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This paper deals with the problem of observability analysis and measurement placement in generalized state estimation, where substations are modeled at the physical-level (bus-section/switching-device model) by explicit representation of circuit breakers. The conventional state estimator is extended by incorporating the active and reactive power flows through circuit breakers as state variables. The generalized measurement model is transformed to a conventional node frame of reference formulation. Any circuit breaker (flow measured or not) is substituted by two ficticious nodes and branches, the two pairs of the corresponding voltage angles and magnitudes, and additional pseudo measurements. A very efficient numerical method is proposed for observability testing and identification of observable islands. When the network is unobservable multiple measurement placement is accomplished in a noniterative manner. Results from a test system are presented.