Electricity: electrical systems and devices – Safety and protection of systems and devices – Arc suppression at switching point
Patent
1991-09-20
1993-06-01
DeBoer, Todd E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Arc suppression at switching point
361154, 323908, H02H 900
Patent
active
052165671
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for the alternating current cut-in limitation of an reactive power supply unit that is wired in series with a first alternating current switch and features a phase control circuit through which the connection of the primary winding with the mains alternating voltage can be retarded from the cut-in moment forward, wherein a control electrode of the first alternating current switch of the supply voltage-buffered phase control circuit is connected with the output of a control circuit by which at the cut-in of the power supply unit at a preselectable phase angle of the mains alternating voltage a firing voltage synchronized with the latter can be generated, which for the shutoff of the power supply unit can be suppressed in due time before reaching a zero pass of the alternating current voltage.
Such a device for the alternating cut-in limitation is known from DE 27 35 736 A1, with which switching interferences during a clock switching operation can be avoided in that a one-sidedly directed premagnetization of the ferromagnetic material of the load is eliminated. But with this device it is not possible to quickly reconnect an reactive power supply unit after a mains voltage failure, since such voltage failure leaves an uncontrolled remanence behind.
DE 25 39 047 A1 teaches a device for the shutoff of transformers where immediately before the cut-in of a transformer a remanence premagnetization can be generated, by a direct current, against the magnetization given by the cut-in process. This direct current can be generated by a defined surge from a capacitor battery and superimposes the first half cycle of the alternating voltage.
EP 0 222 727 A1 describes a device for the minimization of mains repercussions on inductive elements in a high-voltage network, where cut-in moments of the reactive power supply unit other than those at the voltage maximum or current zero pass are selected, with alternating current switches in the form of triacs being used.
A further device for the alternating current cut-in limitation is known from ELV Journal 45, pages 1 through 4. On transformers with an iron core, specifically annular core transformers, which are connected to a 220-volt alternating current service, the cut-in or start-up current, also called inrush, at the cut-in moment is by a multiple greater than the nominal current. This leads frequently to the blowing of the equipment fuse provided, without apparent reason, and to disturbances of equipment in the neighborhood. Besides, the cut-in current peaks require an overdimensioning of some components or even of the transformer itself, leading to higher costs and/or greater construction volumes.
A similar circuit setup for limitation of the cut-in current surge is known from the German patent disclosure 1,591,680, where a triac is provided parallel to a series resistor in the primary circuit of a transformer. A shunt prevents a high flow of current at the cut-in, and the triac fires only after a waiting time of 0.1 to 0.2 seconds, through a capacitor which in the meantime has been charged. This device fails to determine the remanence direction of the transformer that was impressed by the cut-out. The device, furthermore, has the disadvantage that in the case of frequent cut-in and cut-out the magnetic remanence of the transformer, through the current flowing at the beginning, will in the passive state ever more shift into saturation, so that the cut-in peak current which builds up due to successive zero passes will not ebb off. In the process, also the shunt heats up increasingly.
Known from the German patent document 27 46 845 is a further device for the alternating current cut-in limitation where, at continuous phase control, during a start time the conductive angles of the voltage slowly shift from small values toward large ones. Along with it there occur during the cut-in process cut-in current peaks which far exceed the nominal current, because the remanence polarity and voltage polarity are not being allowed for in the cut-in.
From t
REFERENCES:
patent: 3925688 (1975-12-01), Kalfus
patent: 4131927 (1978-12-01), Tsuchiya et al.
ELV Journal 45 Article, pp. 1-4, Jun. 1987.
Deboer Todd E.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
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