Long Term Marginal Costs of Reliability and Inter-zone Reliability Transfers In Power Systems

Reliability at different nodes of a power system is evaluated through a method that performs transportation of reliability indexes through the branches of a network. This approach is intended to consider that in a real system reliability level is not uniform. Nodal reliability is obtained by composition of generation and transmission power-reliability matrices. The topological problem is solved by using as many radial sub-networks as necessary in order to consider the presence of loops in the grid and then apply a superposition procedure. Possibility of transmission congestion conditions and their effects are considered in the solutions since transmission reliability matrix includes contingencies with elements out of service. Reliability values at different zones permit calculation of reliability transfers and their sensitivity to introduction of additional generating units or transmission lines. This approach permits the estimation of long term marginal cost of reliability at a nodal level, which can be used as an additional criterion for energy contracting and thus opening up an element for equipment capacity payment. Simulation of a sample system allows the assessment of nodal reliability indexes, their variation throughout the system, reliability transfers among system zones and values of reliability long term marginal cost. Applications of these properties to the energy market are discussed