Cgee Alsthom

Patrick Charles

A device generates a signal corresponding to a variable magnitude associated with the reactive power of an arc furnace, in order to control a reactive power compensator. It comprises a reactive power or voltage demodulator and a set of filters connected to the output of the demodulator. The set of filters comprises active bandstop filters having a bandwidth of .+-.F relative to frequencies of 2f.sub.O, 4f.sub.O and 6f.sub.O and narrowband active bandstop filters having a bandwidth of substantially .+-.2 Hz relative to frequencies of f.sub.O and 3f.sub.O. f.sub.O is the supply frequency and F is approximately f.sub.O /2. The device further comprises a phase advance corrector circuit operative in the frequency band O-F connected to the output of the set of filters.

Device for generating a signal corresponding to a variable magnitude

Apparatus for generating a signal indicative of a fault occurring in an AC electric circuit connected to an AC network (UW). The AC circuit (1) comprises a series connection of at least one inductance winding (L) and a two-way static switch having thyristors (5, 6) controlled by firing pulses .theta., and the capacitive impedance and the resistive impedance of said AC circuit are negligible relative to its inductive impedance L. The apparatus comprises a differential relay (15) receiving first and second input signals and providing an output signal (Id) when said input signals are unequal. The first input signal is a real image of the current flowing through said AC circuit as provided by the secondary winding of a current transformer (30) inserted in said AC circuit. The second input signal is a theoretical image of the current flowing through said AC circuit as provided by a theoretical image signal generator (16) which generates the theoretical image signal as a function of the said inductive impedance L, the firing pulses .theta., and the driving voltage across said AC circuit as indicated by the secondary winding of a voltage transformer (18), the voltage and current transformers being designed so that said two signals represent images to the same scale of the current of said circuit.

Apparatus for generating a signal indicative of a fault occurring in an

The thyristor control pulse generator consists of a dual slope sawtooth signal generator (11, 13, 17) providing a signal U.sub.sy with slopes a and 2a, said sawtooth generator comprising an input (23) for resetting the signal to zero in response to each generated pulse .theta. and means (15) for controlling the switching of the signal slope from value a to value 2a at the time the current in the reactive power regulating inductor becomes cancelled. A comparator (19) compares said signal U.sub.sy to a control voltage U.alpha. to which a correcting signal .DELTA.U.alpha. is added in a summing circuit (21), which correcting signal is developed from the means value of the current i in the inductor, given by an integrator (36) receiving at its input an image of said current, said image being taken from the output of another integrator (24) which receives the image U of the voltage across the terminals of the inductor at its input and includes a circuit (26 to 33) for resetting and holding its output to zero when no current is flowing in the inductor. The output of the comparator (19) is connected to a pulse converter (22) which outputs the thyristor firing pulses .theta..

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Mareil sur Mauldre, France

Patrick Charles