Study On The Key Parameters Of Self-healing In Metallized Film Capacitor

Metallized film capacitor is one of the key components in pulsed power system. In this paper, the key parameters that affect self-healing characteristics of metallized film capacitor are studied.The paper first analyzes the aging and breakdown mechanism of metallized film, then proposes a test method to study the self-healing characteristics of metallized film. Statistical method is carried out to analyze the capacitance loss of metallized capacitor. The results show that the clearing energy is in positive proportion to breakdown voltage and inverse proportion to sheet resistance. And there is little relationship between sheet resistance and power density of self-healing. The capacitance loss in safety film capacitor is composed of self-healing in active electrode area, electrode recession and self-healing along the edge. The capacitance loss is larger in outer layers and decreases from the outer to inner. Under higher electric field, the capacitance loss increases and the loss along the edge will be a doomed one.The paper then analyzes the influence of electrode parameters on self-healing characteristics. The results indicate that a reasonable electrode structure can efficiently reduce the capacitance loss rate and increase the lifetime of capacitor. Based on conformal transformation, the electric field of nanometer scale electrode is calculated. By definition of the range of electric filed distortion, the influential factor on capacitance loss along the electrode edge is analyzed. The calculation result shows that a thinner electrode, a thicker film brings out a larger range of electric filed distortion and partial discharge is easier to occur. The reverse amplitude of discharge voltage accelerates the electric field distortion of electrode edge. Under the combination effect of space charge, the influence of reverse amplitude on lifetime is large.The influence of inter-layer pressure on self-healing characteristics is studied. Based on film theory, the influencing factors on inter-layer pressure are deduced. The inter-layer pressure is in positive proportion to winding tension and in inverse proportion to film width, core radius and thinkness of film. The inter-layer pressure is small in the outer ones and increase large in the inner ones. The calculated pressure is compared with the measured one using micro-variable stress change, and the results show a same tendency between the calculated and measured ones. By film test, the influence of inter-layer pressure on parameters of self-healing process is studied. Test results show that clearing energy and demetallization area decrease with inter-layer pressure, and power density of self-healing increases with the pressure. And the outer layers have more capacitance loss than the inner ones.The influence of heat treatment on self-healing characteristics is studied. The heat treatment process can evacuated the air and humidity out of the windings, thus the initial partial discharge electrical field increases and the probability of self-healing will be deceased. The heated process should be a slow rising procedure under which condition the outer and inner layers can be shrinkage to a same level. The terminal temperature is related to the sheet resistance. High sheet resistance require a low temperature to void a departure between the base film and metallized electrode and low sheet resistance can have a relative higher heat treatment temperature.