Design Of MOA And Study On The Thermal Characteristics

Metal oxide nonlinear resistors belong to sintered polycrystal ceramics, which is a kind of semiconductor containing ZnO and a small amount of other metal oxide. exhibiting high nonliearity and with much greater current and energy absorption capabilities ,which are widely used as surge arresters in power systems based on their excellent nonlinearity. Main components of Metal oxide surge arresters (MOA) are ZnO resistors. not only in high voltage and exceed high voltage power systems, MOA used for protecting all kinds of overvoltage, but also in other domain, such as power electrical apparatus and test system, MOA can prevent the voltage of the apparatus to be protected. MOA ensure the safe operation of apparatus by suppressing the lightning and switching overvoltage. It is very important for MOA to safely running, for one thing, a reasonable protecting scheme with MOA is taken based on characteristics of overvoltage, for another, whether the arrester could operate well or not depends on its thermal characteristics. When a surge arrester absorbs energy ,the temperature of ZnO resistors inside the arrester would increase, if the arrester cannot quickly disperse the energy into the ambient, then the temperature of arrester would exceed its limited operating temperature, and the arrester would breakdown. So we should optimize the thermal characteristics. of the arrester.Some guidance about design of the arrester is presented. The arresters use in the current-limiting fuse breaking test system to protect the impulse generator, which is the core of the test system. When fuse element melt and bioloff, the arc voltage generated by the fuse would store energy in the inductive elements of the test system, The fuse element melt so quickly that the overvoltage is more higher than other switch-operating overvoltage, which are simulated by EMTP-ATP, the only ZnO resistor is selected.In order to analyze the thermal of the MOA, first, the power loss model should be obtained .The power loss of MOA is a complicated function of temperature and voltage of MOA withstand. So an ANN model is study according to result of test. The thermal performances are analyzed by finite element method.To make the MOA safely running and prolong its life-span, disperse thermal performances is optimized. The simulating result and test result is presented. Some guidance for MOA design and suggestion to improve the thermal characteristics is discussed. Finally, much expectation is put forward.