Static Voltage Stability Region In Cut-set Power Space Of Power System

In recent years voltage instability has aroused several blackouts. It is mainly dueto long-distance transmission lines and heavy loads, loss of electrical source at sinkwith concentrative load or load increasing quickly at sink. In addition with theworld-wide development of electric market, the systems are more often operating neartheir stability limits and there is large probability of voltage instability. In order toreduce or even avoid blackouts led by voltage instability, researchers have done a lotof work. Although the 'point-wise' approach has been widely used in the past, it needsto check the security of operation condition for every contingency in contingency set,which is time-consuming. Hence gradually we pay more attention to the"region-wise" approach. It will not only provide systematic and global information foroperators but also avoid enormous complicated computations online. Because voltageinstability is mainly relative to saddle-node bifurcation, static voltage stability region(SVSR) boundary is our focus in the thesis. Since SVSR in injection space is with strong nonlinearity and extremely largedimension, it is difficult to describe it through a simple analytical expression in thewhole space. Moreover operators have been monitoring stability constraints throughpower flows on critical branches for long time. Therefore displaying SVSR in cut-setspace is our choice. It not only offers an efficient dimension reduction method butalso is convenient to monitor power systems voltage stability margin. As we all know, voltage instability comes of essentially a local part of powersystem. And usually weak nodes also centralize in a certain part of system, which isconvenient for us to determine the cut-set. We can choose right critical cut-set(s) toseparate the system into two parts i.e. the region(s) with weak nodes and the rest ofthe power system. By monitoring the power flows on the branches in the criticalcut-set(s) we can get more useful information about power system voltage stability.Studies on various power systems with different operating conditions haveshowed that SVSR boundary in cut-set complex power space can be approximated byone or several hyper-planes with satisfactory accuracy. All operating points that canguarantee system voltage stability are within the region restricted by the hyper-planesin cut-set complex power spaces. Points that lead to static voltage instability areexcluded from the region. The hyper-plane which describes the boundary of SVSR incut-set power space makes it very easy to analyze, assess and optimize power system.Finally based on static voltage stability region in cut-set space theory mentionedabove, we have put forward the framework of power system stability region real timeanalysis package.