VOLTAGE REGULATION AND REACTIVE POWER COMPENSATION IN ELECTRIFIED RAILWAY POWER SUPPLY SYSTEMS: ANALYSIS, MODERN SOLUTIONS, AND AUTOMATION PROSPECTS

Abstract

The present study investigates the complex problem of voltage regulation and reactive power compensation in the traction power supply systems of electrified railways operating at 27.5 kV and 2×25 kV. The research is motivated by the growing operational challenges at Kazakhstan Temir Zholy (KTZ) network, where extended 220 kV transmission lines up to 400 km in length generate significant capacitive reactive power under light-load conditions, causing voltage deviation beyond permissible limits and complicating automatic voltage regulation. The research object is the external and internal power supply system of electrified railway sections in Kazakhstan; the research subject is the regime characteristics, voltage deviation patterns, and reactive power balance under variable traction load conditions. The paper systematically analyses the influence of traction load harmonics, current asymmetry, and capacitive charging power of long overhead transmission lines on power quality indices. Calculation models based on П-equivalent circuit representation are developed for five operational sections of KTZ, enabling quantitative assessment of voltage losses (2–7 kV range depending on traffic intensity) and charging reactive power magnitudes. Technical solutions are proposed and evaluated: capacitor banks with harmonic filters, on-load tap-changing (OLTC) transformers, off-circuit tap-changing (OCTC) devices, shunt reactors (3.3 MVAr units), and ferroresonance-controlled saturable reactors (SR) for continuous reactive power regulation. The findings demonstrate that ferroresonance-type controlled reactors represent the most technically feasible and cost-effective solution for automated reactive power management under variable load schedules. Intelligent monitoring and SCADA-integrated control algorithms are proposed as a direction for further development toward Industry 4.0-compliant railway power infrastructure.