AU734007B2 - Device for triggering an overload circuit breaker - Google Patents

Description

DEVICE FOR TRIGGERING AN OVERLOAD CIRCUIT BREAKER The invention concerns a trigger device for an overload circuit breaker, such as a line safety switch.

Overload circuit breaker devices currently in use are essentially in the form of fuses, which are only useful for a single cut-out operation, or in the 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 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 devices (line safety switches, fuses or similar). If required, these circuits can be split into further subcircuits that are also protected by protection devices.

In a circuit structure of this kind the protection devices of the supply line, the circuit and the sub-circuit are connected in series.

i oeo S. *o 0o* 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 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 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 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 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 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 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, which deformation activates time-delayed the switching action of the short-circuit current trip device.

These bimetallic strips are components that require 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 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 delayed triggering of the protection device.

An object of the present invention is to overcome one or more of the problems in the prior art, or to provide an improvement or alternative thereto.

It is a further object of the invention to provide a trigger device of the kind described at the outset, which has a selective trigger characteristic but requires 15 for this 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 o.O:O invention is to lose its selectivity and react immediately if the monitored current S**reaches a certain predeterminable value.

According to the present invention, there is provided a trigger device adapted to be used with an overload circuit breaker including a trigger armature *o that operates a switch latch, said trigger armature being operable by a coil through which a monitored current flows, wherein the trigger 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 25 monitored current, and wherein the coil of the electromagnet is adapted to be *short-circuited when a predeterminable current value is reached.

In an exemplary embodiment of the invention, 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 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.

In a further exemplary embodiment 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 provided that can be brought in contact with these sections when predeterminable current value is reached.

Thus a short-circuiting contact connected parallel to the coil, which would have to be rated relatively high in accordance with the expected high currents, is made redundant.

15 Furthermore, said coil may only be provided with a single winding layer, and all turns of this winding layer may have selections 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.

In accordance with a particularly preferred embodiment of the invention the electrically conductive bridge may be attached to a short-circuit armature, which :o :short-circuit o .o 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 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 compact and functionally reliable construction. Through appropriate sizing of the holding force of the shortcircuit armature, the value at which the. coil is shortcircuited can be adjusted very simply.

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 device.

These components are quite small and hence the overall size increase of the trigger device according to the invention is insignificant.

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 application.

In a further particularly preferred embodiment of the trigger device according to the invention the trigger 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 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 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 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.

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.

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 armature at least partly inside the coil.

7 Thus the magnet armature can be moved in an exactly predictable manner by the magnetic forces of the monitored current.

Furthermore, it is preferred 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 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 i 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 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.

o 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 armature.

8 This constitutes a particularly simple design of the electromagnet, which still meets all the demands placed upon it.

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 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.

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o :An exemplary embodiment of the invention is described S" below in detail by way of the particularly preferred embodiments depicted in the enclosed drawings. Shown are in: Fig. la, b a schematic ,front elevation of two options for realising the trigger device according to o an embodiment of the invention; Fig. 2a,b a preferred embodiment of the holding magnet in plan view with two different variations for generating the holding force; Fig. 3 an alternative embodiment bf the holding magnet to those shown in Fig. 2a,b in oblique projection; Fig. 4 a schematic front elevation of a particularly preferred embodiment of the trigger device according to the invention; and 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 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, 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 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 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 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 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 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 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 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.

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 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 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 parallel resistor 29 provides a particularly simple means of influencing the selectivity.

Although it would result in relatively high extra 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.

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 i 15 currents caused by electromagnet 20, which is ooe:"accomplished according to the embodiment by shortcircuiting coil 7.

There are different methods for achieving this short 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 is able to immediately operate the switch lock 18.

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.

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.

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 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 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.

Both embodiment variations presented so far have the disadvantage that an additional control circuit 31 with its respective current sensing devices is required.

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 value of the monitored current, for the movement of bridge 17.

Said bridge 17 is attached to a short-circuit armature 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.

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 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 shortcircuit armature 15 is released, coil 7 is subsequently short-circuited and the trigger process takes place.

The holding force that retains the short-circuit armature in its resting position can be generated in various ways, for example, by the friction forces of components that are in contact with the short-circuit armature 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 part 21 and an elongated projection 151 of the shortcircuit armature 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 17 with the short-circuit armature 15 is effected here via a contact spring Moreover, a preferred design of the electromagnet 20 is clearly recognisable in Fig. 2a,b. Its yoke 14 has a Hlike 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 Fig. 3 depicts a different embodiment of electromagnet 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 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 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 is operable by the coil 6 directly in direction of arrow 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 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 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 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 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 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 due to the holding force applied to it by the electromagnet. As the excursion of magnet armature increases, the tension of coupling element 22 increases progressively, which increases the force applied to trigger armature 11. In this trigger phase magnet 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 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.

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 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 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 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.

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 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 the known electrothermally operating delay devices mentioned at the outset.

Fig. 5 depicts a longitudinal section through a line 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 and the fixed contact 36 to the fixed contact support via coil 6 to coil 7 and from there to the second terminal lb.

A trigger device according to the embodiment 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: 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 oo, armature 11 from a non-magnetisable material such as plastic, for example.

The magnet armature 10 has the form of a tube that is closed at one end, accepting the trigger armature 11i 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 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 made of magnetisable material, which causes the retention of trigger armature 11 in its resting position in conjunction with electromagnet 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 embodiment it is possible to arrange electromagnet 20 at 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 ensure a particularly fast movement of short-circuit Sarmature Switch latch 18 is constructed in the usual manner known per se. The bimetallic element 2 as well as pin 27, which 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.

The terms "comprise", "comprises", "comprised" and "comprising" when used in this specification are taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

o

Claims (15)

1. Trigger device adapted to be used with an overload circuit breaker including a trigger armature that operates a switch latch, said trigger armature being operable by a coil through which a monitored current flows, wherein the trigger 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 wherein the coil of the electromagnet is adapted to be short-circuited when a predeterminable current value is reached.

2. Trigger device according to claim 1, wherein the coil of the electromagnet has an outer winding layer in which the turns of this outer winding layer have sections that are free of insulating material, and wherein an electrically conductive i bridge is provided, which can be brought in contact with the sections when the predeterminable current value is reached. S •o

3. Trigger device according to claim 2, wherein the coil of the electromagnet I.. has only one winding layer and wherein all turns of this winding layer have sections that are free of insulating material. S4. Trigger device according to claim 3, wherein the electrically conductive bridge is fixed to a short-circuit armature, which can be moved by the electromagnet from a resting position into a position that brings the bridge into contact with the sections that are kept free of insulating material, in which the short-circuit armature is retained in its resting position with a predeterminable holding force. Trigger device according to claim 4, wherein the holding force that retains the short-circuit armature in its resting position is generated by an elastic component that is connected to the short-circuit armature and housing of the trigger device.

6. Trigger device according to claim 5, wherein the elastic component is formed by a spiral spring.

7. Trigger device according to claim 6 wherein the spiral spring is a compression spring.

8. Trigger device according to any one of the preceding claims, wherein the trigger armature is operated indirectly through a magnet armature that is operated directly by the coil through which the monitored current flows, in which said magnet armature is connected to the trigger armature by at least one elastic coupling element and, if necessary, one or more auxiliary armatures. leo. S9. Trigger device according to claim 8, wherein the at least one elastic *coupling element is formed by a spiral spring.

10. Trigger device according to claim 8 or 9, wherein the magnet armature is arranged at least partially inside the coil through which the monitored current flows.

11. Trigger device according to claim 10, wherein the trigger armature is also arranged inside the coil through which the monitored current flows, and the trigger armature is made of a non-magnetisable material.

12. Trigger device according to claim 11, wherein the magnet armature has the form of a tube that is closed at one end and wherein the trigger armature and the at least one elastic coupling element are arranged at least partially inside a hollow section formed by the magnet armature.

13. Trigger device according to claim 10, 11 or 12, wherein attached to the trigger armature is a projection that extends through the magnet armature, and fitted to said projection is a component made of magnetisable material, which component is retained by the electromagnet.

14. Trigger device according to claim 13 wherein the projection is aligned parallel to the longitudinal axis of the coil through which the monitored current flows. Trigger device according to any one of claims 4 to 14, wherein the electromagnet features a H-shaped yoke, whose transverse bar carries the coil of 0 0g0 the electromagnet, whose first pair of limbs acts via the component made of magnetisable material on the trigger armature and whose second pair of limbs 0000 acts on the short-circuit armature.

16. Trigger device according to claim 15, wherein the longitudinal axis of the electromagnet is arranged perpendicular to the longitudinal axis of the trigger armature. see. 0*00

17. Trigger device according to any one of claims 4 to 16, wherein the short- 0 circuit armature is laminated.

18. Trigger device according to any one of the preceding claims wherein the overload circuit breaker is a line safety switch. 23

19. Trigger device substantially as hereinbefore described and illustrated with reference to the accompanying drawings. DATED this 2 n' day of March, 2001 FELTEN GUILLEAUME AUSTRIA AG WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA SKP/RJS/MEH P1 6635AUOO 00*