Research On The Small Disturbance Voltage Stability Of Receiving End In Power Systems

As the expansion of power supply distance, the enlargement of load characteristic of constant power tendency as well as the gradual advancement of electric power market after the electric power plant and network separate, these factors make the voltage stability question for the large electrical network, especially the reactive voltage question for the received system more and more serious, and this influence is more sensitive to the load center of economy developed, population concentration, the energy deficient large-scale city. We take the Beijing electrical network as the example, which is a typical received system, in 2005 summer peak load period, the received electricity proportion of the Beijing area network from the outside grid already has achieved approximately 75%, the serious accident may be happened for the electrical network if any received channel appears the question, therefore we should pay more attention on the weakness of received system for the metropolis. This thesis based on the project of voltage stability analysis of the Beijing electrical network, deeply studies on the small disturbance voltage stability question of the received system, the main content of research as follows:Although, the static analysis method is widely used in actual electric power system, there are many concepts that are unclear or even confused. In the analysis of instability mechanism due to voltage's dropping monotonously,the meaning of operation limit of the static voltage stability is thoroughly discussed in this thesis. Key words and expressions which have comparative high occurrence frequency, such as network maximum power transfer capability, maximum load power point, power flow limit, flex point of P-V curve, singular point of power flow Jacobian Matrix, saddle node bifurcation, and so on, are analyzed, and their interrelations are discussed and demonstrated.In the analysis of static voltage stability, P-V curves arise as an appealing method in practice. However, many scholars believe that when loads are not supposed to be constant power loads, there is no power limit, consequently, the flex point of P-V curves does not correspond to load capability limit or is no longer the critical point of voltage stability. The operation of power flow, taking account of the model of static characteristic of load, is studied deeply in this thesis, and the characteristic of the critical point of stable operation is analyzed; P-V curves under different load index of voltage characteristicαare also analyzed, the physical meanings of load flow limit, load capability limit, load power limit of system, flex point of P-V curves, power flow Jacobian Matrix singular points, and their interrelations are discussed under non-constant power loads, the effects of load characteristic to static voltage stability of power system is studied. The eigenvalue analysis method of small disturbance has been widely applied to power angle stability analysis under the low frequency oscillation in multi-machine system. This thesis mostly studies the application of this method in voltage stability analysis, and determines the key factors at the critical point of instability that affect voltage stability as well as the probable instability mode that system may occur. The effects of dynamic induction motors and air conditioners to voltage stability are studied through small- perturbation voltage stability analysis.In modern power system, Static Var Compensator, as a mature technology, has been widely applied to the load compensation and transmission line compensation. This thesis is key to study the application characteristic of SVC in power grid, and proposes an improved U-I characteristic according to the demerits of application of conventional U-I characteristic in actual system.The network topology is the foundation of secure and stable operation of electric power system, this thesis mainly studies the inevitability of the appearance of electromagnetic loop network and its bad effects to stability,and the tendency of the operation mode of voltage-grading & district-dividing in the development of metropolis grid. The rational optimization method of network topology and power supply principle of voltage-grading & district-dividing are discussed by analyzing Beijing grid in detail.