Applied Mechanics and Materials Vols. 291-294

Abstract: Shanghai main power grid is operating in 500 kV ring network and with voltage-grading & district-dividing structure, and its subzone power grids have their own frequency characteristics. The paper has used district-dividing single equivalent model to check the parameters of components in BPA transient simulation program, and the original under frequency load shedding (UFLS) scheme was improved. Then the frequency dynamic characteristics of isolated subzone grid is analyzed, so does the adaptability and frequency safety of power grid under the new UFLS scheme in the condition of peak load in the summer of 2011.

Abstract: Wind speed forecasting is of great significance to the improvement of grid stability and the reduction of operating cost. Because of the high volatility of wind speed, the accuracy of current forecasting methods have yet to be improved. This paper established a time series-state transition model to solve this problem, which uses state transition to revise the results of time series forecasting. The improvement in accuracy is proved by the analysis of a practical example.

Abstract: To compensate harmonics from nonlinear load, the controller of Active Power Filter (APF) need to detect harmonic and generate compensation current in high speed. APF controller functions are divided into two parts: outside controller part and inside controller part. Inside controller part detect harmonic current and control the IGBT to generate grid harmonics current. Outside controller part detect common power parameters and generate signal of management in main circuit. An experiment circuit of APF Controller is established. Some experiments are presented here.

Abstract: The applicability of functionally graded materials (FGM) for solid insulator of gas insulated switchgear (GIS) was investigated. First, a new fabrication method based on layer-by-layer casting technique was demonstrated to prepare FGM insulator possessing spatial distribution of dielectric constants. Then, electric field strength in the FGM spacer model was calculated and optimized by using finite element method (FEM). Three types of truncated cone spacers were fabricated according to the optimization results. Finally, surface flashover tests were performed under AC voltage and lightning impulse voltage applications. Results in both circumstances indicated an evident improvement of flashover voltage when FGM insulator was employed. As a result, we verified the fabrication technique and the applicability of FGM insulator for enhancement of insulation performance in GIS device.

Abstract: Influence of atmosphere corrosion on conductor in the high-voltage overhead power transmission line has been paid more and more attention. This paper carries out experimental test research on atmosphere corrosion forms of aged conductor wires through metallographic analysis, electron microscope scanning etc. technologies, analyzing the influence of corrosion on its mechanical performance, which has provided theoretical reference for operation and maintenance of the overhead power transmission line.

Abstract: In order to improve measurement accuracy of all fiber-optical current transformer (FOCT), an improved demodulation algorithm was proposed for a sine modulation. The formula for effective phase modulation depth (EPMD) was firstly presented, and three kinds of potential external disturbance in EPMD were analyzed. To overcome the current measurement error induced by these EPMD disturbances, we put forward an improved algorithm for time-dependent measurement of EPMD by second- and fourth-order harmonic component of optoelectronic signal. A simulation experiment in different disturbance intensity were carried out, and the results showed that when measured current is between 200A~1500A,the proposed algorithm can enhance the current measurement accuracy by over 30 times than the conventional algorithm, and measurement relative deviation can be maintained below 0.2% if the disturbance intensity is below 5%.

Abstract: The use of direct wave to locate the position of the PD source is of better accuracy in transformer partial discharge ultrasound array positioning. For the signal received by ultrasonic sensor is consisted by direct wave, non-direct wave and a variety of noise, a direct wave separation method based on improved waveform matching is proposed in this paper. It is considered that the direct wave first reaches the ultrasonic sensor. A benchmarks triangle is built and then the attenuation coefficient and the signal frequency are both calculated. In order to search the matching wave, the benchmarks triangle is to pan and zoom. Finally, the best matching waveform is selected from a large number of matching waveforms as a direct wave signal. The result of simulation shows that the method can isolate the ultrasonic direct wave signal from the received signal, which provides some theoretical guidance to improve the position accuracy of the PD source.

Abstract: With the accelerating construction of strong smart grid, and the grid voltage level rising, performance requirements for the electrical insulation of electrical equipment also continue to increase. The ( XLPE ) cable with good electrical and thermal performance and simple structure, the manufacturing cycle is short, safe and reliable power supply etc, which is widely used in power system ; Partial discharge is in the power cable to run a larger security risks is a sign of deterioration of the cable insulation is caused by insulation deterioration of important reasons . In this paper, based on variable frequency resonant damped oscillatory wave voltage XLPE cables and their connectors partial discharge site detection technology, the damped oscillatory wave voltage and power frequency voltage equivalent; the field test requirements, parameter optimization and performance detection impedance, and use advanced digital signal processing methods to analyze the test data processing, to provide a reference for the cables and their joints more accurately determine the insulation condition.

Abstract: Transformer life cycle cost risk was analyzed systematically and scientifically. Risk evaluation index system of the transformer life cycle cost was established based on AHP(Analytical Hierarchy Process) . The 1-9 scale of the risk indicators was used to determine the weight of the evaluation index system, thus the combination of expert experience with quantitative and qualitative evaluation results are realized. Application results show that the method have practicality and effectiveness and has theoretical and practical significance for proposed effective cost risk optimization and control strategies for cost risk factors to minimize the risk of transformer life cycle cost.

Abstract: There are three sampling methods for reactive power compensation controller, including active power factor detecting, reactive power detecting and reactive current detecting. This paper describes the power factor detecting, which use the avr microcontroller to detect load power factor, besides, the principles and characteristics of two different detection methods are presented, the detecting accuracy is compared between the same phase detecting method and using FFT algorithm.