Abstract
Measurements obtained in transformer tests are routinely used for computing associated steady-state model parameters, which can then be used for load flow simulation and other modeling applications. The short circuit and open circuit tests are most commonly performed with this purpose, allowing estimation of series and parallel branch transformer parameters. In this study, an extended model is proposed which does not employ the usually assumed cantilever circuit approximation and explicitly accounts for transformer connection resistance. An estimation of the proposed model parameters is enabled by usage of additional measurements yielded by the direct current (DC) resistance test. The proposed approach is validated by means of an experiment carried out on a real distribution power transformer, whose results demonstrate that the proposed model and parameter computation approach effectively decompose total transformer resistance into winding and contact components. Furthermore, the numerical results show that contact resistance is not negligible especially for low voltage windings, which reinforces the usefulness of the proposed model in providing detailed modeling of transformer resistances.
Highlights
Steady-state transformer models are frequently employed in power system load flow simulations and other applications in which component modeling can be carried out in quasi-stationary regime [1,2,3,4,5,6,7,8,9]
Such test is carried out in practice to assess winding integrity [15] and enable computations with respect to the heating of transformer windings at full-load operation [16]. This consideration and transformer testing practice lead to three observations: (a) the direct current (DC) resistance test is frequently performed in conjunction with open circuit and short circuit tests; (b) it provides additional information regarding r1 and r2 when compared to the latter tests; and (c) such measurement data can be used for adding detail to the standard model
Taking such points as motivation, this study proposes a transformer steady-state model which: (a) does not use the cantilever and r1 ≈ a2 r2 approximations; (b) includes a parameter that corresponds to connection resistance, which becomes separated from the winding resistance; and (c) can be fully determined via measurement results of the DC
Summary
Steady-state transformer models are frequently employed in power system load flow simulations and other applications in which component modeling can be carried out in quasi-stationary regime [1,2,3,4,5,6,7,8,9]. The determination of standard model parameters does not require measurements obtained in the DC resistance test Such test is carried out in practice to assess winding integrity [15] and enable computations with respect to the heating of transformer windings at full-load operation [16]. This consideration and transformer testing practice lead to three observations: (a) the DC resistance test is frequently performed in conjunction with open circuit and short circuit tests; (b) it provides additional information regarding r1 and r2 when compared to the latter tests; and (c) such measurement data can be used for adding detail to the standard model. Since this is usually not feasible in practice (i.e., each winding only has one accessible terminal), an alternative approach is proposed, namely assuming the ∆ connection resistance as being equal to a fraction of the winding resistance and, subsequently, optimizing such a fraction
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