Process for Monitoring the Wear of at Least One Contact in a Switching Device and Switching Device Designed Thereof

The present invention relates to a switching device, in particular a contactor or circuit breaker, having contact elements that are mounted in a switching device housing on contact supports, and having an electrically insulated signal line as means for monitoring contact erosion, damage to or destruction of the insulator and/or the conductor being utilized to generate an external signal as an indication of the end of the service life of at least one of the contact elements.

The service life of switching contact elements is determined by erosion, i.e. by the gradual loss of contact material under the influence of the arc which occurs in the switching operation. Erosion will generally wear away the contact elements in non-uniform fashion. The service life ends when the contact material has either completely eroded away or has been removed to a defined minimum thickness at least at one point in the contact region.

At present, the state of the switch contact elements can be assessed in practice only by opening the switching device and by visual inspection. This is particularly true for the remaining expected service life, a knowledge of which is of central importance for the functionality of the switching device and thus for the operating reliability of the load unit being switched.

DE-OS 40 28 721 discloses a method for determining the remaining service life of switching devices, in which the charge that has flowed during a switching operation is electronically determined and summed for the switching operations. This method is in principle suitable not only for indicating a defined remaining service life, but moreover also for indicating the erosion state of the contact elements at any desired point in time. A comparatively large outlay for the associated electronics is necessary, however, so that profitability may exist only for large switching devices.

In addition, an earlier international patent application (PCT/DE 94/00244) that was not pre-published describes a switching device in which the contact elements are slotted on the rear side and installed on a split contact support. The remaining service life of the contact can be determined with this arrangement: when erosion has eroded away the material located over the slot, two contact halves are created. When switching takes place in this condition, a potential difference occurs between the two contact halves; this is measured as a voltage, and can be used as an indication of contact erosion. Lastly, Germany Patent Application No. 37 14 802 also describes an electronic switch in which a light guide, the transmission properties of which can be measured from outside by means of suitable auxiliary optical equipment, is associated with at least one of the contact elements. The intention in this context is that contact erosion which has progressed impermissibly leads to a change in optical transmission properties and ultimately to destruction of the light guide. In particular, provision is made that each of the contact elements must be fitted with a light guide of this kind.

Accordingly, it is an object of the present invention to provide a switching device with which detection and indication of a defined remaining service life during operation of the switching device are guaranteed in absolutely reliable fashion for all the contact arrangements together. In particular, implementation is to be economical even for smaller switching devices.

This object is achieved, according to the present invention, using an electrical signal line which is guided in a U-shape between the contact elements and the associated contact supports or in the contact material itself.

The insulated signal line consists either of doubly guided wires or a U-shaped loop with two insulated supply leads. In this context, the U-shaped loops of a measuring wire can be guided, insulated from one another, preferably in a metal-sheathed tube. Such lines are previously known, for example, as ungrounded sheathed thermocouples, and can to that extent be used according to the present invention for the present purpose.

In the present invention, the contact element can have on its rear-side soldering surface a groove, a blind hole, or other orifices into which the insulated signal line can be inserted. The insulator can consist, in particular, of a glass-fiber sheath or another temperature-resistant insulator.

The present invention provides an arrangement which guarantees optimum functional reliability under all operating conditions. Multipole switching devices in particular can thereby be monitored for erosion in suitable fashion; wear on a contact element usually results in an indication that does not need to be localized to a specific contact element.

FIG. 1 shows a three-pole grounded contact arrangement with monitoring means arranged in a single circuit.

FIG. 2 shows a first embodiment of a monitoring circuit according to the present invention.

FIG. 3 shows a second embodiment of a monitoring circuit according to the present invention.

FIG. 4 shows a third embodiment of a monitoring circuit according to the present invention.

FIG. 5 shows a fourth embodiment of a monitoring circuit according to the present invention.

FIG. 1 shows a contact arrangement for a three-pole contactor in which contact arrangements 10, 20, and 30, each including two fixed contact elements 11, 21, 31 and 11', 21', 31' that are soldered onto contact supports 12, 22, and 32 and 12', 22', and 32', respectively. Countercontacts 14, 24, 34 and 14', 24', 34', which are each soldered onto a movable contact bridge 15, 25, and 35 will not be discussed in detail in this context. In principle, the measuring means described hereinafter could also be installed on the moving contacts.

A single insulated signal line 300 which passes through the individual contacts and forms a closed signal line circuit is present in FIG. 1. Through holes can be present for this purpose in the individual contacts 11, 21, 31 and 11', 21', 31'. It is also possible to guide signal line 300 between the individual contacts and the contact supports. Milled recesses or grooves can optionally be provided in the contacts.

In FIG. 2, a contact element 1 that is soldered onto a contact support 2 is equipped with a groove 3a in which an insulated signal line, consisting of an insulator 3 and a metal conductor 4, is located. Conductor 4 is connected, via an indicator 5 and a protective resistor 6, to the neutral conductor or another phase of the switched system.

Insulator 3 in FIG. 2 can consist in particular of a glass-fiber sheath. When an erosion state of contact element 1 is reached such that groove 3a and thus insulator 3 are exposed to the switching arc, they are destroyed and conductor 4 receives the electrical potential of contact element 1. A limited current flow occurs via protective resistor 6 and directly activates indicator 5, for example a light-emitting diode (LED).

Height h of the groove in FIG. 2 thus directly defines the erosion state at which, for example, an "X percent remaining service life" indicator can be activated.

In FIG. 3, a U-shaped loop of an insulated wire is laid into groove 3a: this arrangement can consist of a metal-sheathed tube 7 with two wires 8 and 9 installed therein, insulated from one another and also from the sheath. The latter arrangement is implemented by, for example, an ungrounded sheathed thermocouple. In sheathed thermocouples of this kind, the outside diameter of sheath 7 is typically 1 mm. The enlargement in FIG. 3a shows a plan view, the conductor ends of the U-shaped loops being designated 8a and 9b.

In the example according to FIG. 3, a current 2 flows continuously from the contact bridge through indicator 5, both conductors 8, 9 of the sheathed thermocouple, and the limiting resistor 6, to the neutral conductor or another phase in the switched device. In this case, activation of indicator 5, for example a light-emitting diode (LED), means that the remaining service life has not yet been reached.

Destruction of the sheathed element by erosion extinguishes indicator 5 as soon as conductor 9 is either separated from conductor 8 and/or makes contact with sheath 7.

FIG. 4 shows a fixed contact bridge 2 with a contact element 1 on the rear side of which a metal conductor 4 extends in an insulator 3 and has connector ends 4a and 4b. As long as insulator 3 is intact, a current flows from contact bridge 2 through indicator 5, metal conductor 4, and the protective resistor to neutral or to another phase. In this case, the fact that the remaining service life has not yet been reached is indicated. As soon as the switching arc destroys insulator 3 and conductor 4, current flow to the indicator is interrupted. This applies both to the case of a simple interruption of conductor 4 and to the case in which conductor 4 additionally makes contact with contact element 1 and thereby short-circuits indicator 5.

An advantage of the exemplified embodiments described is that the cost outlay is comparatively low, and is determined solely by installation of the signal line in the switch contact. By connecting an indicating means to the contact support, for example, it is possible in this context to utilize the potential for indication purposes. In any case, the fact that the remaining service life of the switching device has been reached is detected and indicated.

The arrangements described with reference to the embodiments shown in FIGS. 2-4 can be designed for multi-phase contactors as illustrated in FIG 1. It is particularly advantageous in this context that only a single signal line is necessary.

FIG. 5 shows an arrangement with three contact elements 41, 51, and 61, each of which has on the rear side a blind hole 42, 52, and 62. Signal lines are introduced into blind holes 42, 52, and 62 by means of suitable insulators 43, 53, and 63. As shown in FIG. 5, for example, a single measuring wire 100 can be guided from indicator device 5 in such a way that the respective branch 104, 105, and 106 for contact elements 41, 51, and 61 is guided in doubled or U-shaped fashion, corresponding to the sheathed thermocouple of FIG. 3a.

The double wire configuration guarantees the reliability of the indicator even if destruction is only partial. In addition, parallel monitoring is possible. As a result, many contacts can be monitored simultaneously and economically by means of a single arrangement.