Advanced Materials Research Vols. 732-733

Abstract: As one of the important hinge equipments in the electric power system, the operating reliability of power transformer has deep influences on security and stability of power system. In order to guide transformer maintenance and assess the risk of the electric power system, it is of important significance to know the state of the running insulation of transformer in time and accurately. Based on the analysis of transformer state parameters, the method determining the evaluation index weight has been studied; methods of entropy value objective weight and improved analytic hierarchy process subjective weight have been combined to calculate the weighting coefficients of evaluation indexes. Its correctness has been verified by analyzing examples of transformer operation.

Abstract: From the angle of voltage distribution, the influence of DG on power network was studied, various access position and access capacity of DG were analyzed, and conclusion can be drew that DG can help optimize the voltage distribution in the power network. Besides, the output of photovoltaic and wind power was characterized by varying with time, and based on that, the voltage distribution was simulated when they were both connected in the same distribution network. According to the simulation result, some valuable principles and necessary procedures have been proposed.

Abstract: One of the most important ways to enhance the speed of state estimation is to establish the constant matrix Jacobian. This essay puts forward the state estimation method of the equivalent current transformation based on the Generalized Tellegen’s Theorem. This estimation method establishes the constant Jacobian matrix without neglecting the secondary factor making use of the Generalized Tellegen’s Theorem, solves the numerical stability problem caused by the establishment of the constant Jacobian matrix in the current state estimation, and has the advantages of a relatively rapid computing rate and an unparalleled astringency. The method put forward in this essay has been verified through IEEE-30 Node System, and the efficiency of it has been fully proved by the example results.

Abstract: Many factors affect the precision of electric energy metering in measuring process, and distorted waveform is one of them. Based on maths principle and equivalent circuit model, the metering error related to electronic energy meter algorithm (metering principle), current transformers and voltage transformers is analyzed. Corresponding improvement metering scheme is put forward. Finally, taking the common nonlinear load-AC EFA (electric arc furnace) as an example, it is simulated in the MATLAB/Simulink simulation platform. The results validate the conclusions of the error analysis and some methods proposed to improve the rationality of actual metering operation significantly.

Abstract: Large power transformers as the the hub of power system equipment, its operation reliability directly related to the security and stability of the power system. When we have to make a more comprehensive and accurate judgment for running health status of the power transformer,we must get the characteristics of the transformer state. In this paper, we can pick out representative indicators from the existing power transformers deterioration state elements. Thereby, we can study more systematic and targeted the deteriorated state of the power transformer. Keywords: power transformers; deterioration state ;evaluation

Abstract: The feasibility of transformer fast reenergizing with neutral point ungrounded after the external fault being removed is analyzed in this paper. By calculating overvoltage and discriminating magnetizing inrush current, it analyzes four ways to restore power of transformer and chooses the optimal strategy which is safe and time-saving. The result shows that in the case of transformer neutral point ungrounded, closing the low-voltage circuit side breaker before the high-voltage, which can effectively limit over-voltage in a safe range. The second harmonic characteristic of magnetizing waveform may disappear, while the intermittent angle characteristics are still significant. With the help of the intermittent angle principle, transformer differential protection may not misuse. The average time for each customer interruption is reduced from 40 minutes to 10 minutes and saves an hour for engineer on the way back and forth. It will greatly improve power supply reliability.

Abstract: This paper introduces the working principle of induction cooker and analyzes the design of power control using MCU; the fuzzy control method put forward when the pans change can keep the output power stable.

Abstract: The traditional GM (1,1) has been used widely in the load forecasting, however, there are many defects in the GM (1,1). In order to overcome these defects and expand the application scope of the grey model in load forecasting, a new load forecasting method based on DDGM(1,1) is presented. First, the recursive solution of DDGM(1,1) is given. Then, based on the solution, the unbiased property for non-homogeneous exponential incremental sequence of this model is proved. It is applied to some load forecasting and is compared with the traditional GM (1,1) model.The results show that the presented forecasting method is superior obviously to traditional methods, and it can be used for the approximate non-homogeneous exponential incremental load forecasting generally.

Abstract: When the system requires reconfiguring or repairing, the load on one of distribution feeder needs to be transferred to another feeder without interrupting. However, there are several conditions which affects the load transfer on distribution feeder, including substation types, feeder loads, and primary side voltage of transformer. Those conditions will result in abnormal high current on load transferring, and the high current will lead to the operation of overcurrent relay. This paper uses ASPEN and Matlab/Simulink to simulate the load transfer of distribution feeder, and investigate the factor that will affect protection relay. An OLTC and a phase shifter is used to improve the high current during load transfer. It will avoid the action of protection relay, and improve reliability in power supply.

Abstract: A simple interconnected power system with periodic load disturbance is considered, an energy storage based adaptive controller is proposed to output tracking and disturbance completely rejection for the system. Since the periodic load disturbance is uncertain with both amplitude and frequency, by constructing a new exosystem, the output tracking and disturbance rejection problem is solved with output regulation theory. By designing an internal model for the complicated system and introducing an appropriate transformation, the output regulation problem is changed into the stabilization problem of a new augmented system. With the help of adaptive control technique, the designed dynamic energy storage controller can solve stabilization problem of the augmented systems as well as the output tracking and disturbance rejection problem for the original system. Finally, the simulation results show the effectiveness of the proposed control strategy.