Degui Chen

A comparison of the effects of different mixture plasma properties on arc motion

A two-dimensional arc magnetohydrodynamic model is presented to study the effects of metallic vapour and gassing material on air switching arc motion based on different mixture plasma properties (pure air, 99% air–1% Cu, 99% air–1% Ag, 99% air–1% Fe, 90% air–10% PA6). It demonstrates that metallic vapours may cool the arc central region and reduce the arc motion velocity, and iron vapours have the strongest action compared with copper and silver vapours; the gassing material may improve the arc motion velocity. In addition, the effect of the net emission coefficient model and the grey body radiation model on the calculation results for pure air arc motion is compared. To verify the simulation results partially, using the integrated imaging diagnostics system, experiments are carried out to measure the average velocity of arc motion with one model chamber. (Some figures in this article are in colour only in the electronic version)

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%.

Experimental Investigation on the Arc Motion with Different Configurations of Quenching Chamber in AC Contactor

SUMMARY Two dimensional optical fiber measurement system is used to investigate experimentally the arc motion and reignition with four different configurations of quenching chamber in an AC contactor. It demonstrates that the splitter plate arrangement has significant effect on the arc motion in arc quenching chamber, and fixing arc runner in the first and last splitter plates benefits to arc motion, and increase the dielectric recovery strength. The results are very useful to design the quenching chamber in AC contactor with high performance.

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.

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

Analysis and Optimization for the Operating Mechanism of Air Circuit Breaker

This paper simulates the dynamic behavior of the operating mechanism of ACB, and analyzes factors influencing the mechanisms operating time. First, it builds a dynamic model for the mechanism with virtual prototype technology. Experiment validation is carried out to prove the correctness of the model. Based on this model, it puts emphasis on analyzing the influence of electro-dynamic repulsion force on the operating time of the mechanism. Simulation and experimental results show that after adding electric repulsion force to the model, the operating time is shortened about 1.1 ms. Besides the repulsion force, other influencing factors including the stiffness of opening spring, locations of every key axis, mass and centroidal coordinates of every mechanical part are analyzed as well. Finally, it makes an optimum design for the mechanism. After optimization, the velocity of operating mechanism is improved about 6.7%.

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.

Analysis and Optimization for a Contactor with Feedback Controlled Magnet System

In the optimum design of AC contactors, it is important to analyze the dynamic behavior. Moreover, movable contact and core bounces have remarkable effect on the lifetime of contactors. According to a new kind of contactor with feedback controlled magnet system, this paper builds two different sets of periodically inter-transferred equations to obtain the dynamic characteristics of the contactor. The equations describe the coupling of the electric circuit, electromagnetic field and mechanical system taking account of the influence of friction. Then, the paper gives an optimum design to the dimension and the duty ratio of the contactor pulse modulated wave (PWM) under different exciting, and proves, by experiment and simulation, that the bounce time of the contactor working in the optimized duty ratio is much less than that of the general AC contactors.