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The state estimator solution quality when it is used to monitor external facilities depends on the accuracy of their models. The external network models could affect the quality of state estimator solutions by:

1 Propagation of errors into the internal model solution from the external model solution. This applies to one‐pass state estimators if the external network model solution is mainly based on forecasted and/or pseudo‐measurements rather than telemetered data. The external network model equivalencing methods could also cause errors to propagate. For two‐pass state estimator, there could be boundary problems (between the internal/observable solution and the external/unobservable solution) that could cause the total network solution to not converge.

2 Measurement density in the external system. Many buses in external models are measurement unobservable. The low values for the external‐status‐point‐to‐external‐bus ratios for many respondents (i.e. less than one status point per bus) indicate that many external buses do not have telemetered breaker/switch information, which implies a bus‐branch‐type external model (i.e. a planning model) for many buses.

3 Convergence issues related to external models and/or telemetry data for external model. Measurements for the external network model usually originate from data links. As a result, data availability depends on data link availability.

4 The impact of interchange transactions, especially for the external portion of the model, could influence the state estimator solution.

5 Adding detail or expanding the external network model could affect the throughput (execution time) of the state estimator application.

External network model improvements are expected to enhance the accuracy of the results.

 Adding breaker/switch detail to the external and internal models

 Adding extensive telemetry to the external and internal models

 Adding lower‐voltage detail to the external and internal models

 Adding one or more control areas to the external model

 Creating a new external model