The aim of the work is to study the effect the variation of the phase-shifting transformer (PST) reactance has on the accuracy of calculating its control angle and the electrical network operating parameters obtained as a result of this control. The operating parameters, in particular, active power flows in the electrical circuit branches, are controlled by changing the PST angle; however, in view of the PST design features, this control entails a change of its reactance. Depending on the design features of different PST models and the control angle value, the PST reactance may be constant or vary in a significant range. In connection with a growing use of PSTs in industrially developed countries and with the fact that the first samples of this equipment have emerged in the CIS countries, including Russia, an increased attention is paid to this topic in a number of domestic and foreign publications. In particular, matters concerned with the stability of electric operation modes are considered in view of the fact that the PST reactance depends on its control angle, and the effect this dependence has on the operating parameters is estimated. The necessity of taking into account the varying PST reactance in calculating its control angle for controlling active power flows is considered for different cases. Forced redistribution of active power flows in the closed loops of an electrical network by means of a PST can be used to reduce active power losses and to maintain the required loading of the power lines for various reasons, for example, for commercial purposes or in the case of transit power flows between different countries. In view of the complexity of calculations, constant values of the PST reactance are usually assumed, but this approach is valid not for all types of PST designs. In the majority of PSTs, their reactance varies with increasing the control angle. Therefore, calculations carried out without taking this feature into account may yield a fortiori incorrect correspondence between the control angle and the transformer reactance value. In turn, an error will be introduced in the accuracy of the PST control angle calculations, as well as in the calculations of the operating parameters that should be obtained from the control action.
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