Ruicheng Dai

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)

Study of the Influence of Arc Ignition Position on Arc Motion in Low-Voltage Circuit Breaker

Arc-motion process is crucial to the interruption capability of the low-voltage circuit breaker. First, to a simplified chamber with full open venting, with a 2-D optical-fiber arc-motion measurement system, experiments were done to measure the arc-motion velocity in order to analyze the influence of different arc ignition position on the arc motion. It demonstrates that the larger the volume behind the arc is, the slower the arc moves. In addition, the influence of the gassing material on arc-motion velocity was also studied experimentally. Then, the commercial computational fluid dynamics software FLUENT was adapted and modified to develop a 2-D magneto-hydrodynamic model of the arc with the same conditions as the experimental model. The simulation result was consistent with the experiment conclusions

Measurement of the Dielectric Recovery Strength and Reignition of AC Contactors

In order to understand the recovery characteristics of AC contactors and improve their performance, experimental measurements were used to investigate the arcing gap recovery process including dielectric recovery strength and reignition, to a pair of splitter plate together and four kinds of arc chamber of AC contactors. A special circuit was designed to perform the work. It demonstrates that under lower current, the dielectric recovery strengths of all kinds of arc chambers in the paper have no significant difference. However, with the increase of current, the difference of dielectric recovery strengths of them is much clear. The reignition characteristics of a pair of splitter plate and arc chambers are similar. With different configurations of arc chambers and prospective currents, the forms of post current zero reignition are distinct.

Study of the Influence of Cu Vapour on Air Arc Characteristics

The arc is one kind of mixture plasma containing air and metallic vapour (Cu, Ag, Fe, etc.) in low voltage circuit breaker. The metallic vapour has important influence on arc characteristics because the properties of the mixture plasma are different with the ones of the pure air. The influence of Cu vapour on air arc characteristics is investigated in the paper. Firstly, commercial computational fluid dynamics software FLUENT is adapted and modified to develop the two- dimensional magneto-hydrodynamic (MHD) models of arc with the thermodynamic and transport properties, net emission coefficient for radiation model of 99% Air-1% Cu and pure air, respectively. Then, relevant experiments are carried out to verify the models by measuring the arc motion average velocities with 2-D optical fiber measurement system. It demonstrates that with the influence of Cu vapour, the arc center temperature is lower and the arc motion is slower.

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%.

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.

Effect of Different Venting Conditions on the Interruption Performance of Arc Chamber

Gas flow in arc quenching chamber has an important effect on the interruption capability of low voltage circuit breakers. In this paper, based on a simplified model of arc chamber with a single break, which can be opened by the electro- dynamics repulsion force automatically, the effect of different vent conditions including middle venting and side venting on the interruption performance is investigated. First, the effect of the different size of side vent type on the chamber pressure, and interruption capability were studied experimentally. It demonstrates that the smaller vent size is, the higher pressure and better the interruption performance will be, but when the vent size smaller than a certain proportion, the arc will re-ignite and when the vent size larger than a certain proportion, the arc will also re-ignite. Experiments are carried out to compare the different performance in the interruption process between middle vent to be conventional vent type and side vent type. In addition, according to the experimental model, a 3-D magneto- hydrodynamic model was developed by adapting and modified the commercial computational fluid dynamics software FLUENT. The simulation results show the same trend in arc motion as explained in the experimental conclusions in theory.

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.