Advanced Materials Research Vols. 1008-1009

Abstract: In urban radial networks, the feeder is often complex with a main line, branches and even sub-branches. It is necessary to optimize the configuration of automation switching devices in distribution automation system (DAS) to reduce the impact range of power outage and improve the power supply reliability. The interruption frequency and the space-time relationship among the switching devices were ignored in the most of researches. This paper presents a new reliability planning scheme of switching devices in DAS which involves three types of circuit breakers and three types of load switches. The model which target is to get the minimal cost, the lowest average annual interruption frequency and the least interruption duration is built thereby. The constraint is the availability rate of electricity supply of load node. Based on the Pareto optimality theory, the multi-objective differential evolution algorithm is adopted to solve the Pareto front efficiently. The proposed algorithm can provide many optional choices and the final scheme can be chosen based on the situation. Finally, a practical example is used to illustrate the developed scheme.

Abstract: The chaos particle swarm optimization algorithm was presented to solving optimal power flow. The proposed OPF considers the total cost of generators as the objective functions. To enhance the performance of algorithm, a premature convergence strategy was proposed. The strategy can be divided into two parts. In the first part, a method is introduced to judge premature convergence, while another part provides an advance method to improve the performance of algorithm with searching the solution in total feasible region. The control strategy used to prevent premature convergence will obtain starting values for initial particle before program iterating, so it can provide bitter probability of detecting global optimum solution. The simulation results on standard IEEE 30-bus system minimizing fuel cost of generator show the effectiveness of the chaos particle swarm optimization algorithm, and can obtain a good solution.

Abstract: In this paper, a new system splitting scheme based on the identification of weak connection is proposed. This paper firstly claims that if two nodes in a transmission line are related to two different generator groups or irrelated to any generator group, the transmission line is regarded as weak connection. And matrix R is presented to reflect the relevance between load nodes and generator groups after faults are cleared. The candidate strategy space is composed of these transmission lines of weak connection. Secondly, the procedure of searching the splitting surfaces is listed to illustrate how the splitting scheme works. Finally IEEE 39-bus system is used to verify the feasibility of this splitting scheme.

Abstract: It becomes common practice to reduce a large-scale power grid into a simplified one using transient stability simulator and have it modeled on electromagnetic transients programs. However, the procedure of network reduction may produce negative resistance, which may result in some problems in electromagnetic transient simulation. This paper firstly demonstrates that the negative resistance will probably lead to numerical instability in electromagnetic transient simulation. And then the forming mechanism of the negative resistance during network reduction using Gaussian Elimination is revealed. Several schemes for negative resistance elimination are presented at last.

Abstract: When DC transmission system adopts monopole earth or bipolar imbalance operation mode, the DC grounding electrode will inject large amount of current into the earth, and then disturb the running of the power grid. In view of the influence which is created by DC transmission system in Guangdong power grid, this paper derived the mathematical expressions of the transformer neutral point current after creating a calculation model, and concluded the main influence factors; The subject applied the linear regressing analysis theory to calculate the regression equations of transformers so that the slope of the regressing equation can be used to estimate the influence scope of grounding DC. Finally it concludes that: transformer neutral point current and the power transmitted by DC system has positive correlation; For ±800kV DC Chu Sui, the transformers ,which is more than 80 km away from DC grounding electrode, will no longer be affected; The application of DC suppression devices will affect the neutral point current of the transformers nearby.

Abstract: The mechanism of power system low frequency oscillation was discussed in this paper. The coupling model between turbine governor system of plant and power system was established in MATLAB. The possibility of power system low frequency oscillation induced by unit-grid coupling was researched in detail. The simulation results indicate that power system low frequency oscillation will occur under disturbance, if a high derivative gain is used in PID controllers of hydraulic turbine governing system and partial derivative of turbine power output with respect to head varies with load. As for steam turbine, the PID parameters of governor system have important effect on small-signal stability of power system when the damp of power system is not very strong. The power oscillations caused by disturbance is decreased with the use of PID controller in governing system, whereas power oscillation is increased with the use of PI controller.

Abstract: Based on the object-oriented programming of MATLAB, we developed a software for visualization and manipulation to indicate whether the transformer works in the economic range. This software can show the curve of relationship between efficiency and load rate, automatically calculate the load range of the transformer to achieve the best efficiency according to the load. Based on the user supplied data, it can also calculate the operation efficiency of the transformer, and show in the graphic. This software has the advantages of efficiency, accuracy and visualization.

Abstract: Contactors as low-voltage electrical products are largely used, contact bounce when contactor closing and arc which produces during opening is the main factor influencing a contactor’s life. This paper proposed a new structure that asynchronous modular, N-pole contactors consist of N independent contact systems, achieved each contact individually controlled by closed-loop control. This is a new idea in the field of structural design and control of contactors. This paper designed the structure size of the electromagnetic system, used Simulink software to build the model, studied dynamic characteristics of the contacts, and obtained a new closed-loop control method at last. This new method can effectively eliminate contact bounce when the contact closing and the arc generated when breaking, and increases the service life of the contactor.

Abstract: The Ship Shaft Power Generation System (SSPGS) is widely used in large and medium-sized container ship, and the SSPGS based on brushless doubly-fed generator (BDFG) has the advantages of smaller capacity of the inverter, lower capital operational costs and higher reliability. The proposed vector control method is developed on the power-winding stator flux frame and can be used to control the power winding voltage amplitude and frequency on the standalone mode. The generator model and the control system are developed in Matlab/Simulink. The results show that the control strategy has good dynamic performance when the ship speed and load are changed.

Abstract: In order to solve the inconvenience of line arrangement under bad environment and the maintenance difficulty, a design method of a wireless temperature monitoring system based on ZIGBEE is given. The system uses RemoDAQ-8000 as temperature sensor and control platform, ZIGBEE wireless communication for wireless communication network. Through five groups based on ZIGBEE. The temperature control experiment, obtained the first-hand information, so as to realize the wireless monitoring; at the same time, the system can be in the local area network, using C/S and B/S two ways to control and query. Experiments show that using wire communication, ZIGBEE wireless communication instead of the traditional, can have an important effect in the field of process control