Topological Design And Research Of A Superconducting Current Limiting High Voltage DC Circuit Breaker With Reclosing Function

Due to the needs of society and population,it is necessary to expand the capacity of the power grid.The existing AC transmission technology can no longer meet the reasonable utilization of energy and resources.With the rise of semi controlled and fully controlled power electronic devices,flexible DC transmission can not only meet the demand for DC power supply,but also solve the problem of uneven energy distribution.Therefore,DC transmission technology can meet the needs of low cost,green and environmental protection,and is loved by many scholars and countries.The essential equipment in the DC transmission system is the high-voltage DC circuit breaker,therefore,developing it is an essential choice.The existing high-voltage DC circuit breakers have the following problems:(1)Due to the high level of DC transmission voltage,more power electronic devices are used to limit fault current,without considering that an increase in the number of devices will result in excessive costs.(2)Due to the presence of two zero points during the AC transmission cycle,arcless breaking can be achieved;However,direct current transmission does not have this characteristic,and when a short circuit fault occurs,it can cause the generation of an arc.(3)Due to the small impedance of the DC transmission system and the rapid rise rate of fault current,it can cause high economic losses.Firstly,this dissertation mainly introduces the development and demand of DC transmission technology under current conditions,analyzes and summarizes the existing fault currents and corresponding measures taken.Subsequently,analyze and compare the proposed DC circuit breaker structure;In order to better limit the fault current,a resistive superconducting current limiter has been added to the DC circuit breaker,It not only prevents damage to electrical equipment and other issues,but also meets lower cost needs,ensuring the reliability and economy of the DC transmission system.Secondly,the construction of a resistive superconducting model is carried out.In order to verify the feasibility of the resistive superconducting current limiter model,an electrical model is built in a simple two port system for simulation analysis.In the future development of society,it is necessary to flexibly apply it,so a combined type of resistive superconducting current limiter is proposed,Analyze the current limiting effect in series and parallel operation modes and draw different conclusions.When operating in parallel,the current limiting effect is not significant;When running in series,the current limiting effect is significant,laying the foundation for subsequent work.Finally,the first step is to propose a topology structure,in which not only a combined resistive superconducting current limiter is added,but also a commutation capacitor is added to reduce the time required to cut off the fault current;The second step is to conduct theoretical analysis and parameter design on the proposed topology structure;The third step is to conduct simulation analysis and compare it with other schemes to verify the feasibility of the topology structure;The fourth step is to perform reclosing operation for better and stable operation of the DC transmission system,and analyze the waveform of transient and permanent faults separately.