Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Reexamination Certificate
2001-12-13
2004-05-18
Tibbits, Pia (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
C361S093500, C361S102000, C361S104000
Reexamination Certificate
active
06738246
ABSTRACT:
The invention relates to an electrical switching device for switching off an overcurrent in a current path. In particular, the invention in this case relates to the field of domestic electrical power supply, to the field of relatively small and medium-size electric motors, to building technology, to lighting systems and to electrical systems in railroad vehicles, ships and the like. These fields of application can be characterized by the fact that the voltages to be switched off are typically 100 V-1 kV, and the typical load currents are in the range 0.1 A-75 A, although these numerical figures should not be regarded as representing any restriction. In particular, very large current values can occur briefly in the event of large overcurrents caused by a short circuit or the like.
The invention relates to a switching device which can switch off not only relatively small overcurrents, which are in the range 1.1 to 10 times the maximum permissible current, but also very large overcurrents of many times the maximum permissible current, in order to protect an electrical device against damage or to be prevent damage to the environment or to personnel. In the prior art, combinations of electromagnetic contactors, fuse links, thermal overload relays with a bimetallic strip as the tripping element, and the like have been used until now.
On the other hand, electrical systems and devices have been becoming ever more complex in recent times, particularly in the low-voltage field, while, on the other hand, there has been an increasing requirement to reduce the total price, the physical volume, the weight and also the power losses.
The invention is based on the technical problem of finding an improved electrical switching device for switching off overcurrents.
The invention solves this problem by means of an electrical switching device having a microrelay switch in a current path, having a short-circuit current limiter in the current path for interrupting a large overcurrent, and having an evaluation device for receiving and evaluating signals from a current sensor which detects the current through the current path, with the switching device being designed such that the microrelay switch opens in response to a tripping signal from the evaluation device in the event of small overcurrents above a threshold value and, in the event of large overcurrents, the short-circuit current limiter limits these currents to currents which can be interrupted by the microrelay switch.
The invention is furthermore also based on an electric motor switching and protection system having such an improved switching device.
The fundamental idea of the invention is thus to use a microrelay switch in conjunction with a further component for short-circuit current limiting, instead of the conventional electromagnetic contactor. In this case, the microrelay switch is intended to be designed to switch off small overcurrents, and furthermore, can also be used for the normal switching on and off of the current in the current path during normal operation. In contrast to this, a further apparatus for short-circuit current limiting is designed specifically for switching off very large overcurrents, which would destroy the microrelay switch. An evaluation device is used for detecting overcurrents and for tripping the microrelay switch but, when required, can also be actuated directly for switching on and off. The invention thus makes it possible to save the conventional components comprising thermal relays with bimetallic strips and electromagnetic contactors, and/or to replace them by a comparatively small and light electromechanical system.
The microrelay switch as such is prior art and is an electrically operated miniature switch. In contrast to a transistor, a microrelay is, however, a mechanical switch with at least one moving contact piece.
This contact piece can be caused to move mechanically by means of an electrical signal in various ways. In general, such microrelay switches are produced using known methods for microelectronics and microsystem engineering.
The devices for the invention are preferably electrostatically operated microrelay cells, that is to say those in which the moving contact piece is operated electrostatically. In this context, reference is made to the exemplary embodiments and to an Si microrelay published by Siemens (H. F. Schlaak, F. Arndt, J. Schimkat, M. Hanke, Proc. Micro System Technology 96, 1996, pages 463-468). Reference is also made to R. Allen: “Simplified Process is Used to Make Micromachined FET-like Four-Terminal Microswitches and Microrelays” in Electronic Design, 8 Jul. 1996, page 31, and to “Micromechanic Membrane Switches on Silicon” in K. E. Petersen, IBM J. RES. DEVELOP., Volume 23, No. 4, Jul. 1979, pages 376-385.
The expression microrelay switch, for the purposes of this invention, relate to a switching device which has at least one microrelay cell. As described in detail further below, the microrelay switch may, however, be a complex system comprising a number of individual microrelay cells, with each individual cell having (at least) one moving contact piece.
In comparison to the described conventional component combinations, the switching device according to the invention thus offers a considerable reduction in weight and physical volume. The geometric flexibility of the overall arrangement is also improved, since the microrelay switch can be installed in widely differing manners, is at the same time particularly robust and insensitive to temperature fluctuations, shocks or the like and, in the case of a relatively large arrangement having a large number of microrelay cells, also provides major design freedom, since the conductor tracks between the microrelay cells can be formed as required.
A further primary advantage of the novel electrical switching device is the very rapid response of the microrelay switch. Due to the very much lower inertia of the moving masses, this represents a fundamental advantage in comparison to solutions using conventional contactors and relays. This is still true without any restriction even in the case of relatively complex microrelay switches having a greater number of microrelay cells, since the response time in this case is essentially the same as that with a single cell.
Furthermore, typical switching ratings and the power consumption of microrelay switches in the quiescent state are considerably reduced in comparison to conventional relays and contactors, and thus contribute to power saving and to reducing thermal problems, in particular in relatively large systems. Furthermore, the switching device according to the invention can also be used in combination with and for integration with other semiconductor-technology devices, in particular transistors and integrated circuits, since there are considerable corresponding features and overlapping areas in the production methods. The weight, volume and cost can thus be reduced further.
The evaluation device is a preferably microelectronic circuit whose more detailed design is immediately obvious to a person skilled in the art with respect to the respectively required functions in the various embodiments of the invention. In this case, the evaluation device can be designed to produce a certain time delay, in particular also as a function of the magnitude of a measured overcurrent, in comparison to the physically fastest-possible response of the microrelay switch. Further details relating to this can be found in the description of the exemplary embodiments.
Since electrical switching devices or overcurrent protection have to cover a very wide range of current and voltage requirements, the microrelay switch can be produced using a largely unchanging standard technology with different layout geometries, that is to say different mask sets. Widely differing electrical specifications can be covered in this case with a high level of technological standardization of the production line.
However, since microrelay switches are invariably subject to certain limits in terms of their current and voltage lo
ABB Research Ltd
Burns Doane Swecker & Mathis L.L.P.
Tibbits Pia
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