Title of Invention

TRIPPING DEVICE FOR AN OVERLOAD CIRCUIT BREAKER

Abstract

Tripping device adapted to be used with an overload circuit breaker comprising a tripping armature (11) that operates a switch latch (18), said tripping armature being operable by a coil (6) through which a monitored current flows, characterized in that the tripping armature (11) is retained in its resting position by a spring (12) and an electromagnet (20) having a coil through which coil flows the monitored current or a current that is proportional to the monitored current, and in that the coil (7) of the electromagnet (20) is adapted to be short-circuited when a predeterminable current value is reached.

Full Text

-1A- The invention relates to a tripping device for use with an overload circuit breaker such as a line safety switch, comprising a tripping armature (also referred to as trigger armature) which actuates a switch latch and can be actuated by a coil through which a monitored current flows. One the one hand, fusible cut-outs, which can be used merely for a single cut-off process, and, on the other hand, over current releases which can be switched on again and can therefore be used repeatedly are used in overload circuit breakers. In an electric installation an overload protection of the mentioned designs is usually provided in the feed line before this it branched off into a plurality of electric circuits which are switched in parallel. Separate protective apparatuses, which usually consist of protection for persons (current-operated earth-leakage circuit breakers or the like) and protection for installations (line safety switches, fusible cut-outs or the like), are usually provided in each of these electric circuits. Optionally, these electric circuits can be subdivided on their part into further electric subcircuits which are also secured by protective apparatuses. In such a structure of circuits a series connection of the protective apparatuses occurs in feed line, electric circuit and electric subcircuits. If an impermissibly high current occurs in a subcircuit, it is desirable that only the protective switch assigned to this subcircuit trips and thus separates its subcircuit from the mains and that all protective switches connected in series remain switched on and thus all fault-free electric circuits and subcircuits remain connected with the mains. The superordinate switch shall only trip if the 2 occurring overcurrent is so high that it can no longer be switched off by the protective switch of the subcircuit. Such a time-variant switching of the superordinate switch is known as "selectivity". In fusible cut-outs this selectivity is determined by the heating capacity required for the melting of the fusible wire which is proportional to the square of the strength of current and the period of influence of the overcurrent. In the field of line safety switches two tripping devices are usually provided. A first device is provided for cutting off overcurrents which are only slightly over the nominal current of the unit and act over longer periods of time. The second device, a so-called short-circuit overcurrent circuit breaker, is usually realized by a coil which is flowed through by the current to be monitored with a movable armature effecting the cut-off. In order to emulate the heating capacity delay, and thus current-strength- and time-dependent delay, which was explained in connection with the fusible cut-outs, thermo-bimetallic strips which are flowed through by the current to be monitored are used, which bimetallic strips deform analogously to the fusible wires proportionally to the square of the strength of current and time and thus enable the switching act of the short-circuit overcurrent tripping in a time-delayed manner. These bimetallic strips constitute components which on the one hand must be adjusted in a mechanically precise manner and on the other hand require additional electric connections. In summary, they thus bring considerable additional complexity to the arrangement of the protective switch and thus a deterioration of the functional reliability and more complicated production. A further disadvantage of such designs is that the time-delayed cutout which is achieved by the bimetallic elements is -3- maintained independent of the amount of the current to be monitored. This leads to a time-delayed response of the protective device even in cases of very high short-circuit currents which for the protection of the unit should be cut off without any delay. It is an object of the present invention to provide a tripping device of the kind mentioned above which is provided with a selective tripping behaviour, but for this purpose, only requires few components which are easy to install and are added to the common tripping coil. Moreover, the tripping device in accordance with the invention is to lose its selectivity and is to respond without delay once the current to be monitored reaches a specific predeterminable value. Accordingly, the present invention provides a tripping device adapted to be used with an overload circuit breaker comprising a tripping armature that operates a switch latch, said tripping armature being operable by a coil through which a monitored current flows, characterized in that the tripping armature is retained in its resting position by a spring and an electromagnet having a coil through which coil flows the monitored current or a current that is proportional to the monitored current, and in that the coil of the electromagnet is adapted to be short-circuited when a predeterminable current value is reached. The triggering of the tripping armature is thus delayed by a simple constructional measure until the force exerted by the coil on the tripping armature exceeds the holding force of the electromagnet. The selectivity is also adjusted automatically to the momentary strength of the current to be monitored, but as a result of short-circuit, however, which causes an immediate removal of the holding magnetism, it is degraded abruptly. In a further development of the invention it may be provided that windings of the outermost layer of windings of the coil have sections which are kept free from insulation material and that an electrically conducting bridge is provided which on reaching a predeterminable -4- strength of current can be brought into contact with these sections. In this way it is possible to omit a short-circuit contact which is connected parallel to the coil and which would have to be provided with a relatively large dimension according to the expected high currents. In this connection it can be provided further that the coil is provided with merely one winding layer and that all windings of this layer of windings are provided with sections which are kept free from the insulating material. This arrangement allows that each winding of the coil can be short-circuited per se, as a result of which a particularly rapid degradation of the magnetic field is ensured. According to a particularly preferred embodiment of the invention it can be provided that the electrically conducting bridge is fixed on a short-circuit armature which can be brought by electromagnets from an idle position into a position which brings the bridge into contact with the sections which are kept free from the insulating material. This short-circuit armature is held with a predeterminable holding force in its idle position. In this way it is necessary to provide only one single component, namely the short-circuit armature, in addition to the electromagnet which is present anyway. This allows for a particularly compact, functionally reliable design. As a result of a respective dimensioning of the holding force of the short-circuit armature it is very easy to set the value at which the coil is short-circuited. In this connection a further feature of the invention can be that the holding force holding the short-circuit 5 armature in its idle position can be produced by an elastic component which is connected with the short-circuit armature and the housing of the tripping device. Such components are provided with a small size, so that the overall size of the tripping device in accordance with the invention is increased only insubstantially. It can be particularly advantageous if the elastic component is formed by a helical spring, preferably a compression spring, as such components can be produced very simply with the forces required for this application. In a further particularly preferable embodiment of the tripping device in accordance with the invention it can be provided that the tripping armature can be actuated indirectly by a magnetic armature which is preferably connected with the tripping armature by means of an elastic coupling member and, optionally, one or several auxiliary armatures and is directly movable by the coil. As a result of the elastic coupling the magnetic armature can be moved even before reaching the holding force. As a result of this movement the force acting on the tripping armature can be built up continuously by way of the coupling member. This is of advantage particularly in the case of overcurrents with long build-up time, as the magnetic armature has already covered a large section of its path on reaching the switching threshold, the same will only be released on reaching the switching threshold in the case of rigid coupling or direct influence of the coil on the tripping armature and must cover the entire path up to the switch latch. In a further development of this preferred embodiment of the invention it can be provided that the at least one elastic coupling member is formed by a helical spring. Such -6- coupling members require little space, but at the same time are provided with a favourable elasticity which remains relatively constant over time. It can be particularly beneficial if the magnetic armature is arranged at least in sections in the interior of the coil. In this way the magnetic armature is movable in a precisely predictable manner by the magnetic forces of the current to be monitored. In this respect it can be further of advantage if also the tripping armature is arranged in the interior of the coil, with the tripping armature being formed of non-magnetizable material. This leads to a further possibility to reduce the overall size of the tripping device. It may be further provided that the tripping armature is provided with a nose which reaches through the magnetic armature and extends preferably parallel to the longitudinal axis of the coil. A component of magnetizable material is fixed on the nose which is held by electromagnets. This allows a further geometrical reduction in size of the tripping device in accordance with the invention. Apart from the electromagnets holding the tripping armature, it is only dependent on the size of the coil. Outside of the same there are no movable components any more. A further feature of the invention can be that the electromagnet comprises an H-shaped yoke whose transversal bridge carries the coil, whose first pair of legs acts upon -7- the tripping armature by way of the component and whose second pair of legs acts on the short-circuit armature. This represents a design of the electromagnet which is easy to manufacture, but which still fully meets the requirements placed on it. It can further be provided that the electromagnet is arranged with its longitudinal axis normal to the longitudinal axis of the tripping armature. In this way the longitudinal extension of the entire tripping device can kept small. In a further embodiment of the invention it can be provided that the short-circuit armature is laminated. In a laminated armature considerable fewer magnetic reversal and eddy current losses will develop, as a result of which the armature movement is accelerated and in the end it is possible to achieve a reduction of the response time of the entire tripping device. The invention is now explained in closer detail by reference to the particularly preferred embodiments which are shown in the accompanying drawings, wherein : Figs. 1 a, b show schematic elevated views of two possibilities to realize the tripping device in accordance with the invention; Fig. 2 a, b show preferred embodiments of the holding magnet in plan view with two different ways of producing the holding force; Fig. 3 shows an embodiment of the holding magnet which is an alternative to figs. 2 a b in an oblique elevated view; 8 Fig. 4 shows a schematic elevated view of a particularly preferred embodiment of the tripping device in accordance with the invention and Fig. 5 shows the longitudinal sectional view through a line safety switch provided with a short-circuit tripping device in accordance with the invention. The tripping device for an overcurrent interrupting device such as a line safety switch as shown in figs, la, b is provided with a tripping armature 11 which by way of a pin-like projection 27 can actuate a switch latch 18. Said switch latch 18 is operatively connected with one or several movable contacts 28 which conduct a current to be monitored and opens the same in case of actuation by the pin-like projection 27. The tripping armature 11 is arranged in the interior of a coil 6 which is flowed through by a current to be monitored and, because it is made from a magnetizable material, can be moved in the direction of the switch latch 18 as a result of the magnetic field produced by the coil 6, as is shown symbolically with the arrow 110. The return of the tripping armature 11 to its idle position, as is represented symbolically with arrow 120, occurs by a spring 12 whose first end rests on a merely symbolically shown stationary component 34 and whose second end rests on the tripping armature per se. The tripping armature 11 is held by an electromagnet 20 in its idle position in which the pin-like projection 27 is lifted off from the switch latch 18. This electromagnet 20 comprises a yoke 14 bearing a coil 7, with the coil 7 being flowed through by the current to be monitored. This is achieved by the series connection of the two coils 6 and 7 which is shown in the thick lines. The tripping armature 11 is provided with a nose 24 on whose end a component 13 made of magnetizable material is fixed. Said component 13 forms 9 in combination with the yoke 14 of the electromotor 20 a magnetic circuit through which the explained fixing of the tripping armature 11 in its idle position is achieved. The purpose of the fixing of the tripping armature 11 in its idle position is the delay in tripping which can thus be achieved. A tripping can only occur if the force acting by the coil 6 on the tripping armature 11 is higher than the result of the spring force of spring 12 and the holding force of electromagnet 20. As a result of the fact that the electromagnet 20 is excited by the current to be monitored itself, the tripping delay, which is also known as selectivity, is automatically set depending on the current strength of current, namely in such a way that a high strength of current causes a high selectivity. It is understood that for achieving this property of selectivity adjustment it is not necessary that the current to be monitored per se flows through the coil 7. It is sufficient to subject coil 7 to a current which is proportional to a current to be monitored. Such a current can be produced in such a way that a part of the current, to be monitored is guided past coil 7 by way of a parallel resistor 29, as is shown in fig. la with a broken line. This can make sense if the electromagnet 20 is designed constructionally in such a way that merely a part of the current to be monitored is sufficient for the realization of the described selectivity, but that the full current, however, would cause an intensive fixing of the tripping armature 11 in its idle position. By changing the parallel resistor 29 it is possible to influence the selectivity in a particularly simple way. Even if this would entail, a relatively high amount of additional complexity, it is also possible within the terms of the invention to charge coil 7 with a current which is 10 electrically separated from the current to be monitored, but which extends proportional to the same. In the case of particularly high strengths of current a time-delayed cut-off is no longer desired. In the interest of downstream consumers such particularly high currents should be switched off in the shortest possible time. For this purpose it is necessary to switch off the delaying effect, which is caused by the electromagnet 20, during any occurrence of such high currents. This is achieved in accorance with the invention by short-circuiting coil 7. This short circuit can be realized in various ways. For this purpose there is provided in fig. la a switching contact 30 which is switched parallel to coil 7. In addition there is a triggering circuit 31 which detects the current strength of current, which is performed via the measurement of the voltage drop caused on a shunt resistor R by the current to be monitored. On reaching the maximum permitted strength of current the triggering circuit 31 closes the switching contact 30, as a result of which the magnetic field penetrating the component 13 and yoke 14 breaks down abruptly. The tripping armature 11 is thus released and can actuate the switch latch 18 immediately. The embodiment pursuant to fig. 1b substantially corresponds to the one pursuant to fig. la, but the short-circuiting of coil 7 is realized differently. Concerning the arrangement of coil 1 notice shall be taken that the same is provided in the embodiments of the drawings only with one winding layer. Although this constitutes a preferred embodiment, it shall in no way be understood as limiting. Conversely, said coil 7 can be provided with any desired number of winding layers. 11 Pursuant to fig. 1b all windings of the single winding layer of coil 7 are provided with sections 71 which are kept free from insulating material. Adjacently, there is provided an electrically conductive bridge 17 which on reaching a predeterminable strength of current can be brought into contact with said sections 71. A further electromagnet, consisting of an armature 32 connected with the bridge 17 and a coil 33 acting upon armature 32, is provided for the thus required movement of said bridge 17 in the direction of arrow 170. This electromagnet is driven analog to the embodiment pursuant to fig. la by a triggering circuit 31 in the manner as explained above. Both previously presented realization variants have the disadvantage that a triggering circuit 31 with associated current detection devices is required additionally. In contrast to this, the embodiments pursuant to figs. 2 a, b use the magnetic field for the movement of bridge 17, which field is present anyway, is produced by the coil 7 itself and is thus a measure for the strength of the current to be monitored. For this purpose this bridge 17 is fixed on a short-circuit armature 15, which short-circuit armature 15 is held with a predeterminable holding force in its idle position and can be moved by the electromagnet 20 from said idle position to a position which brings the bridge 17 into contact with the sections 71 which are kept free from insulating material. The fixing of the short-circuit armature 15 in the idle position is necessary in order to maintain the tripping delay produced by the electromagnet 20 at low strengths of current. The holding force of the short-circuit armature 15 is dimensioned in such a way that during the occurrence of 12 the strength of current from which an undelayed tripping is to take place it is exceeded by the force which acts on the short-circuit armature 15 and is built up in the air gap. In this way the short-circuit armature 15 is released, the coil 7 is subsequently short-circuited and the tripping is performed. The holding force holding the short-circuit armature 15 in its idle position can be produced in any way, e.g- by frictional forces and the like produced by components touching the short-circuit armature 15. In a particularly preferable embodiment of fig. 2a there is provided for this purpose an elastic component 16 which is formed by a helical spring, arranged functionally as a compression spring. It extends between a stationary housing part 21 and an oblong nose 151 of the short-circuit armature 15. Fig. 2b shows an embodiment which corresponds in respect of its function to fig. 2a. An extension spring is used here as an elastic component 16, which spring is fixed on the short-circuit armature 15 and on a housing part 21. The connection of bridge 17 with the short-circuit armature 15 occurs through a contact spring 35. It can further be clearly seen from figs. 2a, b that there is a preferred constructional arrangement of the electromagnet 20. Its yoke 14 is arranged in the shape of an H, with the transversal bridge 140 carrying the coil 7 and its first pair of legs 141, 142 acting upon the tripping armature 11 by way of component 13 and its second pair of legs 143, 144 acting upon the short-circuit armature 15. Another embodiment of the electromagnet 20 is shown by fig. 3: The first pair of legs 141, 142 stands normally to the second pair of legs 143, 144. The arrangement at a right angle shall again not be understood as limiting. The chosen 13 angle between the pairs of legs is irrelevant for the electrotechnical function and can therefore be chosen at will or according to constructional requirements. Fig. 4 shows a further development of the embodiment pursuant to fig. la. The special aspect in this respect is that the tripping armature 11 is not directly actuatable by coil 6. Instead, a further armature, which shall be designated hereinafter as magnetic armature 10, is provided. Said magnetic armature 10 can be actuated by coil 6 directly in the direction of the arrow 100 and is in connection with the tripping armature 11 by way of an elastic coupling member 22 which is formed by a helical spring. The tripping armature 11 is thus moved only indirectly by coil 6 in the direction of arrow 110. This indirect coupling can naturally be expanded further at will by providing auxiliary armatures with respective further elastic coupling members {not shown in the drawings any more) between magnetic armature 10 and tripping armature 11. For the purpose of fixing the armature 11, the same is provided analog to fig. la, b with a projection 24 carrying a magnetizable component 13, which projection is guided through a respective bore of the magnetic armature 10 and extends approximately parallel to the longitudinal axis of the coil 6. The tripping process of such an arrangement can be broken down into two tripping phases which are described below. In a first tripping phase, which immediately follows the occurrence of the overcurrent, the overcurrent produces by way of coil 6 a magnetic field which is proportional to its strength and moves the magnetic armature 10 in the direction of the tripping armature 11. This movement is transmitted by way of the elastic coupling member 22 onto the tripping armature 11 which, for the time being, remains 14 in its idle position as a result of the holding force exerted on it by the electromagnet. During further progressing deflection of the magnetic armature 10 the coupling member 22 is increasingly biased, as a result of which the force acting upon the tripping armature 11 increases. In this tripping phase the magnetic armature 10 and the coupling member 22 represent an oscillation system which is excited by the magnetic force generated by the overcurrent. The time which the magnetic armature 10 requires in order to bias the coupling member until the holding force is exceeded and the tripping armature becomes deflectable from its idle position results in the time delay, i.e. the selectivity of the tripping device in accordance with the invention. If the force produced by the overcurrent exceeds the holding force, the second tripping phase will occur. The tripping armature 11 will start to move abruptly, as a result of which the switch latch 18 is actuated and the contacts 28 are opened subsequently. In this tripping phase the now coupled masses of magnetic armature 10 and tripping armature 11 represent the oscillation system in cooperation with the return spring 12. It works like a common magnet tripping device formed merely by a coil and armature, with the exciter force arising from the result of the system of forces consisting of current force and holding force. In summary, the tripping is not initiated by an armature actuated directly by the overcurrent, but occurs indirectly by the movement of the magnetic armature 10 which is connected by means of the elastic coupling member 22 with the tripping armature 11 and is immediately movable by the coil 6. The time delay of the tripping is substantially brought about in the first tripping phase. It is determined by the mechanical properties of the oscillation system of magnet- 15 armature mass, spring rate of the coupling member 22 and magnet-armature stroke and by the current force. As is known, the current force is proportional to the square of current, and as a result so is the movement of the magnetic armature 10. In this way the delay is proportional to the square of current, similarly as in the aforementioned known electrothermally operating time elements. Fig. 5 shows a longitudinal sectional view through a line safety switch which is equipped with a short-circuit current tripping device and is in the switched-on condition. The path of current leads from the first connecting terminal la by way of the bimetallic strip 2 via a flexible conductor cable 3 to the contact bridge 4 and from there via the movable contact 28 and the fixed contact 36 to the fixed-contact carrier 5, via coil 6 to coil 7 and from there to the second connecting terminal 1b. The tripping device in accordance with the invention is arranged in its principle according to the embodiment pursuant to fig. 2a. Constructional details which are worth mentioning and contribute to the reduction of the overall size are as follows: The magnetic armature 10 as well as the tripping armature 11 are arranged in the idle position in sections in the interior of coil 6. In order to prevent the tripping armature 11 from being moved by the magnetic field of coil 6 in such an arrangement, it is necessary to produce it from non-magnetizable material such as plastic. Magnetic armature 10 is arranged as a pipe section which is closed off on one side and receives the tripping armature 11 at least partly within its hollow space. In the represented embodiment no elastic coupling member 22 is 16 provided between the magnetic armature 10 and a tripping armature 11. The closed pipe end rests directly on tripping armature 11. If such a coupling member 22 is to be built in, it is preferably also arranged in the hollow space of the magnetic armature 10. As in fig. 4, the projection 24 of the tripping armature 11 is arranged so as to reach through the magnetic armature 10 and again carries a component 13 made of magnetizable material which in cooperation with the electromagnet 20 causes the fixing of the tripping armature 11 in its idle position. The electromagnet 20 is provided with an H-shaped yoke 14 and is arranged with its longitudinal axis 25 normally to the longitudinal axis 26 of the tripping armature 11. In this way the overall size of the line safety switch can be reduced to a considerable extent. Notwithstanding the above, it is possible within the terms of the invention to arrange the electromagnet 20 at any other angle to the longitudinal axis 26 of the tripping armature 11. The short-circuit armature 15 is preferably provided with a laminated design in order to reduce magnetic reversal and eddy current losses and thus to ensure a particularly rapid movement of the short-circuit armature 15. The switch latch 18 is arranged in a common design which per se is known. Both the bimetallic strip 2 as well as the pin 27 moulded onto the tripping armature 11 act upon the contact bridge 4. It is spring pretensioned, as a result of which the slight deflection caused by the two tripping mechanisms is amplified to a complete swivelling into the off position. -17- WE CLAIM : 1. Tripping device adapted to be used with an overload circuit breaker comprising a tripping armature (11) that operates a switch latch (18), said tripping armature being operable by a coil (6) through which a monitored current flows, characterized in that the tripping armature (11) is retained in its resting position by a spring (12) and an electromagnet (20) having a coil through which coil flows the monitored current or a current that is proportional to the monitored current, and in that the coil (7) of the electromagnet is adapted to be short-circuited when a predeterminable current value is reached. 2. Tripping device as claimed in claim 1, wherein the coil (7) of the electromagnet has an outlet winding layer in which the turns of the outer winding layer have sections (71) that are free of insulating material, and wherein an electrically conductive bridge (17) is provided, which is capable of being brought in contact with the sections (71) in the event of when the predeterminable current value is reached. 3. Tripping device as claimed in claim 2, wherein the coil (7) of the electromagnet has only one winding layer and wherein all turns of this winding layer have sections (71) that are free of insulating material. 4. Tripping device as claimed in claim 3, wherein the electrically conductive bridge (17) is fixed to a short-circuit armature (15), which is capable of being moved by the electromagnet (20) from a resting position into a position that brings the bridge (17) into contact with the sections (71) that are kept free of insulating material, and in which the short-circuit armature (15) is caused to be retained in its resting position with a predeterminable holding force. 1. -18- 5. Tripping device as claimed in claim 4, wherein the holding force that retains the short-circuit armature (15) in its resting position is generated by an elastic component (16) that is connected to the short- circuit armature (15) and housing (21) of the tripping device. 6. Tripping device as claimed in claim 5, wherein the elastic component (16) is formed by a spiral spring. 7. Tripping device as claimed in claim 6, wherein the spiral spring is a compression spring. 8. Tripping device as claimed in any one of the preceding claims, wherein the tripping armature (11) is adapted to be operated indirectly through a magnet armature (10) that is operated directly by the coil (6) through which the monitored current flows, and in which said magnet armature is connected to the tripping armature (11) by at least one elastic coupling element (22) and, if necessary, one or more auxiliary armatures. 9. Tripping device as claimed in claim 8, wherein the at least one elastic coupling element (22) is formed by a spiral spring. 10. Tripping device as claimed in claim 8 or claim 9, wherein the magnet armature (10) is provided at least partially inside the coil (6), through which the monitored current flows. 11. Tripping device as claimed in claim 10, wherein the tripping armature (11) is also provided inside the coil (6) through which the monitored current flows, and the tripping armature (11) is made of a non-magnetisable material. 5. -19- 12. Tripping device as claimed in claim 11, wherein the magnet armature (10) has the form of a tube that is closed at one end and wherein the tripping armature (11) and the at least one elastic coupling element (22) are provided at least partially inside a hollow section formed by the magnet armature (10). 13. Tripping device as claimed in claim 10, 11 or 12 wherein attached to the tripping armature (11) is a projection (24) that extends through the magnet armature (10) and fitted to said projection is a component made of magnetisable material, which component (13) is retained by an electromagnet (20). 14. Tripping device as claimed in claim 13, wherein the projection is aligned parallel to the longitudinal axis of the coil through which the monitored current flows. 15. Tripping device as claimed in any one or more of claims 4 to 14, wherein the electromagnet (20) comprises a H-shaped yoke (14), whose transverse bar (140) carries the coil (7) of the electromagnet, whose first pair of limbs (141, 142) acts via the component (13) made of magnetisable material on the tripping armature (11) and whose second pair of limbs (143, 144) act on the short-circuit armature (15). 16. Tripping device as claimed in claim 15, wherein the longitudinal axis of the electromagnet (20) is disposed parallel to the longitudinal axis (26) of the tripping armature (11). 17. Tripping device as claimed in any one or more of claims 4 to 16, wherein the short-circuit armature (15) is laminated. 17. -20- 18. Tripping device as claimed in any one of the preceding claims wherein the overload circuit breaker is a line safety switch. 19. An overload circuit breaker incorporating a tripping device as claimed in any one or more of claims 1 to 18. 20. A line safety switch incorporating a tripping device as claimed in any one or more of claims 1 to 18. 21. Tripping device, substantially as herein described, particularly with reference to and as illustrated in the accompanying drawings. Dated this 17 th day of June 1998. (S.CHAKRABORTY) of DP. AHUJA & CO. Applicants' Agent Tripping device adapted to be used with an overload circuit breaker comprising a tripping armature (11) that operates a switch latch (18), said tripping armature being operable by a coil (6) through which a monitored current flows, characterized in that the tripping armature (11) is retained in its resting position by a spring (12) and an electromagnet (20) having a coil through which coil flows the monitored current or a current that is proportional to the monitored current, and in that the coil (7) of the electromagnet (20) is adapted to be short-circuited when a predeterminable current value is reached.

Documents:

01074-cal-1998 abstract.pdf

01074-cal-1998 claims.pdf

01074-cal-1998 correspondence.pdf

01074-cal-1998 description(complete).pdf

01074-cal-1998 drawings.pdf

01074-cal-1998 form-1.pdf

01074-cal-1998 form-13.pdf

01074-cal-1998 form-2.pdf

01074-cal-1998 form-3.pdf

01074-cal-1998 form-5.pdf

01074-cal-1998 gpa.pdf

01074-cal-1998 priority document other.pdf

01074-cal-1998 priority document.pdf

1074-CAL-1998-CORRESPONDENCE.pdf

1074-CAL-1998-FOR ALTERATION OF ENTRY IN THE PATENT REGISTER.pdf

1074-CAL-1998-FORM 27.pdf

1074-CAL-1998-FORM-27.pdf

1074-cal-1998-granted-abstract.pdf

1074-cal-1998-granted-claims.pdf

1074-cal-1998-granted-correspondence.pdf

1074-cal-1998-granted-description (complete).pdf

1074-cal-1998-granted-examination report.pdf

1074-cal-1998-granted-form 1.pdf

1074-cal-1998-granted-form 13.pdf

1074-cal-1998-granted-form 2.pdf

1074-cal-1998-granted-form 5.pdf

1074-cal-1998-granted-gpa.pdf

1074-cal-1998-granted-priority document.pdf

1074-cal-1998-granted-reply to examination report.pdf

1074-cal-1998-granted-specification.pdf

1074-cal-1998-granted-translated copy of priority document.pdf