Fuchang Lin

The capacitance loss mechanism of metallized film capacitor under pulsed discharge condition

The metalized capacitor has high energy storage density for its self-healing characteristic and is often used in pulsed power applications. The pulse life is defined as the number of charge/discharge cycles before 5% decrease in capacitance. In order to reduce the capacitance loss in the active electrode area (AEA), segmented electrodes are designed to decrease the clearing energy. In this electrode pattern, a large capacitance loss is observed along the segmented electrode edge (SEE). The loss along the SEE is caused by two reasons: electrode recession caused by electrochemical corrosion and self-healing induced by the combined effect of partial discharge and electric field distortion. According to teardown observation, there is an unexpected capacitance loss competition in the AEA and along the SEE under various voltages. Based on the analysis of the capacitance loss mechanism, three kinds of metalized electrode patterns are designed and tested. The result indicates that a proper electrode pattern helps to increase the pulse life of capacitor.

Design and Performance of a Resistive-Divider System for Measuring Fast HV Impulse

A measuring system based on a resistive divider using a copper sulfate (CuSO4 solution) has been developed to measure high-voltage impulses with rise times of several tens of nanoseconds. The response and temperature characteristics of the resistive divider have been studied. The divider has excellent response characteristics (<; 1-ns theoretical rise time) and good immunity from interference from a Marx generator and spark-gap switch. Stray parameters of the resistive divider are theoretically calculated, and their influences on the square-wave response are studied by Alternative Transients Program/ ElectroMagnetic Transient in DC System simulations. The measuring system is shielded using coaxial construction techniques. The experimental results show that it is capable of maintaining the output impulse of the Marx generator with rise time of 13 ns and amplitude of 170 kV.

Development of a Compact 450-kJ Pulsed-Power-Supply System for Electromagnetic Launcher

A 450-kJ pulsed-power supply (PPS) for electromagnetic launcher has been built up. It consists of six 75-kJ pulse forming units (PFUs). Each PFU is composed of a 75-kJ capacitor (1000 /12.2 kV), a thyristor stack as main switch, a diode stack as crowbar, a specific pulse-shaping inductor , and a coaxial cable. The peak value of the output current of one PFU is 85 kA with a peak time of 190 . The influencing factors of overvoltages on the series thyristor valves are studied by experiments and simulations based on PSCAD/EMTDC. A proper protection is used to prevent the series thyristor valves from being damaged by overvoltage when a switch is turned on. At the end, the total discharge currents of the PPS test with a short-circuit load and a railgun load are presented, respectively.

An improved capacitor charging power supply for a power conditioning system

Capacitor charging power supply (CCPS) is one of the most important components of a pulsed power system. The CCPS studied in this paper is used in power conditioning systems for Laser Nuclear Fusion. With a view to enabling multiple CCPSs to work concurrently in an environment of high voltage, high power and strong electromagnetism, this paper carries out a profound and systematic research into the characteristics of a capacitor charging power supply, including charging rate, harmonic features, efficiency and voltage precision, etc. Furthermore, some measures to improve the characteristics of CCPS are put forward. The advantages of high charging rate, low harmonic, high efficiency and accurate charging voltage are proved by the results of experiments and the performance in practical operation on a 23.5 kV, 50 kW, 4400 μF CCPS.

Analysis on Useful Lifetime of High-Power Closing Switch With Graphite Electrodes

High-power closing switches with graphite electrodes have been used in power-supply system for a large laser pump. The useful lifetime of this kind of switch is an interesting and important issue. Previous researchers have observed that the graphite erosion loss is proportional to the amount of transfer charge in a high-power pulsed discharge. Therefore, the erosion rate of graphite may be used for predicting and estimating the electrodes useful lifetime. According to the mathematical model proposed in this paper, the lifetime of a closing switch with graphite electrodes is dependent upon several key parameters, including the dimensions of electrode, density, the erosion rate of graphite electrodes, undervoltage ratio, working temperature, and the amount of energy transfer. A mathematical formula describing the relationship between lifetime and those parameters has been deduced. Based on a newly developed spark-gap switch which can support over 100-C single transfer charge, this proposed lifetime model has been verified. This paper may quantitatively perform the function of guidance in engineering applications of graphite electrode switches in large pulsed-power facilities.

Calculation of Electric Field in Safety Film Capacitors

The failure mechanism of a safety film capacitor is a little different from that of an all-film capacitor. Experiments were carried out on a number of safety film pulse capacitors. A careful examination is made of the capacitor film after discharge. It is found that the failure of the capacitor comes from the capacitance loss, which is caused by the partial discharge (PD) at the edge of the segment electrode. The electric field is calculated in the paper and the results show that the electric field distortion is the main reason for PD at the edge of electrodes. The paper uses the electric field distortion range (EFDR) to review the influences of thickness of electrode, thickness of film and reversal coefficient of discharge voltage on PD at the edge of electrodes. As a result, the EFDR will be more intense and the PD at the edge of electrode will be more obvious if the electrode is thinner, the film is thicker or the amplitude of reversal coefficient of discharge voltage is higher. And when there is free surface charge on the film near the electrode, the PD will be more serious.

Initial Plasma Development of Field-Breakdown Triggered Vacuum Switch

A triggered vacuum switch (TVS) is an important component in pulsed power systems due to its quick switch, rapid dielectric recovery, small volume, convenient trigger system, simple structure, etc. A sample of field-breakdown TVS is fabricated, and its turning-on process is described in this paper. The initial plasmas play an important role in the process of TVS operation; its development includes two parts: (1) generation and (2) expansion. Based on the field breakdown principle, an electron emission model is chosen to describe the generation of initial plasmas. A heat conduction model is set up to deduce the expansion of initial plasmas. The model calculated result is accordant with the delay experiment.

Operational characteristics of a surface breakdown triggered vacuum switch with six gap rod electrode system

A triggered vacuum switch (TVS) is one of the important apparatuses in the field of pulsed power system. It has many advantages, such as wide working voltage range, high current capability, high transfer charge, flexible trigger system, high trigger reliability, rapid dielectric recovery, long life, compact fabric, low noise, etc. A small and compact sample of surface-breakdown TVS with six-gap rod electrode system was fabricated in this paper, and a test platform of TVS was set up. The test results show that, the TVS sample has working voltage of 0.05-28 kV, current peak of 225 kA and transfer charge of 45Cb. Due to the ceramic surface in the trigger gap, the time delay of TVS is controlled in less than 1.5 μs, and long trigger life is in prospect. Lastly, the working polarities are discussed, showing that the positive working mode is more reliable and advantageous.

Research on applications of TVS and thyristor in a pulsed power supply system used for EMG

A compact pulsed power supply (PPS) system is important for the electromagnetic gun (EMG) system, which should supply high energy and large current. The paper presents the setup of compact PPS system based on high energy density capacitors. The PPS system includes ten 50 kJ modules, which can be triggered in sequence. Each module is composed of a capacitor (1000 ¿F/10 kV), a pulse shaping inductor (20 ¿H), a crowbar diodes with a crowbar resistor(30 m¿), as well as a main switch which can be a triggered vacuum switch (TVS) or thyristors. The peak value of the output current of each module is 70 kA. Characteristics of the TVS and thyristors are comparatively studied to determine their influence on the output current and energy. The requirements for the diode-stacks of the crowbar are fast-recovery, high voltage withstanding. A proper protection measure is used in order to protect the crowbar diodes from the damage of over-voltage when switch is fired. In the end, the overall discharge currents of the PPS triggered in sequence are presented.

Calculation and measurement of metalized film capacitor's inner pressure and its influence on self-healing characteristics

Self-healing is the main cause to capacitance loss of metalized film capacitors, and it might finally lead to the failure of a capacitor. Teardown analysis shown that capacitance loss decreased gradually from the outer layers to inner layers in a capacitor, and it is said that the elastic films add compressive radial force to every wound wrap, the pressure brought up by the radial force has an significant effect on self-healing, with the increasing of the pressure in the inner layers, the capacitance loss become stabilized. This paper analyzed the essential relationship between capacitance loss and pressure between film layers firstly. After that, the inner pressure was calculated based on the film theory, result shows that the inner pressure of a capacitor is related to the tension in the film, the width of the film and the location of the calculated film layer in a capacitor. Finally, the inner pressure was measured to confirm the calculated results. It shows that the measured and theoretical value are almost consistent at outer layers, but the theoretical value become large than that of the measured value when near to the inner layers, and both of them are show that the outer layers pressure is less than that of the inner layers, and cleared area at the out layers is larger than that at the inner layers.