Methodologies and Tools for Electric Power System Reliability Assessment on HL I and HL II Levels

By J Paska

Even, or may be particularly, in the time of disintegration, deregulation and competition in a power system, its reliability is one of the most important criteria which must be taken into consideration during planning and operation phases of its life. Historically, the power system reliability has been assessed using deterministic criteria, techniques and indices. Nowadays it is assessed using probabilistic criteria, techniques and indices as well as applying complex mathematical models and sophisticated computer tools for their realization.

The reliability of subsystems, constituting the power system, i.e. generation, transmission, distribution, can be analyzed separately. So, the reliability of the fulfillment of single function: generation, transmission, distribution and supply to the particular customers are considered. Three hierarchical levels can be also distinguished in the system:

• first level (HL I) containing the equipment and units generating electricity;
• second level (HL II) containing both the units and equipment for generation and transmission of electricity;
• third level (HL III) containing whole system, including distribution.

In this paper the approaches, models and tools to the electric power system reliability assessment on the first two hierarchical levels are described and assessed, with special attention to: GRA (Generating Reliability Assessment) computer program for generation adequacy evaluation, and TRELSS (Transmission Reliability Evaluation of Large Scale Systems) computer program for composite (generation and transmission) system reliability evaluation.