--The adoption of the best available estimate for the stator Leakage reactance is the first step in several equivalent circuit of synchronous machine parameter estimation. However, there is no specific test for its direct measurement. This paper presents a simple and riskless procedure to estimate the Leakage reactance using the information obtained from the Constant Excitation Test. The method theory is described and is applied to several machines from laboratory to hydro power plants. In the absence of absolute values of the Leakage reactance, the estimates are compared to the Potier and sub-transient reactances.Index Terms--Synchronous machines, leakage reactance, parameter estimation. I. NOMENCLATURE E Induced voltage (pu) ILoad current (pu) Quadrature axis synchronous reactance (pu) X l Leakage reactance (pu) Power angle (rad) Power-factor angle (rad) II. INTRODUCTIONHE ARMATURE leakage may be defined as the reactance due to the difference between the total flux produced by an armature current and the flux in the airgap produced by the same armature current. There are a number of components of stator leakage. Each component represents flux paths that do not cross the airgap linking into the rotor.The leakage inductance, or its referred reactance, is the summation of the most pronounced components, commonly referred to as slot, zigzag, belt, skew and end-winding leakage paths, and are well described in [1].The determination of the equivalent circuit parameters of a synchronous machine is strongly dependent of the leakage reactance value; otherwise, an infinity number of circuits could be obtained to represent stator quantities. In fact, no matter which value of leakage reactance is adopted, with consequent variation of the equivalent circuit parameters, that the traditional parameters values will always be preserved. This issue was early pointed in [5] and formally treated in [6][7].Therefore, the great majority of the machine modeling techniques starts with the adoption of the best available estimate for the stator leakage reactance which, in general, is considered as a given or assumed value [2][3][4]. This value is of utmost importance for the machine operation prediction, in both steady and transient states. Though, inappropriate specification of the leakage reactance also implies severe consequences on the saturation evaluation as the mutual reactances will vary accordingly [8].For more than a century, the determination of the leakage reactance have fascinating researchers who work with synchronous machines modeling and parameters determination. This because the leakage reactance is neither easy to calculate nor a direct measurable quantity on the assembled machines. Therefore, many methods and tests for the leakage reactance estimation have been proposed along the years.The Potier reactance has been largely employed as a substitute of the armature leakage reactance. It is obtained from the Potier triangle constructed with information from the open circuit, short circuit, and zero power factor ...

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This paper introduces the constant excitation test to be applied in synchronous machines. The results obtained from this test allow the determination of the quadrature axis synchronous reactance of the salient pole synchronous machines. Despite standard present methods for its determination, the proposed method is suitable for large installed machines. The method basis is described and it is applied to several existent hydrogenerators. The calculated quadrature axis synchronous reactances are compared with the values supplied by the manufacturers, resulting in very good agreement. The appendix shows the quadrature axis location from the previous calculations results to obtain transient parameters from load rejection test.

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