Advanced Materials Research Vols. 1008-1009

Abstract: Lack of dynamic reactive power compensation result in power system transient voltage instability. To improve the transient voltage stability, an optimization strategy for setting the excitation system difference coefficient of the generator is presented in this paper. The concept of the excitation system difference coefficient is introduced. Then the impacts of difference coefficients of generator excitation system on generator stability are analyzed and adjustment range is proposed. The calculation results of Guangdong province system show that the transient voltage stability level is enhanced effectively after optimizing the excitation system difference coefficient.

Abstract: Aiming at the insufficiency of Equivalent Resistance Method for a low-voltage distribution line loss calculation, this article has been improved. Then this paper presents the method of using three-phase quantity of electricity to calculate three-phase current, it can calculate the three-phase unbalanced line loss without current date and facilitate the application of Three-phase Unbalanced Method. It develops our own program based on Visio to calculate low-voltage distribution line loss. The results showed: Improved Equivalent Resistance Method improves the accuracy; in the three-phase unbalanced the method of using three-phase quantity of electricity to calculate three-phase current is more easily modified and more practical value.

Abstract: A reactive power optimization method based on interval arithmetic is presented to solve the uncertainty of the output of distributed generation (DG) and the effects of load fluctuation. The concept of interval number and interval arithmetic is introduced to model the interval power flow of distribution system, which is iterated by using the Krawczyk-Moore operator. The objective function is to minimize the interval midpoint value of system’s power loss, with taking the interval voltage constraints into consideration for the interval reactive power optimization model. A modified IEEE 14-bus system is used to validate the proposed model and its Particle Swarm Optimization (PSO) algorithm. The simulation results show that the proposed method is effective.

Abstract: In this paper advantages and disadvantages of island mode generator operation are considered. There are significant difficulties when it is necessary to provide operational stability and power quality in the system isolated from utility electric power system (EPS). Operation of the isolated system (referred to as “island”) is possible but only in case special technical requirements are met and protection and automation devices are adjusted properly. The absence of technical requirements in Russia led to the necessity of foreign guides and instructions investigation. The analysis of the possibility of foreign experience implementation in the field of autonomously operating systems in Russian power systems is conducted.

Abstract: When making an updating strategy for aging transformer, both the condition of transformer and the risk effect of its aging on power system needed to be taken into account. Based on the model of aging transformer failure rate by insulation age, a comparative analysis of the risk caused by aging failure within the planned period and the profit from delaying updating was undertaken; then the optimal timing strategy to retire transformer was developed on the basis of a balance between risk and profit. The analysis of examples indicated that the proposed process of the strategy could be applied to plan the retiring time according to both the actual condition of transformer and the impact of the risk to the grid, thus making full use of transformer and allowing the power company to get the maximum benefit.

Abstract: Using the user-defined model (UDM) provided by the power system analysis software package ( PSASP), This paper constructs traction power supply system model. The correctness of interface between user-defined model and PSASP is verified by independent dynamic characteristic program. It offers a new way of available practical model applying to power system simulation and research on the influence of traction loads to power system.

Abstract: According to the resonance mechanism, power system forced low frequency oscillations can be aroused by power disturbance of prime mover. Therefore, the causes of turbine power disturbance were analyzed. The coupling model between turbine-governing system and power system was established in MATLAB. The possibility of governing system disturbance inducing the variation of control valve position and turbine power was researched in detail. The simulation results indicate that high level variation of control valve can be induced by the rotor speed deviation disturbance, if the speed-droop ratio of turbine-governing system is too small in local running position; power system low frequency oscillations of resonance mechanism might be caused by the disturbance of rotor speed deviation, when it’s frequency is close to power system natural oscillations frequency. Oil-pressure pulsation is easily happened in hydraulic governing system. If the frequency of oil-pressure pulsation is near to power system natural oscillations frequency, power system low frequency oscillations of resonance mechanism can be induced.

Abstract: The root-locus technique in automatic control theory was applied to study the effect of power-frequency control system parameter on power system dynamic stability. The one machine infinite bus system model with power-frequency control system was established and the corresponding root-locus equation was deduced. The parameter stability region of power-frequency control system to ensure the power system dynamic stability was achieved through drawing root locus graphs of different system running modes. If the gain value of power-frequency control system is higher than the critical value, power system low frequency oscillation will occur. The above conclusion was validated by time domain simulation results.

Abstract: Commutation failure theory in HVDC transmission system is proposed and its reason is analyzed. Anomalous commutation failure phenomenon related to concurrent CF or successive CF in multi-infeed HVDC transmission system is presented. Six kinds of ac system strength are used in simulating the anomalous commutation failure, and the results show that this phenomenon is more and more serious at first as the system strength increases, and then become less serious as the strength becomes stronger. The reason of anomalous CF is found when analyzing phase A voltage with Fourier analysis in one period after fault, that is because of the major dc components and the low-order harmonics existing in voltage waves.

Abstract: As the interconnected power grid becomes increasingly complicated and external environment is changeable, the difficulty of power grid dispatching is increased. Thus, the forecasting track of power grid operation state based on risk assessment can be used to predict the operation trend of power grid state and provide a reference for real-time operation state and guide power grid dispatching. Based on overall power grid risk index system, the operation trend for a period in the future is predicted to diagnose the state of power grid by using fuzzy inference, fuzzy clustering and AHP. In this paper, Ningxia Power Grid is simulated as an example to describe the forecasting track of its operation state in the next 100 minutes. The results present that the track can be used to analyze the causes, which increase or decrease the risk degree of overall power grid, then major leading factors are specifically analyzed. And the track can be also used as guidance for dispatching operators to take measures. Furthermore, the track is proved to be reasonable.