| Voltage transformer plays a very important role in energy measurement and safe and stable operation of 10 k V neutral point ungrounded system.In order to protect voltage transformer and avoid the harmful effects to voltage transformer,a fuse is generally installed on primary side of voltage transformer.The principle of the normal fusing is that when a fault current exceeding the nominal minimum breaking current flows through the fuse for a duration of time,the heat generated by and current what causes the temperature rise to exceed the fusing temperature,which causes to melt what to vaporize and start an arc.Under the action of the arc extinguishing medium,the arc fuse extinguish and circuit is broken.However,many field operating experiences show that when the fuse parameters related to the heating and heat dissipation of the fuse change,which causes the melt resistance value R to increase and the heat dissipation to decrease,the current below the nominal minimum breaking current flow through the fuse for a period of time.The heat generated by current will also cause temperature rise to exceed the fuse melt temperature and cause to vaporize and arc,which will cause an undergo abnormal fusing that shouldn’t happen under normal case.This abnormal fusing fault is defined as a light fusing fault.Frequent light fuse failures of the primary side of the voltage transformer will seriously affect the normal operation of the power supply equipment,and may even affect the safe and stable operation of the entire power system,and bring unnecessary economic losses to social development.Therefore,it is particularly important to study the principle of light fusing of the primary side fuse of a 10 k V voltage transformer,which is of great significance for ensuring the safe operation of power grids and equipment and reducing economic losses.At present,scholars at home and abroad have almost studies the pre-arc process and the melt reason,there is almost no research on the cause of the abnormal fuse of the fuse.The light melt fault is the abnormal melt fault.At present,there is still a lack of research on the principle of light fusing failure of the fuse.This paper takes the common 10 k V voltage transformer primary fuse as the research object,and carries out theoretical and simulation research on the principle of light fusing fault of the fuse.First,according to the working principle of the fuse,the mathematical model of the fuse temperature rise process is derived.Accordingly,the stable temperature expression of the fuse under the action of the current lower than the nominal minimum breaking current is obtained,and the parameters that affect the melt time are analyzed,and the actual results are obtained.The actual reasons that may cause the above-mentioned parameter changes are mainly the poor quality of the fuse and the failure of the power system.The essence of a light fusing fault is that when a current lower than the nominal minimum breaking current acts on the fuse for a period of time,the stable temperature of the melt exceeds the fusing temperature,causing the fuse to be abnormally fused under the action of this current.Therefore,the poor quality of the fuse and the parameter change caused by the power system failure may cause the stable temperature rise to cause the light fusing fault of the fuse for the primary side protection of the 10 k V voltage transformer.Secondly,ANSYS simulation was carried out for the influence of parameter changes caused by inferior fuse.Inferior fuse fuse will cause the physical and structural parameters of the melt material to fail to meet the standards,which will cause changes in parameters such as melt thermal conductivity,room temperature resistivity,cross-sectional radius,length,and quartz sand thermal conductivity.In order to study the influence of the above-mentioned parameter changes on the fuse,a finite element model of melt thermoelectric coupling was established,and the temperature rise process of nominal parameter melt and non-nominal parameter melt under different AC currents was simulated and calculated.It is shown that if the quality of the fuse is not good,the resistivity at room temperature increases,the radius of the melt section decreases,the length of the melt increases,and the thermal conductivity of the quartz sand increases,which may lead to the fuse for the primary side protection of the 10 k V voltage transformer.A light fuse failure has occurred.At the same time,based on the analysis of the simulation results,measures to suppress the light fusing fault of the fuse are obtained.Finally,the ATP-EMTP simulation analysis is carried out for the influence of fuse parameter changes caused by power system faults.The 10 k V voltage transformer working circuit was established in the simulation,and the primary current value after the single-phase ground fault of the system and the unstable inter-turn short-circuit fault of the single-phase primary winding of the voltage transformer was calculated.If the fault current is between the nominal rated current of the fuse and the minimum breaking current,and the fault exists for a long time,it may cause an oxide layer on the surface of the fuse melt,causing changes in the effective current passing area of the melt to decrease,etc.Which leads to the occurrence of fuse light fusing failure.The simulation results show that when the range of the short-circuit fault is certain,the fault current caused by the single-phase unsteady inter-turn short-circuit fault of the voltage transformer primary winding is between the nominal rated current and the minimum breaking current,and the fault will be long-term Exist,so this fault may cause a light-blow failure of the fuse for the primary side protection of the 10 k V voltage transformer.At the same time,based on the analysis of the simulation results,measures to suppress the light fusing fault of the fuse are obtained. |
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