AU7897598A - Device for triggering an overload circuit breaker - Google Patents

Description

Translation from Gennan of PCTIAT98/00154 Device for triggering an overload circuit breaker 5 The invention concerns a trigger device for an overload circuit breaker, such as a line safety switch, comprising a trigger armature that operates a switch latch and which 10 can be actuated by a coil, through which flows the current to be monitored. Overload circuit breaker devices currently in use are essentially in the form of fuses, which are only useful 15 for a single cut-out operation, or in form of automatic cut-out switches that can be reused multiple times. Overload protection of the type mentioned above is usually provided in the supply line of an electrical 20 installation, prior to the point where this supply line is split into multiple parallel circuits. Each of these circuits features its own protection devices, which usually consist of personal protection devices (residual current circuit breaker or similar) and plant protection 25 devices (line safety switches, fuses or similar). If required, these circuits can be split into further sub circuits that are also protected by protection devices. In a circuit structure of this kind the protection 30 devices of the supply line, the circuit and the sub circuit are connected in series.

2 If, for instance, an inadmissibly high current occurs in a sub-circuit it is desirable that only that circuit breaker trips that is assigned to this sub-circuit and hence disconnects its sub-circuit from the mains. All 5 other preceding circuit breakers, however, should remain switched on and thus keep all functional circuits and sub-circuits connected to the mains. The preceding, higher order circuit breaker should only trip if the occurring overcurrent is so high that it can no longer be 10 switched off by the circuit breaker of the sub-circuit. The time-delayed switching of this kind of the preceding circuit breaker is called "selectivity". In fuses this selectivity is determined by the heating 15 power required to melt the fusible wire, which heating power is proportional to the square of the current and the period of the overcurrent. There are usually two trigger devices provided in the 20 field of line safety switches. The first device has the purpose of switching off at an overcurrent that is only slightly above the rated current of the plant but acts over a longer period. The second, so-called short-circuit current trip device is usually implemented by a coil with 25 a moveable armature that trips the circuit breaker, and in which the current to be monitored flows through said coil. In order to recreate the heating power dependent, and hence current and time dependent, delay as explained in connection with fuses, thermal bimetallic strips are 30 used through which the monitored current flows. Analogous to the fusible wires, said bimetallic strips are deformed proportional to the square of the current and the time, 3 which deformation activates time-delayed the switching action of the short-circuit current trip device. These bimetallic strips are components that require 5 accurate mechanical adjustment as well as electrical connections. In summary, they make the circuit breaker design significantly more complex, which reduces functional reliability and makes production more difficult. A further disadvantage of this type of design 10 is that the time-delayed cut-out achieved by the bimetallic elements is retained independent of the level of the monitored current. This results even at very high short-circuit currents, which should be switched off without any delay for the protection of the plant, in a 15 delayed triggering of the protection device. It is the object of the invention to provide a trigger device of the kind described at the outset, which has a selective trigger characteristic but requires for this 20 purpose only a few sturdy components that can be easily installed in addition to the usual trigger coil. Moreover, the trigger device according to the invention is to lose its selectivity and react immediately if the monitored current reaches a certain predeterminable 25 value. This object is achieved according to the invention in that the trigger armature is held in its resting position by a spring and an electromagnet, through whose coil 30 flows the monitored current or a current proportional to the monitored current, and that the coil can be short circuited when a predeterminable current value is reached.

4 The response of the trigger armature is thus delayed by simple constructive means until the force applied by the coil on the trigger armature exceeds the holding force of 5 the electromagnet. The selectivity, furthermore, is automatically adapted to the actual value of the monitored current, but is reversed abruptly through short-circuiting, which immediately collapses the holding magnetism. 10 In a further development of the invention provision can be made in which the turns of the outermost winding layer of the coil have sections that are free of insulating material, and that an electrically conductive bridge is 15 provided that can be brought in contact with these sections when a predeterminable current value is reached. Thus a short-circuiting contact connected parallel to the coil, which would have to be rated relatively high in 20 accordance with the expected high currents, is made redundant. Furthermore, said coil may only be provided with a single winding layer, and all turns of this winding layer may 25 have sections that are free of insulating material. This embodiment permits the short-circuiting of each turn of the coil, which ensures a particularly rapid collapse of the magnetic field. 30 In accordance with a particularly preferred embodiment of the invention the electrically conductive bridge may be attached to a short-circuit armature, which short-circuit 5 armature can be moved by the electromagnet from a resting position into a position that brings the bridge in contact with sections that are free of insulating material. Said short-circuit armature is retained in its 5 resting position with a predeterminable holding force. Thus only a single component, that is, the short-circuit armature, has to be provided in addition to the already present electromagnet. This permits a particularly 10 compact and functionally reliable construction. Through appropriate sizing of the holding force of the short circuit armature, the value at which the coil is short circuited can be adjusted very simply. 15 In this connection a further characteristic of the invention may lie in that the holding force that retains the short-circuit armature in its resting position can be generated by an elastic component that is attached to the short-circuit armature and the housing of the trigger 20 device. These components are quite small and hence the overall size increase of the trigger device according to the invention is insignificant. 25 It may be particularly advantageous for the elastic component to be in form of a spiral spring, preferably a compression spring, since components of this kind can be produced very simply with the forces necessary for this 30 application. In a further particularly preferred embodiment of the trigger device according to the invention the trigger

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6 armature may be operated indirectly through a magnet armature that is operated directly by the coil, in which said magnet armature is connected to the trigger armature by means of at least one elastic coupling element and, if 5 necessary, one or more auxiliary armatures. As a result of the elastic coupling the magnet armature can already be moved before the holding force is reached. Thus the force acting on the trigger armature through 10 this movement builds up continuously via the coupling element. This is primarily of advantage in the instance of excess currents with long build-up times since the magnet armature has in this case already travelled a large portion of its path when the switching threshold is 15 reached. In the instance of rigid coupling, or when the coil acts directly on the trigger armature, said magnet armature is only released when the switching threshold is reached and must then travel the entire distance to the switch latch. 20 In a further development of this preferred embodiment of the invention at least one elastic coupling element can be in form of a spiral spring. 25 Coupling elements of this kind require little space and retain a satisfactory and relatively constant elasticity over time. It may be of particular advantage to arrange the magnet 30 armature at least partly inside the coil. A41 7 Thus the magnet armature can be moved in an exactly predictable manner by the magnetic forces of the monitored current. 5 Furthermore, it can be of advantage to arrange the trigger armature also inside the coil, and to produce the trigger armature of non-magnetisable material. This provides another opportunity to reduce the overall 10 size of the trigger device. The trigger armature may also feature a projection that extends preferably parallel to the longitudinal axis of the coil and through the magnet armature. Attached to 15 said projection is a component of magnetisable material that is held by the electromagnet. This permits a further geometrical reduction of the trigger device according to the invention. Apart from the 20 electromagnet, which retains the trigger armature, said trigger device is now only dependent on the size of the coil. Besides the coil there are no longer any moving parts. 25 A further characteristic of the invention may be in that the electromagnet features a H-shaped yoke, whose transverse bar carries the coil, whose first pair of limbs acts via the component on the trigger armature and whose second pair of limbs acts on the short-circuit 30 armature.

8 This constitutes a particularly simple design of the electromagnet, which still meets all the demands placed upon it. 5 It may, furthermore, be arranged so that the longitudinal axis of the electromagnet is oriented perpendicular to the longitudinal axis of the trigger armature. The longitudinal extension of the entire trigger device 10 can thus be kept small. In a further embodiment of the invention the short-circuit armature may be laminated. There are significantly less hysteresis and eddy current losses in a laminated armature, which increases the speed 15 of the armature movement and thus reduces the reaction time of the entire trigger device. The invention is described below in detail by way of the particularly preferred embodiments depicted in the 20 enclosed drawings. Shown are in: Fig. la,b a schematic front elevation of two options for realising the trigger device according to the invention; 25 Fig. 2a,b a preferred embodiment of the holding magnet in plan view with two different variations for generating the holding force; 30 Fig. 3 an alternative embodiment of the holding magnet to those shown in Fig. 2a,b in oblique projection; 9 Fig. 4 a schematic front elevation of a particularly preferred embodiment of the trigger device according to the invention; and 5 Fig. 5 a longitudinal section through a line safety switch fitted with a short-circuit trigger device according to the invention. The trigger device for an overload circuit breaker shown 10 in Fig. la,b, such as a line safety switch, comprises a trigger armature 11 that is able to operate a switch latch 18 via a pin-like extension 27. Said switch latch 18 is operatively connected to one or more moveable contacts 28, through which flows the monitored current, 15 and opens these contacts when operated by the pin-like extension 27. The trigger armature 11 is arranged inside a coil 6, through which the monitored current flows. Since it is manufactured of a magnetisable material, said trigger armature 11 can be moved towards the switch latch 20 18 by means of the magnetic field generated by coil 6, as indicated symbolically by arrow 110. The trigger armature 11 is returned into its resting position, as indicated by arrow 120, by means of spring 12, whose first end is braced against a symbolically depicted, rigid component 25 34 and whose second end is braced against the trigger armature 11. The trigger armature 11 in its resting position, in which the pin-like extension 27 is withdrawn from switch latch 30 18, is retained by an electromagnet 20. Said electromagnet 20 comprises a yoke 14 carrying a coil 7, through which flows the monitored current. This is achieved by connecting the two coils 6 and 7 in series as 10 depicted by the heavy lines. The trigger armature 11 is fitted with a projection 24 at whose end is attached a component 13 made of magnetisable material. Said component 13 together with the yoke 14 of electromagnet 5 20 forms a magnetic circuit, which effects the above explained retention of the trigger armature 11 in its resting position. Retaining the trigger armature 11 in its resting position 10 has the purpose of effecting the trip delay function. Tripping can only take place if the force exerted by coil 6 on trigger armature 11 is greater than the product of the spring force of spring 12 and the holding force of electromagnet 20. Since the electromagnet 20 is excited 15 by the monitored current itself, the trip delay, also called selectivity, is adjusted automatically depending on the actual current value, where a high current results in a high selectivity. 20 To achieve this characteristic of selectivity adaptation it is, of course, not necessary that the monitored current itself flows through coil 7. It is sufficient to apply a current that is proportional to the monitored current. Such a current can be generated, for example, in 25 that part of the monitored current is passed by coil 7 via a parallel resistor 29, as shown in Fig. la with broken lines. This would be sensible in instances where the electromagnet 20 is designed such that only part of the monitored current is sufficient to achieve the 30 described selectivity, but where the full current would cause a too forceful retention of the trigger armature 11 in its resting position. Changing the value of the 11 parallel resistor 29 provides a particularly simple means of influencing the selectivity. Although it would result in relatively high extra 5 expenses, as far as the invention is concerned it is also possible to apply a current to coil 7 that is galvanically separated from the monitored current but is proportional to it. 10 At particularly high current values a time-delayed tripping is no longer desirable. In the interest of loads connected downstream, such particularly high currents should be switched off as quickly as possible. To do this it is necessary to switch off the delay effect at high 15 currents caused by electromagnet 20, which is accomplished according to the invention by short circuiting coil 7. There are different methods for achieving this short 20 circuit. Fig. la shows for this purpose a switch contact 30 connected parallel to coil 7. Provided is also a control circuit 31 that senses the actual current value, which is achieved according to Fig. la by measuring the voltage drop on a shunt resistor R generated by the 25 monitored current. When the maximum admissible current value is reached, control circuit 31 closes the switch contact 30. This causes an abrupt collapse of the magnetic field that flows through component 13 and yoke 14. The trigger armature 11 is consequently released and 30 is able to immediately operate the switch lock 18.

12 The embodiment according to Fig. lb is essentially the same as that of Fig. la, the short-circuiting of the coil 7, however, is achieved in a different way. 5 Concerning the design of coil 7 it should be noted that its embodiment in the drawing depicts always one layer of windings only. Although this represents a preferred embodiment, it is not to be understood as a limitation. Said coil 7 may have any number of winding layers. 10 According to Fig. lb all turns of the single winding layer of coil 7 have sections 71 that are free of insulating material. An electrically conductive bridge 17 is also provided, which can be brought in contact with 15 said sections 71 as soon as a predeterminable current value is reached. A further electromagnet for the movement of said bridge 17 in the direction of arrow 170 is necessary for this 20 purpose. Said electromagnet consists of an armature 32 that is attached to bridge 17, as well as a coil 33 that acts upon armature 32. Said electromagnet according to the embodiment shown in Fig. la is controlled by a control circuit 31 in the way described above. 25 Both embodiment variations presented so far have the disadvantage that an additional control circuit 31 with its respective current sensing devices is required. 30 The embodiments according to Fig. 2a,b, in contrast, use the already existing magnetic field, which is generated by the coil 7 itself and is therefore a measure for the 44 13 value of the monitored current, for the movement of bridge 17. Said bridge 17 is attached to a short-circuit armature 5 15, which is retained in its resting position with a predeterminable holding force. Said bridge 17 can be moved by electromagnet 20 from this resting position into a position that brings bridge 17 into contact with sections 71, which are free of insulating material. 10 It is necessary to fix the short-circuit armature 15 in the resting position to retain the trip delay function generated by electromagnet 20 at low current values. The holding force of short-circuit armature 15 is calculated 15 such that it is exceeded by the magnetic force that acts upon short-circuit armature 15 and is built up in air gap 19, when the particular current value occurs at which undelayed tripping should take place. Thus the short circuit armature 15 is released, coil 7 is subsequently 20 short-circuited and the trigger process takes place. The holding force that retains the short-circuit armature 15 in its resting position can be generated in various ways, for example, by the friction forces of components 25 that are in contact with the short-circuit armature 15, or similar. In the particularly preferred exemplary embodiment of Fig. 2a an elastic component 16 in form of a spiral spring, in this application a compression spring, is provided. It extends between a fixed housing 30 part 21 and an elongated projection 151 of the short circuit armature 15.

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14 Fig. 2b depicts an embodiment that is functionally equal to that of Fig. 2a, in which a tension spring located between short-circuit armature 15 and a housing part 21 forms the elastic component 16. The connection of bridge 5 17 with the short-circuit armature 15 is effected here via a contact spring 35. Moreover, a preferred design of the electromagnet 20 is clearly recognisable in Fig. 2a,b. Its yoke 14 has a H 10 like shape, in which the transverse bar 140 carries coil 7, and where its first pair of limbs 141, 142 acts via component 13 on the trigger armature 11, and its second pair of limbs 143, 144 acts on short-circuit armature 15. 15 Fig. 3 depicts a different embodiment of electromagnet 20: Here the first pair of limbs 141, 142 extends perpendicular to the second pair of limbs 143, 144. Again, the right-angle arrangement is not to be understood to be limiting. The angle chosen between the 20 pairs of limbs is unimportant as far as the electrotechnical function is concerned, and thus can be selected as desired or as required by the design. Fig. 4 depicts a further development of the embodiment 25 according to Fig. la. The special feature here is that the trigger armature 11 is not operable directly by coil 6, but that a further armature, in the following called magnet armature 10, is provided. Said magnet armature 10 is operable by the coil 6 directly in direction of arrow 30 100 and is connected to trigger armature 11 via an elastic coupling element 22, provided in form of a spiral spring. Hence the trigger armature 11 is moved only indirectly in the direction of arrow 110 by coil 6. It 15 is, of course, possible to expand said indirect coupling mechanism as desired, in that further auxiliary armatures with corresponding further elastic coupling elements are provided between magnet armature 10 and trigger armature 5 11. These are not represented in the drawings, however. For the purpose of retaining trigger armature 11, said armature features, analogous to Fig. la,b, a projection 24 carrying magnetisable component 13. Said projection 24 10 extends through a bore hole of magnet armature 10 and is aligned approximately parallel to the longitudinal axis of coil 6. The tripping process of an arrangement of this kind can 15 be split into two tripping phases, which are described in the following. In a first tripping phase, which immediately follows the occurrence of an overload, the excess current generates via coil 6 a magnetic field that is proportional to the value of the current. Said 20 magnetic field moves the magnet armature 10 in the direction of the trigger armature 11. This movement is transmitted via the elastic coupling element 22 to trigger armature 11. Said trigger armature 11, however, remains for the time being still in its resting position 25 due to the holding force applied to it by the electromagnet. As the excursion of magnet armature 10 increases, the tension of coupling element 22 increases progressively, which increases the force applied to trigger armature 11. In this trigger phase magnet 30 armature 10 and coupling element 22 constitute an oscillatory system, which is excited by the magnetic force generated by the excessive current. The time required by the magnet armature 10 to apply the amount of 16 tension on the coupling element that will exceed the holding force and release the trigger armature 11 from its resting position is the time delay or the selectivity of the trigger device according to the invention. 5 Provided that the force generated by the overload exceeds the holding force, the second trigger phase takes place. In this instance the trigger armature 11 is moved suddenly, which operates the switch latch 18 and 10 subsequently opens contacts 28. In this trigger phase the now coupled masses of magnet armature 10 and trigger armature 11 constitute, in conjunction with the reset spring 12, the oscillatory system. This operates like an ordinary magnetic trip unit consisting of coil and 15 armature, in which the excitation force is the product of the force system of current force and holding force. The trigger process is, therefore, not initiated by an armature operated directly by the overload, but takes 20 place indirectly through the movement of the magnet armature 10, which is connected via the elastic coupling element 22 to the trigger armature 11 and moveable directly by coil 6. 25 The time-delayed triggering is effected essentially in the first trigger phase. It is determined by the mechanical characteristics of the oscillatory system of magnet armature mass, spring characteristic of the coupling element 22 and stroke of the magnet armature as 30 well as the current strength. Since the current strength is proportional to the square of the current, so is the movement of magnet armature 10. Hence the delay is also proportional to the square of the current, the same as in 17 the known electrothermally operating delay devices mentioned at the outset. Fig. 5 depicts a longitudinal section through a line 5 safety switch, which is fitted with a short-circuit current trigger device and is in the switched-on state. The current path leads from the first terminal la via bimetallic element 2 and via a flexible conductor 3 to contact bridge 4, from there via the moveable contact 28 10 and the fixed contact 36 to the fixed contact support 5, via coil 6 to coil 7 and from there to the second terminal lb. The trigger device according to the invention is designed 15 according to the principle of the embodiment depicted in Fig. 2a. The following design details, which are all contributing to the reduction in overall size, are worth mentioning: 20 The magnet armature 10 as well as trigger armature 11 are partially located inside coil 6 in the resting position. To prevent the trigger armature 11 from being moved inside the magnetic field of the coil in this type of 25 arrangement, it is necessary to produce said trigger armature 11 from a non-magnetisable material such as plastic, for example. The magnet armature 10 has the form of a tube that is 30 closed at one end, accepting the trigger armature 11 at least partially inside its hollow space. There is no elastic coupling element 22 provided between magnet armature 10 and trigger armature 11 in the embodiment 18 depicted. The closed end of the tube rests directly against trigger armature 11. If a coupling element 22 of this kind is to be installed, it is advantageously arranged also inside the hollow cavity of magnet armature 5 10. As illustrated in Fig. 4, projection 24 of trigger armature 11 is designed such that it extends through magnet armature 10, and it also carries a component 13 10 made of magnetisable material, which causes the retention of trigger armature 11 in its resting position in conjunction with electromagnet 20. Electromagnet 20 features a H-shaped yoke 14 and is 15 arranged with its longitudinal axis 25 perpendicular to longitudinal axis 26 of the trigger armature 11. This allows a significant reduction in the overall height of the line safety switch. Nevertheless, according to the invention it is possible to arrange electromagnet 20 at 20 any desired angle to longitudinal axis 26 of the trigger armature 11. The short-circuit armature 15 is preferably laminated to reduce hysteresis and eddy current losses and hence 25 ensure a particularly fast movement of short-circuit armature 15. Switch latch 18 is constructed in the usual manner known per se. The bimetallic element 2 as well as pin 27, which 30 is attached to trigger armature 11, are acting upon contact bridge 4. Said contact bridge is spring-loaded, which amplifies the small excursion caused by the two 19 trigger mechanisms into a complete swivel movement into the off-position.

Claims (15)

1. Trigger device for an overload circuit breaker, such as, for example, a line safety switch, comprising a 5 trigger armature (11) that operates a switch latch (18), in which said trigger armature (11) can be operated by a coil (6) through which the monitored current flows, characterised in that the trigger armature (11) is retained in its resting position by 10 a spring (12) and an electromagnet (20), through whose coil (7) flows the monitored current or a current that is proportional to the monitored current, and that coil (7) can be short-circuited when a predeterminable current value is reached. 15

2. Trigger device according to claim 1, characterised in that the turns of the outer winding layer of coil (7) have sections (71) that are free of insulating material, and that an electrically conductive bridge 20 (17) is provided, which can be brought in contact with these sections (71) when a predeterminable current value is reached.

3. Trigger device according to claim 2, characterised 25 in that coil (7) has only one winding layer and that all turns of this winding layer have sections (71) that are free of insulating material.

4. Trigger device according to claim 3, characterised 30 in that the electrically conductive bridge (17) is fixed to a short-circuit armature (15), which can be moved by electromagnet (20) from a resting position into a position that brings bridge (17) into contact 21 with the sections (71) that are kept free of insulating material, in which this short-circuit armature (15) is retained in its resting position with a predeterminable holding force. 5

5. Trigger device according to claim 4, characterised in that the holding force that retains the short circuit armature (15) in its resting position can be generated by an elastic component (16) that is 10 connected to short-circuit armature (15) and housing (12) of the trigger device.

6. Trigger device according to claim 5, characterised in that the elastic component (16) is formed by a 15 spiral spring, preferably a compression spring.

7. Trigger device according to one of the preceding claims, characterised in that the trigger armature (11) may be operated indirectly through a magnet 20 armature (10) that is operated directly by the coil (6), in which said magnet armature (10) is connected to the trigger armature (11) by means of at least one elastic coupling element (22) and, if necessary, one or more auxiliary armatures. 25

8. Trigger device according to claim 7, characterised in that the at least one elastic coupling element (22) is formed by a spiral spring. 30

9. Trigger device according to claim 7 or 8, characterised in that the magnet armature (10) is arranged at least partially inside coil (6). 22

10. Trigger device according to claim 9, characterised in that the trigger armature (11) is also arranged inside coil (6), and the trigger armature (11) is made of a non-magnetisable material. 5

11. Trigger device according to claim 10, characterised in that the magnet armature (10) has the form of a tube that is closed at one end and that the trigger armature (11) and the at least one coupling element 10 (22) are arranged at least partially inside the hollow section formed by magnet armature (10).

12. Trigger device according to claim 9, 10 or 11, characterised in that attached to the trigger 15 armature (11) is a projection (24) that extends through the magnet armature (10) and is aligned preferably parallel to the longitudinal axis of coil (6), and fitted to said protrusion (24) is a component (13) made of magnetisable material, which 20 component (13) is retained by electromagnet (20).

13. Trigger device according to one of the claims 4 to 12, characterised in that the electromagnet features a H-shaped yoke (14), whose transverse bar (140) 25 carries coil (7), whose first pair of limbs (141, 142) acts via component (13) on trigger armature (11) and whose second pair of limbs (143, 144) acts on short-circuit armature (15). 30

14. Trigger device according to claim 13, characterised in that the longitudinal axis (25) of the electromagnet (20) is arranged perpendicular to the longitudinal axis (26) of the trigger armature (11). 23

15. Trigger device according to one of the claims 4 to 14, characterised in that the short-circuit armature (15) is laminated.