US3668577A

US3668577A - Leakage circuit breakers

Info

Publication number: US3668577A
Application number: US98875A
Authority: US
Inventors: Horst Harings
Original assignee: Felten & Guilleaume Schaltanl
Current assignee: Felten & Guilleaume Schaltanl; Felten & Guilleaume Schaltanlagen GmbH
Priority date: 1970-01-02
Filing date: 1970-12-29
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: NL7018552A; JPS5137433B1; GB1295150A; BE759996A; DE2000138A1; NL156536B; AT314645B; FR2075891B1; ES383950A1; CA925550A; DE2000138B2; CH528815A; FR2075891A1; ZA708651B; LU61823A1

Abstract

The balanced armature pivots on one pole piece and has a small contact surface that cooperates with the other pole piece. Movement of the armature is coupled to the tripping catch that operates the circuit breaker by a lever connected by an axle to the armature. One spring biases the armature open and closed when the latter is respectively closed and open. Another sprig biases the armature open at all times. The lever arms through which the springs and the magnetic attractive force act on the armature are so chosen that the magnetic tripper is highly sensitive and vibration proof.

Description

United States Patent Harings 1 June 6, 1972 s41 LEAKAGE CIRCUIT BREAKERS 3,543,203 11/1970 Alletru ..33s/229 2,914,632 11 1959 Ne 11 .335 192 [72] Inventor: Horst Harings, Nordenham, Germany uman [73] Assignee: Felten & Guilleaume Schaltanlagen Examiner-Harold BrQome GmbH, Krefeld am Neuerhof, Germany ney-Mi ael riker [22] Filed: Dec. 29, 1970 [57] ABSTRACT [21] Appl' 98875 The balanced armature pivots on one pole piece and has a small contact surface that cooperates with the other pole [30] Foreign Application Priority Data piece. Movement of the armature is coupled to the tri ing PP Jan 2 1970 German P 20 0O 38 I catch that operates the circuit breaker by a lever connected by y an axle to the armature. One spring biases the armature open [52] U s 335/192 335/229 and closed when the latter is respectively closed and open. 51 ln t. Cl. ..H 0lh 3/32 Sprig biases armature The [58] Field of Search .335 170 174 179 229230 arms hmugh which Springs the mhghehc mmhve 5 force act on the armature are so chosen that the magnetic tripper is highly sensitive and vibration proof. [56] References Cited 21 l i V 6 gfigp g UNITED STATES PATENTS 3,123,742 3/1964 Moser et al. ..335/229 I 7 /I Z a M 7 SHEET 10F 3 FIG.

INVENTOR Imsr 04mm:

ATTORNEY PATENTEDJUR elm 3.668.577 SHEET 20F 3 g Q 0 Q INVENTOR mmsr [/ANMJ 4104/ ha- ATTORNEY PATENTEDJUH 5 I972 3. 668 577 sum 3 0F 3 FIG. 6

INVENTOR f mr fill/ll;

ATTORNEY LEAKAGE CIRCUIT BREAKERS BACKGROUND OF THE INVENTION The invention relates to a magnetic tripper for an earth leakage circuit breaker.

Earth leakage" circuit breakers are used to protect life and property in power plants, during unusual occurrences, such as ground leaks or the touching of a live part. The operation and construction are described, for example, in Giinter G. Seip's article Allgemeiner Uberblick iiber die Bestimmungen fil'r das Errichten von Starkstromanlagen mit Nennspannungen bis 1,000 V, VDE 0100/1265 (General Survey of the. Requirements for Constructing Power Plants Having Nominal Voltages of Up to 1,000 Volts, VDE 0100/1265), printed in the German journal VDI-Zeitung 111 (1969), issue No. 15, pages 1,081-1087.

The effectiveness of the circuit breaker is largely determined by a magnetic tripper that is used in conjunction with the breaker. The magnetic tripper has a magnetic circuit of which a winding is connected to the secondary circuit of the totalizing current transformer, a determined fault current causing the tripper to release the breaker, which opens. The tripper should be as sensitive as possible, so that it releases the breaker at small fault currents. Since the circuit breakers are robust units that should be mountable anywhere in the power plant, the magnetic tripper must be vibration and shock proof as possible.

In one prior art tripper, the two pole pieces are stamped out of the same base, each pole piece carrying a coil of insulated wire, which is connected to the secondary winding of the totalizing current transformer of the earth leakage circuit breaker. A permanent magnet is located on the base between the two pole pieces. This part of the piece acts as a magnetic shunt to the main magnetic circuit closed by these pole pieces. By suitably dimensioning the magnetically effective cross-section of this shunt, the flux caused by the permanent magnet can be so adjusted that it is sufficiently large to ensure a satisfactory attractive force to hold the armature against the pole pieces and yet sufficiently small to obtain a satisfactory sensitivity. A magnetic tripper of thiskind is described in the French Patent of Addition 78880 and in the parent thereof 1265883. The French Pat. 1242875 describes a similar magnetic tripper, the north-south axis of the permanent magnet being rotatable with respect to the axis of the main magnetic circuit so as to enable further adjustment of the sensitivity of the tripper.

Since the armature of these two known magnetic trippers has a relatively large mass, and consequently is sensitive to vibration and shock, a relatively large attractive force is required to hold the armature against the two pole pieces, and the sensitivity is consequently low.

In an endeavor to reduce the armature mass, and thereby to make the tripper more sensitive to fault currents and less sensitive to vibration and shock, magnetic trippers with a single coil have been described. For example, the German Patent 1 197695 describes a concentric arrangement having a single trip coil and a plunger type magnet. Even in this arrangement the armature has a relatively large mass, because the entire armature must be moved. Moreover, the sensitivity is reduced by an unavoidably large amount of friction, which the armature must overcome when moving in its concentric air gap.

The same German Patent mentions that the flux produced by the trip coil, which flux opposes that produced by the permanent magnet, could eventually demagnetize the permanent magnet. For this reason the magnetic tripper described in the German Patent has no permanent magnet at all. The restoring force is applied only by a spring.

SUMMARY OF THE INVENTION An object of the invention is a magnetic tripper for earth leakage circuit breakers that better fulfills the requirements of high sensitivity to fault currents and low sensitivity to vibration and shock than do the magnetic trippers of the prior art.

Another object of the invention is a magnetic tripper of the previous object, whose sensitivity to fault currents can be coarsely and finely adjusted.

The magnetic tripper of the invention consists essentially of a magnetic circuit including first and second spaced pole pieces and an armature movable between a first position in which the circuit breaker is closed and a second position in which the circuit breaker is open, the position of the armature determining whether the magnetic circuit is open or closed, a trip coil wound on the first pole piece, resilient means for biasing the armature towards the second position at least when the armature is in the first position and towards the first position at least when the armature is in the second position, the resistance of the magnetic circuit, size of wire and turns of the trip coil, and the force of the resilient means coarsely determining the size of the fault current at which the armature moves from the first to the second position, a permanent magnet mounted on the second pole piece free to move so as to change the direction of the north-south pole axis of the magnet with respect to the second pole piece and thereby vary the amount of magnetic flux, due to the magnet, in the magnetic circuit, the position of the permanent magnet finely determining the size of the fault current at which the armature moves from the first to the second position, trip means for opening the circuit breaker when the armature moves to the second position, and coupling means for connecting the trip means to the armature to move therewith, the coupling means and the armature cooperating to provide a one arm lever arrangement for multiplying the force for holding the armature'in the first position and a two arm lever arrangement for multiplying the force of the resilient means acting on the armature when the armature is in the second position.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of the magnetic tripper of the invention, with the armature closed;

FIG. 2 is a side view of the tripper, with the armature closed;

FIG. 3 is a side view showing part of the tripper, with the armature open;

FIG. 4 is an end view of the tripper;

FIG. 5 is a perspective view of the tripper; and

FIG. 6 is an exploded view of the magnetic circuit of the tripper.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the Figures, and particularly to FIGS. 1, 2, 5, and 6, the reference numeral 1 denotes the base or support structure of the magnetic tripper. The base 1 comprises rail-like extensions that each carry respective electrically insulating mounting members 19 and 20, which latter will be referred to later. In a variant of the invention, the base can consist of a U-shaped piece, which, by injection molding, is embedded in a housing, not shown, preferably made of a thermoplastic material. The base 1 is made of soft iron having a high permeability and low retentivity and coercive force. The two pole pieces 2 and 3 are stamped out of the base 1. A permanent magnet 5 is mounted free to rotate in a hole, not shown, incorporated in the rear pole piece 3. A lever 6 of nonmagnetic material is fixed to the permanent magnet. The permanent magnet 5 is made of a material having high coercive force and retentivity, the material preferably being sintered. The magnet is so magnetized that its north and south poles define a diametrical axis that is coincident with, or an extension of, the longitudinal axis of the lever 6. The magnetic circuit is closed by an armature 7, which is also made of an easily magnetized material. When the armature 7 is in its first, at-

tracted, position, the front, or left, end 8 of the armature has a contact surface which is in contact with the opposed abutment face of the pole piece 2. The rear, broad, end of the armature 7 incorporates an opening 9. The entire armature is bowed along a line A-A (see FIG. 6), this line being coincident with the front lower edge of the opening 9. The edge formed along the line A-A contacts the pole piece 3 along the line B--B. Since the opening 9 is wider than the pole piece 3, the armature is free to pivot on this line in the manner of a balance. The plate spring 10 is fixed to the underside of the rear end of the armature. The other end of the plate spring is fixed to the trip coil 4. In this way, the armature is fixed against lateral movement with respect to the pivot line AA.

Two V-shaped recesses define between the apices a bridge 1 1 over which is caught one end of a tension coil ring 12. The other end of the coil spring 12 is fixed to a cross tie 13, which is mounted on the rear end of the base 1. The coil spring 12 pulls'on the armature to pivot the latter and to break the magnetic circuit at the pole piece 2.

When the armature is in its first position, shown in FIG. 2, the position at which the spring 12 is hooked to the bridge 11 is advantageously a determined distance higher than the pivot line AA. When the armature pivots to its second position, shown in FIG. 3, the position at which the spring is hooked to the bridge describes an arc. The lever arm through which the spring 12 acts is the horizontal projection of this arc. The reduced tension of the spring as the latter contracts can be compensated, or overcompensated, by so choosing the hooked position of the upper end of the spring 12, in the first position of the armature, that the equivalent lever arm through which the spring acts increases as the armature pivots to the second position. The position of the upper end of the spring 12, in the first position of the armature 7, is thus made somewhat above that of the line AA; in other words, the position of the upper end of the spring is angularly displaced in a plane normal to the line AA.

The armature 7 incorporates a slot 14, which is covered with non-magnetic material and is approximately centered between the ends of the armature. A trip lever 15 is free to move with play in this slot. An axle that bridges this slot is fixed to the underside of the armature. The axle passes freely through an opening in the tripping lever, so that the latter is moved whenever the armature pivots. An opening 17 in the base 1 so guides the movement of the tripping lever 15 that the trip catch 18, located at the lower end of the lever 15, moves in a direction substantially parallel to the longitudinal axis of the lever 15. The front and rear rails of the base I carry electrically insulating mounting members 19 and 20, each incorporating

respective holes

21 and 22 for fixing the magnetic tripper to the circuit breaker.

The plate spring l0, in the position of the armature 7 shown in FIG. 2, reinforces the pull of the spring 12. In the armature position shown in FIG. 3, it opposes the pull of the spring 12 and acts to urge the armature towards its closed position, shown in FIG. 2.

When the armature 7 is in its first position, the force acting to hold it there, composed of the resultant of the magnetic attractive force and the opposed force of the plate spring 10 and of the coil spring 12, is multiplied by the ratio between a first lever arm and a third lever arm, the first lever being that arm extending from the left end 8 of the armature to the line A- A, the third lever arm, which is necessarily shorter than the first, being from the axle 16 to the line AA. When the annature is in its second position, the restoring force of the plate spring 10 is multiplied by the ratio between a'second lever arm and said third lever arm, the second lever, which is necessarily longer than said third, being that arm extending from the right end of the armature, as seen in FIG. 3, to the line AA.

The operation of the magnetic tripper will be explained in conjunction with the Figures of the drawings. The permanent magnet 5 has a coercive force l-I. If the efiective length of the magnet is 1 and if its north-south axis makes an angle (b with the vertical, it has, in the direction of the axis of the pole piece 3, an effective internal magnetic circulation@, H cos (I) 1. This magnetic circulation has the same effect as though the magnet were replaced by a corresponding soft iron body that carried a coil through which there flowed a current producing the same magnetic circulation. The lever 6 is so attached to the magnet 5 that when the lever is in'its end position, the north-south axis of the magnet coincides with the vertical axis of the pole piece 3. When the lever 6 is moved, the angle 4) is chan ed, and thereby the effective internal magnetic circulation -of thepermanent magnet is varied. The effect is exactly the same as though the magnitude of the current flowing through the imaginary coil were changed.

The pole piece 2 carries the coil 4, which is connected to the secondary winding of the totalizing current transformer of the earth leakage circuit breaker. The fault current flows through the coil 4. In dependence on the number of turns of the coil 4, there is produced a magnetic circulation The two magnetic circulations VI and 2 cause in the entire magnetic circuit a flux I the magnitude of which depends on the magnetic resistances (1 .q) of the different parts of the n ti s w t hsrs ssya sths sn l w Permeability,

and qthe cross section of a given part ofthe magnetic circuit. This flux I corresponds to the force with which the armature 7 is held in its first position, shown in FIG. 2. At some defined strength and direction of the current in the coil 4 this attractive force is so weakened that the plate spring 10 and the coil spring 12 cause the armature to pivot upward and thereby to raise the tripping lever 15. The tripping catch 18 consequently disengages the circuit breaker, which latter opens the circuit.

The value of the current through the coil 4 at which the magnetic tripper acts is coarsely dependent on the shape and cross-section of the magnetic circuit composed of the base 1, pole pieces 2 and 3, support surface A-A, and the contact between 8 and the pole piece 2 as well as on the force of the

springs

10 and 12. The sensitivity of the magnetic trigger is finely determined by moving the lever 6 to turn the permanent magnet 5.

The attractive force between 8 and 2 acts through such a leverage against the opposed force of the

springs

10 and 12 that it can be relatively small. It is consequently possible to obtain the required magnetic circulation for the necessary flux with a single coil 4 and a correspondingly small permanent magnet 5. Another consequence is to render the magnetic tripper more vibration insensitive. This latter feature is also made possible by the very secure manner in which the broad, rear, part of the plate spring 10 holds the armature 7. Since the permanent magnet 5 is made from sintered material having a particularly high coercive force and retentivity it is not weakened by the frequent release of the magnet tripper, caused by the opposing force produced by the fault currents. The sensitivity of the tripper is further improved by the following constructive details of the armature 7.

The armature is designed so that the mass of that part of the armature to one side of the line A-A is as nearly equal as possible to that on the other side of the line A-A. This means that the weight of the forepart of the armature, which is attracted to the pole piece 2, is balanced by the weight of the rear part of the armature. Consequently, the amount of attractive force required to act on the part 8 is reduced.

Where these two parts of the armature are balanced, vibration does not cause inertial forces, which could interfere with correct operation of the tripper, to act exclusively on the one or the other of these parts. The result is that the balanced construction of the armature improves the vibration insensitivity of the magnetic tripper.

By keeping the armature front end 8 very small, it is possible to ensure that it lies plane parallel on the face of the pole piece 2. The so-called end mass effect acts to keep the end 8 in contact with the pole piece 2 even when the tripper is vibrated. The forepart of the armature, which is that part most accelerated when the armature moves from its one position to the other, has a very small inertia. The design of the armature also ensures that the air resistance is kept very low during movement of the armature.

The magnetic resistance in the rear part of the armature is kept very low, because the armature contacts the pole piece 3 for a major part of the long line A-A. The resulting magnetic flux, which is the resultant of the magnetic circulation caused by the permanent magnet 5 and the magnetic circulation caused by the fault current in the trip coil 4, is inversely proportional to the resistance of the magnetic circuit. The surface area of the armature in contact with the pole piece 3 is large compared to the surface area of 8 in contact with the pole piece 2.

The force acting on the armature is dependent on the mag nitude of this resultant magnetic flux; and, of course, it is also inversely proportional to the resistance of the magnetic circuit. The magnetic resistance is greatly dependent on the precision with which the contact surfaces between 8 and 2, on the one hand,

andbetween

3 and 7, on the other, are machined and finished. The smaller is the contribution of these contact surfaces to the total resistance of the magnetic circuit, the less is the effect of the unavoidable variations in the contribution, caused by the limitations of machining and finishing, on the attractive force between 8 and 2.

The movement of armature 7 is coupled to the tripping catch 18 by a two-arm step-up lever arrangement that multiplies the force of the

springs

10 and 12 that cause the armature to pivot upwards when the magnetically attractive force becomes too weak. As long as the armature 7 is held to the pole piece 2, a one-arm step-up lever arrangement holds the armature to the pole piece 2.

A further advantage of the invention is that the leverage through which the attractive force and the holding force (of the forepart of the armature) act on the tripping catch 18 enables the forepart, which undergoes the greatest acceleration when the armature moves, to be made with so little mass that it is insensitive to vibration. The lever arrangement, as previously explained, nevertheless ensures that the tripper releases with sufficient force to operate the catch 18.

The weight of the forepart of the armature 7 is balanced, or at least very nearly balanced, by the weight of the rear part, a

fact that further increases the sensitivity of the magnetic tripper of the invention. The contact face of the end 8 is small to ensure that it lies plane parallel on the opposed face of the pole piece 2, thereby obtaining the maximum attractive force between 8 and 2 for a given flux. The shock proof, or vibration proof, characteristics of the tripper imply that the armature, once attracted to the position shown in FIG. 2, must be securely held. When two plane steel surfaces are pressed together, the air between them is largely squeezed out, and the pressure between the surfaces is less than the atmospheric. Assuming that there is a perfect vacuum between these two surfaces, this holding force, aside from the resultant holding force of the magnetic attraction and the opposing force of the springs 10 and I2, is equal to the product of the contact area and the atmospheric pressure. This means that the two surfaces must be as intimately in contact as possible, a condition the better fulfilled as the contact area of 8 is smaller. The high quality of the surface finish is also better ensured if the area of contact between 8 and 2 is small. This additional holding force is the same that appears with so-called end masses, with precisely plane parallel and highly polished faces, when these end masses are pressed together.

When the magnetic tripper releases, the holding force due to the end mass effect should not be too great, since the opposed force of the

springs

10 and 12 must be correspondingly increased. The greater the force of the

springs

10 and 12, the greater must be the magnetic attraction produced by the current in the coil 4, a fact that reduces the sensitivity of the tripper, since the coil 4 also carries the fault current. In accordance with the invention, the sensitivity is increased by keeping the contact area between 2 and 8 small. In this wise, there is obtained, in accordance with the invention, both very high sensitivity and great resistance to shock and vibration.

Further in accordance with the invention, the base 1 can be contained in a housing, not shown, preferably injection molded of thermoplastic material, the pole pieces 2 and 3 being embedded in the housing.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a magnetic tripper for earth leakage circuit breakers, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:v

1. Magnetic tripper arrangement for a circuit breaker, comprising, in combination, a support structure; an elongated armature at least partly of ferromagnetic material having opposite end portions and mounted on said support structure on a pivot axis spaced from said opposite end portions so as to form between said pivot axis and said opposite end portions first and second lever arms, said armature being tiltable about said pivot axis between two tilting positions; magnetic means cooperating with one of said portions of said armature and tending when actuated to move the same and thereby tilt the armature from one to the other of said tilted positions thereof; spring means cooperating with the other of said end portions of said armature and tending to move the same from said other to said one position thereof when said magnet means is not actuated; and trip means engaged by said armature at a point between one of said end portions and said pivot axis of said armature so that the portion of said armature located between said trip means and said pivot axis forms a third lever arm shorter than either of said first or said second lever arms, whereby the force exerted by one of said means on said armature is transmitted to said trip means by said first and third lever arms which form a one-arm step-up lever arrangement, and the force exerted by the other of said means is transmitted to said trip means by said second and third lever arms which form a two-arm step-up lever arrangement.

2. An arrangement as defined in claim 1, said support structure including a first and a second pole piece, said armature being mounted on said second pole piece, said armature and said pole pieces forming part of a magnetic circuit which is opened or closed depending on the position of said armature, and said magnetic means producing flux through said magnetic circuit.

3. An arrangement as defined in claim 1, wherein said one of said end portions of said armature is a low-mass end portion. I

4. An arrangement as defined in claim 2, wherein the portion of said support structure between said pole pieces is at least partly of magnetic material and forms a further part of said magnetic circuit.

5. An arrangement as defined in claim 2, said magnetic means including at least a first magnet and a second magnet, said first magnet being a trip coil electromagnet.

6. An arrangement as defined in claim 5, said second magnet producing flux through said magnetic circuit in one direction, whereby to exert on said armature a force tending to maintain it in its position closing said magnetic circuit, and said first magnet producing flux through said magnetic circuit in opposite direction, whereby to counteract the flux of said second magnet the force of said second magnet tending to maintain said armature in its position closing said magnetic circuit.

7. An arrangement as defined in claim 5, wherein said second magnet is a permanent magnet movably mounted on said support structure, whereby to permit adjustable varying of the force exerted by said permanent magnet for tilting said armature to said other of its positions by moving said permanent magnet.

8. An arrangement as defined in claim 2, said one of said end portions having a contact surface, and said first pole piece having an abutment surface which is large relative to said contact surface, and wherein said contact surface abuts against said abutment surface when said armature is in one of its positions.

9. An arrangement as defined in claim 2, said second pole piece having along said pivot axis a width which is at least substantially equal to the width of said first pole piece along said pivot axis of said armature.

10. An arrangement as defined in claim 1, wherein the mass of said armature is substantially balanced with respect to said pivot axis.

11. An arrangement as defined in claim 1, wherein said spring means is a compound spring means and includes an expansion spring connected to said support structure and one of said end portions, and a plate spring connected to said support structure and to said armature, said plate spring cooperating with said expansion spring when said armature is in one of its positions and opposing said expansion spring when the armature is in the other of its positions effect of the compound spring means will be to provide a non-linear spring characteristic.

l2.' An arrangement as defined in claim 1, wherein said first lever arm is substantially longer than said second lever arm, and wherein the armature portion associated with said first lever arm has a mass substantially equal to the mass of the armature portion associated with said second lever arm, and wherein the former armature portions has a width in direction of said axis substantially less than the width in said direction of the latter armature portion.

13. An arrangement as defined in claim 12, said latter armature portion including at least one mass-reducing cut-out.

14. An arrangement as defined in claim 1, wherein said support structure includes guide means, and wherein said trip means comprises an elongated member having one end pivotably coupled with said armature, said member cooperating with said guide means to be guided by the same when said armature is tilted between its positions.

15. An arrangement as defined in claim 5, said trip coil electromagnet being connected to the secondary winding of a circuit breaker totalizing transformer.

16. An arrangement as defined in claim 2, wherein said support structure comprises a one-piece U-shaped body, the legs of said U including said first and second pole pieces, and said one of said armature end portions being in contact with said first pole piece when said armature is in one of its positions.

17. An arrangement as defined in claim 5, wherein said first and second magnets produce opposing flux, and wherein said permanent magnet has so high a coercive force as not to be weakened by magnetic fields produced by said trip coil electromagnet.

18. An arrangement as defined in claim 11, and further including housing means for housing said support structure.

19. An arrangement as defined in claim 18, wherein said housing means is of injection-molded thermoplastic material, and wherein said support structure is embedded in said housing means.

20. An arrangement as defined in claim 7, wherein said permanent magnet is mounted for rotation on said second pole piece and forms part of said magnetic circuit, and wherein said permanent magnet has a North-South axis whose orientation is changed with respect to said magnetic circuit by rotation of said permanent magnet.

21. An arrangement as defined in claim 6, wherein said second magnet is a permanent magnet having so high a coercive force as not to be weakened by fault currents in said trip coil.

Claims

3. An arrangement as defined in claim 1, wherein said one of said end portions of said armature is a low-mass end portion.

12. An arrangement as defined in claim 1, wherein said first lever arm is substantially longer than said second lever arm, and wherein the armature portion associated with said first lever arm has a mass substantially equal to the mass of the armature portion associated with said second lever arm, and wherein the former armature portions has a width in direction of said axis substantially less than the width in said direction of the latter armature portion.