Study Of Protection For High Density Pulsed Capacitor Banks

Pulsed power technology has been used extensively in the fields of scientific experiments, national defense, biomedicine and environmental protection etc. The power module of laser fusion system takes the high density pulsed capacitor to store energy, in which the capacitors work in parallel and discharge to Xe-lamps to produce high power laser via serials dealing with optical methods.In the short condition, the current will be increasing highly as the capacitors work in parallel. There are two short conditions. One is internal capacitor fault. When an internal breaking occurs in one capacitor, all of the other capacitors which are full of energy will discharge to it and the energy of the whole module will be released in a very tiny time in the faulty channel, which would lead to the capacitor's exploding. The other is the main bus's earthing, the current rising to several hundreds of kilo amperes. That huge current would effect other equipments deeply. So capacitor's protection is one of the key technology of the whole set. Currently, fuse and inductance were accepted to the protective for the capacitor banks. The inductance is mainly used to limit the current of short circuit, especially an internal capacitor fault. The fuse can cut off the current. When the short current rises up to a certain value, the fuse will fusing and cut off the circuit, which makes the storing energy in capacitors not be released fully. The main flaw of that protection method is that the di/dt is very huge during the process of cutting off the current and there will be an overload voltage on the inductance, which could cause the inductance's broken, leading to exploding. And then the energy of the group of the capacitors will be released fully with huge mechanical and electromagnetic breakage, which would break other components of the set. The article is mainly about the fuse of the protection components, analyzing the fuse's performance and discussing some questions during the process of the fuse's broken. In allusion to the flaw of the current method of protection, we bring forward three new suggestions of protection.(1) To add a gap and a small size but big power resistance connecting parallel at each end of the inductance, the resistance can absorb a part of energy when the voltage of the inductance rises to gap's broken value, which could limit the voltage of the inductance.(2) To connect a ZnO arrester parallel with the inductance, the lightning arrester can limit the voltage of the inductance because the ZnO arrester has a very good non-linearity which makes itself works in a voltage-limited protective area.(3) Only use the inductance directly to absorb the energy released by capacitors working in broken situation, considering overload voltage at each end of the inductance comes from the fuse's cutting off to limit the current. But it's very hard to design the protective inductance.With the comparing among those three protective ways, this paper analyses the experimental data and gives us a theory support. Each of those methods has its own advantages and disadvantages and which is our best choice needs to be proved by further experiment and analysis.