Capacitive current interruption with high voltage air-break disconnectors

Disconnectors are low-cost switching devices in high voltage electrical power supply systems that basically have an insulation function only. Nevertheless, they have a very limited capability to interrupt current (below one Ampere), e.g. from unloaded busbars or short overhead lines. The present study is a search for possibilities to increase the current interruption capability with auxiliary devices interacting with the switching arc. In this project the state of the art of disconnector switching is investigated and an inventory is presented of models of the free burning arc in air. A series of experiments were arranged at different laboratories. The switching arc and the interruption process are studied in detail through electrical and optical measurements during the switching process for a disconnector with (without) auxiliary devices under high voltage (300 kV) conditions. Three options for auxiliary devices were investigated: (i) arc cooling by forced air flow; (ii) fast interrupting by high-velocity opening contacts; (iii) reduction of arc energy by added resistive elements. Finally, a qualitative description is provided on the physical nature of the arc and how the evaluated methods affect the arc characteristics. All results are obtained by analysis of highresolution measurement of arc current (including all relevant transients), voltages across the disconnector and high-speed video observation. It was found that, depending on the current to be interrupted, the interruption process is governed by dielectric and/or thermal processes. In the dielectric regime, the interrupted current is low (roughly below 1A) and the switching arc is characterized by a high rate of repetition of interruptions and restrikes that only cease after a sufficient gap spacing has been reached. The restrikes interact severely with the circuitry in which the disconnector is embedded, exciting transients in current and voltage with frequencies up to the megahertz range. High overvoltages can be generated. Their magnitudes can be limited by a proper choice of the capacitance at supply side of the disconnector. The arc-circuit interaction has been studied and relevant processes have been modelled and verified by experiments in full-power test-circuits. In the thermal regime, the switching arc behaves less vehemently, interrupting and re-igniting basically occur at every power frequency current zero. Because of the presence of sufficient thermal energy in the switching gap along the arc path, the voltage to re-ignite the arc is limited, and the arc-circuit interaction is less pronounced. Though not producing very severe overvoltages, the arc duration is longer and the current may not be interrupted at every current zero crossing. The ultimate thermal regime is reached when the arc continues to exist after power frequency current zero without any appreciable voltage to re-ignite. This situation must be avoided because arcing goes on until a higher level breaker interrupts the current. Before this, the arc can reach far away from its roots and can greatly reduce insulation clearance. The main factors influencing the interruption performance are the level of current to be interrupted, the system voltage, the ratio of capacitances at both sides of the disconnector and the gap length. These factors influence the energy supplied to the arc upon re-strike. This energy extends the arcing time by lowering the breakdown voltage. It has been observed that the arc in its thermal mode always re-ignites in its former trajectory. Key to the interruption process is the reduction of breakdown voltage in this path, created by hot gases remaining from the former arc. The existing breakdown models are reviewed in order to understand the influence of high temperature air on the breakdown process. Based on the observed arc behaviour, various methods have been researched to increase the interruption capability. The most successful methods are those that remove the residual (partially) ionized air from the arc path. Experiments were carried out to demonstrate the effectiveness of air flow directed into the arc’s foot point. A substantial gain in interruption capability is demonstrated, but at the cost of generating re-ignition transients at a very rapid succession. Specifically, the experiments showed that 7.5 A could be interrupted successfully at 90 kVrms voltage with a shorter arcing duration (a factor of 0.5 was observed) than without air flow. With application of air flow, the frequency of re-ignitions occurring, and the breakdown voltage are much higher than without air flow. Another method, the assistance of an auxiliary switch able to produce a very fast opening, was also successful. Herein, the arc is forced mechanically into ambient cool air, thus avoiding accumulation of thermal energy in the arc path. Specifically, it can interrupt currents up to 7 A at 100 kVrms safely and 9 A at 90 kVrms in the experiments with arcing time only a few tens of milliseconds instead of a few seconds. The arc exhibits a "stiff" (linear) character instead of the "erratic" (randomly moving) arc mode with a disconnector alone. This method reduces the number of re-strikes. The possible influence of energy absorbing elements (resistors) is investigated through circuit modelling, supported by some laboratory experiments. Other methods, such as the application of series auxiliary interrupting elements (vacuum, SF6 interrupter and ablation assisted approaches) have been evaluated. From the practical point of view, the auxiliary fast-opening interrupter is recommended due to its economic, simple and effective merits. Other approaches have certain disadvantages. The method with air flow needs a complex construction in order to introduce the compressed air flow into the disconnector, and the hazard for nearby equipments from the overvoltages caused by the interruption is greater. The method of inserted resistor requires very expensive arrangement. Regarding the application of auxiliary interrupters, vacuum interrupters have to be applied in considerable numbers in series and SF6 interrupters have good performance but at very high cost. An ablation assisted approach seems less promising because the level of the interrupted current is too low to be effective

High-Efficient Parallel CAVLC Encoders on Heterogeneous Multicore Architectures

This article presents two high-efficient parallel realizations of the context-based adaptive variable length coding (CAVLC) based on heterogeneous multicore processors. By optimizing the architecture of the CAVLC encoder, three kinds of dependences are eliminated or weaken, including the context-based data dependence, the memory accessing dependence and the control dependence. The CAVLC pipeline is divided into three stages: two scans, coding, and lag packing, and be implemented on two typical heterogeneous multicore architectures. One is a block-based SIMD parallel CAVLC encoder on multicore stream processor STORM. The other is a component-oriented SIMT parallel encoder on massively parallel architecture GPU. Both of them exploited rich data-level parallelism. Experiments results show that compared with the CPU version, more than 70 times of speedup can be obtained for STORM and over 50 times for GPU. The implementation of encoder on STORM can make a real-time processing for 1080p @30fps and GPU-based version can satisfy the requirements for 720p real-time encoding. The throughput of the presented CAVLC encoders is more than 10 times higher than that of published software encoders on DSP and multicore platforms

Mrs. K. : Oral History of a Korean Picture Bride

Introduction In 1923, Mrs. K., a nineteen-year-old picture bride-to-be, left a small mountain village in Kyong-sang province, Korea, to marry a forty-five-year-old Korean immigrant who awaited her arrival in Honolulu, Hawaii. Now seventy-five years old, Mrs. K. has spent fifty-five years of her life as a resident of the island of Oahu. For Mrs. K., one of the 101 remaining out of 1,000 Korean picture brides who came to Hawaii between 1910 and 1924, life in Hawaii followed a similar pattern to that of other picture brides. She worked alongside her husband at an army laundry service; then she ran a laundry shop, a boarding house, a vegetable farm; and finally she built and managed multi-unit apartment buildings. Mrs. K.\u27s life story reads like an American dream-come-true

Early detection of rice blast (Pyricularia) at seedling stage in Nipponbare rice variety using near-infrared hyper-spectral image

Blast rice is the worst biological disaster in rice cultivation. It reduces the yield at least up to 40 to 50% (in the worst period of disease). In this study, the near-infrared hyper-spectral image was investigated to detect blast rice in Nipponbare at seedling stage. Two hundred rice seedlings were segregated into two classes: infected and healthy. All of rice seedlings were scanned with a hyper-spectral imaging system in the NIR (900 to 1700 nm) wavelength range. Principal component analysis (PCA) was performed on the images and the distribution of PCA scores within individual leaf were measured to develop linear discriminant analysis (LDA) models for predicting the infected leaves from healthy leaves. An LDA model classified all the leaves into infected and healthy categories, with an overall accuracy of 92% on validation set. Meanwhile, the classification model base on five selected wavelengths (1188, 1339, 1377, 1432 and 1614 nm) was comparable to that base on the full-spectrum image data.Key words: Rice blast (Pyricularia), Nipponbare, near-infrared hyper-spectral image, principal component analysis, linear discriminant analysis

Ensemble of ANN and ANFIS for Water Quality Prediction and Analysis - A Data Driven Approach

The consequences of un-clean water are some of the direst issues faced by humanity today. These concerns can be addressed efficiently if data is pre-analyzed and water quality is predicted before its effects occur. The aim of this research is to develop a novel ensemble of Artificial Neural Network (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) models using averaging ensemble technique, producing improved prediction accuracy. Measurements of different water quality parameters have been used for predicting the overall water quality, applying ANN, ANFIS and ANN-ANFIS ensemble and their results have been compared. The data used in this study is obtained by USGS online repository for the year of 2015, with a 30-minutes time interval between measurements. Root Mean Squared Error (RMSE) has been used as the main performance measure. The results depict a significant improvement in the Ensemble ANN-ANFIS model (RMSE: 0.457) as compared to both the ANN model (RMSE: 2.709) and the ANFIS model (1.734). The study concludes that the ensemble of ANN and ANFIS model shows significant improvement in prediction performance as compared to the individual models. The research can prove to be beneficial for decision making in terms of water quality improvement

An ectopic hamartomatous thymoma compressing left jugular vein

Ectopic hamartomatous thymoma (EHT) is an extremely rare benign neoplasm. It is usually found at the root of the neck (frequently on the left) and does not usually impact adjacent tissues in clinically significant ways. While EHT manifests distinct pathological features, the lesion is either asymptomatic or may show nonspecific clinical features. We report one case of EHT which was assumed to be of low malignant potential since it severely compressed the inlet of left internal jugular vein as seen by computed tomography scan. To the best of our knowledge, this clinical finding of EHT is very rare. After the diagnosis and treatment of this patient, we believe that EHT or suspected EHT should be treated less invasively.Key words: Ectopia, harmatoma, mini‑sternotomy, thymom

Kinematic Modeling and Optimization of a New Reconfigurable Parallel Mechanism

This paper investigates a new reconfigurable parallel mechanism consisting of three SvPS kinematic limbs. Induced by phase changes of a metamorphic spherical variable-axis joint (Sv), the SvPS limb is capable of changing to two typical configurations, of which one exerts no constraint and the other exerts a constraint force to the moving platform. Reconfiguration of the three limbs enables the 3-SvPS parallel mechanism to have four distinct configurations with degrees of freedom (DOF) varying from 3 to 6. Analytical model of position and workspace analysis of the reconfigurable parallel mechanism are first investigated. In terms of the screw theory, a unified Jacobian matrix covering all the mobility configurations is established and utilized for analyzing singularity of the parallel mechanism in different configurations. Further, performance analysis and optimization are explored using the motion/force transmission method. The 3-SvPS parallel mechanism can be used as structure of reconfigurable robotic machine center with adaptability to changing task requirements