Study On Some Problems Of Metallized Pulsed Power Capacitors

Metallized capacitor is one of the key components in pulsed power system. The dissertation gives a detailed research by theoretical analysis and experimental investigation of improving energy density of the metallized capacitor and exploring its applications in pulsed power system.The development of the pulsed power system and pulse power capacitor was introduced firstly in this dissertation. Self healing characteristics of metallized polypropylene (PP) film were studied by experiments. The experimental results show that influence of the impact current on the self healing characteristics is evident. Self healing capability of hybrid electrode capacitors is weaker than that of metallized capacitors. The diameter of self healing spot increases with increase of the applied voltage, and new -emergying self healing spot is found when voltage is up to a certain value. Self healing current and energy increases with times of self healing in the same self healing spot. Capacitors of hybrid electrode can be used in lower electric field to improve the reliability of self healing and the security of the capacitors.Liquid surface tension model is used to calculate the pressure between the layers of capacitors before and after thermal treatment. The calculation results indicate that the pressures between layers decreases from inside to outside of the capacitor. And the thermal treatment has a strong influence on the pressure. Influence of pressure on self healing characteristics was studied by experiments of single layer of metallized film. The experimental results indicate that the diameter of self-healing point and self-healing energy decrease with the increase of pressure. But diameter, energy and voltage tend to be stable when the pressure reaches a certain value. The experimental results of single layerof metallized films are similar to entire winding of metallized capacitorsCharacteristics of fuse in safety film capacitor are studied by two types of pulse discharge experiment methods. The experimental results show that thickness of polypropylene film has a little influence on the break-off energy, while sheet resistance has a strong influence on break-off ernrgy. Break-off energy decreases with increase of the discharge time. The highest temperature rise after discharge is calculated, and the calculation results show that the highest temperature rise has a relationship with sheet resistance and discharge time. When the discharge time is short (says less than one microsend), small crack is emerged due to mechanical force on the fuse, and then the metallized layer would then be evaporated as the crack became long enough to generate creeping discharge. When the discharge time was long (says more than several microseconds), the small crack in the fuses is produced due to the heat causing by flowing current, and the metallized layer will be evaporated when the crack became long enough to generate creeping discharge.The factors influencing the temperature rise of metallized capacitor are studied under repetitive pulse in experiments. Eenergy and highest temperature rise of single time of discharge, highest temperature rise on surface and inter temperature distribution in stable state, influence of element height are all calculated by simulation. The results show that temperature rise of capacitors increase with the increase of the line current intensity and frequncey. And the convection of oil decreases the temperature rise of capacitors. The calculated temperature rise of single time of discharge is little. Diameter of capacitor element has influence on inner temperature rise. Temperature difference between inside and surface of capacitor decreases with the decrease of capacitor height.At last, influences of DC and steep front impulse injection on space charge of polypropylene by thermally stimulated discharge current (TSDC) method are studied. The experimental results show that space charge of polypropylene film is almost irrelative to the rise time of pulse. But the space charge has relationship with polarized field intensity and polarized time. The experimental result is agreed with the theory of TSDC. As a result, improved experimental method should be employed to study the influence of the steep front impulse injection on the space charge.