US3475708A - Relay having a permanent magnetic shunt circuit - Google Patents

Description

oct. 28, 1969 5 SCHRECKENBERG ETAL 3,475,708

RELAY HAVING A PERMANENT MAGNETIC SHUNT CIRCUIT Filed May 24, 1967 United States t US. Cl. 335-229 14 Claims ABSTRACT OF THE DISCLOSURE A magnetic relay of high sensitivity operable by a changed value of flux in its magnetic circuit. An electrical coil connected to an external system is associated with the relay to generate a flux in opposition to the flux generated by the permanent magnet in the relay, and in this manner activate the relay. A shunt magnetic circuit is provided to improve the performance characteristics of the relay, and the opposition flux from the electrical coil is elfective on the main magnetic circuit. An armature is provided across the pole pieces of the permanent magnet so that when the relay operates the armature opens the main magnetic circuit.

The relay may be used in electrical systems where small changing parameters are available, for example, the detection of current leakage to earth in power supply systems.

This invention to relays of high sensitivity. Powers required to operate relays of the kind in question are normally in the order of a few hundred microwatts, but their sensitivity may be adjusted so that they operate either substantially below or above this power rating.

Difliculties have been experienced with relays of the kind which are characterised in a permanent magnet as a flux generator, two pole pieces and an armature to provide a low reluctance path, and a coil associated with the magnetic circuit to establish a cancelling flux, thereby to allow movement of the armature. Among these difficulties have been the problems of operating from extremely low powers and the control and adjustment of these operating powers at values lower than one hundred microwatts. Reasons for these difficulties have been varying magnetic values in the relay magnetic circuit as well as varying requirements of the associated circuitry.

Problems have also arisen with regard to relays of the above kind which operate in conjunction with circuit breakers. In the past there has been the difficulty of obtaining suificient mechanical advantage from the relay by which to effect the operation of a circuit breaker trip bar. Coupled with this problem has been the difficulty of keeping the relay and circuit breaker within oflicial operating requirements.

It is an object of the invention to overcome, or at least partially reduce, some of the difficulties experienced with relays of this kind.

According to the invention a relay includes a substantially U-shaped magnetic unit having two pole pieces constituting the arms of the U and a permanent magnet defining at least part of its base, an armature adapted to bridge the pole pieces, and being responsive to a net magnetic flux mechanical means anchored to the armature to bias the armature to open position, and at least one coil around a limb of the U to vary the effective flux acting on the armature, and at least one element introduced into the flux path associated with the magnet to increase its reluctance relative to the flux path associated with the coil which path by-passes the element, the bias ing means acting to move the armature to open position Patented Oct. 28, 1969 when the strength of the net magnetic flux falls below a predetermined value and the armature acting as a switching element.

Further according to the invention the armature is pivoted for see-saw movement about one of the pole pieces and the mechanical biasing means is preferably a spring arrangement anchored to a limb of the armature projecting from the pivot zone.

Also according to the invention at least portions of the pole pieces are united through a magnetisable bridging element located in parallel with the permanent magnet, the bridge constituting part of a shunt flux path for the permanent magnet flux.

According also to the invention the permanent magnet has its poles in contact with two angled arms of the magnetic material which form a cradle for the pole pieces, the uniting section being flanked by the arms. Preferably the section is spaced from the arms by means of a spacer plate of high reluctance material resting on the limbs directly above the permanent magnet. In some preferred examples of the invention the arms actually constitute parts of the pole pieces.

In a preferred application of the invention the relay is coupled with a circuit breaker, the armature being adapted to operate the breaker. Preferably, the relay and breaker are mechanically coupled.

A further aspect of the invention is a coil wound substantially around one pole piece, the coil being adapted to reset the armature after operation.

In order to illustrate the invention examples are described below with reference to the accompanying drawings in which:

FIGURE 1 is a front elevation, partly in section, of the relay in accordance with the invention mechanically coupled to a circuit breaker,

FIGURE 2 is a sectional plan view along line II-II of FIGURE 1 of the relay in accordance with the invention,

FIGURE 3 is a part sectional side elevation along the line III-III of FIGURE 1 of the relay in accordance with the invention, and

FIGURE 4 is a part front elevation of the relay in accordance with the invention electrically coupled to a circuit breaker.

A relay consists basically of a permanent magnet 5 with two poles pieces 6 located thereon and an armature 7 across the ends of the pole pieces to bridge the substantially U-shaped unit formed by the magnet and pole pieces. The pole pieces are constituted by two angle arms 8 positioned on the magnet poles 9 and two upright arms 10 which are located on the angle arms 8 thereby to form the limbs of the U element.

The upright arms 10 are connected by a uniting section 11 which in eilect forms a second base for the U element, the first base being formed by the base limbs 12 of the angled arms 8. This second base acts to unite the pole pieces 6 at the point other than their ends, namely, point 13, thereby to create a magnetic shunt path between the magnet poles 9. For design requirements a gap 14 of high reluctance is included in this path. This is conveniently achieved by a mylar strip or an air gap. The main magnetic path is that through the armature 7 across the ends of the pole pieces 6.

To prevent a short circuit of the magnetic shunt across the magnet poles 9 a brass spacer plate 15 is positioned on the angle arms 8 between the two bases of the U element. A further brass strip 16 is included in the relay between one of the angle arms 8 and the upright arm 10 forming the one limb of the pole piece 6 of the U, its purpose being to provide a pivot point 17 on which the armature 7 can move in see-saw fashion into closed or open contact with the second pole piece 6.

The armature permanent magnetic circuit of the relay is traced from one magnetic pole 9 through an angle arm 8, point 13, an upright limb 10 of the U, the armature 7, the second upright limb 10 of the U, gap 14, the second angle arm 8, and finally to the second pole 9 of the magnet 5. The shunt permanent magnetic circuit is traced from one magnet pole 9, point 13, through an angle arm 8, the uniting base 11 of the U element, high reluctance gap 14, the second angle arm 8, and finally to the other pole 9 of the magnet 5.

Operation of the relay is achieved by anchoring to the limb 18 of the armature 7 which projects from the pivot zone 17, a spring 19 which acts to bias the armature 7 to the open position, i.e. with the armature 7 raised from the second pole piece 6. Under normal conditions the armature circuit establishes a magnetic force sufficient to hold the armature 7 in closed position. It is against this force that the spring action operates.

A coil 20 is wound around one pole piece 6 so that a current flowing therein establishes a flux in the armature circuit part defined by limb 10, armature 7 and a second upright limb 10 in opposition to that of the permanent magnet 5. When the flux from this source is sufliciently great that the resultant flux in the defined part of the circuit falls to a predetermined value the armature 7, under the action of the spring bias, will be caused to move to the open position. As the armature moves to this position it may cause the operation of a further switch, say, due to a simple positional movement.

The magnetic circuit is designed so that about 80% of the flux from the permanent magnet passes through limb 11 of the shunt circuit and 20% through the limbs 10' and armature 7 of the permanent magnetic armature circuit. This ensures that the relay operates at a magnetically stable working point and on a constant workline technically termed recoil line. The division of flux is ensured by providing in the shunt circuit gaps 13 and 14 of relatively high reluctance. In the example under consideration, this is achieved by a mylar strip or ele ment between one upright 10 of the U element and the upright 21 of the angle arm 8 over that portion where they have a common surface area.

One factor influencing the sensitivity of the relay is the direction of flux from the coil 20 through the armature 7 and uniting base 11 of the U element, and the prevention of the coil-flux passing through the shunt circuit, except in as much as the base 11 forms part of the shunt. Thus the flux from the coil 20 passes through a substantially low reluctance flux path circuit which includes the first, limb 10, armature 7, second limb 10 and the uniting base 11.

The sensitivity is further improved by ensuring that the air gap 22 between the pole piece 6 and the armature 7 is precisely determined and maintained. Accurate machining of these parts as well as lapping of the contact surfaces might be necessary to achieve air gaps of the order and accuracy required. Another factor enhancing sensitivity of the relay is its adjustment and control by means independent of the magnetic field, namely the variation of the spring tension. This may be achieved by adjusting the nut mechanism 23 underneath the base plate 24 of the relay.

Resetting of the relay after the armature has opened is done by a further coil 25 provided on one of the pole pieces 6. This is preferably the pole piece not holding operating coil 20. This coil 25 is capable of generating a flux to aid that of the permanent magnet 5, so that when the resultant flux is of sufiicient magnitude the armature 7 is attracted to its closed position. The coil 25 is obviously much larger than the operating coil 20 since it will be necessary in this case for the flux to bridge the air gap created when the armature 7 is open.

The relay of the invention has many applications. Amongst them is an apparatus for the detection of leakage currents in power supply systems. The advantage of this relay in such a system is that it is itself independent for its operation of supply systems and hence not liable to be rendered inoperative due to open circuit condition in the system.

Referring to FIGURE 1 of the drawings, a system is shown in which the armature 7 is adapted, when it moves to an open position, mechanically to activate a trip mechanism 26 in a circuit breaker 27 and in such a manner isolate the supply from the load (not shown). The relay will be connected in circuit such that an earth leakage current will be detected by the operating coil 20. The I 25 can be connected to the supply or load l. substantial current may be drawn for its operation. is this example of the invention electrical energy is required to reset the armature of the relay.

Referring to FIGURE 4 of the drawings, a system is shown in which the relay is electrically coupled to power supply system, for example, of the kind in which earth leakage faults in the system are to be detected and the power supply is to be isolated from the load. In this arrangement the movement of the armature 7 to the open position activates a microswitch 28 which closes electrical contacts (not shown) within the microswitch to cause a current to flow through the coil 29 which thereupon will activate a circuit breaker (not shown).

The intensity of the magnetic field in the relay may be varied by adjusting the position of the permanent magnet 5 relative to the base portions 12 of the angle arms 8 which constitute part of the pole pieces 6. For this purpose an adjusting nut 30 is provided in the magnet 5 so that it screws into the elements 15, 11 and 24. This assembly of the relay provides a construction which is mechanically rigid.

Problems usually encountered with earth leakage units can be substantially eliminated by the relay of the invention operating in conjunction with a circuit breaker, as such a unit. These problems, which usually relate to keeping the unit within ofiicial safety requirement, while still remaining practical, revolve for instance around resistance to mechanical shock forces, operating from defined latch loads, from set fault currents, within defined temperature limits, and varying requirements of mechanical biasing within the unit. With the relay of the invention an earth leakage unit falling within the required standards and having the additional advantage of being operable by small leakage powers and being independent of supply systems can be obtained.

A further application of the invention will be in thermocouple circuits.

The range of operation for the relay of the invention can vary from about 10 microwatts to several hundred microwatts, adjustable by varying the tension of the spring 19 on the armature limb 18.

Many more examples of the invention exist each differing from the other in matters of detail only but in no way departing from the scope of the invention as set out in the appended claims. For instance, the biasing force tending to open the armature may be provided by a simple weight mechanism. Further, the high reluctance gap in the shunt magnetic circuit can be obtained using any other suitable material for example, brass, paper, aluminium, or mica. Also, the resetting of the armature may be done by mechanical means. In another alternative arrangement an additional coil may be located around one of the pole pieces, the coil being responsive to the magnetic flux in the pole piece, such that when the armature opens the change of flux flowing through the pole piece causes the additional magnetic coil to pass an activating signal to a circuit breaker or the like.

We claim:

1. A relay including a substantially U-shaped magnetic unit providing two pole pieces constituting the arms of the U and a permanent magnet defining at least part of its base, an armature adapted to bridge the pole pieces and being responsive to a net magnetic flux, mechanical means anchored to the armature to bias the armature to open position, and at least one coil around a limb of the U to vary the efiective flux acting on the armature, and at least one element in the flux path associated with the magnet to increase its reluctance relative to the flux path associated with the coil which path by-passes the element, the biasing means acting to move the armature to open position when the strength of the net magnetic flux falls below a predetermined value and the armature acting as a swtiching element.

2. A relay as claimed in claim 1 in which at least portions of the pole pieces are united through a magnetisable bridging element located in parallel with the permanent magnet, the bridge constituting part of a shunt flux path for the permanent magnet flux.

3. A relay as claimed in claim 2 in which the arms of the unit are located upright in a cradle sandwiched between the arms and the permanent magnet.

4. A relay as claimed in claim 3 in which the cradle forms part of the magnetic circuit.

5. A relay as claimed in claim 4 in which the cradle forms the holder for a spacer of non-magnetisable material located between the cradle and the bridging element.

6. A relay as claimed in claim 5 in which the cradle is constituted by flanged platforms projecting outwardly from the poles of the permanent magnet in substantially diametrically opposed directions.

7. A relay as claimed in claim 6 in which the armature is pivoted for see-saw movement about one of the pole pieces, and the mechanical biasing means is a spring arrangement anchored to a limb of the armature projecting from the pivot zone.

8. A relay as claimed in claim 7 including means to vary the spatial relationship of the poles of the permanent magnet relative to the adjacent zones of the arms of the unit.

9. A relay as claimed in claim 8 in which the means permits the permanent magnet to be rotated relative to the adjacent zones of the arms of the unit.

10. A relay as claimed in claim 9 in which the means acts to bind the elements of the relay into an integrated unit.

11. A relay as claimed in claim 10 in which a reset means is provided to return the armature to closed position.

12. A relay as claimed in claim 11 in which the reset means includes a coil embracing an arm of the unit, the coil when energised acting to move the armature against the action of the biasing means.

13. A relay as claimed in claim 6 in which the armature is pivoted for see-saw movement about one of the pole pieces.

14. A relay as claimed in claim 13 in which the mechanical biasing means is a spring arrangement anchored to a limb of the armature projecting from the pivot zone.

References Cited UNITED STATES PATENTS 362,135 5/1887 Wilson 335-230 2,205,669 6/ 1940 Pye 335-229 XR 2,483,658 10/1949 Miller 335-234 2,881,365 4/1959 Bernstein 335-229 2,869,050 l/1959 Urk et a1. 335-229 G. HARRIS, Primary Examiner US. Cl. X.R. 335-234

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