Metallized Film Capacitors Research Articles

Effect of Biaxial Stretching on the Dielectric Performance of Long-Chain Branched Polypropylene for Metallized Film Capacitors

Effect of Biaxial Stretching on the Dielectric Performance of Long-Chain Branched Polypropylene for Metallized Film Capacitors

Polycyclic aromatic compounds surface modulation of TiO2@SiO2 nanoparticles enhances the insulation performance of polypropylene film

Polypropylene (PP) film is an important component of metallized film capacitors. However, the insulation issues of polypropylene film significantly affect the safe and stable operation of capacitors. In this study, polycyclic aromatic compounds (PAC) were introduced to the surface of TiO2@SiO2 nanoparticles via chemical grafting, preparing Ti@Si-PAC nanofillers, to achieve modulation of the nanoparticle/PP interface. The experimental and simulation results indicate that Ti@Si-PAC/PP exhibits excellent insulation performance. The study indicates that the surface modulation of nanoparticles by PAC introduces a ‘soft interface’ between the nanoparticles and the polypropylene matrix. The ‘soft interface’ enhances the interfacial interaction, reduces dielectric loss, and introduces deep traps, exhibiting a significant inhibitory effect on carrier migration. Additionally, the introduction of PAC enhances the electron trapping capability in the interface region, which plays a positive role in quenching free radical chain reactions and reducing the damage of high-energy electrons to polypropylene molecular segments. This study provides an effective method for enhancing the insulation performance of polypropylene.

Reassessing Self-Healing in Metallized Film Capacitors: A Focus on Safety and Damage Analysis

Reassessing Self-Healing in Metallized Film Capacitors: A Focus on Safety and Damage Analysis

Self-Healing in Metallized Film Capacitors: Theory of Breakdown Interruption

Self-Healing in Metallized Film Capacitors: Theory of Breakdown Interruption

Compact hard x-ray flash radiography device based on wire-shorted low-impedance rod pinch diode.

A rod pinch diode (RPD) is a feasible load configuration to generate a high-brightness, small-size hard x-ray radiation source. In this paper, the radiography performance of a wire-shorted low-impedance RPD on a compactly designed table-top driver (WRPD-1) is demonstrated for the first time. The driver consists of four high-power discharge branches connected in parallel, with each branch consisting of two metal-film capacitors and one multigap field-distortion switch in series. The four branches are triggered synchronously to generate a fast-rising current pulse: the inductance of the load section at the short circuit is ∼10 nH, and the short-circuit current amplitude is ∼325kA at ±90kV charging voltage, with a 10%-90% rise time of 110ns. With a low-impedance RPD shorted by an 18-µm-diameter aluminum wire, a quasi-spherical x-ray focal spot with diameter <0.6mm (width of the half-maximum grayscale) and a pulse duration of ∼25ns (half-width of the radiation pulse) is obtained at ±70kV charging voltage, and the imaging resolution excels 10 lp/mm under 1.56× magnification. According to the transmission-absorption x-ray spectrum estimation, the average emitted photon energy is ∼30keV with a distinct peak in the 10-15keV range that corresponds to the L-lines of tungsten, and the total energy of photons >10keV reaches ∼1.16J. The present results show that the device can serve well for the flash radiography diagnosis and potentially as an efficient light source for dynamic x-ray diffraction.

Dielectric performance improvement of polypropylene film by hierarchical structure design for metallized film capacitors

In this paper, hierarchical structure design method is proposed for improving the dielectric performance of polypropylene (PP) for metallized film capacitors. The results show that the composite film with 0.02 wt% terephthalaldehyde doping and functional layer thickness occupying 25% shows the best dielectric properties. The leakage conductivity declines by 89.0%–94.3%, the DC breakdown strength grows by 15.6%–19.7% and the discharged energy density improves by 50.6%–53.4%. Terephthalaldehyde doping introduces sites that could capture free holes, thereby blocking the carrier migration path. The hierarchical structure design results in the holes accumulating in the functional layer and the reverse electric field formed suppresses the charge injection from the anode. Furthermore, the probability of intrinsic charge excitation due to the band gap width reduction is greatly reduced. The method provides a reference for improving the dielectric performance of PP films from the perspective of regulating the charge transmission behavior.

Failure mechanism of metallized film capacitors under DC field superimposed AC harmonic: From equipment to material

AbstractThis study focuses on the degradation behaviour of metallised film capacitors, which are the essential components for the stability of converter valves in flexible ultra‐high voltage direct current (HVDC) transmission systems. Through systematic experimentation, we investigated the failure mechanisms of MFCs under HVDC fields with superimposed harmonics, considering both equipment and material perspectives. The experiments subjected capacitors to 500 h of ageing under two conditions: a DC/AC‐superimposed field with a constant DC component of 290 kV/mm and an AC ripple rate varying from 12% to 28%, and a control group aged solely under a DC field. Our findings indicate that capacitors aged under the DC/AC‐superimposed field exhibited shorter lifespans and more significant capacitance loss than those aged under only the DC field. This difference in performance is primarily attributed to the distinct electrode loss behaviours observed under each ageing condition, which are key factors in the capacitors' capacitance decay. Moreover, the biaxially oriented polypropylene films in the DC‐aged samples showed more severe deterioration, characterised by more noticeable molecular chain scission and reduced breakdown strength, compared to those aged under the DC/AC superimposed field. This difference is partly due to the moderate temperature increase caused by harmonics, which benefits the aggregation structure, and partly to the reduced molecular structure damage from the AC field.

Accelerated Degradation Testing and Failure Mechanism Analysis of Metallized Film Capacitors for AC Filtering

Accelerated Degradation Testing and Failure Mechanism Analysis of Metallized Film Capacitors for AC Filtering

Study of the in situ test setup and analysis methods for self-healing properties of metallized film capacitors.

Metallized film capacitors (MFCs) are widely used in the power electronics industry due to their unique self-healing (SH) capability. SH performance is an essential assessment for MFC reliability verification in industrial production. The SH phenomenon of metallized films usually occurs rapidly in a very short period, and its real-time evolution details are often difficult to capture and analyze. In this paper, a test system for the SH performance of metallized films for capacitors was constructed. The system consists of three components: a voltage-current characteristic testing and current pulse capture device, a microscopic image real-time acquisition device, and an integrated analysis processing device. Through the voltage-current characteristic testing and current pulse capture device, the electrical parameters of the SH point, such as SH times, breakdown field strength, SH current, and SH energy, are obtained; through a microscopic image real-time acquisition device, the real-time spatial positioning of the SH point was obtained, and the interconnection between the morphology of the SH point and the electrical properties was established. The relationship between the SH point and the temperature distribution was further established using thermal imaging technology, which lays the foundation for a thorough and timely assessment and analysis of the failure mechanism and the real-time evolution of the metallized film SH process. This significantly improves the effectiveness of SH property research.

Non‐uniform voltage distribution characteristics of metallized film capacitors in flexible HVDC projects

AbstractThe problem of non‐uniform voltage distribution in the internal element of metallized film capacitors in flexible HVDC transmission systems exists, the influence of electrical parameters of dielectric and metal copper row are not considered in the existing metallized film capacitor equivalent circuit model. In this paper, the conductance of biaxially oriented polypropylene film (BOPP) for metalized film capacitors is measured at different electric field intensity and dielectric properties at different frequencies. The current density distribution and voltammetric properties of the metalized film capacitor elements under AC and DC superimposed voltages are calculated by the finite element method, and the voltammetric properties of the copper row considering the skin effect are derived. The equivalent circuit model of the metalized film capacitor under the AC‐DC superposition voltage is proposed. The simulation results of the capacitor equivalent circuit model show that the voltage distribution of the internal elements of the capacitor is uniform at low frequency AC voltages (&lt;102 Hz), and the voltage amplitude and phase difference between the elements of the capacitor gradually increases with increasing AC voltage frequency. At an AC voltage frequency of 105 Hz, the difference in magnitude between the two capacitor elements on the same copper row was up to 2.01% and the phase difference was 13.5%, while the difference in magnitude between capacitors at the same horizontal position on different copper rows was up to 56.8% and the phase difference was 10.44%. The results of this paper provide some guidance for the modeling of the internal components of metalized film capacitors, the calculation of voltage distribution and the structural optimization design.

Heterostructured n-ZnO@p-CuO nanosheets filled in a polymer matrix for enhanced electrostatic energy storage performance.

Metallized film capacitors use plastic films as the dielectric spacer, and these polymer films generally have low dielectric constants. To boost the electrostatic energy storage density of a film capacitor, advanced high-k films with high electrical breakdown strength and low dielectric loss are highly desired. Herein, polymer nanocomposite films were made by filling ZnO@CuO nanosheets into poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)]. The n-type ZnO nanosheets are synthesized in an aqueous solution. Through a calcination process, thin layers of p-type CuO are coated over the ZnO nanosheets. Compared to pure P(VDF-HFP) and ZnO/P(VDF-HFP) films, the ZnO@CuO/P(VDF-HFP) films exhibit higher dielectric constant and higher breakdown strength. The optimal content of ZnO@CuO nanosheet in the polymer matrix is determined to be 3 wt%, which leads to a dielectric constant of 15.6 at 1 kHz and the highest energy density of 5.6 J cm-3. The efficacy of ZnO@CuO nanosheets in enhancing the dielectric performance of the polymer nanocomposite is elucidated in detail. This research provides a scalable and low-cost strategy to produce polymer nanocomposite films with high capacitive energy storage performance.

Enhanced Dielectric Performance of Polypropylene Film by Surfacing Grafting and Crosslinking for Metalized Film Capacitors

Enhanced Dielectric Performance of Polypropylene Film by Surfacing Grafting and Crosslinking for Metalized Film Capacitors

Calculation of Current Distribution Inside the Metallized Film Capacitor Element at High Frequency

Calculation of Current Distribution Inside the Metallized Film Capacitor Element at High Frequency

Discharge Monitoring and Aging Assessment Method for Metallized Film Capacitor Based on Acoustic Signal

Discharge Monitoring and Aging Assessment Method for Metallized Film Capacitor Based on Acoustic Signal

Parametric and Catastrophic Failures of Metallized Film Capacitors Under High Voltage Stress

Parametric and Catastrophic Failures of Metallized Film Capacitors Under High Voltage Stress

ESR Modeling for Atmospheric Corrosion Behavior of Metallized Film Capacitors

ESR Modeling for Atmospheric Corrosion Behavior of Metallized Film Capacitors

Metallized stacked polymer film capacitors for high-temperature capacitive energy storage

Metallized film capacitors towards capacitive energy storage at elevated temperatures and electric field extremes call for high-temperature polymer dielectrics with high glass transition temperature (Tg), large bandgap (Eg), and concurrently excellent self-healing ability. However, traditional high-temperature polymers possess conjugate nature and high S value (C/(H + O) ratio), which compromises Eg and self-healing properties. Herein, we provide a series of novel molecules-fully alicyclic polymers based on commercial Kapton PI (Al-PIs), which exhibit intrinsic decoupling conjugate and decreasing S, leading to high Eg and robust self-healing. The Al-PIs possess much increased Eg of 5.23 eV (Tg of 242 °C) or Eg of 5.01 eV (Tg of 280 °C) with a lowered S < 0.7, which approaches Eg of 5.93 eV and S of 0.5 for the commercial benchmark biaxially oriented polypropylene (BOPP) applied at low temperatures (≤70 °C). Consequently, Al-PI delivers a record discharge energy density with 90 % discharge efficiency (Uη90) of up to 8.04 J/cm3 at 150 °C, 5.74 J/cm3 at 200 °C, and 3.12 J/cm3 at 250 °C, respectively. Besides, Al-PI is capable of self-healing even at 200 °C. We also demonstrate a stacked Al-PI metallized film capacitor with discharge energy density up to 1.6 J/cm3 and discharge efficiency of 98 % at 150 °C. These results confirm that alicyclic polymers are promising candidates for high-performance dielectric films and capacitors under extreme thermal and electric field conditions.

Novel Polyetherimide Dielectrics: Molecular Design, Energy Storage Property, and Self-Healing Performance.

The development of high-temperature resistant dielectrics with excellent dielectric properties and self-healing behavior is crucial for the application of metallized film capacitors. In this work, a series of polyetherimide (PEI) dielectric films are designed and fabricated. The introduction of polar groups is in favor to the increase of permittivity, and the flexible connection such as the ether group will facilitate the reduction of dielectric loss. Moreover, the oxygen elements are beneficial to the "self-healing" of metallized film capacitors. Consequently, the permittivity of 3.53-4.00, dissipation factor of 0.281-0.517%, and Weibull breakdown strength of 347-674MVm-1 are obtained for the PEI dielectrics. In addition, PEI-4 (BPADA-BAPP) and PEI-8 (BPADA-MDA) are selected to further investigate dielectric breakdown (150°C), electrical displacement-electric filed (D-E) loop (at room temperature and 150°C) as well as self-healing performance, which will evaluate their potential in practical applications. The results show that PEI-8 has stable breakdown field strength and high charge-discharge efficiency at elevated temperatures. Metallized film capacitor based on PEI-8 exhibits excellent self-healing performance, with pleasing self-clear morphology, high breakdown voltage, and reduced self-healing energy. Therefore, PEI-8 is considered as a potential candidate for metallized film capacitors applied under harsh conditions.

Nanoscale thinning of metal-coated polypropylene films by Helium-ion irradiation

Polypropylene (PP) films have a wide range of applications, e.g. as dielectric materials for metallized film capacitors. In this article, we present a method for thickness reduction of PP films by ion irradiation, which has a direct effect on device capacitance. We show that the thickness of PP layers can be reduced by irradiation with He+ ions and controlled on the nanometer scale by the irradiation dose. The effect of different thin metal film coatings on PP surface was also investigated. The metal coatings were used for two reasons: they function as one of the metal electrodes in the capacitor structure, and they minimize sample charging during ion irradiation. Three different metallization materials were investigated: 5 nm Pt60Pd40, 5 nm Au, and 15 nm Al. We studied two technologically relevant PP films: the thinnest commercially available biaxially oriented polypropylene (BOPP) and spin-coated polypropylene (SC-PP) thin films. The irradiation was done with a focused Helium-ion beam (He-FIB) in a Zeiss Orion NanoFab Microscope at a landing energy of 30 keV with doses in a range of 5.4 × 10–5 nC/μm2 to 8.1 × 10–3 nC/μm2. An atomic force microscope (AFM) was used to analyze the details of surface modification: the surface height of the irradiated regions and surface morphology changes caused by the irradiation. For all applied doses, the Al-coated samples demonstrated smaller surface-height reduction compared to the Pt60Pd40 and Au-coated samples. We speculate that the possible factors responsible for this effect include differences in the thickness and the crystalline-grain orientation (texture) of the metallization films. Both BOPP and spin-coated PP presented surface ridges at the borders between the irradiated and non-irradiated regions. It can be attributed to the mechanical strain induced by the material modification.

Accelerated Damage in Metallized Film Capacitors Under Pulse Surge Combined With Rated DC Voltage

Metallized film capacitors (MFCs) have good self-healing performance and are widely used in pulsed power supplies, power systems, and aerospace equipment. The self-healing time of MFCs is often in the order of microseconds. When the pulsewidth of overvoltage is close to the self-healing time, MFCs are at risk of insulation failure. In this article, self-healing energy and time under pulse surge combined with rated dc voltage are investigated by analyzing the effect of the number of applied pulses on the capacitance loss, dielectric loss, and equivalent series resistance (ESR) of MFC. The correlation between the number of applied pulses and the capacitance loss of MFC at different repetition frequencies, pulse components, and temperatures is studied, fitting the 5% turning points of capacitance loss. The experimental results show that the multiple types of self-healing occur in an active period of one pulse under microsecond overvoltage. According to the level of injection energy and several typical waveforms from voltage and current, the self-healing process of MFC can be classified into effective self-healing, disruptive self-healing, and fatal self-healing. When effective self-healing occurs in the MFC, the performances remain stable for a certain time. As the number of tolerated pulses increases, disruptive self-healing and fatal self-healing significantly decrease capacitance value but increase dielectric loss and ESR.