Honggang Xiang

Calculation of the Short-time Withstand Current for Air Circuit Breaker

In the optimization design of contact system for the air circuit breaker (ACB), it is important to calculate the short-time withstand current. Introducing the contact bridges to describe contact spots between movable and fixed contacts, transient analysis is carried out by coupling electromagnetic field and thermal field to parallel contact systems, where nonlinear of ferromagnetic splitter plates and properties of conduct material varying with temperature are under consideration. In each time step of calculation, the cross-sectional areas of the contact bridges are changed with the contact forces by Holm formula. The proposed method could be used to analyze the short-time withstand current of ACB.

A New Method to Evaluate the Short-Time Withstand Current for Air Circuit Breaker

Short-time withstand current is one of the crucial nominal parameters in air circuit breaker. A numerical method to evaluate the short-time withstand current is proposed. Cylindrical current carrying bridge is introduced to describe the contact spot between movable and fixed contacts. Taking into account the action of ferromagnetic splitter plates, the variation of the conductor properties with temperature and the variation of contact spot radius with the electro-dynamic repulsion force, a transient finite element calculation model is developed by coupling the electromagnetic field and thermal field. The loaded short circuit current is considered as the short-time withstand current once the highest temperature is near to the melting point of the contact material. It demonstrates that the method is useful to evaluate the performance of the air circuit breaker.

Investigation on the Dynamic Characteristics of a Magnetic Release in Molded Case Circuit Breaker

SUMMARY A method is proposed to investigate the dynamic charac-teristics of a magnet release in molded case circuit breaker. With the staticfield assumption, two grids of the magnetic torque and flux linkage are cal-culated with the variation of the current and air gap, firstly. Considering theinfluence of tripping torque, coupled with circuit equation and mechanismmotion equation, the dynamic characteristics may be obtained with Runge-Kutta 4 method. Experiments have been done to verify the method, andthe difference between the calculated results and the experimental resultsis below 10%. In addition, the influence of the reaction spring on the pro-tection characteristics is analyzed using this method. It demonstrates thatthe setting current varies with the initial angle and the stiffness of the reac-tion spring, and the variation with the initial angle of the reaction spring isclosely linear but the stiffness nonlinear. key words: magnetic release, dynamic characteristics, finite elementmethod

Effect of Back-Volume of Arc-Quenching Chamber on Arc Behavior

The gas-puffer effect has important effects on the interruption capability of a molded case circuit breaker (MCCB). In this paper, on the basis of a simplified model of an arc chamber with a single break, the effect of back-volume of an arc-quenching chamber on arc behavior in an MCCB is investigated. Firstly, using a 2-D optical-fiber arc-motion measurement system, experiments are performed to study the effect of back-volume on the arc-motion and gas pressure in an arc-quenching chamber. We demonstrate that the lower back-volume of the arc-quenching chamber is, the higher the pressure and the better the arc motion will be. Then, corresponding to the above experiments, the gas pressure inside the arc-quenching chamber is calculated using the integral conservation equation. The simulation results are consistent with the experimental results.

Investigation on the Interruption Process of Molded Case Circuit Breakers Including the Influence of Blow Open Force

To one double-breaker model, experimental investigation on blow open force was carried out. It demonstrates that the ratio between the emerging blow open force and arc power F B /ui decreases with the arcing time, the contact gap has less effect on F B /ui, and the characteristics of the blow open force are similar when the peak value of the short circuit current is beyond 4 kA. Then, according to the experimental data and conclusions, considering the influence of blow open force, the interruption process of molded case circuit breakers (MCCBs) was investigated. It demonstrates the blow open force has significant influence on interruption process and the proposed method is effective to evaluate new design of MCCBs.