SUMMARY This paper proposes an index, called Undetectability Index (UI), to classify the measurements according to their characteristics of not reflecting their errors into the residuals of the weighted least squares state estimator (WLS) from a geometric analysis of this estimator. Gross errors in measurements with high UIs are very difficult to be detected by methods based on residual analysis, because the errors in those measurements are “masked”, i.e. they are not reflected in their residuals. The paper also presents a very simple algorithm to compute the UI of all available measurements in a metering system. This algorithm is very simple and uses routines already available in the existing WLS Estimator software. Two UI applications are investigated (i) to design more reliable metering systems for bad data processing, i.e. metering systems formed by measurements with UI lower than a pre‐specified value and (ii) to estimate the measurement errors. Several simulation results (with IEEE‐14 and 30 bus systems) have validated the propositions. Copyright © 2013 John Wiley & Sons, Ltd.

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In this paper, a geometrical based approach is used to define the undetectability index (UI) that gives the distance of a measurement from the range of the jacobian matrix. The higher the value of this index the closer this measurement will be to the range of that matrix; the error in measurements with high UI is not reflected in their residues. A critical measurement has infinite UI, belongs to the range of the Jacobian matrix, and its error is totally masked. Using the UI, it is shown measurements not classified as leverage points, and having large masked gross errors in the state estimation process. As example to illustrate the way that UI index works, a two bus power system will be used; to test the index efficiency in identifying the measurements that have the gross errors masked by the state estimation process the IEEE-14 bus system will be used.