Study of vacuum arc plasma transport characteristics during the DC interrupting process

The mechanical DC vacuum circuit breaker based on forced-over-zero technology will inevitably generate vacuum arc during the actual interrupting process. Since the current drop frequency is usually very high, the vacuum arc usually exhibits obvious transient characteristics, and the excessive transient characteristics may even become a key factor limiting the interruption capacity. In order to improve the mechanical DC vacuum circuit breaker arc interrupting capability, this paper establishes a vacuum arc transient magneto-hydrodynamic simulation model in the DC interrupting process and studies the plasma transport characteristics of the vacuum arc under different DC interrupting conditions. The results show that the ion pressure, ion density and ion temperature decrease with decreasing arc current, while the ion velocity gradually increases during the DC interrupting process. The increase in breaking current and current drop frequency will increase the ion density in the arc column at the moment of current crossing zero, resulting in more difficult vacuum arc interrupting. The results of the study can provide an important theoretical basis for a deeper understanding of the vacuum arc transient process in the DC interrupting process and improve the DC vacuum circuit breaker arc interruption capability.

Dissolution and Online Monitoring of Nd and Pr Oxides in NdF3–PrF3–LiF Electrolytes

Concentrations of dissolved rare earth metal oxides, Nd2O3, and Pr2O3 or their mixtures in different fluoride electrolytes composed of NdF3, PrF3, and LiF at ca. 1040 °C were monitored using a graphite probe inserted into the electrolyte during the dissolution process. Fast voltage sweeps of 100 V/s were applied to the graphite probe, and the current response was measured. As the oxide concentration in the diffusion layer towards the electrode depletes, a passive layer is, at a certain point, formed on the probe, resulting in a current drop. The magnitude of the peak current attained before the formation of the passive layer reflects the concentration of the dissolved oxide and, thus, is applied to determine the oxide concentration. The oxide concentration in the electrolyte samples determined using the inert gas fusion technique showed a good correlation to the peak current determined by the probe.

Study on Effects of Common Rail Injector Drive Circuitry with Different Freewheeling Circuits on Control Performance and Cycle-by-Cycle Variations

This paper provides a new common rail injector drive circuitry for practical use. The new drive circuitry with variable freewheeling circuit was developed based on the requirements for the rate of current drop in the peak-and-hold solenoid model. The variable freewheeling circuit exhibited superior performance in the control accuracy compared to the conventional circuit with a resistor in series with diode (RD) freewheeling circuit. Furthermore, the current cutting process was 30 µs shorter, and the control accuracy of the cycle fuel injection mass was improved by at least 0.36% or exactly 2.86% when a small fuel injection mass was used. In addition, the variable freewheeling circuit consumed less power because the drive power charging was done through the feedback from electromagnetic energy to electrical energy. When the fuel injection mass was large, the fall range of the driving power voltage became 1 V smaller, its recovery time was 1ms shorter, and the highest temperature of the drive circuitry was only 37 °C, which was 127 °C lower than that of the RD freewheeling due to the decrease in energy consumption. Finally, experimental tests with a multi-cylinder engine showed that the variable freewheeling circuit reduced the cycle-by-cycle combustion variations by 0.5%, and lessened the NOx and soot emissions significantly by 3.5% and 4%, respectively, in comparison to the RD freewheeling circuit.

Behaviour of single-phase self-excited induction generator during short-circuit at terminals

PurposeThe purpose of this paper is to present analysis of short-circuit transients in a single-phase self-excited induction generator (SP-SEIG) for different capacitor topologies.Design/methodology/approachThe paper presents field analysis of the short-circuit problem in the SP-SEIG on the base of two-dimensional field-circuit model of the generator.FindingsThe carried-out field computations of the tested SP-SEIG show that the self-excited induction generator is intrinsically protected from the results of sudden short-circuit, as output voltage and current drop rapidly to zero. Short-circuit is a problem when a series capacitor is used to improve output voltage regulation. Experimental results show that re-excitation of the generator is possible after the short-circuit is removed.Originality/valueThe originality of the paper is the presented analysis of short-circuit transients at terminals of SP-SEIG. A finite elements method-based field circuit model was used. The simulation results were validated by the measurements conducted on a laboratory test setup.