Weixiong Tong

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.

Dynamic Simulation of Operating Mechanism for Molded Case Circuit Breaker

A dynamic model of the operating mechanism for a low voltage molded case circuit breaker (MCCB) was built based on virtual prototype technology, and then a test was done to verify this model, which showed that simulation results of virtual model were in agreement with test results of real prototype. After adding electric repulsion force to model, the operating time of mechanism was shortened about 2 ms. Using this model, besides the repulsion force, the factors including the stiffness of opening spring, the shape of mechanism parts affected the dynamic characteristics of operating mechanism are analyzed as well, and it also indicates that centroidy coordinates of trip has the greatest influence on angular velocity of operating mechanism. Selecting x and y coordinates of mechanism axes as the design variables, after optimum design, average angular velocity of operating mechanism has risen 15.3%.

Dynamic Characteristic Analysis and Optimization for the Energy-Saving and Bounce-Reducing Double-Coil Contactor

SUMMARY In the optimum design of contactors, it is important to analyze the dynamic behaviors. In this paper, it proposes a new computational approach for analyzing dynamic characteristic of the energy-saving and bouncing-reducing double-coil contactor. According to the contactor’s unique characteristic that it has two transferable coils, the paper builds two different sets of equations. One describes the period before the transfer position, and the other describes the period after the transfer position. The equations deal with the electrical circuit, electromagnetic field that can be calculated by using 3-D finite element method and mechanical system considering the influence of friction. The validity of the proposed method is confirmed by experiment. Finally, the paper gives an optimum design for the transfer position of the two coils. The result of the optimum design reduces both of the first and the second bounces of the movable contact.

Research on Contact Force Pairing of MCCB with Double Repulsive Contact Structure

MCCBs with double repulsive contact structures (DRMCCBs for short) are helpful for improving their shortcircuit breaking capacities. A calculation model that enables us to simulate the interruption process of the DRMCCB is realized by carrying out second-development of ADAMS, in which a set of differential equations describing the coupling of complex mechanical movement, electric circuit, magnetic field and dynamic mathematic arc model is constructed. With this model, influence of contact force pairing on breaking capacity of DRMCCB is analyzed. Other factors affected by contact force pairing are analyzed as well. KeywordsDRMCCB; dynamic mathematic arc model; multifield coupling; interruption process; ADAMS

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.