Abstract: The circuit contains a primary coil on the core (2) of a magnetic circuit with an air gap and switchable into a line carrying the measurement current. A secondary compensation coil (5), with an order higher winding count and mounted on the core, is connected to the output of a controllable compensation current source (6). The output of a Hall element (11) in the air gap is connected to the control input of the compensation source. A further coil (14) on the core is connected to an additional controllable current generator (15) whose control input (16) is driven by a measurement device (13) for the compensation current via a control and evaluation circuit (17). USE/ADVANTAGE—Measuring a.c. and d.c. Can be produced at low cost and all drift occurring during measurement can be compensated.

Abstract: A method and circuit arrangement for measuring a current are described, which can be used in electrical engineering to precisely trigger electronic tripping devices in circuit breakers. The current is measured according to magnitude and phase in such a way that only the fundamental wave of the current between precisely determined current zero crossings is sampled at a low sampling rate, and the root mean square is calculated on the basis of the measured phase angle and amplitude. The exact phase angle is measured using a conventional PLL circuit with a downstream zero switch.

Abstract: An electronic tripping device for a circuit breaker contains circuitry for simulating the response curve of a fuse. This circuitry can be controlled by a single setting mechanism representing the nominal currents or rated currents of fuses. This improves the coordination of protection in sophisticated power supply equipment containing both circuit breakers and fuses. Tripping devices equipped with microprocessors or operating in an analog fashion can be configured for the mode of operation. The new protection system achieves particularly safe operation for the user in that the setting mechanism is combined with a rating plug for the “fuse” mode, thus directly setting the tripping device to one current value. In a manner similar to a true fuse, consequently, the setting mechanism is provided with appropriate labeling. The simulated curves may contain a point of inflection below a limit in a lagging manner, to increase the nominal switching capacity and selectivity limit of a circuit breaker.

Abstract: In power circuit breakers including a current transformer with a current detection coil without any iron and including an integration circuit connected downstream from the current detection coil, the unavoidable time constant of the integration circuit can lead to spurious trappings. This is avoided by a method in which the instantaneous values of the current are detected and stored at defined periodic intervals. The stored measured values are compared on the basis of polarity and magnitude. If it is found that the stored values have the same polarity and fall monotonally, it is assumed that the DC element is originating from the integrator and a tripping inhibit signal is set in the electronic release of the power circuit breaker.

Abstract: In power breakers which have a current transformer (6) with a current detection coil (7) without any iron and have an integration circuit (8) connected downstream from the current detection coil (7), the unavoidable time constant of the integration circuit (8) can lead to spurious trippings. This is avoided by a method in which the instantaneous values of the current are detected and stored at defined periodic intervals (n, n+l, n+2). The stored measured values are compared on the basis of polarity and magnitude. If it is found that the stored values have the same polarity and fall monotonally, it is assumed that the DC element is originating from the integrator (8) and a tripping inhibit signal is set in the electronic release of the power breaker.

Abstract: A circuit arrangement is described for monitoring an electronic tripping device for low-voltage switches having a microprocessor device which, in conjunction with a digital-analog converter, evaluates an overcurrent so that line power supply system. The microprocessor device (MPE) has a zero crossing comparator with which a constant test current pulse is transmittable, at zero crossings, to the electronic tripping device via an additional current transformer winding to measure the amplitude. In the case of deviations from the setpoint value, (re)calibration or actuation of the line tripping contacts, with an alarm signal being emitted, takes place.

Abstract: An undervoltage circuit breaker has an electromagnet for triggering a switching device and a driver circuit that supplies power to the electromagnet. The driver circuit contains a pulse generator for generating a holding current for the electromagnet and a capacitance dimensioned so that delayed triggering of the electromagnet is possible. Due to the variable pulse duty factor of the pulse generator, the energy content of the capacitance is utilized favorably. An elevated operating voltage can also be selected and therefore a smaller capacitor may be selected to advantage.