Development of the 110 kV electrical grid scheme of PrJSC «Lvivoblenergo» with the new substation «Pohirtsi-1» and analysis of steady-state operation conditions
Students Name: Metlushko Mariia Ihorivna
Qualification Level: magister
Speciality: Electrical Energetics, Electrical Engineering and Electromechanics
Institute: Institute of Power Engineering and Control Systems
Mode of Study: full
Academic Year: 2025-2026 н.р.
Language of Defence: ukrainian
Abstract: Ensuring reliable and high-quality electricity supply to consumers in conditions of growing loads and the need to increase the stability of the power system is a priority task for the modern electric power industry of Ukraine. The relevance of the topic of the master’s thesis is due to the need to reconstruct and develop the 110 kV electrical network of PJSC ‘Lvivoblenergo’ to provide power to new domestic and industrial consumers in the area of the settlement of Pohirtsi, where a significant increase in electricity consumption is forecast. The commissioning of the new substation will relieve the load on existing network nodes, reduce electricity losses and increase the reliability of electricity supply in the region. The object of the study is the development of the 110 kV electrical network of PJSC ‘Lvivoblenergo’, which is subject to modernisation, and the new ‘Pogirtsi-1’ substation. The subject of the study is the impact of the new substation on the power grid development scheme, their technical and economic indicators, parameters of steady-state and post-failure modes of operation of the power grid, as well as the methodology for calculating power and electricity losses in power transformers. The aim of the work is to develop, technically and economically justify and select the optimal scheme for the development of the 110 kV electrical network of PJSC Lvivoblenergo with the integration of the new Pogirtsi-1 substation, as well as a comprehensive analysis of its steady-state modes, including the selection of the main power equipment and refinement of the methodology for calculating power losses in power transformers to improve the reliability of engineering calculations. The paper analyses the initial data and develops two competitive options for connecting the planned 110/35/10 kV Pogirtsi-1 substation to the existing network, for which a technical and economic comparison is performed. The first option involved radial power supply from the Komarno substation through the construction of new lines, while the second option involved connection to the existing 110 kV Komarno-Dobrivlyany overhead line (transit scheme). For both options, the cross-sections of overhead line wires (unified AC-150/24 wire was selected) and power transformers were selected. Based on the calculation using the consolidated cost method, it was established that option No. 2 is more economically feasible: capital investments amount to about UAH 21.2 million, which is 40% less than in the radial option (UAH 35.6 million), while ensuring the required category of power supply reliability [1]. Using the DAKAR software package, comprehensive modelling of the operating modes of the proposed network scheme was performed. In the maximum load mode, a voltage drop was detected in remote nodes (in particular, at the Dobrivlyany substation to 96.5 kV). To normalise voltage levels on 10-35 kV consumer busbars, the use of on-load voltage regulation devices (OLVD) for power transformers was justified, which made it possible to maintain the voltage within acceptable deviations. In minimum load mode, an increase in voltage beyond the nominal values [3] was recorded, which was eliminated by correcting the transformation coefficients. Particular attention was paid to the analysis of the post-failure mode when the 110 kV Pivdenna-Shchyrets trunk line was disconnected. It was established that the throughput capacity of the backup connection is insufficient to cover the full load of the winter maximum. Emergency measures have been developed, including the introduction of consumer restriction schedules (by 30%) and the forcing of the OLVD to operate, which ensures the static stability of the load node. Based on the calculation of maximum operating currents and short-circuit currents (SC), the main equipment for the Pogirtsi-1 substation was selected. The calculated values of three-phase SC currents were as follows: on 110 kV busbars – 0.931 kA, on 35 kV busbars – 2.175 kA, on 10 kV busbars – 7.328 kA. Taking into account the aperiodic component and thermal impulse (27.56 kA?·s for 110 kV), modern high-voltage equipment was selected: 1.Power transformers: two three-winding transformers of the TDTN-16000/110/35/10 type with a capacity of 16 MVA. 2. Switchgear: for 110 kV switchgear – ABB LTB-145-D1/B gas-insulated circuit breakers; for 35 kV and 10 kV switchgear – VB4-P series vacuum circuit breakers. The selected equipment has been tested for electrodynamic and thermal stability, switching capacity and reliability. The main electrical connection diagram of the substation has been adopted: for 110 kV – ‘Bridge with circuit breakers in transformer circuits and a repair jumper on the transformer side’ [3], for 35 and 10 kV – ‘A single busbar system sectioned by a circuit breaker’ [3]. A study was conducted on the impact of the choice of power transformer replacement circuit on the accuracy of steady-state calculations. A comparative analysis of the traditional H-shaped circuit [4] and the refined asymmetrical T-shaped replacement circuit [5] was performed. It has been proven that the use of a refined model in the DAKAR software package allows reducing the error in calculating active power losses in transformer steel by approximately 8%, which increases the reliability of technical and economic design indicators. The practical significance of the work lies in the development of a network section development plan and recommendations for configuring OLVD devices to ensure power quality in various operating modes.