental data by effective lifetime prediction model (LPM). This paper first introduces the characteristics of CL in lifetime test. Then, it introduces traditional LPMs such as least square method (LSM) and Weibull distribution model (WDM). LSM is only appropriate when CL is uniform and steady, and it cannot analyze the lifetime reliability. WDM works best when large quantities of lifetime experiment data are acquired. In this paper, some new LPMs such as Birnbaum-Saunders distribution model and Poisson distribution model are introduced. New LPMs fully use CL in each shot, and it could faithfully reflect the work conditions of the capacitor. The analysis methods and steps of each model are put forward. In order to fully introduce these models, lifetime calculations are carried out based on the aforementioned LPMs.

Investigation of performance degradation in metallized film capacitors

Zn–Al metallized film capacitors in two different production stages were investigated to explain the decrease of capacitors performance with time. Unsealed and sealed capacitors with different aluminium content in metallization layer were investigated. Scanning electron microscopy (SEM) was used to image the surface of the metallization layers, energy dispersive X-ray spectroscopy (EDS) was used to determine the chemical composition and Auger electron spectroscopy (AES) was used to determine the chemical composition of the top of the metallization layers as well as to estimate the degree of oxidation. It was found that air humidity degraded the metallization layer of unsealed capacitors, especially at lower Al contents. Sealed capacitors were exposed to high electric fields, typical for standard usage. It was found – rather unexpectedly – that the performance was decreased by increasing Al content. A crystallographic explanation was proposed.

Metallized Film Power Capacitors End-of-Life Study Through Monitored Destruction Tests

A wide range of experiments was performed on metallized film capacitors. The monitoring of destruction tests was used to analyze the electrical properties of artificial critical defects. It is shown herein that these defects in the windings of the capacitors have a wide range of electrical properties and the behavior of the capacitor in the test is strongly related to these properties. A model is proposed to describe the degeneration of dielectric failure, the use of this model can help to predict the behavior of capacitors when they reach the end of life and to a more accurate design of the protection systems.

A Dual-Capacitors Type Energy Recovery Power System for Repetitive Pulsed High Magnetic Fields

As a flexible and convenient tool, a repetitive pulsed high magnetic field (RPHMF) would be employed for scientific research and industrial applications. A novel RPHMF system design adopting a dual-capacitors type energy recovery power system is introduced in this paper. The energy stored in the magnet can be fed back to the capacitor by a choke coil and a resonant capacitor while the energy dissipated in the discharge will be replenished to the capacitor through a high frequency resonant capacitor charging power system (CCPS). The main advantages of the design are as followed: first, the energy feedback make the system more efficient; second, during the whole process there is no reverse voltage on the metalized film capacitors, improving the energy storage capacitors’ service lifetime and reliability remarkably; finally, convenience can be brought to the high frequency CCPS’s application. In this paper, theoretic analysis of RPHMF system is described and an experimental device with a bitter magnet as the load is built to test the design for its verification. A 1.2 Hz, 8 T repetitive pulsed high magnetic field is generated. Experimental results show that there is no reverse voltage on the energy storage capacitors in the whole process. The factors influencing the efficiency and frequency of the system are analyzed in detail.

ENHANCING PERFORMANCE OF HIGH VOLTAGE METALLIZED FILM CAPACITORS BY USING NEW INDUSTRIAL NANO-COMPOSITES

This paper explains the enhancement on the performance of conventional High voltage metalized film capacitor doped with the Nanoparticles; the studied model has been discussed how the characteristics of High voltage metalized film capacitor has been enhanced depending on the concentration of the doped Nanoparticles and also their electric and dielectric properties. Also, this research investigates novel Nano-metric industrial materials for enhancing the electrical performance of multi section metalized film capacitors which satisfy a large variety of ac applications, electronic applications, and optimizing the characteristics of metalized film capacitors for specific applications by selecting suitable nanocomposite materials. Adding nanofillers to the conventional materials of multi section metalized film capacitors has enhanced the dielectric constant, dielectric strength, self-healing properties, temperature stability and volumetric efficiency that allowing achieving the highest capacitance per unit volume for this type of capacitors. Theoretical results have been investigated for comparing with conventional structure materials and new nanocomposite industrial materials of multi section metalized film capacitor. Finally, the present contribution has computed equivalent series inductance (ESI), equivalent series resistance (ESR), volumetric energy density, peak discharge current …etc. for multi section, high voltage windings, including limitations caused by various new nanocomposite materials.

Reliability Assessment of Metallized Film Capacitors using Reduced Degradation Test Sample

Metallized film capacitor is a type of product with a long lifetime and high reliability. It is difficult to assess the lifetime and reliability using the traditional statistical inference method which is based on the large number of testing data. This paper presents a new testing methodology, called T‐performance degradation test, by dividing the test process into several stages. In each stage, the sample size of working capacitors under test decreases stage by stage until the test lasts enough time with few survival capacitors. Leveraging the T‐performance degradation data, this paper further presents a reliability assessment model to predict the lifetime of the high‐performance capacitors. Finally, the reliability assessment model is demonstrated on a type of high‐performance metallized film capacitors used in the energy module of the laser facility. Copyright © 2012 John Wiley & Sons, Ltd.

高场强下金属化膜电容器绝缘电阻特性

高场强下金属化膜电容器绝缘电阻特性

500 kV全固态Marx发生器

The paper presents a 500 kV all-solid-state Marx generator adopting Z type circuit. In this Marx generator, twenty-eight isolated gate bipolar transistors(IGBTs) serial modules were utilized as controllable switches. The maximum working voltage of each IGBTs module was designed as high as 22 kV, and the repetition rate at full load condition was designed as high as 200 Hz. The ladder type pulse-forming-networks (PFNs) consisting of metallized film capacitors and wound inductors were designed as energy storage and pulse-forming components. Experimental results indicate that the Marx generator can run with 500 kV output pulses and 50 Hz repetition rate in burst-mode successfully. The peak output pulse voltage of this generator is approximately the same as that of the highest power solid-state Marx generator ever reported, while the peak current is almost twice, reaching 1 000 A. The maximum pulsed power of the generator is as high as 500 MW. As the capacitors were utilized as energy storage components, the pulse width can be adjusted from 3 s to 10 s continuously.

The capacitance loss mechanism of metallized film capacitor under pulsed discharge condition

The metalized capacitor has high energy storage density for its self-healing characteristic and is often used in pulsed power applications. The pulse life is defined as the number of charge/discharge cycles before 5% decrease in capacitance. In order to reduce the capacitance loss in the active electrode area (AEA), segmented electrodes are designed to decrease the clearing energy. In this electrode pattern, a large capacitance loss is observed along the segmented electrode edge (SEE). The loss along the SEE is caused by two reasons: electrode recession caused by electrochemical corrosion and self-healing induced by the combined effect of partial discharge and electric field distortion. According to teardown observation, there is an unexpected capacitance loss competition in the AEA and along the SEE under various voltages. Based on the analysis of the capacitance loss mechanism, three kinds of metalized electrode patterns are designed and tested. The result indicates that a proper electrode pattern helps to increase the pulse life of capacitor.

Effect of interlayer air on performance of dry-type metalized film capacitor in DC, AC and pulsed applications

The metalized film capacitor can work under a high electric field due to its self-healing characteristic. Firstly, this study indicates that inter-layer air is one of the most important factors which influence the process of self-healing. The interlayer air not only increases the duration of self-healing process, but also increases the self-healing energy and self-healing area. The interlayer air between the outer layers is more than that between the inner layers, so the self-healing area in the outer layer is larger than that in the inner layer. Secondly, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in the air are the necessary conditions of electrochemical corrosion. So if the capacitor is used in ac or pulsed applications, electrochemical corrosion will occur in the aluminum electrode. The product of electrochemical corrosion is alumina (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ), which leads to capacitance loss. For the safety film capacitor, electrochemical corrosion, which is caused by the air along the segmented gap causes electrode recession, resulting in rapid decrease of the capacitance. This paper provides three methods: wrap strengthening, heat treatment and end-sealing after vacuum to exclude or decrease the interlayer air. The experimental results show that all three methods can improve the lifetime of the capacitor to some extent.

전력전자용 금속증착 필름 커패시터 설계 및 신뢰성 평가

This paper presents the design and reliability evaluation of metallized film capacitor for power e lectronics application. The rated voltage of development capacitor is DC 3300[V], the capacitance is 5 <TEX>${\mu}F$</TEX> and the ripple current capability is 130 <TEX>$A_{rms}$</TEX>. Film metallization and patterns are an important design factor that has been development enhance the electric and reliability properties of film capacitor for power electronics. In term of capacitor construction and metallized pattern is one of the parameters that can be modified to further improve the rating in the terms of maximum ripple current and lifetime. This capacitor can be used as snubber capacitor application such as power train invertor system.

250°C Operating Temperature Dielectric Film Capacitors

High operating temperature electronic components are needed for a variety of military, aerospace, down-hole, and electric vehicle applications. One of the limiting technologies is the availability of highly reliable capacitors that operate at temperatures greater than 150°C and up through 250°C. This paper introduces a high breakdown strength dielectric film Gore has developed for metallized film capacitors. In addition to exceptionally high breakdown voltages, the 6 μm PTFE film exhibits low dissipation factor and stable capacitance over a wide temperature range. Film properties were tested from −50°C to 250°C and both wound film/foil and metallized film capacitors were fabricated and tested from RT to 300°C.

Calculation and measurement of metalized film capacitor's inner pressure and its influence on self-healing characteristics

Self-healing is the main cause to capacitance loss of metalized film capacitors, and it might finally lead to the failure of a capacitor. Teardown analysis shown that capacitance loss decreased gradually from the outer layers to inner layers in a capacitor, and it is said that the elastic films add compressive radial force to every wound wrap, the pressure brought up by the radial force has an significant effect on self-healing, with the increasing of the pressure in the inner layers, the capacitance loss become stabilized. This paper analyzed the essential relationship between capacitance loss and pressure between film layers firstly. After that, the inner pressure was calculated based on the film theory, result shows that the inner pressure of a capacitor is related to the tension in the film, the width of the film and the location of the calculated film layer in a capacitor. Finally, the inner pressure was measured to confirm the calculated results. It shows that the measured and theoretical value are almost consistent at outer layers, but the theoretical value become large than that of the measured value when near to the inner layers, and both of them are show that the outer layers' pressure is less than that of the inner layers, and cleared area at the out layers is larger than that at the inner layers.

Limits to the performance and design of high voltage metalized film capacitors

The use of multiple sections within a metalized film capacitor facilitates high voltage and reduced equivalent series resistance within a compact winding. As a result of high voltage and low inductance, large peak currents are, in principle, possible. The limitation to the peak current and power density is the ability of the end connection to withstand the peak current. As a result, the power density of such capacitors is limited not by materials but by the end connection current density, and improved materials, such a capacitor films with greater dielectric constant, will not result in increased energy density as the limiting factor is the length of the end connection necessary to achieve the required peak current. The energy density of multisection windings is also limited by the margins which are required between sections, the total width of which is limited solely by the rated voltage and margin operating field. The margins cause a substantial reduction in energy density, especially when the overall design is dictated by end connection current density. These issues are explored and quantified.

Study on Metallized Film Capacitor and Its Voltage Maintaining Performance

High energy density capacitor is a key device in power supply source in electromagnetic gun (EMG) system. The increase of energy density of capacitor is beneficial from emerge of metallized technology in electrode and advancement in manufacturing. The paper studies a kind of high energy density capacitor made of polypropylene with metallized electrode. The self-healing ability is improved by optimization of the structural parameter of the metal electrode. First, aimed to be used in EMG, experiments such as lifetime test and voltage withstand test are carried out to study the performance of the capacitor. The metallized film capacitor has an energy density of 1.6 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> under 10 kV. And the lifetime test finds its lifespan of 2000 shots. Then, the influences of different impregnating materials on the voltage droprang are compared in the paper for manufacture improvement purpose. Last, voltage maintaining test are carried out to observe the voltage drop of the capacitor. The output precision of the launch system will be consequently influenced. In order to obtain a stable voltage, a constant current and micropower charge control technique is applied to realize fast and high accuracy charge of capacitor to avoid fluctuation of output energy. Using micropower charge control, the voltage deviation in maintaining stage is less than plusmn1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> / <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> . And the charge system has a repeat accuracy of 0.520 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> / <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> with high reliability.