对中长期电压失稳机理的定性探讨

为理解中长期电压失稳现象的本质,采用小扰动分析法在系统特性曲线上展示静态特性不同的具体负荷的静态电压稳定域的确定过程,解释了失稳过程中系统电压稳定于低水平的现象,指出不同负荷在系统特性曲线下半支的稳定情况由负荷的静态特性所决定;在此基础上还讨论了目前两类截然不同的中长期电压失稳现象的机理解释,即无功功率和有功功率不平衡解释,指出这两种机理之间存在着紧密的联系和统一之处。

Conceptual Analysis on the Mechanisms of Mid and Longer-term Voltage Instability

Mid and longer-term voltage instability are usually caused by the continuing increase of the load, and is characterized by a period when the voltage drop down quite slowly. In this paper, the small disturbance method is used on the study of how the static voltage stability region concerning different load characteristics that can be fixed on the system characteristic curve and the phenomenon of the power system operating at the abnormally low voltage during the times of mid and longer-term voltage instability is studied. Although the system inherent steady-state voltage stable region is restricted in the upper-side of P-V curves. The systems can stably operate at abnormally low voltage(under-side of P-V curves) during the period of slow voltage decay .The analysis shows, when power system operate at the under-side of the system characteristic curve, the load characteristic has important influence to the system static-state voltage stability. Whether certain kind of load can operate at the lower part of the system characteristic curve depends on its static character, and the voltage stable region changes along with the load characteristic. The mechanism of the long term voltage instability will be discussed also. Now there are two kinds of mechanism of voltage instability, the reactive power imbalance mechanism and the active power imbalance mechanism. The former one considers the reactive power imbalance the cause of the voltage instability while the latter one considers the active power imbalance the cause of the voltage instability. The paper discusses the relations between these two kinds of mechanisms and points out that they should not be treated separately. The static mechanism (the reactive power imbalance mechanism) and the dynamic one (loads and network interaction mechanism) explain the phenomenon from different point of views, and there exist close links between two of them. Integrating these two analysis methods can help to understand the essence of the phenomenon more clearly.