Study On The Threshold Model For Stablely Arcing Of Low Voltage DC Distribution System And Design Of Arcless Circuit Breaker

The wide application of distributed generator,power electronic technology and DC load promote the development of DC distribution network.However,it is difficult to extinguish the DC arc without crossing the zero point,which seriously threatens the safety of DC distribution network.DC circuit breaker is an important protection equipment of DC system.The realization of arcless breaking circuit is beneficial to prolong the service life and ensure the safe and stable operation of the system.The existing arc detection methods can only make a signal warning after the occurrence of arc,and can not suppress the occurrence of arc from the root,which is not enough to achieve reliable protection of the system.In order to ensure the safe and reliable operation of DC distribution network and suppress the occurrence of arc,it is necessary to study the characteristics of arc ignition and arcing.In this paper,the arc experiment is carried out on the simulated arc generation experimental platform.Combined with the arc theory,the ignition characteristics and ignition conditions of arc are studied.The stable ignition conditions of arc are analyzed.The mathematical model of stable ignition threshold voltage is established.The arcless DC circuit breaker is designed.The breaking performance and economy of the circuit breaker are compared with the common circuit breakers on the market.The main research work is as follows:（1）A simulation experiment platform including DC low-voltage bus are generator and load is built.Based on the Nuottingham equation,the volt ampere characteristics and ignition characteristics of arc with different spacing are studied.The arcing experiment is designed to obtain the stable burning point of the arc under both the resistive and inductive load and also the influence of the load on the arcing process and arc characteristics.The threshold value for arcing of stable voltage source on condition of the maximum equivalent load（resistance 280Ω,inductance 30m H）is obtained.Combining the volt-ampere characteristic of the arc with the voltage balance equation,the stable burning point and the burning time are theoretically deduced.The mathematical model of the threshold voltage of the stable burning DC arc is established,and the accuracy of the model is verified by the numerical fitting method with MATLAB.The correlation coefficient obtained from both the model data and the experiment data is 0.9924,which means the model may determine the voltage threshold of stable arc on condition of low voltage inductive load,and provide theoretical basis for determining the stable arc conditions of low voltage and small current DC arc.（2）Through the simulated arc experiment,the arc starting conditions of DC arc are explored.The results show that only if both the voltage is higher than the threshold voltageV_th（28）15 V and the electric field strength is higher than the threshold electric field strengthE_th（28）5.0×10⁵ V/m,arcing is capable.Based on this theory,it is possible to design an arcless breaker if these two conditions can not be attained at the same period.This provides a research basis for the realization of arcless breaking circuit.（3）Then,arcless DC circuit breaker is developed including mechanical switch K,CB1 and CB2.CB1 plays a role of switching off normal load and also short circuit fault and parallel arc fault,and CB2 acts to suppress the occurrence of series arc.Through Simulink simulation analysis,it is proved that arc may not happen during operation of this newly designed arcless circuit breaker,such as cutting off normal load,short circuit fault and artificially-made series arc fault.At the same time,a low-voltage DC distribution network experimental platform is built.The experimental results show that the self-made DC circuit breaker can realize cutting off normal load without arc and restrain the series arc along the bus on conductor.The research results have a good theoretical and practical value for arcless cut-off of low-voltage DC power equipment and ensuring the safe and stable operation of DC distribution network.