Development of a nonlinear model of a three-phase transformer to study the effect of asymmetry of the magnetic system on the operation of the device in arbitrary modes

Abstract

Currently, when designing power transformers in order to take into account the influence of the asymmetry of the magnetic system on the operation of the device, especially in transition modes, engineering analysis packages based on field models are increasingly being used. However, such models are slow. At the same time, dynamic transformer models based on the magnetic circuit model are not inferior in accuracy to field models. Existing chain models of a three-phase transformer either do not take into account the asymmetry of the magnetic system or poorly integrate with simulation packages. The purpose of this article is to develop a dynamic model of a three-phase transformer which would allow considering the design features at the design stage, in particular, the asymmetry of the magnetic system and the influence of these features on arbitrary modes of the device operation. A contour current method was used to calculate a non-linear magnetic circuit of a three-rod transformer, and a single-step method based on a modified 2nd order Rosenbrock formula was used to calculate the electrical circuit. A nonlinear dynamic model of a three-phase three-core transformer based on the use of controlled current sources and EMF has been developed. This model is able to integrate with simulation packages including MatLab Simulink SimPowerSystem. The model allows taking into account the influence of the asymmetry of the magnetic system on the transformer operation in various operating modes including emergency and asymmetric ones. The novelty of the developed model can be seen in the approach to constructing a nonlinear matrix of magnetic resistances without explicitly using inductance matrices, which increases the accuracy and stability of the model considering the asymmetry of the magnetic system. The curves of transients in the characteristic operating modes of the transformer are given. The developed models can be used in the design of power transformers, including specific ones. They enable to increase the accuracy of the verification calculation and bring it to the level of simulation modelling. These models can also be applied for constructing digital twins of power transformers taking into account the influence of the design features of transformer equipment on the operation of power grids.