Load modeling for voltage stability studies

Voltage stability continues to be a limiting phenomenon in many power systems world-wide. When combined with a continual growth in load, the lack of sufficient and optimally located generation together with the failure to build new transmission facilities has lead many systems to be vulnerable to situations of uncontrollable system voltages. In its most severe form, voltage instability can result in localized or even cascading system blackouts. To deal with this serious issue, many utilities have mandated the study of voltage stability as a normal component in system planning and operation. While acceptable methods of voltage stability analysis have emerged in recent years, and comprehensive tools have been developed, the issue of load modeling remains a challenge. It can be argued that the details of load modeling are, because of the nature of the phenomena, more critical for voltage stability than for other forms of stability, and this has perhaps been partially responsible for the lack of widely acceptable load modeling practices. This paper discusses some of the factors that make load modeling for voltage stability a challenge and provides insight into key issues which must be considered when performing practical studies.