This paper describes the simulation of currents in the synchronous condenser windings at turn-to-turn fault in the rotor winding, which is used in electrical power systems for compensation of reactive power and maintain the normal voltage level in the areas of concentration of the consumer loads. To this end, we have developed a mathematical equation model with the method of contour currents for line-to-line voltages, which allows simulating a turn-to-turn fault in the rotor winding of synchronous condenser in a stationary mode. To implement this model, mathematical expressions were proposed to determine active resistances and inductance of winding elements of a mathematical model, in which the active resistances and the data for the calculation of inductances of stator and rotor windings are determined experimentally. The offer a description of the experimental unit and equipment used in the experiments, as well as results of current simulation and measurement in the turn-to-turn mode in the stationary mode. Experiments shows that the proposed mathematical model allows determining currents in the rotor windings by closing its turns with an accuracy of 5-10%.

In this work, a mathematical model of a three-phase nonlinear transformer is suggested. The model enables simulating the transformer operation with allowance for its nonlinearity and covers needs of the relay protection. Our model has been developed on the basis of a mathematical model with phase coordinates, where differential equations are composed by the Kirchhoff’s phase-voltage law. Based on this model, we first compose a mathematical model for simulating steady-state operation modes of a transformer, taking into account the asymmetry and nonlinearity of its ferromagnetic core. In this model, the initial values of inductances and mutual inductances of loops are determined from the main phase inductance calculated by the experimentally found no-load current, and their current values are determined from the currents in windings and the magnetic fluxes in legs of the transformer core. The magnetic fluxes are calculated by the nodal-pair method. This improved mathematical model is verified through a comparison between the calculated harmonic components of the phase currents and the experimental results. The harmonic components are calculated with the use of Fourier expansion of the calculated phase currents. Their experimental values are determined with a spectrum analyzer. The calculated and experimental harmonic components of the currents of phase A during no-load and rated-load operation of the transformer are tabulated. The comparison of these results shows that the mathematical model of a three-phase transformer we suggest makes it possible to simulate currents in transformer windings under steady-state operation modes with accuracy acceptable for relay protection.

In this paper, results of comparison of the ground-short-circuit currents in electrical machines obtained using a new simplified calculation method and some circuit simulation systems, as well as by experiments, are reported.

A mathematical model of a compound single-phase transformer that allowing currents to be determined in its winding during a coil short circuit for various operating modes for the needs of relay protection is presented. The results of the simulation and the experimental study of currents in the main transformer are presented.

A method is developed for determining the resistance of a high-current system in a furnace, and a model is proposed for a single-phase furnace transformer