The Study Of Transient Process Of High-Voltage Expulsion Fuse For Power Transformer Protection

As the major non current-limiting fuse,High-Voltage Expulsion Fuse is widely used to protect the power transformers and power lines,which makes its stable performances and safe breaking-capacity of great importance.Excellent circuit-interrupting performances can determine the successful interruption of High-Voltage Expulsion Fuse,but up to now,there's still few deep research on its physical process of breaking.This dissertation divides the transient process of High-Voltage into pre-arcing period and arcing period to research.Firstly,in per-arcing period,the pre-arcing time of High-Voltage Expulsion Fuse is mainly calculated with the COMSOL Multiphysics Software,by simulating the pre-arcing temperature fields of the short-circuit current under different closing phase angle and different time constant separately.The pre-arcing time is caculated by analyzing the pre-arcing mathematical model of fuselink and the characteristics of short-circuit current characteristics,loading the actual short-circuit current parameters,considering the physical variation with temperature of fuselink's resistivity and thermal conductivity,ignoring the factors of Joule's thermal diffusion and thermal radiation only to regard the heat conduction between the fuselink.And when the maximum point temperature of fuselink reached the melting point of fuse element,the corresponding time is pre-arcing time.In this way,it could not only reduce the simulation time,but also can guarantee the accuracy.Combining the pre-arcing time--current characteristics curves with the example of the prospective breaking current 5kA can verify the feasibility of this simulation method.Secondly,in arcing period,the paper did some breaking researches on several different prototype of High-Voltage Expulsion Fuse according to the standard of GB/T15166.3-2008 and IEC 60282-2:2008 mainly based on the Test Station SystemPlatform of breaking large short-circuit current.It extracted phase current and voltage data point of arcing period from breaking test oscillogram,get the curves of arc power and finally computed the value of arc energy in the method of discrete integral.And then make an comparative analysis of the impact of fuselink on the characteristics during breaking process and parameters of acing voltage,arc power,arc energy,breaking performance under various factors such as different closing phase angles,different rated current,different prospective breaking current,different rated current of fuselink etc.Comparing the pre-arcing time from breaking test oscillogram with the time obtained from the simulation of breaking current 8kA and 12.5kA,we can find that the relative error of test and simulation is within ± 5%.The bigger prospective breaking current is,the smaller simulation error is,and even in the same group breaking test,the relative error of different closing phase angles is 0°<135°<90°,which proves the feasibility and correctness of the simulation model for the large breaking current again.Finally,this thesis studied the entire transient process of breaking short-circuit current for High-Voltage Expulsion Fuse systematically and analyzed the physical phenomena of transient process and the change of each characteristic parameters.This dissertation could provide some important references for fuselink selection,tube matching,the thermal effect while using,the performance of breaking process,even the exploitation and improvement of fuse products,which has great theoretical significance and practical value.