FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
Magnetic Tripping Arrangement for Electrical Protection Devices
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: LARSEN & TOUBRO LIMITED,
L&T House, Ballard Estate, P. 0. Box: 278, Mumbai 400 001, India
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

Magnetic Tripping Arrangement for Electrical Protection Devices
Field of the invention
The present invention relates to electrical protection devices and more particularly, to a multiple differential gap magnetic tripping arrangement for lower rated circuit breakers in a given frame size.
Background of the invention
Electrical control and protection equipments that use magnetic principles for protection purpose are circuit breakers, miniature circuit breakers (herein after MCBs): thermo-magnetic molded case circuit breakers (herein after MCCBs) and the like. These equipments comprise a short circuit tripping mechanism. One such mechanism is shown in figures la and lb wherein a moving flapper/ magnet (1) and a fixed magnet (2) are kept apart with certain air gap. The arrangement of the moving and fixed magnets (1, 2) is primarily responsible for giving trip actuation at the time of short circuit.
As shown in figure 1, a current carrying conductor (3) is used to generate certain amount of magnetic force. However, this force is not sufficient to bring the moving magnet (1) closer to the fixed magnet (2). This ensures no tripping in normal case of rated current operation and certain amount of overload conditions. When current reaches a pre-defined level that is for example 3 times, 6 times or 9 times of rate current, enough force is produced and the moving magnet (1) gets attracted towards the fixed magnet (2). This is a magnetic flux linkage (represented as 4 in figure lb). The air gap (represented as 5 in figure lb) is responsible for the flux linkage and the trip travel. Movement of the moving magnet (1) also results in rotation of a trip

plate (not shown) and hence gives mechanical tripping command to the trip
mechanism.
Usually highest rating in a given frame size does not pose any problem due to sufficient amount of the magnetic flux linkage and force. When the same frame is used for lower ratings, usually amount of force available for tripping also keeps on reducing proportionate to the current due to space constraints. This results in usually higher multiples of rated current to be generated as a tripping threshold. For example 100A MCCB with a tripping threshold of 9In would become 20In MCCB when used for deriving lower ratings of the MCCBs such as 50A, 40A, 32A and any other lower ratings.
In order to increase the force either the air gap has to be reduced or more turns of current carrying conductors (3) need to be provided. The air gap reduction also reduces trip travel of the trip plate causing the trip mechanism to incapacitate. In view of this, air gap cannot be reduced beyond certain limits to improve flux linkage for producing more force. Further providing more turns requires space which is usually a constraining factor for contemporary compact designs. All these constraints effectively result in higher magnetic tripping thresholds for lower rating of the circuit breakers.
Accordingly, there exists a need to provide a magnetic tripping arrangement for electrical protection device that overcomes drawbacks of the prior art.
Objects of the present invention
An object of the present invention is to reduce magnetic tripping threshold of protection devices in a short circuit condition.

Another object of the present invention is to provide an improved flux linkage and force by reducing an air gap without affecting a trip travel available for tripping.
Summary of the invention
Accordingly, the present invention provides a magnetic tripping arrangement for electrical protection devices. The magnetic tripping arrangement comprises a fixed magnet, a moving magnet/flapper, a current carrying conductor, a trip plate and a tripping mechanism.
The moving magnet is arranged with the fixed magnet with an air gap there between. The moving magnet is capable of moving towards the fixed magnet in a short circuit condition. The current carrying conductor is adapted to generate force in the short circuit condition thereby causing movement of the moving magnet towards the fixed magnet. The movement of the moving magnet causes rotation of the trip plate to generate and send a trip signal to the tripping mechanism connected thereto. The tripping mechanism upon receiving the trip signal trips the electrical protection device.
The moving magnet is selected from any one of a single rectangular structure and a multiple rectangular structure being connected to each other. Each rectangular structure includes an open side facing towards the fixed magnet to enable the conductor to generate additional magnetic forces due to differential gap arrangement and ensure sufficient trip travel at the same time during short circuit condition for achieving multiple flux linkages between the fixed magnet (10) and the moving magnet (20) thereby reducing the multiple differential air gaps without affecting the trip travel and thus resulting in a reduced tripping threshold and an overall thermal stress on an electrical system.

Brief description of the drawings
Figures 1 a and 1 b show a perspective view of a magnetic tripping arrangement for a circuit breaker, in accordance with a prior art;
Figures 2a and 2b show a perspective view of a magnetic tripping arrangement for circuit breakers, in accordance with an embodiment of the present invention; and
Figures 3a and 3b show a perspective view of the magnetic tripping arrangement for circuit breakers, in accordance with another embodiment of the present invention.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.
The present invention provides a magnetic tripping arrangement for electrical protection devices such as a lower rated circuit breaker. The magnetic tripping arrangement reduces tripping threshold of the circuit breaker in a short circuit condition by improving a flux linkage and force. The flux linkage is improved by reducing multiple differential air gaps for lower rated circuit breakers in a given frame size without affecting a trip travel available for tripping.

The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures.
Referring now to figures 2a-3b, there is shown a magnetic tripping arrangement (hereinafter 'the arrangement (100)') for an electrical control and protection device (not shown). Specifically, the electrical protection device is a lower rated circuit breaker, miniature circuit breakers (herein after 'the MCBs'), molded case circuit breakers (herein after 'the MCCBs') and the like. Specifically, the arrangement (100) is an improved multiple differential gaps arrangement that reduces short circuit magnetic threshold of thermo-magnetic protection devices. The arrangement (100) comprises a fixed magnet (10), a moving magnet (20), a current carrying conductor (30). a trip plate (not shown) and a tripping mechanism (not shown).
The moving magnet/flapper (20) is arranged with the fixed magnet (10) with an air gap there between (as shown in figures 2a and 3a). The moving magnet (20) is capable of moving towards the fixed magnet (10) in a short circuit condition. Specifically, the moving magnet (20) is a rectangular structure with one-side open. The open side is either a top side or a bottom side. In an embodiment, the moving magnet (20) is a single rectangular structure having one side open. In another embodiment, the moving magnet (20) is a multiple rectangular structure such as three or more rectangular structures being connected to each other. Each rectangular structure includes an open side facing towards the fixed magnet (10). However, it is understood that any other similar shapes of the moving magnet (20) can be arranged to give identical benefits in alternate embodiments of the present invention.
The rectangular structure of the moving magnet (20) enables the conductor (30) to generate additional magnetic forces during short circuit condition to cause the

moving magnet (20) to move towards the fixed magnet (10). This forms a multiple differential gap arrangement between the moving magnet (20) and the fixed magnet (10). The additional magnetic forces generate multiple flux linkages between the fixed magnet (10) and the moving magnet (20) (as shown in figures 2b and 3b). The flux linkages reduce the multiple differential air gaps between the fixed magnet (10) and the moving magnet (20) without affecting trip travel and thus resulting in a reduced tripping threshold of the electrical protection device and also reducing an overall thermal stress on an electrical system. However, it is understood that any other similar shape can be arranged to give identical benefits of reducing the effective tripping threshold without affecting the trip travel.
The movement of the moving magnet (20) causes the trip plate to undergo rotation to generate a trip signal. The trip signal so generated is sent to the tripping mechanism. The tripping mechanism is connected to the trip plate and upon receiving the trip signal trips the electrical protection device.
Advantages of the present invention
1. The arrangement (100) results in drastic improvement/reduction in magnetic tripping threshold in short circuit conditions. The prior art showed tripping at 20In while the arrangement (100) of the first embodiment showed 13In as tripping threshold that is at 35% reduction in tripping threshold.
2. The arrangement (100) enables simultaneous flux linkages between the fixed magnet (10) and the moving magnet (20) at more points that otherwise is a limiting factor due to space constraints. This is achieved by reducing multiple differential air gaps.
3. Improved flux linkage results in generating additional tripping force.

4. Unique shape of the moving magnet (20) of the arrangement (100) helps in maintaining the trip travel at current level and hence helps to standardize the mechanisms between higher and lower ratings.
5. The arrangement (100) effectively results in lower tripping threshold of the electrical protection devices.
6. The arrangement (100) eliminates the need for providing more turns of the conductor (30) and hence of copper material.
7. Within all constraints, the arrangement (100) results in drastic change in performance from protection perspective without adding must cost and thereby reducing overall thermal stress on the electrical system.
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention.

We claim
1. A magnetic tripping arrangement (100) for electrical protection devices, the magnetic tripping arrangement (100) comprising:
a fixed magnet (10);
a moving magnet/flapper (20) arranged with the fixed magnet (10) with an air gap there between, the moving magnet (20) being capable of moving towards the fixed magnet (10) in a short circuit condition;
a current carrying conductor (30) adapted to generate magnetic force in short circuit condition thereby causing movement of the moving magnet (20) towards the fixed magnet (10);
a trip plate adapted to rotate in response to movement of the moving magnet (20) to generate a trip signal; and
a tripping mechanism adapted to receive the trip signal from the rotating trip plate to trip the electrical protection device,
characterized in that the moving magnet (20) is selected from any one of a single rectangular structure and a multiple rectangular structure being connected to each other, each rectangular structure having an open side facing towards the fixed magnet (10) to form multiple differential gap arrangement that enables the conductor (30) to generate additional magnetic forces and ensure sufficient trip travel at the same time during short circuit condition for achieving multiple flux linkages between the fixed magnet (10) and the moving magnet (20) thereby reducing the multiple differential air gaps without affecting the trip travel and thus resulting in a reduced tripping threshold and an overall thermal stress on an electrical system.