Static Voltage Stability Index Using Multiple Load Flow Solutions

Abstract

The voltage stability problem, which is caused by the heavy loading of long-distance transmission lines and the insufficient local reactive power supply, has become one of the most important problems to be solved urgently in a modern bulk power system.
Earlier, it was made clear that the voltage instability phenomena of the bulk power system under heavily loaded conditions are closely related to multiple load flow solutions which are caused by the nonlinearity of load flow equations. In addition, the dynamic characteristics of loads of constant power type play an important role for this unstable phenomenon. Since the dynamic load characteristics are not known correctly, it is desired to develop an effective voltage stability index and remedial measures to prevent the voltage collapse taking into account a static structure of multiple load flow solutions.
A new static voltage stability index proposed in this paper indicates the extent to which the current operating point is close to the static voltage stability limit, or the limit of total load demand (active power) of the whole power system from a static viewpoint. The proposed index is defined on the basis of multiple load flow solutions and it physically means the first order approximation of a stability margin of total load demand. It is possible to calculate it on the on-line basis by using operating conditions which are always changing with time.