Citation: ˙ Zurek, S.; Przygrodzki, M. The Use of a Regulating Transformer for Shaping Power Flow in the Power System. Energies 2023, 16, 1548. https://doi.org/10.3390/en16031548 Academic Editors: Cheng-I Chen and Yu-Jen Liu Received: 14 December 2022 Revised: 16 January 2023 Accepted: 19 January 2023 Published: 3 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article The Use of a Regulating Transformer for Shaping Power Flow in the Power System Szymon ˙ Zurek 1, * and Maksymilian Przygrodzki 1,2 1 Department of Power System and Control, Faculty of Electrical Engineering, Silesian University of Technology, 44-100 Gliwice, Poland 2 PSE Innowacje Sp. z o.o., Al. Jerozolimskie 132, 02-305 Warsaw, Poland * Correspondence: szymon.zurek@polsl.pl Abstract: The current situation in world energy requires a new approach to the control of the power flow in power systems. On the one hand, regulations within the EU require the transition to renewable energy. On the other hand, there are no conventional sources available. Thus, there is a need to use known control tools in non-standard applications. One such example is the use of a regulating transformer inside the power grid to use it to shape the power flow in the system. This article presents a proposal of an algorithm for determining new locations for regulating transformers from the point of view of active power control. By analyzing the parameters of the power grid, it is possible to determine which branch of the grid is the most suitable for installing a regulating transformer in it. The use of a regulating transformer inside the grid improves the transmission capabilities of the national power system. Keywords: regulating transformer; phase-shifting transformer; power system; power flow regulation; regulatory tools in the power system 1. Introduction 1.1. Planned and Unplanned Power Flows The transformations in the power sector that have taken place in recent years have resulted in significant changes in the functioning of national power systems and cross- border connections in Central Europe. The reasons behind this lie in the liberalization of electricity markets and the large-scale integration of renewable sources. One of the main effects of these changes is the increase in unplanned compensatory flows of active power between interconnected systems (also known as loop flows). These flows primarily reduce the operational security of interconnected national power systems, reduce the transmission capacity of cross-border connections made available to electricity market participants, and increase transmission losses. All of this worsens the economics of UCTE operation. Unplanned flows adversely affect not only the entire interconnected UCTE system but also national power systems (NPS). Specifically, NPSs not only experience an increase in transmission losses but above all they experience significant overloads on network elements such as transmission lines and power transformers. As a result, there are also large voltage drops and, consequently, an increase in reactive power flows in power systems in order to align the voltage levels. The increasing number of cases in which the safe operation conditions of an NPS in Europe is not maintained increases the risk of accidents with a wide scope. Hence, it is increasingly important for power system operators (TSO) (including the Polish TSO [1]) to control active power flows. One method of power flow regulation is the use of phase-shifting transformers (PSTs). These are special transformers installed in power grids (most often on cross-border lines) which adjust the load angle of the network. This angle is the difference of the nodal voltage Energies 2023, 16, 1548. https://doi.org/10.3390/en16031548 https://www.mdpi.com/journal/energies