Quantifying Observability in State Estimation

Observability means the aptitude for estimating the system state in its entirety from data currently available. As such, the problem of quantifying this aptitude assumes practical interest. Dealing with observable grids, this paper concentrates on proposing indicators capable of establishing unobservability risks. These indicators are based on measurement criticality analyses (with the aid of Venn diagrams) for a given network configuration. They are obtained in terms of the probability of unobservability, assuming that an event has occurred, such as the unavailability of: a single measurement; one pair of measurements; one k-tuple of measurements; a single metering unit; a single network branch; one pair of network branches. The potential/practical application of the proposed indicators is illustrated by the introduction of metric patterns, capable of reducing the information on unobservability risks to a single quantity. Numerical results obtained with the IEEE 14- and 118-bus test systems exemplify the computation of the proposed indicators.