| At present,the inductive load still occupies the main position in the load of power system.In order to prevent problems such as voltage drop and power quality reduction caused by the transmission of inductive reactive power through long lines and multistage transformers,reactive compensation is required for distribution lines near the load side.Shunt capacitor is widely used in reactive compensation for its great advantage.With the improvement of technology and production skill,internally fused capacitor is widely applied in MV and HV transmission and distribution lines.In order to obtain the maximum capacitance value of the capacitor per unit mass,when designing the capacitor,the electric field strength between the electrodes of the capacitor element needs to be increased as much as possible,which leads to its vulnerability to breakdown.Moreover,the frequent switching of capacitors as the load changes further increases the probability of component breakdown.The above reasons make the component breakdown of the capacitor the most common power capacitor fault.The capacitance components are all encapsulated inside the capacitor,which makes it even harder to detect the component breakdown.Therefore,the research on component breakdown fault detection and protection of internally fused capacitor is of great necessity.Aiming at the component breakdown of internally fused capacitor,the transient characteristics of component breakdown are analyzed detailly in this paper,thermal breakdown and electrical breakdown are both included.Firstly,through analysis of the equivalent circuit of the fault distribution line,the superposition principle is used to simplify the circuit.Then the differential equation of the fault circuit is acquired on the basis of simplified circuit,and by solving the time domain differential equation,the transient signal expression is obtained.Finally,the transient characteristic is extracted from the transient signal expression.Based on analysis and summarization,a breakdown information library of internally fused capacitors is established.In the two cases,the transient process of component breakdown is different,but the internal fault mechanism has a consistent law.The difference is that electrical breakdown tends to occur in the process of capacitor input and has one more transient than thermal breakdown.The transient characteristic caused by capacitor input and its impact on component breakdown is analyzed in the paper.The reliability and accuracy of theoretical derivation have been verified by simulation analysis and lab experiment.Therefore,this paper can provide new ideas for the development of capacitors in the field of fault detection and line monitoring.In the first chapter of this paper,the background of the use of power capacitors is introduced.The necessity and significance of the breakdown of internally fused capacitor are analyzed,and the current research status of capacitor fault detection and on-line monitoring are also described.In the second chapter,aiming at the solidly neutral grounding system,the transient characteristics of the component breakdown in pole-mounted capacitors are analyzed.Both the thermal breakdown and electrical breakdown are discussed,through circuit simplification and theoretical derivation,mathematical expression of feeder current is established.Based on that,the transient characteristics of fault current are further studied.The third chapter uses the MATLAB/Simulink simulation platform to verify the theoretical analysis,the transient signal of capacitor breakdown is measured and the transient characteristics of fault signal are obtained.By comparing the simulation value with the theoretical value,the validity and rationality of the theoretical analysis are verified.Subsequently,the result of lab experiment is presented in chapter 4,in which model breakdown is carried out in a internally fused capacitor of solidly neutral grounding system.At the end,chapter 5 presents the summarization and prospect of the research. |
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