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ZnO varistor ceramics with a high potential gradient, as well as a high nonlinear coefficient, were reported and analyzed in this paper. With the use of nano-sized ZnO powders, the average grain size was reduced to about 2.6 μm, which successfully raised the potential gradient to 1172 V/mm. Moreover, the nonlinear coefficient increased to 48, and the leakage current was decreased to 8.4 μA/cm2 by doping a moderate amount of MnO (0.9 mol%). This was proven to be caused by the high Schottky barrier height formed at the grain boundary, where the Mn element segregated and, consequently, led to the increased density of interface states. Therefore, this could be considered as a potential method to simultaneously enhance the potential gradient and the nonlinear coefficient of ZnO varistor ceramics.

Cu–W nano-multilayered films show great potential applications in microelectronic, plasma and nuclear fields due to the unique interfacial structure. In this paper, Cu–W films with different microstructures were synthesized by co-sputtering at different deposition temperatures. At room temperature, a nano-multilayered structure with the modulation period (λ) of 5 nm appears with alternatively arrayed W-rich and Cu-rich regions. With the increase of the deposition temperature, the periods of the nano-layers become larger and fuzzy, and finally the totally separated phases of Cu and W grains can be identified at temperature higher than 300 °C. The dominant mechanism of such microstructural evolution can be ascribed by the surface diffusion ability of the deposited atoms as evidenced by temperature as well as deposition time. The hardness of the films declines with the elevated temperatures and by analyzing the hardening mechanisms, the interfacial strengthening effect was verified due to the high hardness in nano-multilayered Cu–W films.

The contacts and fingers in the traditional high-voltage circuit breakers are all made of copper-tungsten alloy materials by powder metallurgy process at present. The conductivity and hardness of existing materials have reached the bottleneck, which can’t meet the requirements of working conditions. Graphene has good electrical conductivity, mechanical properties and high specific surface area. Doped into the traditional copper-tungsten alloy, graphene is expected to greatly improve the electrical conductivity and hardness of copper-tungsten electric contacts, which could make the alloy have excellent mechanical and electrical properties at the same time. It has become the main development direction of current electrical contact materials research. In this paper, the research progress of strengthening methods of traditional copper-tungsten electric contact materials by graphene and other reinforcing agents is systematically reviewed, and the strengthening mechanism of graphene on copper-tungsten electric contact materials is explored, which can provide technical guidance for the development and application of new high strength and high conductivity graphene-reinforced copper-tungsten electric contact materials with new performance and long electrical life.

Tri-post insulator is the key insulation component of UHV and EHV gas insulated transmission pipeline (GIL), and its mechanical reliability is directly related to the operation safety of GIL. In this paper, the principal stress distribution of the tri-post insulator in 1100 kV GIL is systematically analyzed, considering the thermal expansion, electromagnetic vibration and conductor deflection. Finally, according to the simulation results, the reliability analysis of insulator operation under multiple operating conditions is carried out based on the ultimate stress and safety factor.

When the DC voltage applied, the electric field distribution of the DC GIL basin insulator will change from the initial capacitive distribution to the steady-state resistive distribution. This process is accompanied by the accumulation and dissipation of surface charges, which may cause a decrease in the flashover voltage along the insulator. Therefore, it is of great significance to study the charge accumulation characteristics of basin insulators under DC voltage. In this paper, a DC GIL experimental platform is built, and a set of surface charge measurement system based on electrostatic probe method is established. The surface charge accumulation characteristics of basin insulators and the transformation of main accumulation methods are studied in 0.4MPa SF6 gas. The results show that: the surface charge distribution of basin insulators is related to the DC voltage amplitude and applied time. At low voltage amplitudes, the concave side of the insulator mainly accumulates negative charges (opposite to the applied voltage), and the charge source is mainly conducted on the solid insulation side; At high voltage amplitudes, the concave side of the insulator mainly accumulates positive charge (the same polarity with the applied voltage), and a small amount of negative charge accumulates near the ground electrode. Positive and negative charges coexist on the surface of the insulator, and the charge accumulation gradually transforms into gas side conduction. As the applied voltage time increases, the surface charge of the insulator reaches saturation, and the saturation time is about 60 minutes.

In the DC GIL, the accumulation of surface charges could cause electric field distortion and thus even cause the flashover. In the numerical simulation of surface charge accumulation, only the charge carriers generated by natural ionization are considered in some of the studies. But in fact, during the operation of DC GIL, due to the rough surface of the insulator and other reasons, weak discharges always exist. These weak discharges are called micro discharges. In this paper, the micro discharge on the surface of the insulator is modeled, and the influence of the micro discharge on the surface charge accumulation time characteristics of the DC basin insulator is studied. The simulation results show that the existence of micro discharge will shorten the time constant for surface charge accumulation.

The flashover of the DC basin insulator is the limiting factor for the safe and stable operation of DC-GIL and DC-GIS. It is of great significance to study the probability distribution model of the flashover. In this paper, the DC voltage experiment platform is built for the basin insulator in DC-GIL. The relationship between the flashover voltage and the flashover time of the basin insulator is obtained through experimental measurements. The probability distribution of flashover is established by using the Weibull distribution. The experimental results show that the flashover probability is related to the flashover voltage and flashover time. The higher the applied voltage, the greater the flashover probability, and the longer the applied time, the greater the flashover probability, and the steady state flashover voltage of this basin insulator is obtained. U 0.1% is 300kV.

In this paper, the DC flashover characteristics of the insulators when the linear metal particles are attached to the surface of the basin insulator in GIS/GIL are studied. Firstly, the finite element numerical calculation method was used to analyze the electric field distribution of the surface of the basin insulator in the absence of metal particles. According to the calculation results, four positions were selected for the convex and concave surfaces of the insulator to manually place the metal particles. Meanwhile simulated the linear metal particles with the metal copper needle, and measured the flashover voltage of the insulator under the condition of metal particle adhesion by experimental means, the effects of gas pressure, particle position change and particle length change on the DC flashover voltage of the insulator were considered in the experiment. Results show that the electric field near the particle is severely distorted when the metal particles are present on the surface of the insulator, and the distortion effect decreases as the metal particles move away from the high voltage electrode. However, the flashover voltage variation of the convex and concave surfaces of the insulator is not completely consistent ,this is mainly due to the difference in surface electric field distribution between the convex and concave surfaces of the insulator. The experiment also found that the effect of metal particles on the flashover voltage of the insulator is more significant at high pressure. This study can provide reference for the development and maintenance of DC GIS/GIL basin insulators.

A charge transport model based on ion drift in gases of strong electron affinity has been studied in details and validated against experimental results in air and SF 6 at different pressure and voltage levels. The size of the insulators also differs significantly. The choice of the model parameters, i.e. the solid and gas material properties, is carefully examined with information from existing literature. Results show that using the selected parameters, satisfactory agreement between predicted and measured potential distribution and surface charge density along the insulator surface can be obtained. Computational results for an 1100 kV epoxy spacer for use in HVDC wall bushing show that the concept of electrical conductivity as a material property is no longer valid in strong electric field for the gas surrounding the insulator. The polarity and density of the accumulated surface charge depend on the relative largeness of the electrical conductivity of the insulator material and the effective conductivity of the gas. The nonlinear effect due to ion generation and recombination becomes significant at very high voltage. The metallic cap providing shielding to the triple junction at the high voltage end of the insulator can induce much stronger local electric field near the insulator surface, by a factor of 1.48, if its shape is not optimized against the insulator geometry.

The curing kinetics of epoxy/amino-functionalized alumina composites was investigated by non-isothermal differential scanning calorimetry (DSC) experiments. DSC bimodal curves can be divided into pre-stage and post-stage curing processes. The two-stage curing processes accord with not only KAS but also Vyazovkin isoconversional equations. In the pre-stage process, the apparent activation energy (Ea) of epoxy/alumina composites decreases gradually with increasing the alumina content. In the post-stage process, Ea of the composites decreases slowly at first and then increases. The results show that curing catalytic reaction control is dominant in the pre-stage process, but diffusion control and reaction control have a competitive effect in the post-stage curing, which indicates that amino-functionalized alumina has a dual effect on the curing of epoxy resin. In Epoxy/41Alumina composite, the catalytic effect of amino-functionalized alumina is stronger than its inhibition effect, resulting in minimum Ea. The simulated curves calculated by SB(m, n) model show a good agreement with that experimentally determined.

This paper describes an operating mechanism driven by a three-phase permanent magnet synchronous motor (PMSM) for high voltage circuit breakers (HVCB). It analyzes the relationship between the optimal moving contact travel of HVCB and the PMSM torque, and proposes the main parameters and requirements of PMSM to be suitable for the optimal contact travel. The simulation model of the operating mechanism driven by PMSM was builtusing Matlab. It simulates and calculatesthe mechanism’sopening and closing operations characteristics. The voltage waveforms of stator currentsanalyzing, offers a helpful reference to compile the Digital Signal processing (DSP) programs. The performances of the opening and closing operationscould be improved by debugging the DSP programs in the control unit. Introduction High Voltage Circuit Breakers (HVCB) isthe most important switches apparatus in the electric power system. They are responsible forcontrol and protect of the power system. The operating mechanism is the basic device which controls the opening and closing operations of HVCB. At present, there are several conventional types of operating mechanisms which have been widely used, such as spring, hydraulic or pneumatic. Such mechanisms have many prominent merits, but also have some insurmountable limitations. These conventional mechanismsconstructedby complex frames, need periodic check-ups, highly costsoperating and maintenance,and they are quite difficult to be debugged. Additionally, they are especially incontrollable and non-detectable during the opening and closing operations. To overcome such inherent limitations, and to improve the performance of conventional mechanisms, the operating mechanism driven by PMSMis introduced to meet the requirements. The proposed operating mechanism is based on power electronic and motor digital control technologies. This mechanism has quite a lot of good advantages: simple frames, manipulative opening and closing operations, wide range of uses and so on. Design of the operating mechanism The suggested operating mechanism consists of AC (or DC) power supply, energy buffer, converter unit, control unit, and the motor. Fig.1 (a) shows the System diagram of motor driven mechanism.The motor is controlled by an IGBT Converter, rotate speed and positions of the motor aremeasured using a fixed sensor on the rotating shaft. The travel of the moving contactor is measured by the position sensor.The control unit adopts DSPas the processing core, and according to the vector control of the motor, the control unit generates PWM signals to activate the IGBT Converter, and then drives the motor to implement the opening and closing operations of HVCB. International Industrial Informatics and Computer Engineering Conference (IIICEC 2015) © 2015. The authors Published by Atlantis Press 959 AC R ec tif ic at io n ci