FEATURES OF DETERMINING OF THE PARAMETERS OF POWER TRANSFORMERS BY CIRCUIT- FIELD MODELING METHOD
Purpose of the work. The research of a new highly effective approach for determining power transformer parameters in no-load and short circuit modes, based on the scheme-field modeling of electromagnetic processes which allowing to consider design features, influence of conductor nonlinear properties and ferromagnetic materials, possesses high accuracy and simplicity of numerical realization was developed. Research methods. Mathematical modeling of electromagnetic fields of three-phase transformers with flat magnetic systems in no-load and short-circuit modes by methods of theory electromagnetic fields, finite elements, the theory of electrical circuits; generalization of modeling data by linear and polynomial regression methods. The obtained results. Scheme-field model of electromagnetic processes in power transformer for no-load and short circuit mode are developed, which allowing to consider the influence of design features in the active part, also non- linearity of conductor properties and magnetic materials. It’s established that in no-load mode magnetic flux is localized in the rods of the magnetic system, and in short-circuit mode it is displaced in the windings region and main dispersion channels. The design features of flat three-phase magnetic system causes uneven distribution of magnetic fluxes lengthways rods and yokes by symmetry of the phase magnetization currents. Therefore, the largest values of magnetic flux density in no-load mode are characteristic for B phase rod, and their effective values are higher by 15-18% than the analogous values in the rods A and C phases. In experimental short circuit mode, magnetic flux density values are two orders lower in comparison with no-load mode, and its distribution is symmetric for all phases of transformer active part. A highly effective method for determining power transformer parameters in no-load and short circuit modes, which is based on the scheme-field modeling of electromagnetic processes, is researched. Approbation of a new technique for transformers second and third dimensions showed the simplicity of numerical implementation and high accuracy, due to design features and influence of conductor nonlinear properties and ferromagnetic materials. Thanks to this approach is provided the decreasing an error during parameters determination for no-load mode by 12-16% and short circuit mode by 5-8% in comparison with well-known method. The method of parameters correction for various stages of the load control device is researched. This method uses linear and parabolic regression equations, which generalize the standardized no-load and short circuit characteristics for various transformers series. This significantly reduces the time spent at the stages of production design preparation, and significantly increases calculation accuracy of no-load and short circuit parameters. The relative error of the correction parameters method for no-load mode does not exceed 2.82%, and for the short-circuit mode it’s 0.7%. Scientific novelty. A new effective approach for determining power transformer parameters in no-load and short circuit modes is researched and implemented. The approach is based on the scheme-field modeling of electromagnetic processes in the power transformer and subsequent correction by the linear and polynomial regression methods of the standardized no-load and short circuit characteristics with taking into account the set positions of the load control device. This approach has high accuracy and efficiency, simplicity of numerical realization, which allows take into account the influence of design parameters, nonlinearity of electrophysical and magnetic properties of materials, and can be used for transformers of various series. Practical significance. Application of the proposed approach for determining transformer parameters based on the methods of scheme-field simulation and standardization makes it possible to reduce the error of calculating of no-load and short-circuit parameters by 12-16% and 5-8%, respectively in comparison with wellknown engineering methods.