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| Finite Element Simulation and In-Situ Testing of Electrothermal Coupling in Dielectric Energy Storage Pulse Capacitor for Electromagnetic Launch |
| Zhu Bofeng, Zhang Xiao, Zhang Guanxiang, Wang Xin, Lu Junyong |
| National Key Laboratory of Electromagnetic Energy Naval University of Engineering Wuhan 430033 China |
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Abstract The pulse power supply for electromagnetic launch has significant characteristics such as high power and long pulse width. Therefore, its dielectric energy storage pulse capacitors generally have the indicators of high voltage and large capacity. The discharge current amplitude and pulse width of a single pulse capacitor are generally in the order of 100 kA and several milliseconds, the working voltage is usually 5~10 kV, the repetition frequency is less than 1Hz, and the capacity and energy storage scale can generally reach the order of several millifarad and 100 kJ. Among various dielectric insulation materials used in the manufacturing of capacitor, biaxially oriented polypropylene (BOPP) has become one of the preferred materials for high energy storage density pulse capacitor due to their high breakdown field strength, low loss, good temperature resistance, machinability, and relatively low cost.
Continuous temperature rise is an important factor that leads to deterioration or even failure of the energy storage pulse capacitor for electromagnetic launch. The phenomenon of local breakdown caused by defects in polymer films is inevitable. Although pulse capacitor has a certain self-healing ability, the increase in temperature will increase the probability of electric thermal breakdown, leading to accelerated life decay. In addition, an increase in temperature can also lead to an increase in the conductivity of dielectric film, resulting in a decrease in the insulation resistance of capacitor, an increase in the leakage current, and a decrease in the voltage holding capacity. References point out that thermal aging is one of the important reasons for the failure of pulse capacitor. Related studies indicate that for every 8℃ increase in temperature, the lifespan of pulse capacitor decreases by half of its original. Thermal model for pulse capacitor has been established in reference, but the corresponding model has been extensively simplified and only considers axial heat distribution. Anisotropic thermal conductivity and its impact on the insulation safety, self-healing phenomenon and its impact on the operating temperature, deterioration phenomenon and pattern under the repeated frequency discharge conditions, such similar topics are also introduced in the existing references surrounding the pulse capacitor. In summary, the research methods and conclusions of temperature distribution of polymer film pulse capacitor lack the consideration of the equivalence of extreme application conditions and the comprehensiveness, accuracy and real-time of measurement results. In addition, relevant references have mainly studied the heat transfer problem at the single-core level of capacitor and there is no reference that has analyzed the continuous temperature rise of full-size high-voltage high-capacity pulse capacitor. The latter has important practical significance for the safety of electromagnetic launch devices.
In this paper, by means of theoretical analysis, finite element simulation and in-situ test, the internal temperature rise of a high-voltage large-capacitance pulse capacitor under continuous surge pulse current is systematically studied. The results show that after 50 times of pulse discharge, the temperature rise caused only by the Joule heat and self-healing heat inside the capacitor is about 0.7~0.9℃, but under the effect of parallel copper bar heat conduction, the temperature rise at the end of capacitor core unit can reach up to 21℃, which shows that the main factor affecting the maximum temperature rise of the inner capacitor core unit and its application safety is the heat conduction outside the capacitor core unit. The research methods and conclusions of this paper have positive significance and reference value for improving the heat dissipation process of pulse capacitor for electromagnetic launch and improving its working reliability under extreme application conditions.
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Received: 17 November 2023
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2025, Vol. 40 
