Probabilistic Assessment of Transient Stability

Fixed, deterministic criteria have traditionally been used to conduct transient stability studies in power utilities in both planning and operation functions. Normally, a three phase fault is assumed to occur very close to generator terminals, and applied to a worst case background condition. In reality, however, the main factors affecting transient stability of a power system are random events. These include type and location of fault, fault clearing phenomena and
initial operating conditions.

Probabilistic methods have been investigated to understand whether they could offer useful information not usually apparent with the use of deterministic methods. One such information is the calculation of risk-based stability indices that could relate the reinforcements (investments) being proposed to the level of reliability.

A methodology has been developed for performing a probabilistic assessment of transient stability. A representative network of a portion of the National Electricity Transmission System (NETS) has been used to demonstrate main principles. Probabilistic modelling of generation, demand, fault clearing time and fault location has been demonstrated. A number of risk indices have been developed which include fault type indices, line indices and system indices.

In general, this study has demonstrated the availability of tools and a consistent
methodology to allow the probabilistic assessment of transient stability studies.