Jouya Jadidian

A Compact Design for High Voltage Direct Current Circuit Breaker

The absence of current-zero points in the direct current (DC) waveform of high voltage DC (HVDC) circuit breakers makes the interruption process more severe than the case of conventional AC networks with sinusoidal currents. In this way, in the current HVDC networks, a parallel precharged capacitor is inserted to inject the reverse current into the interruption chamber of the vacuum circuit breaker and create the artificial current-zero points. In this paper, a novel method for reverse current injection has been proposed. In this method, two separate helical flux compression generators (HFCGs) have been applied to generate the reverse current and an intense axial magnetic field (AMF), respectively. Numerical simulation of high-current vacuum arc (VA) in the presence of very strong AMF has been presented. For this purpose, the magnetohydrodynamic equations describing the behavior of the VA are coupled to a simple circuit analysis and the previously developed multiphysics model of HFCG. The results indicate that the explosively driven current injection set can make current-zero points properly in a typical HVDC network and lead to successful interruption of fault current. This method needs much less volume and cost in comparison to the parallel precharged capacitor sets.

In-situ insulation test of 400 kV GIS

To guarantee the insulation strength of gas insulated substations (GIS), a number of different voltage waveforms, e.g., switching, lightning and AC have to be applied to the GIS after installation. Because of very huge dimensions of GIS for nominal high voltages, it is not possible to carry out these tests in the factory and parts of the whole system have to be delivered and put together to build the complete GIS. As the result, all insulation tests have to be performed on site. Even if different parts of the system are tested in the factory, because some of the problems occur during the transportation and installation, the insulation strength of the whole GIS can be degraded. In this paper, a novel test set-up and the measurement results of a 400 kV GIS have been installed for the Mobarakeh steel industries, Isfahan, Iran, are presented. This system has a length of about 100 m, which corresponds to a total capacitance of about 10 nF per phase. Because of this relatively large capacitance, the power ratings of the test voltage sources have to be very high. For achieving such a high power, a two step cascade voltage transformer (each 800 V/300 kV with a maximum output current of 2 A) fed through an autotransformer enhanced with a number of inductors to compensate the capacitive current and to minimize the input current of the test transformers have been used to apply the necessary 515 kV to perform the AC tests of the whole GIS. The measurements carried out on the system showed that the first two phases passed the test successfully; however the third phase could not withstand the applied voltage because of the pollution near one of the spacers. After replacing the faulty spacer, the insulation strength of the third phase has been recovered.

Visualization of a Copper Wire Explosion in Atmospheric Pressure Air

Experimental and computational images of a 90-μm thick copper wire explosion in atmospheric pressure air are presented. A Marx generator is used to produce a pulsed current density into the wire with a maximum rate of rise of ~ 1018 Am-2 s-1. A multiphase numerical model includes mass and momentum conservation equations, thermofield ionization, Maxwells equations, and heat transfer between the phases. Visual records of the experiment agree with the simulation results.

Subnanosecond Breakdown Mechanism of Low-Pressure Gaseous Spark Gaps

Subnanosecond breakdown of low-pressure gaseous spark gaps has been investigated by using a combined modeling of the volume discharge in gas and the electron emission at the electrodes. Simulation results predict minimum breakdown delays of about 400 ps for the geometries considered in this paper. These results are in good accordance with the measurements.

Improved Output Current Rise Time From Modified Helical Flux Compression Generators

Flux compression generators (FCGs) are widely used to generate extremely high power pulses. When a peak current from a seed source is flowing through the generator circuit, the chemical energy of high explosives is used to increase the amplitude of the output current pulse applied to the load. During the transfer of explosive energy to the output electrical pulse, the critical issue is achieving a change in the inductance in a fast and controlled way. There have been many significant experiments on different kinds of FCGs, and almost all of the theoretical models used to describe generator behavior are based on empirical equations. In this paper, simultaneous detonic, electromagnetic, and circuit simulations are used to study the characteristics of helical FCGs. For this purpose, the magnetic field diffusion and losses due to the induced currents in metallic components are considered in more detail. Based on the results of these theoretical considerations, new modifications for the FCG are proposed. It will be shown that the proposed modified FCG geometries yield output current rise times that are about 60% of those achieved with conventional helical FCGs generating the same current pulse amplitudes.

The evaluation of prominent parameters on post-arc current characteristics in vacuum interrupters

Summary form only given. The appropriate performance of vacuum interrupters is mainly divided in two phases; current interruption phase which supposed to be fulfilled before current zero and post-arc or voltage recovery phase after current zero. The particles in residual plasma after current zero are accelerated by transient recovery voltage (TRV). Therefore a current in the order of some ampere and duration of some microseconds commences after current zero which is called post-arc current. The characteristics of the post-arc phase are in close relation with initial ion density and its distribution between cathode and anode. These two parameters are strongly dependent on the arcing time and extinguished fault current amplitude and the intensity of the externally applied axial magnetic field in the interruption chamber. In this paper, the propagation of ions after current zero is simulated and the effect of external magnetic field and its strength on post-arc phase is investigated. Furthermore, some modifications have been applied in the shield of vacuum interrupter to improve the ability of interrupter in dielectric strength recovery of vacuum.

Simultaneous Three-Dimensional Thermodynamic and Electromagnetic Simulation of Explosively Driven FCG Applied to Magnetic Coupled Plasma Modeling

In some plasma applications, such as confinement and pinches, an ultrahigh magnetic field (several teslas) is required. Such magnetic flux densities can be produced by using flux compression generators (FCGs). This paper has proposed a joint thermodynamic and electromagnetic simulation method for a common type of FCGs (i.e., helical type) with respect to the magnetic coupled plasma studies. The images of displacements, pressure, and magnetic flux density distribution in generator and plasma chamber are presented as simulation results.

Three-dimensional simulation of an AC plasma display panel with T-shaped electrodes in waffle rib structure

Two parameters which mainly affect the performance of Plasma Display Panels (PDPs) are electrode and rib geometries of the PDP cell. T-shaped electrode geometry leads to slightly higher efficacy in comparison with conventional coplanar electrodes geometry because of extending the discharge path. This allows more uniform illumination of the phosphors by the vacuum ultraviolet (VUV) photons (reduction of possible saturation effects).

Optimization of electronic ballast drive for the high power sodium vapor lamps based on two-dimensional plasma finite element modeling

High power sodium vapor lamps (up to 2-kW) are widely used for illuminative purposes. Foremost application of these lamps is in the large scale environment lighting such as highways. These lamps are used with appropriate reflectors control the light propagation direction and pattern. Accomplishment of proper characteristics of such lamps, e.g., ignition and continuity of the lamp operation requires a drive circuit, known as ballast, which generates the applied voltage to the plasma tube. Two types of ballasts are mainly used in the industries: electric (conventional circuit using chuck) and electronic ballasts. Different characteristics of these two types of ballasts affect the plasma behavior and consequently the emitted light properties. In this paper, the effects of electronic ballast, such as high frequency harmonics, controlled power factor, have been investigated and compared with conventional approaches. A typical plasma tube which is commonly used in high power sodium vapor lamp structures has been considered without any reflectors. Plasma channel of the lamp has been modeled by a finite element method, solving particle continuity, momentum conservation and thermal balance equations in gaseous medium, in 2-D geometry. Cylindrical symmetry of the lamp structure has been applied. As a result of the simulations, light spectrum distribution is achieved by use of electron and ion density and velocity distribution along the plasma channel. These parameters have been compared at two different cases: conventional electric and electronic ballasts.

Improvement of efficiency and luminous efficacy of RF Plasma Display Panels by modified cell structure

Application of Radio Frequency (RF) voltages with frequency of around 60MHz has been proposed to replace the conventional several hundreds of kHz sustaining voltage. Multiphysics simulation of the RF discharge plasma has been presented for a Plasma Display Panel (PDP) cell structure. The frequency of the applied voltage to the micro-discharge cell has been changed incrementally from 500-kHz to 100-MHz in the calculations and the behavior of the plasma has been discussed. Simulation results indicate that if the frequency of the RF voltage is high enough so that the average amplitude of electron oscillations is less than the gap length, the plasma is efficiently confined by the RF field. In these conditions, the discharge can be sustained at much lower voltages than in the conventional AC PDPs. The ion heating in the sheath is considerably reduced and the electrons excite xenon more efficiently in the lower electric fields. Calculations show that the xenon excitation efficiency can be increased by a factor of 3.7, with respect to conventional AC PDPs. According to this model a novel structure for RF PDP cell structure has also been proposed. It has been shown quantitatively that the luminous efficacy of the proposed structure can reach 4.4 lmW−1.