Покращення режиму роботи симетричного трифазного навантаження при несиметрії живильних напруг

Abstract

UA: У роботі розглянуто вплив несиметрії живильних напруг джерела на роботу симетричного трифазного навантаження. Установлено, що найгіршим випадком трифазної системи з несиметричним джерелом і симетричним навантаженням є чотирипровідна. Запропоновано для покращення режиму роботи трифазного симетричного навантаження за умови несиметрії живильних напруг включати в лінійні проводи симетрувальні елементи, які не є джерелами. Установлено, що на практиці таке симетрування живильних напруг можна здійснити тільки за найменшим значенням електрорушійної сили джерела. Для такого випадку отримана методика розрахунку комплексів повних опорів симетрувальних елементів. /// EN: The work considers the issue of asymmetry of supply voltages of a symmetrical three-phase load, which arises during its operation due to various reasons that do not depend on it. The consequences of the influence of such asymmetry on the operation of a three-phase load are shown. Existing methods of improving the load operation mode under such conditions are analyzed and it is determined that all of them have a high cost of technical implementation and are not adapted for a separate load. Therefore, the paper considers various types of three-phase system circuits, which include an asymmetrical source and a symmetrical load. The negative sequence voltage is chosen as a criterion for assessing the influence of load voltage asymmetry, for which a calculation method has been developed for various circuit solutions of a three-phase system. It is determined that for any load switching scheme without the use of balancing elements, the effective value of its negative sequence voltage does not change. The worst of these cases is a three-phase four-wire system due to the presence in it not only of negative sequence currents, but also of zero sequence currents. It is proposed to improve the operation of a symmetrical load in conditions of supply voltage asymmetry to include balancing elements that are not sources in linear wires. It is proven that with such balancing of load voltages according to the nominal voltage value, the complexes of impedances of such elements have phase shift angles that cannot be implemented in practice. Therefore, it is proposed to balance the voltages of a three-phase load according to the smallest value of the electromotive force of an asymmetrical three-phase source. For such a condition, a method for calculating the complexes of impedances of balancing elements has been developed. Such elements can be implemented in practice using devices that have active and reactive resistance. They allow to establish symmetrical, but reduced voltages on the phases of a three-phase load. Such balancing is proposed to be performed for a short time for the period of action of an unacceptable voltage asymmetry, if the production conditions of a particular load allow.