Why is the temperature rating of biaxially oriented polypropylene film capacitors limited to 85°C?

It has been found that the long-term thermal aging at the temperature of 100 °C and relative humidity 54 %, causes a low change of the capacitance and a high change of the loss factor of polypropylene (PP) film capacitors. The goal of the work has been to find main reasons of these changes. Dismounting of aged capacitors has shown that the metal layers on the PP film, which form the capacitor electrodes, near the metal contacts on the ends of the body of the capacitor are strongly corroded and sometimes even totally absent. On the other hand, the change of the total electrodes area is not significant, because the capacitance decreases only slightly during the thermal aging. Because the PP film as well as the sprayed contacts are resistant to heat aging, the main reason of a significant increase in the loss factor must be the increase the resistance of the metal layers that form the capacitor electrodes.

Metallized polypropylene film capacitors (MPPFC) are usually used in modular multilevel converters (MMC) in HVDC transmission due to their good self-healing, strong current capacity, high energy density, and high reliability. However, due to the low dielectric constant of polypropylene film material (only 2.2), the capacitance value of polypropylene film capacitors is constrained, so the volume, weight, and cost of metallized film capacitors occupy a large part of the MMC system. For this reason, this paper considers reducing the volume of metallized film capacitors by increasing the dielectric constant of polypropylene film and analyzes a feasible range for the increased dielectric constant. Through the Comsol finite element simulation calculation, it is found that the volume can be reduced by 26.7%. Although the ESR of the capacitor increases, the capacitor temperature drops by 3.5 ℃ when the capacitor temperature is close to the steady-state due to the reduced diameter of the capacitor and better heat dissipation. This result can provide a reference for the optimal design of film capacitors in MMC applications.

Metallized biaxially oriented polypropylene film (BOPP) capacitors are widely used in pulsed power systems. When the capacitor is used as the energy storage equipment under high electric field, more charges should be provided to maintain the voltage of the capacitor. This should be ascribed to the completion of the slow polarization which may take several hours or even longer. This paper focuses on the stored charge in metallized BOPP film capacitors. The modeling of the stored charge by the equivalent conversion of circuits is conducted to analyse the slow polarization in the BOPP film. The 3-RC network is proposed to represent the time-dependent charge stored in the capacitor. A charging current measurement system is established to investigate the charge storage property of the capacitor. The measurement system can measure the long time charging current with a sampling rate of 300 Hz. The total charge calculated by the charging current indicates that the stored charge in the capacitor under the electric field of 400 V/μm is 13.5% larger than the product of the voltage and the capacitance measured by the AC bridge. The nonlinear effect of the electric field on the slow polarization charge is also demonstrated. And the simulation of charge storage based on the 3-RC network can match well with the trend of the stored charge increasing with the time.

With the rapid development of the aerospace industry and nuclear technology, metallized film capacitor (MFC), as energy storage unit for pulsed power sources, begin to operate in various high-energy radiation environments. In order to ensure the working reliability of MFC, it is of great significance to study its voltage maintaining performance (VMP) and aging law after irradiation. In this paper, metallized polypropylene (PP) film capacitors (MPPFC) are used as the research object to analyze the irradiation reaction mechanism of polypropylene, and the effect of irradiation dose on the capacitance, dielectric loss and VMP of MPPFC under aerobic conditions is studied. The results show that there is a critical value of 100 kGy for the effect of irradiation dose on MPPFC. When the irradiation dose is less than 100 kGy, the capacitance and dielectric loss of MPPFC remain almost unchanged, and the voltage drop increases with the dose as a power function. When the irradiation dose reached 500 kGy, the macromolecules in PP film were completely cleaved, and the voltage drop of the MPPFC increased from 1.62% to 2.96% without irradiation within 10 s. In order to ensure the energy output efficiency of the power supply, the irradiation dose of MPPFC should be controlled not to exceed 5 kGy. At this time, the voltage drop of the MPPFC within 10 s is 2.30%, and the output efficiency is 95.41%. This paper serves to provide a certain basis for the application of MPPFC in irradiation environment.

The life expectancy and long term reliability of grid-connected three-phase photovoltaic (PV) inverters can be increased by replacing the conventional electrolytic film capacitors by metallized polypropylene film capacitors. This paper presents a detailed evaluation of a three-phase grid-connected PV inverter performance when replacing the electrolytic capacitor with a minimum value of metallized polypropylene film capacitor-one. The minimum dc bus capacitance leads to larger voltage ripples. However, such ripples were found to be within acceptable limits to run the inverter satisfactorily. Simulation results are presented for a 15-kW grid-connected inverter at nominal voltage of 700V dc and experimental results are provided for a 3.0-kW system at a nominal voltage of 400V dc, built in the laboratory.

When the metallized polypropylene film capacitor (MPPFC) is used under high electric field in pulsed power systems, an obvious voltage decay phenomenon will occur. The voltage decay is mainly resulted from the relaxation polarization in dielectric applied under high electric field. This paper focuses on the relaxation polarization in metallized biaxially oriented polypropylene (BOPP) film capacitors. The extended Debye model of relaxation polarization is discussed and the parameters of each RC branch are obtained. Meanwhile, the relationship between the increasing proportion of polarization charge (ΔQ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> /Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> ) and temperature is investigated. The experimental results show that under 1kV, ΔQ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> /Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> varies from 0.018 to 6.868 with the temperature varing from 10 to 70 /spl deg. Moreover, the equivalent capacitance of capacitors in frequency domain is analyzed with consideration of slow polarization. The analysis shows that both a lower frequency and a higher temperature can accelerate the relaxation polarization and increase the voltage decay. Based on the extended Debye model developed from the polarization charge test, the voltage drop is calculated and the results can match well with those of the voltage maintaining test.

Electrolytic and metallized polypropylene film (MPPF) capacitors are among the most popular capacitors used in electronic equipments. The choice of capacitors is of major importance because one of the most frequent causes of the equipment breakdowns results from the failure of capacitors, and will therefore determine the overall lifetime of the system. Electrolytic capacitors present higher capacity per volume unit and lower cost than MPPF capacitors; however, they appear as the most life-limiting components exhibiting a high failure rate. MPPF are a good alternative to electrolytic capacitors thanks to their high dielectric breakdown strengths, low dissipation factors and good stability over a wide range of frequencies and temperatures. Even though MPPF capacitors are very reliable components due to their unique selfhealing capability, they are not free of failures and they release noxious gases in this case. Therefore, suitable diagnostic techniques are needed to prevent catastrophic failures. The typical failure mode of electrolytic and polypropylene film capacitors lays on the increase of the capacitor Equivalent Series Resistance (ESR) and the decrease of its capacitance. This paper presents an approach for the monitoring of the capacitor’s electrical parameters in function of the ageing time when used as DC-link capacitors. A comparison between the film and electrolytic technologies will be also made in this paper.

Polyvinylidene fluoride based materials have good dielectric properties and withstand voltage. The film capacitors made of polyvinylidene fluoride based materials have high energy storage density. It is of guiding significance to study the charging and pulse discharge temperature characteristics of polyvinylidene fluoride film capacitors for their application in the field of pulse power. In this paper, the influence of capacitor structure and heat generation mechanism on temperature rise is studied. Through capacitor charging and pulse and slow discharge tests and temperature measurement experiments combined with simulation analysis, it is found that the central temperature of the capacitor is the highest, the heat generated by the capacitor during discharge only accounts for a part of the charging and discharging process, and the heat generated during charging contributes the most to the temperature rise. Polyvinylidene fluoride capacitors generate more heat than polypropylene film capacitors, and the temperature rise can be further reduced by reducing the equivalent series resistance through material research or improved process.

Some cases of premature failure of impregnated PP (polypropylene) film capacitors have been reported. One of the main reasons for such failures appears to be the poor quality of the PP film. The performance of PP films obtained from different sources has been evaluated by conducting various short-time and long-term tests in the laboratory. Some of the properties of the PP film which appear to be sensitive to reflect aging have been identified. The behavior of PP films under identical aging conditions has been found to be different. Some of the properties which appear to deteriorate due to aging are tan delta, breakdown strength, mechanical properties, and percentage of crystallinity. The life expectancy of all PP film power capacitors is strongly dependent on the aging characteristics of the PP film. >

The feasibility of a gravure ink‐containing nanoclays as an alternative oxygen (O2) barrier material to oriented polypropylene (OPP) film was investigated. The gravure ink was effectively dispersed through the clay using an ultrasonic homogenizer. Barrier properties of OPP films coated by the gravure ink‐containing nanoclays were evaluated with respect to dispersion time, clay content, and different types of nanoclays (Cloisite Na+, Cloisite 25A, and Cloisite 30B). Barrier and morphology properties of the OPP films were tested by measuring selected film properties such as O2 transmission rate (OTR), and water vapor transmission rate, and by field emission scanning electron microscopy, X‐ray diffraction (XRD), and transmission electron microscopy (TEM). OTR of control OPP film coated solely with gravure ink was 1653 cm3 m−2 day, while use of OPP films coated by the three different types of gravure ink‐containing nanoclays (nanoclay content: 1% w/w) reduced OTR by 12–37%. OTR values measured using the gravure ink‐containing modified montmorillonite (Cloisite 25A and Cloisite 30B) were markedly lower than measured by pristine gravure ink‐containing unmodified montmorillonite (Cloisite Na+). On the other hand, no remarkable differences were evident in the water vapor barrier performance of control OPP film and gravure ink‐containing nanoclay‐coated OPP film. As nanoclay content and dispersion time increased, OTR values of the OPP films coated by gravure ink‐containing nanoclays decreased. And the TEM and XRD observation indicated that intercalated and exfoliated types were generated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Power electronics are a key technology for hybrid and plug-in electric drive vehicles (EDV) and represent 20% of the material costs. DC bus capacitors are one of the critical components in EDV power inverters and they can occupy ~35% of the inverter volume, contribute to ~23% of the weight, and add ~25% of the cost. Current polypropylene (PP) film capacitors have dielectric constant K of 2.2 and temperature stability lower than 105°C. We recently developed a modified Polyvinylidene fluoride (PVDF) which combines high dielectric constant, low dielectric loss, low leakage current, high dielectric breakdown strength, and high temperature stability. The modified PVDF capacitor film also has graceful failure feature which is critical to applications demanding high reliability and long lifetime. The thermoplastic nature of the modified PVDF ensures that they can be processed into thin capacitor film using inexpensive melt extrusion and biaxial orientation process. In this report, DSC and dielectric spectroscope test results of the novel capacitor film will be presented.

Improved discharge energy density and efficiency of polypropylene-based dielectric nanocomposites utilizing BaTiO3@TiO2 nanoparticles

Introduction. Waste management and poorly degradable polymer packaging are one of the main environmental issues. Biodegradable materials based on a composition of native and modified starches can solve the problem of polymer waste in food packaging. They are environmentally friendly and harmless during decomposition. However, the barrier properties of biodegradable films still remain understudied. Study objects and methods. The research featured the safety profile of gelatinous confectionery products during storage in biodegradable and polypropylene films. It focused on moisture transfer and microbiota growth in glazed jelly marmalade. The first sample was wrapped in oriented polypropylene film (40 microns), while the other sample was packaged in a biodegradable film (50 microns). A set of experiments was conducted to measure the mass fraction of moisture, water activity, fatty acid composition of the fat fraction of the glaze, active acidity, microbiological parameters, and lipase activity during storage. Results and discussion. The activity of water during storage remained the same. The specific rate of moisture transfer for the polypropylene film sample was approximately 1.4 times higher than for the biodegradable sample. It equaled 1.16×10–6 g/m2·s for the polypropylene film sample and 0.83×10–6 g/m2·s for the biodegradable sample. The dynamics of growth of QMAFAnM, mold, and yeast was the same in both samples; it did not exceed the regulated indicators of microbiological safety after 12 weeks of storage. The lipase activity of the glazed marmalade samples packed in the polymer film did not increase during storage. Replacing the polypropylene film with a biodegradable film did not significantly affect the safety profile of confectionery products. Conclusion. Research results confirmed the possibility of using a biodegradable film for packaging confectionery products.

High-voltage high-current pulse power sources such as linear transformer driver, Marx generator and magnetically driven flyer device require that the capacitors have a long life and high reliability. To meet requirements, life tests of five capacitors which have been used in pulse power systems were carried out. A capacitor test facility capable of ~3,000 shots/month, which is a portable high-voltage test facility designed primarily for testing high voltage capacitor that may be used in future, has been designed and operated. This paper summarizes the results of our lifetime testing of the selected five kinds of high energy storage low inductance capacitors. Different combinations of insulating mediums (polypropylene film and high quality capacitor paper) and impregnating agents (benzyl toluene and castor oil) were studied in order to optimize the structure of capacitors and improve performance of capacitors in future. The effects of high reversal on the lifetimes of capacitor for given insulating medium and impregnating agent show that the selected insulating medium and impregnating agent are suitable for capacitor working under high reversal. The life test data which shows that the design of these capacitors is successful may be combined to estimate the reliability of pulse power sources in the future. These work and results may give us some guidelines to design and apply a capacitor.

Commercial biaxially oriented polypropylene (BOPP) film capacitors have been widely applied in the fields of electrical and electronic engineering. However, due to the sharp increase in electrical conduction loss as the temperature rises, the energy storage performance of BOPP films seriously degrades at elevated temperatures. In this study, the grafting modification method is facile and suitable for large-scale industrial manufacturing and has been proposed to increase the high-temperature energy storage performance of commercial BOPP films for the first time. Specifically, acrylic acid (AA) as a polar organic molecular is used to graft onto the surface of commercial BOPP films by using ultraviolet irradiation (abbreviated as BOPP-AA). The results demonstrate that the AA grafting modification not only slightly increases the dielectric constant, but also significantly reduces the leakage current density at high-temperature, greatly improving the high-temperature energy storage performance. The modified BOPP-AA films display a discharged energy density of 1.32 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> with an efficiency of >90% at 370 kV/mm and 125 °C, which is 474% higher than that of the pristine BOPP films. This work manifests that utilizing ultraviolet grafting modification is a very efficient way to improve the high-temperature energy storage performance of commercial BOPP films as well as provides a hitherto unexplored opportunity for large-scalable production applications.