Siemens Aktiengesellschaft

Hans-Eberhard Simmel

Helmut Fornsel

Robert Kugler

A method for generating a circuit-breaking signal in dependence upon the magnitude and duration of an excess current, where a measured quantity, derived from the excess current, is sampled, is converted into digital values, and these values are weighted in accordance with a predetermined function and are added in order to obtain a circuit-breaking signal when the sum exceeds a predetermined comparison value. In order to improve upon a method of this kind in such a manner that, in the case of a diminishing excess current, a false interruption of the circuit is safely prevented, an auxiliary quantity (.DELTA.i) is formed which corresponds to the difference quotient or differential quotient of the measured quantity (M) and when the absolute amount of the auxiliary quantity (.DELTA.i) is already below a predetermined limit value and the sampled value of the excess current is below a predetermined threshold (S), the addition is interrupted.

Method for generating circuit-breaking signals

A method for generating a tripping signal as a function of an overcurrent. Sampled measurement values are converted into digital values which are weighted and added up according to a predetermined function. If the sum value is above a predetermined reference value, the tripping signal is formed. In order to cancel the addition before the tripping signal is formed in dependence on the wave shape of the overcurrent if the overcurrent is decaying, the digital values of the respective last period of time corresponding to at least a half-period of the overcurrent are stored and a comparison of all digital values simultaneously stored with each other is made. The determined largest stored value is weighted and added up as a digital value and the addition is cancelled if a largest digital value is below the predetermined threshold.

Method for generating a tripping signal as a function of the magnitude

A method for generating a tripping signal in dependence on an overcurrent, in which sampled measurement values are converted into digital values. These values are weighted and summed in accordance with a predetermined function. A tripping signal is formed if a predetermined sum value is reached. In order to cause in such a method the delivery of a tripping signal only for true overcurrents, and in order to prevent the delivery of a tripping signal when an overcurrent is decaying and below a threshold, the summation is cancelled while the overcurrent is decaying, immediately in dependence on the waveform of the overcurrent. The digital values of the respective last period of time corresponding to at least one half-period of the overcurrent are stored and a comparison of all the then stored digital values with each other is made. At a determined highest stored value below a predetermined threshold, the summation is cancelled.

A digital overcurrent tripping arrangement having a nonpermanent digital memory. The arrangement further contains a resistor-capacitor stage that simulates the cooling-down process of a body. In accordance with the invention, a microprocessor uses a thermal excitation state digital value stored in the nonpermanent memory to calculate a digital normalized voltage value which is then stored in the nonpermanent digital memory. A digital comparator means within the microprocessor compares the digital normalized voltage value in the nonpermanent memory with a digital output of an analog-to-digital converter, the digital output corresponding to a voltage across the resistor-capacitor stage. If they agree, a charging switch between a current supply and the resistor-capacitor stage is opened. Upon reconnection of the main current supply after disconnection, the microprocessor stores the digital output of the analog-to-digital converter in the nonpermanent memory, the digital output corresponding to a residual voltage across the resistor-capacitor stage.

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Karlsruhe, Germany

Hans-Eberhard Simmel