Advanced Materials Research Vols. 614-615

Abstract: Harmonics and reactive currents detected in precision is the key whether active power filters work well. Methods on detecting affect compensation currents and detecting precision. A novel harmonics and reactive currents detecting algorithm in three phase circuit is proposed. It extracts positive fundamentals of source voltages and load currents using three-phase sinusoid and cosine signals with arbitrary phase, and then detects harmonics, reactive and negative currents by accurately separating positive fundamental active component from load currents. Whether waveforms of voltages are non-sinusoidal or unbalanced, the results can not be affected. Furthermore, it is without phase lock loop. Finally, it is proved to be precision and feasibility from simulation.

Abstract: In this paper, a calculation method of static security analysis based on section topology relation is proposed. When topological structure of current data section is the same as that of the basecase section, it fully utilizes the factor tables of Jacobian matrix, and inverse matrix information of the basecase data section in rapid filtration of DC power flow. On the contrary, If topology changes compared with the basecase section, it adopts substation partial topological analysis technology as well as the method of partial factor table correction to increase the speed of calculation. Case studies with a practical power system indicate that the proposed method is correct and reasonable.

Abstract: This paper describes Detecting Methods for Harmonics of power system has been considered one of the serious harms for power system. The research of harmonics has obtained high attention among people. The researches of harmonics detection have many methods, such as Based on Fryze theory of harmonic power detection, Instantaneous reactive power theory detection method, Fourier Transformation harmonic detection method, wavelet transform detection method, neural networks harmonic detection method etc. Aiming at harmonic detection, the different detection methods of power system harmonics are summarized and compared. This paper reviews the existing harmonic detection methods, and discuss their advantages and disadvantages in terms of detection accuracy and response speed, and finally summarizes the development trend of the harmonic detection method.

Abstract: To develop an economic and effective online monitoring method is necessary as the normal running of distribution line is critical to ensure the reliability of power system. And the distribution line state monitoring technology improved steadily nowadays, the monitoring of operating status can be achieved by using online monitoring devices. However, its installation and maintenance cost a lot, it is poor in economy. A new method, in which line resistance was selected as a reference quantity, was proposed in this article. The monitoring of distribution line running status can be realized by analyzing the line resistance value that calculated by real-time measurement data. The method improves the utilization of information system and requires no additional investment costs. And the example verified the validity of the method; it is possible to learn about the operational status timely through analyzing the changes in line resistance value.

Abstract: Technology of Micro-grid emerges, and power distribution system faults, allowing for the distributed generation keeping alive the islanded operation with the important load . But if the interior of Micro-grid happens a fault again, the short-circuit current of Micro-grid is so insufficient that traditional current protection can not play a part in the protection. In order to solve this problem, it introduced a new relay protection strategy, and provided the basis for the relay protection design of Micro-grid in the future.

Abstract: This paper addresses the research on the Voltage Quality Control (VQC) for the 110kV-substation. The VQC with ‘Nine District-Circuit Diagram’ strategy utilizes two parameters, voltage and reactive power, to realize the integrated control of the high-voltage-side reactive power and the low-voltage-side target voltage of the transformer. A practical example analysis is involved and its computing results show that it is essential to control the busbar voltage within the operational range, while keeping the reactive power in the operational range as far as possible.

Abstract: It is possible to prevent collapse of whole post-fault power system, which is in unstable condition, by determining the splitting boundary to calm down system oscillation. A fast splitting boundary-searching method for power system controlled islanding is presented in this paper. The aim of this method is that the generation load imbalance in each island is as small as possible. The method contains three phases: firstly, domain of each generator is formed according to power flow tracing algorithm; secondly, initial splitting boundary is determined based on generators’ grouping information; thirdly, the final splitting boundary is got based on initial splitting boundary. A program is developed based on the method. Simulations on IEEE 118-bus power system show the proposed method is effective and fast.

Abstract: In high-voltage lines protections, directional elements based on negative sequence voltages available can not work well when negative voltages protection equipments capture are relatively low, which may lead to malfunctions or failure to actuate. A new directional element based on negative sequence reactance is presented in this paper. The negative sequence reactance is negative and then it is less than the line negative sequence reactance when a forward fault occurs. And when a reverse fault occurs, the negative sequence reactance is greater than the line negative sequence reactance. Hence, which direction a fault occurs can be distinguished according to the sign and the magnitude of the reactance. The direction element based on the negative sequence reactance has high sensitivity with no influence by transition resistances. The directional element proposed can work well when the negative sequence voltage is very low or even close to be zero and it is easy to realize.

Abstract: This paper analyzes the necessity of constructing integrated operation system as well as the current situation and development goal of substation operation management, it proposes the design of technical support system for dispatching and control integration that adapts to integrated operation system, it demonstrates the support system’s structure, basic technical requirements and key technologies and introduces practical applications of integrated dispatching and control system, providing a reference for the construction of integrated operation system.

Abstract: As the coupling between active and reactive power is enhanced along with the expansion of the grid scale and the AC-DC hybrid operation, voltage stability is not only closely related to reactive power, but also related to active power. By the constraints of generator power circle and its operating limits, the mechanism of interaction between the active and reactive power is clarified. Also, the hierarchy structure of coordinated optimization and control technology between them is established, and an improved AGC control strategy consideration to static voltage stability is proposed. By optimizing the active power output of the AGC unit, the dynamic reactive power reserve capacity of each unit is improved and the system voltage is supported. The strategy is verified through a variety of experiments on the IEEE-39 bus system.