Applied Mechanics and Materials Vol. 492

Abstract: Gas insulated transmission line (GIL) is increasingly being utilized in the power system because of its advantages, such as large transportation capacity, no insulation ageing, low loss, and low electromagnetic radiation. However, even GIL equipment in operation can go wrong under the influence of various factors. This paper is an in-depth analysis on a 500kV GIL fault resulting in the tripping operation of a substation chief transformer. The causes of the accident are discussed from several aspects, such as insulation defect, design of gas inlet port, and effect of temperature on the water in the GIL. Some suggestions are given for the structure design, manufacture, installation, and operation of GIL.

Abstract: To improve the management level of latent troubles that perhaps happened in transmission line passage, a transmission line passage protection system (TLPPS) based on web map service is developed in this paper. In this system whose structure is selected as B/S, Baidu Maps API is creatively used to construct the Web GIS platform and its network database is built by Microsoft SQL Server 2005. Android mobile APP by Java is designed to exchange latent troubles information with network database. The system can achieve latent troubles information real-time uploaded, displayed on map, queried and other management of the entire process.

Abstract: Partial discharge (PD) detection is a technique widely used for high voltage equipment insulation condition assessment. The metal protrusion is a situation that often appear in transformer. Metal protrusion will cause the electric field concentration and lead to partial discharge. In this paper, PD characteristics in transformer oils are examined under AC conditions, using a needle-to-plane electrode system. The PD activity in transformer oil is confirmed as appearing in pulse burst form and the PD number and amplitude will increase with the applied voltage increase. The PRPD pattern display behavior typical of corona PD in oil.

Abstract: This paper mainly studies the effects of low temperature on the reliability of electrical connectors. Based on the theory of constant stress accelerated life test, this paper provides a kind of scheme of low temperature reliability test, which includes magnitude of the temperature stresses, the parameters measured during the test and so on. The detecting circuit is designed; the test is carried out and finally, according to the experimental data, it can be concluded that 1) both the absolute change and the relative change of contact resistance are small for each temperature stress; 2) the forecast data show a tendency toward slightly lower value of contact resistance for each low temperature stress; 3) the lower the test temperature stress, the smaller the value of contact resistance, but the difference in contact resistance is tiny; 4) stress analysis of samples under low temperature is also helpful for correctly evaluating the effects of low temperature on the reliability of electrical connectors.

Abstract: A method calculating the failure frequency of sensitive equipment caused by voltage sag in the monitoring period is proposed. In life and production, destruction of sensitive equipments fault caused by voltage sag is a serious power quality problem. It is a transition process that sensitive equipments fault caused by voltage sag, which is from a safe state to fault state, and it is uncertain whether it is fault in the region of the voltage tolerance curve (VTC), Probability density function is used to characterize failure state caused by voltage sag which happened in the voltage tolerance curve, and using the cumulative method to calculate sensitive equipment fault frequency through the voltage sag characteristic parameters in the period of monitoring time. Using personal computers as experiment equipments, and comparing the outcome with the result calculated by using the ITIC curve, its proved this method is superior and accurate.

Abstract: This paper proposes a practical mitigation solution to the voltage sag problem by resonant grounding for a 22-kV distribution system of Provincial Electricity Authority (PEA) at the Patumthani 1 substation in Pathumthani province in Thailand. A computer simulation by ATP-EMTP was carried out to investigate the voltage sag impact at the low voltage side of the delta/wye distribution transformer connected at a fault location in the existing solidly grounded system and proposed resonant grounded system. The results indicate that the proposed resonant grounding can help all customers connected at the same bus survive from voltage sag problems and also keep the customers on the faulty feeder connected to the system being continuously supplied for single-to-ground faults. To evaluate the benefits of the resonant grounding, the different voltage-tolerance curves are proposed by Information Technology Institute Council (ITIC) curve and laboratory testing of Personel Computer (PC) curve, Programable Logig Coltroller (PLC) and Adjustable Speed Drive (ASD). The saving from the cost of customer interruption and voltage sag is calculated comparing between the existing solid grounding and the proposed resonant grounding with different voltage-tolerance curves

Abstract: The principle of an online monitoring and diagnosis system suitable for various kinds of High-voltage Circuit Breakers (HVCB) is presented in the paper. The system consists of distributed data acquisition devices, a communication system based on field bus, and a host based on B/S structure. The research presents the methods to select the main monitoring signals of high-voltage circuit breakers, to acquire data, and to calculate operational feature values, as well as realizes high-speed process to monitoring signals, valid online monitor to high-voltage circuit breakers, and fault diagnosis.

Abstract: This paper deals with power transformers technical state assessment based on technical diagnostics using Bayes method. Present a model for integral power transformers technical state assessment on the three types of technical diagnostics. Determining state of power transformers is based on expert judgment using the membership functions.

Abstract: This paper discusses a novel research and implementation of dynamic voltage restorer (DVR).The phase diagram is shown based on the principle and the steady-state equivalent circuit. The initial phase of the source fundamental voltage and angle are given according to instantaneous reactive power (IRP) theory. The voltage function is determined by the optimum voltage injection angle which is based on minimum energy compensation (MEC). A prototype and the design process are given. The experimental results verify the rationality .

Abstract: In this paper, the magnetic force actuator (MFA), a new type of actuator, is applied for long stroke driving with simple structure and high reliability. Ansys and Matlab are adopted to study its static and dynamic characteristics and conduct parameter design. The static simulation concludes static magnetic field, end shield material, structure size of permanent magnet and processing deviation of the actuator, which will impact the characteristics of the actuator in varying degrees. Then the state equations describing the dynamic characteristics of MFA are solved by four-order Runge-kutta method and finite-element method. Interactive interface of the APDL-file and M-file and Macrosoft Visual Basic (VB) is designed to combine Ansys and Matlab to realize optimization design of structure parameters, which simplifies the operation methods and enhances the efficiency. The dynamic simulation results show its good work performance compared with the experiment characteristics of practical 40.5kV SF6 circuit breaker with the spring mechanism.