Abstract: A better filtering effect for disturbing harmonic currents in a high-tension direct current transmission installation is described. A balancing winding is provided between a primary winding as an outer winding and a secondary winding in a 3-winding transformer with a transformer core. The distances between the balancing winding and the primary winding and the secondary winding, respectively, are selected such that the equivalent reactance of this balancing winding is equal to or less than zero. A second balancing winding can be provided as the inner winding in a series with the first balancing winding. In the case of a 4-winding transformer, two winding arrangements are provided with two parallel-connected primary windings as the outer windings, with a separate secondary winding for each and a balancing winding for each between the primary and secondary windings, the two balancing windings being connected in series.

Abstract: Subsynchronous oscillations in a polyphase power network can be effectively damped with a switching arrangement having a thyristor-switched regulation and a phase shifting polyphase power system. The arrangement is controllable and is periodic in nature, being responsive to a measurement signal representing a physical parameter of the subsynchronous oscillations. This signal preferably represents the difference between the instantaneous rotational frequency of the generator and a set-point value for that frequency. Control windings are connected in series with the power-network-side polyphase windings of a block transformer. Voltages induced in these control windings are phase shifted with respect to the voltages in the respective associated power-network-side polyphase windings of the block transformer. These voltages in the control windings produce a very effective damping torque on the generator, to damp out the subsynchronous oscillations.

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.