Other

Asea Brown Boveri Ab

John J Vithayathil

Kadry Sadek

Per-Erik Bjorklund

Bernt Bergdahl

Urban Astrom

Joseph Vithayathil

The novel circuit arrangement is used for the static generation of a variable electric output, as is common in static reactive-power compensation systems. According to the invention, a voltage is applied to a consumer, i.e. to a capacitor and/or an inductor, and a transformer (T) has at least two power-control windings (WW) in a secondary circuit, said windings being connected electrically in series via bridge circuits (BB). In their branches, the bridge circuits contain static switches (BSS) in an inverse-parallel connection, said switches can be selectively connected or disconnected.

Circuit arrangement for the static generation of a variable electric output

An ac-dc converter using bi-directional thyristor valves made up of back-to-back connected thyristors as converter valves. The bi-directional thyristor valves permit operation of the converter as a rectifier or an inverter with both polarities of the voltage across the dc terminals of the converter. The bi-directional valves can be used to prevent the reversal of the polarity of the dc voltage across the dc terminals of the converter or to minimize the magnitude of the reverse voltage. The bi-directional thyristor valves can be used to provide protection against overvoltage across the converter valves and eliminate or reduce the energy rating of converter valve arresters. AC-DC converters could also be provided with some bi-directional thyristor valves as converter valves while retaining regular thyristor valves in other converter valve positions

AC-DC converters with bi-directional thyristor valves

A switching scheme that permits a thee phase capacitor bank to have two ratings depending on whether the circuit is connected in delta or star configuration The capacitor per phase consists of two sections. In delta connection the two sections are connected in series. In the star connection the two sections are connected in parallel. Both the changes &mdash;the delta connection to the star connection of the circuit and the series connection of the capacitor sections to the parallel connection of the capacitor sections&mdash;are accomplished simultaneously by a single switching operation of three star connected switches. In the case of isolated neutral, the number of switches can be reduced from three to two.

Method and circuits for changing the ratings of a three phase circuit by delta-star switching

An AC generator whose field winding (,) on the rotor is excited by AC so that the resultant speed of the rotating field is the algebraic sum of the rotor speed and the speed of the field relative to the rotor itself. This makes it possible to generate AC at a frequency different from that of conventional DC excited generators by the appropriate choice of the frequency of the AC input to the rotor field circuit. It enables the stabilization of the output frequency of the alternator when speed changes occur, by the adjustment of the AC frequency of the rotor input. The AC fed to the rotor is from an auxiliary winding (,) which may be housed on the rotor itself, thereby eliminating the need for any brushes or slip rings. The AC is induced in the auxiliary rotor winding by having an auxiliary winding on the stator (,), distinct from the main stator winding (,). The input to the stator auxiliary winding may be from an inverter (,) whose frequency may be adjustable. By varying the frequency of the inverter output, the frequency of the AC fed to the main rotor field winding may be varied to achieve the desired output frequency of the generator or to stabilize the generator frequency when speed changes occur. Voltage control of the alternator may be implemented by adjustment of the inverter output voltage. The need for a separate exciter machine may be avoided by housing the main and auxiliary winding in the generator itself By the appropriate choice of different pole numbers for the main and auxiliary windings, these two sets of windings can function independently without magnetic coupling, making the machine both exciterless and brushless The restriction on the choice of pole numbers will not apply if the auxiliary windings are housed in a separate exciter machine, in which case it becomes a brushless machine with exciter.

Brushless AC field system for stable frequency variable speed alternators

An HVDC transmission has two converters (SR1, SR2). Each converter is connected between an alternating-voltage network (N1, N2) and a d.c. link (L1, L2) common to the converters. At least one converter is connected to its alternating-voltage network without the use of any full transformer, for example directly, or via an inductor or an autotransformer, or via series capacitors. The transmission has a mutual inductor (IB) which is arranged on the d.c. side of the converter and which has two windings (IB1, IB2) which are each connected to a respective one of the d.c. supply lines of the converter and are magnetically coupled to each other, the inductor being designed and connected so as to exhibit a high impedance to ground mode currents.

HVDC transmission with a converter connected between an AC voltage and a

A static controlled reactance device is inserted in series with an AC electric power transmission line to adjust its transfer impedance. An inductor (reactor) is serially connected with two back-to-back connected thyristors which control the conduction period and hence the effective reactance of the inductor. Additional reactive elements are provided in parallel with the thyristor controlled reactor to filter harmonics and to obtain required range of variable reactance. Alternatively, the static controlled reactance device discussed above may be connected to the secondary winding of a series transformer having its primary winding connected in series to the transmission line. In a three phase transmission system, the controlled reactance device may be connected in delta configuration on the secondary side of the series transformer to eliminate triplen harmonics.

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Portland, OR, United States of America

John J Vithayathil