Energy efficiency issues of thyristor-controlled reac-tive power compensators

Abstract

Relevance: In railway power supply systems, traction loads vary sharply depending on train operating modes, which leads to an increase in reactive power in the contact network and traction substations. High levels of reactive power cause voltage drops, a reduction in the power factor, and deterioration of power quality. Failures in reactive power compensation systems negatively affect traction stability, resulting in reduced train speeds and decreased freight transportation volumes. Conventional compensation devices do not provide sufficient accuracy and response speed under variable and unbalanced load conditions characteristic of railway systems. Therefore, the study of devices that ensure fast, reliable, and energy-efficient reactive power compensation in railway power supply systems is a relevant scientific and practical task.

Aim: The objective of this study is to conduct a scientifically grounded analysis of the impact of reactive power on voltage stability and power factor in railway power supply systems, to evaluate the operating characteristics of a reactive power compensation system based on a thyristor-controlled capacitor, and to identify ways to improve its energy efficiency and reliability.

Methods: In this study, formulas for active, reactive, and apparent power based on sinusoidal circuit theory were used to determine and evaluate reactive power. To calculate and control reactive power in real time, a mathematical model based on the instantaneous power theory proposed by Akagi was developed, and its suitability for fast control algorithms was substantiated. A comparative analysis of the technical characteristics of various reactive power compensators was performed. In the thyristor-controlled capacitor, heat dissipation processes, the thermal resistance chain, cooling methods (natural and forced air cooling, and liquid cooling), as well as commutation processes were analyzed.

Results: The technical advantages of applying a thyristor-controlled capacitor with a star connection scheme were identified. This configuration enables independent phase-by-phase reactive power compensation and effectively maintains voltage stability under three-phase unbalanced load conditions. The results show that the overall efficiency of the compensation system depends not only on the selected electrical scheme but also on the thermal operating conditions of the thyristors, the reliability of the cooling system, and proper organization of maintenance.