Zbornik Radova: Elektrotehnički Institut "Nikola Tesla" (Jan 2014)
Method for indirect determination of turbogenerator parameters under operating condition
Abstract
A new method for determining the operational saturated synchronous reactances (Xd,sat and Xq,sat) and the rotor angle (δ), under the normal operating condition, was presented in this paper. At the power station the voltages (U), active (P) and reactive power (Q) are recorded. It is necessary to fit the no load generator saturation curve with appropriate analytical function. The output results obtained by corresponding calculations includes values of Xd,sat, Xq,sat and power angle δ, that reflect the level of generator saturation. Procedure by proposed method is following: - first the synchronous reactance Xd,sat value is determined by no load saturation curve using the voltage behind from leakage reactance (Xℓ) value or the voltage behind Potier reactance (XP), then - quadrature-axis reactance (Xq,sat) and load angle (δ) are determined by corresponding per-unit equations that connects generator parameters and characteristics d-axis and q-axis. The proposed method was verified using reported case study of 500 MW generator [1], where are used, besides U, P, Q and E(if) curve, the recorded rotor load angle value δ at rated load. Obtained results by new method differ up to 1-2 % from results in [1] obtained by more complex procedure, i.e. (i) by method with direct measurement of power angle δ, and corresponding Xd,sat, Xq,sat values determined by indirect method, i.e. on the base by corresponding per-unit equations, and (ii) by the finite-element method, when Xd,sat, Xq,sat and power angle (δ) values are calculated. Obtained results proved that synchronous reactance Xd,sat values can be as much as 30% below unsaturated vales (Xd,unsat), and measured values Xq,sat can be up to 20 % below Xd,sat values. Based on obtained results the proposed method is verified for indirect measurement of synchronous turbine-generator parameters and characteristics under load condition.
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