F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention: MAGNETIC FIELD SHIELDING USING FERROMAGNETIC PLATES AROUND CONDUCTORS FOR USE IN CIRCUIT BREAKERS

2. Applicant(s):

(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY : An Indian Company
(c) ADDRESS : L & T House, Ballard Estate, Mumbai 400 001,
State of Maharashtra, India

3. PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to an improved arrangement for magnetic field shielding and more particularly, to an arrangement for magnetic field shielding using ferromagnetic plates around conductors for use in circuit breakers.

BACKGROUND AND THE PRIOR ART

The present invention relates to electric Circuit Breakers which are used in electric transmission and distribution networks. Circuit Breakers are used for protection of electric network/circuit and equipments. A Circuit Breaker consist of an outer enclosure in which switching (make/break) takes place, a current path which is connected to the main supply line and make/break electric supply, a mechanism which may be a combination of a number of mechanical links or may be any arrangement which stores energy and releases in mechanical form when required. The current path/conductor of Circuit Breakers is made of highly electric conductive materials to reduce the I2R losses. In current path mainly two types of losses takes place which are I2R losses (DC losses) and eddy current or AC losses (skin and proximity effect losses).
Currently the use of ferromagnetic material plates or conducting material plates is common to provide magnetic shielding between adjacent conductors to reduce eddy current losses. In case of near shielding the ferromagnetic plate shielding is more effective as compare to conducting plate shielding. There are various arrangements available to shield adjacent conductors. The efficiency of the shielding varies arrangement to arrangement. Generally a flat ferromagnetic plate is used between two adjacent running conductors. This plate provides a less reluctance path to the flux generated by conductors and thus restricts the flux of one conductor to reach to another. Since the plate is placed between to conductors the flux impinging on the plate is not exactly perpendicular to the plate. So the less amount of the flux cut by the plate this reduces the efficiency of the shielding. For maximum shielding efficiency the flux should be impinge on the plate exact perpendicularly. For increase the flux impinges on the plate either the surface area of plate has to be increased or the permeability of the plate material be high. In both of the cases the overall cost of shielding goes up. Some arrangements also provides exact perpendicular impinging of the flux on plate but because of lack of proper flux flow path in doesn’t provide effective shielding and the efficiency of shielding drops.

US 2007/0210885/A1 provides an arrangement of a double break circuit breaker in which they have interposed a magnetic plate between two pairs of the fixed and movable contacts.

The present invention provides an improved arrangement of ferromagnetic plates around the conductor paths which provides more effective shielding between adjacent conductors thus reduce Proximity effect losses (eddy current losses) in the conductor paths. It provides an efficient and easy to assemble arrangement of ferromagnetic plates to provide shielding between adjacent conductors of a circuit breaker. This arrangement provides maximum flux impinge on the shielding plate by assembling plates in such a way that the flux impinges on the plates exact perpendicularly. Thus provides high shielding efficiency.

OBJECTS OF THE INVENTION

A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.

Another object of the present invention is to provide an improved arrangement of ferromagnetic plates around the conductor paths which provide more effective shielding between adjacent conductors.

Another object of the present invention is to reduce proximity effect losses (eddy current losses) in the conductor paths.

Another object of the present invention is to provide an efficient and easy to assemble arrangement of ferromagnetic plates.

Another object of the present invention provides for maximum flux impinge on the shielding plate by assembling plates in such a way that maximum flux impinge on the shielding plate by assembling plates in such a way that the flux impinges on the plates exact perpendicularly.

Yet another object of the present invention is to provide for high shielding efficiency.

These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

There is provided an improved arrangement for magnetic field shielding using ferromagnetic plates around conductors for use in circuit breakers.

According to one embodiment of the present invention, there is provided an improved arrangement of ferromagnetic plates around the conductor paths which provide more effective shielding between adjacent conductors.

Other embodiment of the present invention provides for reduced proximity effect losses (eddy current losses) in the conductor paths.

Other embodiment of the present invention provides an efficient and easy to assemble arrangement of ferromagnetic plates.

Other embodiment of the present invention provides for maximum flux impinge on the shielding plate by assembling plates in such a way that maximum flux impinge on the shielding plate by assembling plates in such a way that the flux impinges on the plates exact perpendicularly.

Yet other embodiment of the present invention provide for high shielding efficiency.

Additionally the present invention can be used in all kind of transmission and distribution Circuit Breakers having various size, shapes and current carrying capacities of conductor paths. Dimensions and the permeability of the plates may vary according to the requirement and size of the terminals and housing. Though the arrangement is more effective for three phase configuration, a reduced efficiency can be achieved for any number of phases by repeating the arrangement of middle conductor path for all inner paths. Further the arrangement can be used for upper terminals and lower terminals as well as according to the requirement.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig 1 illustrates the outer enclosure/housing and current /conductor path assembly.

Fig 2 illustrates another view of outer enclosure/housing and current/conductor path assembly.

Fig 3 illustrates outer enclosure/housing and current/conductor path with shield plates.

Fig 4 illustrates different views of shield plate of outer terminals.

Fig 5 illustrates different views of shield plate of middle terminal.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.

Reference is first invited to Fig 1 where the back view of the housing is shown. All three conductor paths have upper/ top terminals 2, 3, 4 and lower/bottom terminals 9, 10, 11 respectively which project outside of the housing.

Fig 2 shows Slots 5, 6, 7 and 8 provided on the back side of the housing to fix the shield/ferromagnetic plates in them.

Fig 3 shows Shielding plates 12, 13, 14, and 15 assembled on the slots 5, 6, 7, and 8 respectively.
Fig 4 shows Plate 12/15 having three main surfaces 16, 17 and 18. Surface 18 comes around terminals 2 or 4. Surfaces 16 and 17 comes exact perpendicular and on the centre line of the terminal.

Fig 5 shows two shield plates 13 and 14 similar to each other and assembled facing opposite to each other. These plates have surface 19, 20 and 21 which provides a minimum reluctance path to flux.

The invented system is thus a system and method of magnetic field shielding using ferromagnetic plates around conductors for use in circuit breakers.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly in the present invention provides for the reduction of AC losses i.e. proximity effect losses in conductor paths of a circuit breaker. This is achieved by use of an arrangement of ferromagnetic plates around conductors to shield the magnetic flux lines of individual conductor path. Plates are arranged in such a manner that the maximum flux lines impinge on the plates perpendicularly thus maximum flux lines will be shorted by plate and restricted in a particular path. The arrangement requires less surface area of plates and less permeability of plate material as compare to existing cases to achieve certain efficiency.

The said arrangement consists of housing / outer enclosure 1 of the circuit breaker. Fig 1 and Fig 2 show the back view of this housing. The circuit breaker has three conductor paths which are intended to connect to three phase (R, Y, B) electric supply. All three conductor paths have upper/ top terminals 2, 3, 4 and lower/bottom terminals 9, 10, 11 respectively which project outside of the housing (Fig 1, Fig 2). All three conductor paths are assembled in housing 1 as shown in Fig 1. Slots 5, 6, 7 and 8 are provided on the back side of the housing to fix the shield/ferromagnetic plates in them. Similar slots can be provided if shielding is required on bottom side also. Shielding plates 12, 13, 14, and 15 are assembled on the slots 5, 6, 7, and 8 respectively (Fig 3).

Shield plates 12, 15 and 13, 14 are similar and assembled facing opposite to each other. Plate 12/15 (Fig 4) has three main surfaces 16, 17 and 18. Surface 18 comes around terminals 2 or 4. Surfaces 16 and 17 comes exact perpendicular and on the centre line of the terminal (Fig 3). Surface 18 also provides a joining path between surface 16 and 17. So now when the electric current through the terminal 2 or 4 the magnetic flux lines generate. This generated magnetic field rotates clockwise and anti clockwise depending on the direction of the current flow. For example if we consider the terminal 4 has the magnetic field lines rotating in the clockwise direction. When these rotating field lines reaches on the surface 16 of the shield plate 12, the maximum number of lines impinge perpendicularly on the surface. These all impinged flux lines enter in the less reluctance path and flow from surface 16 to 18 then 18 to 17 and finally come in air again to complete the loop. In this process maximum number of flux lines going towards the middle terminal 3 are shorted in a loop much closer to the terminal 4 thus have very less influence on middle terminal 3. Same process takes place on terminal 2 and shield plate 15 and so maximum number of flux lines going towards the middle terminal 3 are shorted in a loop much closer to the terminal 2 thus have very less influence on middle terminal 3. Up to this point the magnetic fields of outer terminals 2 and 4 has been restricted more effectively to reach to the middle terminal 3.

The only thing now remains is to restrict the magnetic field of middle terminal 3 so it can’t reach to terminal 2 and 4. For this purpose two shield plates 13 and 14 (Fig 5) are used. These two plates are similar to each other and assembled facing opposite to each other (Fig 3). These plates have surface 19, 20 and 21 which provides a minimum reluctance path to flux. Flux flows from plate 13 to air gap to plate 14 then to air gap and comes back to plate 13.These plates are just used to bind the magnetic field of the terminal 3 in particular region so flux can’t reach to terminals 2 and 4. It may also have close shield in place of plates 13 and 14. We have used above said arrangement to compromise between cost and efficiency.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM:

1. An improved arrangement for magnetic field shielding in conductors used in circuit breakers, said arrangement comprising:
housing (1);
plurality of slot means (5,6,7 and 8) provided in the said housing, preferably on the backside of it;
plurality of shielding plate means (12, 13, 14 and 15) accommodated in said slot means whereby said plate means being arranged in such a manner that the maximum flux lines impinge on the said plate means in a substantially perpendicular direction thereby shorting and restricting the flux lines generated due to flow of electric current through the terminals (2, 3, 4).
.
2. Arrangement as claimed in claim 1 wherein said shielding plate means (12 and 15) comprising three substantially mutually perpendicular surfaces (16, 17 and 18).
3. Arrangement as claimed in claim 2 wherein said surfaces (16, 17) being substantially perpendicular to the centre line of the terminals (2 or 4).
4. Arrangement as claimed in claim 1 wherein said shielding plate means (13 and 14) comprising three surfaces (19, 20 and 21) mutually substantially perpendicular to each other adapted to provide minimum reluctance path said flux lines.
5. An improved arrangement for magnetic field shielding in conductors used in circuit breakers as herein substantially described and illustrated with reference to the accompanying drawings.