Illustration of an analytical method for selecting signals and locations for power system modal-estimators

For the purposes of planning it is necessary to determine, in a transmission system, which are the best signals for estimating the parameters of the electromechanical modes, given the characteristics of the modal estimator. Closed-form mathematical expressions are derived in another paper for the Power Spectral Densities (PSDs) of the candidate signals at selected locations due to random fluctuations in the system loads. The expressions for the PDSs comprise the separate identifiable contributions of every system mode to the PSD of the signal within a specified frequency band. Also, an expression has been derived which provides a measure of the contribution of the mode to the PSD. The measure is called the Modal Power Contribution which reveals the suitability of a given signal for modal estimation, especially when modes are closely-spaced. The paper demonstrates the practical application of the theoretical analysis.