Observability and bad data identification when using ampere measurements in state estimation

The authors address the problems encountered when using ampere magnitude measurements to extend the observability of a power system. The use of ampere magnitude measurements is shown to lead to multiple solutions for certain network topologies and measurement configurations. The issues of bad data identification and observability are studied when line current measurements are part of the measurement set. Phasor diagrams are used to demonstrate the critical topologies for which multiple solutions are inevitable. Cases where the systems have unique observable states, are also presented. Numerical examples supporting the conclusions reached by the phasor diagrams are also given