In this study, the challenging problem of computing the frequency-dependent lumped parameter ladder network model for transformer winding based on impedance frequency response is investigated. It is shown that the existing conventional model is not capable of simulating the non-dominant resonances; rather, this phenomenon can be adequately modelled using extra intersection capacitors. As usual, this large-scale non-linear optimisation problem is addressed using properly lined-up genetic algorithm. To accelerate the success of the estimation, the dimension of the problem and the search space is reduced by using logical and real constraints and equations derived from the transformer geometry and its electromagnetic specifications; if this is not done, the optimisation fails. The test results on a 20/0.4 kV, 1600 kVA transformer indicates that the computed model, which is improved and detailed, is superior to the conventional one in terms of simulating the non-dominant resonances of the transformer winding. Therefore, it is more reliable for the transformer transient behaviour analysis.

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Abstract:Researchers have used various methods to determine the parameters of transformer-equivalent circuits in transient studies. But most of these previous algorithms had difficulty finding the equivalent circuit parameters in a bigger model. This paper presents a new method to extract the inductance matrix of a detailed model for an air core winding for transient studies using frequency-response measurement data. This matrix can be determined with acceptable accuracy by using the proposed method. The biggest advantage of the proposed method is a reduction in the search space, and thus, speedier problemsolving. Simulations showed that the use of the proposed method leads to better behavioural quality of a transformer winding. The simulation results of the previous and proposed methods were compared with the help of a 20/0.4 kV, 1600 kVA transformer. This comparison showed the accuracy and superiority of the proposed method.

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