A plant for transmitting electric power comprises at least one VSC-converter (1). It comprises also at least one DC/DC-converter (33, 34) having two current valves connected in series and an inductance connected to a midpoint therebetween. The DC/DC-converter is through said inductance connected to a first of the poles of the direct voltage side of the converter and through a first output terminal connected to one of the current valves to the second of the poles so as to obtain an unbalanced step-up-transformation of the direct voltage between the two poles while obtaining a potential having a higher value on the second output terminal (27) of the DC/DC-converter connected to the second current valve than on said first output terminal (28).

Plant for transmitting electric power, including VSC-converter and DC/DC-converter

A presently-preferred capacitor discharge system for a circuit breaker adapted for use in a switchgear enclosure comprises a capacitor discharge circuit adapted to be electrically coupled to the capacitor, and a contact switch electrically coupled to the capacitor discharge circuit and adapted to be mechanically coupled to a support truck of the circuit breaker. The contact switch is movable between a first and a second position. The system also comprises a resistor electrically coupled to the capacitor discharge circuit, and a lever arm adapted to be rigidly coupled to a racking mechanism of the circuit breaker and adapted to urge the contact switch into the closed position when a locking arm of the racking mechanism disengages from the switchgear enclosure. The capacitor discharge system is adapted to electrically couple the capacitor and the resistor when the contact switch is in the second position thereby discharging the capacitor.

Circuit breaker with capacitor discharge system

A power transmission system for high-voltage direct current comprises a rectifier station (1) and an inverter station (2), which are interconnected by a dc connection (4), as well as a third converter station (3) connected between the dc connection and an ac network (3c). The third converter station comprises a converter (3a) connected to the dc connection via a direct-voltage converter (5). The direct-voltage converter comprises at least a first and a second converter stage (8:1, 8:2), each with a positive terminal (TP:1, TP:2), a negative terminal (TM:1, TM:2) and an output terminal (TO:1, TO:2) and comprising a voltage-source converter circuit (V, C1, SL) with at least one extinguishable semiconductor valve (T1, T2). The positive terminal of the second converter stage is connected to the output terminal of the first converter stage and the output terminal of the second converter stage is connected to the negative terminal of the first converter stage.

HVDC transmission system with multiple converter stations

An apparatus for tapping electric energy from an HVDC power transmission system comprises at least one voltage source converter. The apparatus contains an intermediate ac network containing the VSC, and a switching arrangement for disconnecting the intermediate ac network in dependence on the transmission direction of the HVDC power transmission system.

Tapping power from a hvdc transmission system

PCT No. PCT/SE90/00425 Sec. 371 Date Nov. 19, 1991 Sec. 102(e) Date Nov. 19, 1991 PCT Filed Jun. 15, 1990 PCT Pub. No. WO90/16104 PCT Pub. Date Dec. 27, 1990.A system for discharging electrical power from a high-voltage direct-current (HVDC) transmission line to a local network, utilizes a first, single-phase converter bridge comprising semiconductor switches which are energized by signals and which are de-energized solely with current zero crossing, and a first, single-phase transformer having a primary winding connected to a HVDC line and a secondary winding; a second converter bridge connected to the secondary winding; a secondary direct voltage network connected to the second converter bridge; a third converter bridge connected to the secondary direct voltage network for generating an alternating current for the local network; and the second and the third converter bridges each comprise ON/OFF controllable semiconductor switches, and the first and the second converter bridges commutate with a frequency that is 2-4 times higher than the normal frequency of the local network and the third converter bridge commutates at the normal frequency of the local network.

System for discharging electrical power from a high-voltage direct current line to local network

Improved apparatus for discharging power from a high-voltage direct current line. A direct voltage convertor is connected in series with a smoothing filter and a DC high voltage line on one side and a second smoothing filter and a power discharge inverter on the other side. The rated voltage of the discharge inverter is substantially lower than the line voltage and the direct voltage convertor applies the lower voltage to the discharge inverter.

High voltage direct current transmission

a. Installation de transport d'energie en courant continu a haute tension. b. Pour decharger de l'energie d'une ligne 3 de courant continu a tension elevee, il est prevu un convertisseur 6 de tension en serie avec un onduleur 5 dont la tension nominale est inferieure a la tension de la ligne. Un filtre 7 de lissage est connecte entre la ligne 3 et le convertisseur 6 et un second filtre 8 de lissage est connecte entre le convertisseur 6 et l'onduleur 5. c. Transport d'energie electrique.

Juhlin Lars-Erik

Papers

High voltage direct current transmission

Installation de transport d'energie en courant continu a haute tension