The microstructure and electrical properties of ZnO-Bi2O3-Yb2O3 based varistor ceramics were investigated with various temperature effects from 900°C to 1050°C.From the results,it was observed that the incre...The microstructure and electrical properties of ZnO-Bi2O3-Yb2O3 based varistor ceramics were investigated with various temperature effects from 900°C to 1050°C.From the results,it was observed that the increase of sintering temperature offers a reduced capacitive effect from 0.460 nF to 0.321 nF.Furthermore,the grain sizes of varistors were varied from 6.8μm to 9.8μm.The consequence of such smaller grain sizes provided a better voltage gradient of about 895 V/mm for the disc sintered at 900°C and fallen drastically to 410 V/mm for the sample sintered at 1050°C.In addition,there was an increase of non-linearity index to a maximum value of 36.0 and reduced leakage current of 0.026 mA/cm2.However,the density of the varistor decreased with an increase of temperature from 5.41 g/cm3 to 5.24 g/cm3.With this base,the influence of varistor capacitance and high voltage gradient were scrutinized and it led an improved transition speed of the varistor assembly from non-conduction to conduction mode during intruding nanosecond transients.展开更多
Environmental issues associated with the aviation industry are getting more attention as air traffic increases.Stringent standards are imposed for fuel consumption and pollution emissions for next-generation aircraft....Environmental issues associated with the aviation industry are getting more attention as air traffic increases.Stringent standards are imposed for fuel consumption and pollution emissions for next-generation aircraft.Superconducting electrical propulsion aircraft(SEPA)have been seen as an efficient way to achieve this goal.High-temperature superconducting(HTS)devices are extensively used in the power system to supply enormous energy.Power is distributed to the different loads via a DC distribution network.However,it will generate an inrush current over ten times higher than the rated current in short-circuit state,which is very harmful to the system.Therefore,it is essential to adopt an appropriate protection scheme.This paper discusses one protection scheme that combines DC vacuum circuit breakers(DC VCB)and resistive superconducting current limiters(RSFCL)for superconducting aircraft applications.Considering problems of cost and loss,the auxiliary capacitor is pre-charged by system voltage,and mechanical elements extinguish the arc.Furthermore,combined with RSFCL,the interrupting environment is fully improved.RSFCL limits fault current,and then the VCB breaks this limited current based on creating an artificial current zero(ACZ).The prospective rated power is 8MW,rated voltage and current are 4 kV and 1 kA,respectively.In this paper,we discuss and simulate switching devices that protect SEPA.The interrupting performance of the circuit breaker is analysed in the DC short-circuit fault that occurs on the transmission line.Finally,the residual energy consumption of different situations is calculated.A comparison is made between using RSFCL with metal oxide varistor(MOV)and just using MOV.The scheme with RSFCL shows a significant advantage in energy consumption.展开更多
文摘The microstructure and electrical properties of ZnO-Bi2O3-Yb2O3 based varistor ceramics were investigated with various temperature effects from 900°C to 1050°C.From the results,it was observed that the increase of sintering temperature offers a reduced capacitive effect from 0.460 nF to 0.321 nF.Furthermore,the grain sizes of varistors were varied from 6.8μm to 9.8μm.The consequence of such smaller grain sizes provided a better voltage gradient of about 895 V/mm for the disc sintered at 900°C and fallen drastically to 410 V/mm for the sample sintered at 1050°C.In addition,there was an increase of non-linearity index to a maximum value of 36.0 and reduced leakage current of 0.026 mA/cm2.However,the density of the varistor decreased with an increase of temperature from 5.41 g/cm3 to 5.24 g/cm3.With this base,the influence of varistor capacitance and high voltage gradient were scrutinized and it led an improved transition speed of the varistor assembly from non-conduction to conduction mode during intruding nanosecond transients.
基金supported by the 2022 Open funding of the State Key Laboratory of Electrical Insulation and Power Equipment(EIPE22211)the National Natural Science Foundation of China,“Research Fund for International Young Scientist(RFIS-1)”,Project:52150410419the 2021 Jiangsu“Shuang-Chuang Doctor(Mass Innovation and Entrepreneurship)Talent Program”,Fund:JSSCBS20211187.
文摘Environmental issues associated with the aviation industry are getting more attention as air traffic increases.Stringent standards are imposed for fuel consumption and pollution emissions for next-generation aircraft.Superconducting electrical propulsion aircraft(SEPA)have been seen as an efficient way to achieve this goal.High-temperature superconducting(HTS)devices are extensively used in the power system to supply enormous energy.Power is distributed to the different loads via a DC distribution network.However,it will generate an inrush current over ten times higher than the rated current in short-circuit state,which is very harmful to the system.Therefore,it is essential to adopt an appropriate protection scheme.This paper discusses one protection scheme that combines DC vacuum circuit breakers(DC VCB)and resistive superconducting current limiters(RSFCL)for superconducting aircraft applications.Considering problems of cost and loss,the auxiliary capacitor is pre-charged by system voltage,and mechanical elements extinguish the arc.Furthermore,combined with RSFCL,the interrupting environment is fully improved.RSFCL limits fault current,and then the VCB breaks this limited current based on creating an artificial current zero(ACZ).The prospective rated power is 8MW,rated voltage and current are 4 kV and 1 kA,respectively.In this paper,we discuss and simulate switching devices that protect SEPA.The interrupting performance of the circuit breaker is analysed in the DC short-circuit fault that occurs on the transmission line.Finally,the residual energy consumption of different situations is calculated.A comparison is made between using RSFCL with metal oxide varistor(MOV)and just using MOV.The scheme with RSFCL shows a significant advantage in energy consumption.
