Reactive power compensator with capacitor and capacitor discharge circuit

Abstract

In a reactive power compensator used for capacitive or inductive reactive powers in alternating-voltage networks, a capacitor is connected to an alternating-voltage network for a short time by means of a thyristor switch. In order to reduce the voltage load on the thyristor switch, a discharge circuit is connected in parallel with the capacitor. Via this circuit, the capacitor can discharge, after being disconnected from the alternating-voltage network, with such a speed that the voltage occurring at the thyristor switch is no greater than about 1.5 times the maximum network voltage. In the discharge circuit, a variable inductive reactive resistance can be a discharge circuit choke having an iron core or the primary winding of a transformer. When the capacitor is connected to the alternating-voltage network, the discharge circuit choke is unsaturated and its reactive resistnace is large (or the transformer secondary is open) so that no significant leakage current can flow via the discharge circuit. After the capacitor is disconnected from the alternating-voltage network, the discharge circuit choke is saturated and its reactive resistance is small (or the transformer secondary is shortcircuited) so that a large discharge current can flow. No switching element is required in the discharge circuit. In order to limit the rectifier current of the thyristor switch and to change this rectifier current with time, an air choke is provided. The maximum rectifier voltage is limited by surge dissipators of zinc oxide.