FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"Mechanism For An Electromagnetic Actuator"
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.

Mechanism For An Electromagnetic Actuator
Field of the invention
The present invention relates to the field of electromagnetic actuators, and more particularly, to improved electromagnetic actuator design for low voltage circuit breakers.
Background of the invention
The circuit switching devices and circuit interrupters such as circuit breakers, motor starters, motor controllers and other load controllers are used to protect electrical circuitry and equipments damage due to abnormal conditions, such as an overload condition or a relatively high level short circuit or fault condition. Specifically, the circuit switching devices and circuit interrupters have an overload protection module consisting of bimetallic element as an actuator and short-circuit protection module consisting of coil and armature as an actuator. Signal from both of these modules will be given to the mechanism for opening the contacts, thereby interrupting the circuit during abnormal condition. Short circuit module of the circuit breaker is usually of solenoid or CI type electromagnet, where the CI type electromagnet consist of coil wound on the C shape fixed core, an armature of I shape and a retaining spring which holds the armature in place for the desired stroke. This circuit breaker is usually connected in series to main current path. When the over current flows through the coil it generates strong electromagnetic force on armature which can overcome the force of retaining spring at some desired current level and starts to produce a rotary motion. The electromagnetic force produced in the armature is dependent on value of the current flowing through the coil, number of turns accommodated and the magneto motive force across the air gap.
However, the presently existing circuit breakers are not compact or optimized in enough and thus the incorporation of new features in them becomes difficult. In

light of the same there exists a need for a circuit breakers that overcomes the drawbacks of the prior art.
Objects of the invention
The objective of invention is to provide a reliable, cost effective, easy to manufacture, and simple circuit breaker.
Another object of the present invention is to provide a circuit breaker which is in a compact form to allow introduction of new features or to improve the compactness as whole.
Another object of the present invention is to enable reduction in size of the electromagnetic actuator in an optimized and compact form.
Further objects and features of the present invention will become apparent from the following detailed description when considered in conjunction with the drawings.
Summary of the invention
Accordingly, the present invention provides an electromagnetic actuator comprising a fixed core, a movable core associated with the fixed core such that an x and y direction motion of the movable core is arrested and a restricted motion of movable core is allowed, depending on a required stroke length, a coil wound on the fixed core; ends of the coil being connected to terminals of main current path, a spring locater fitted on the fixed core through interference fit, a resilient expansion member connected to the spring locator and the movable core, the resilient expansion member exerts a force on the movable core and a

resolved component of spring force has higher magnitude in horizontal direction compared to vertical component, wherein, passage of a predetermined current through the coil generates an electromagnetic force in the movable core having components in a positive X and negative Z direction, the Z axis & X axis component of electromagnetic force is comparatively higher & lower than the corresponding force component of retaining spring respectively, thus the resultant force has higher magnitude in negative Z direction which rotates the moving core with the said hinge point to break a circuit of the circuit breaker.
Brief description of drawings
Figure 1 shows a perspective view of the assembled electromagnet, according to an embodiment of this invention;
Figure 2 shows a perspective view of a C-shaped fixed core, according to an embodiment of this invention;
Figure 3 shows a block diagram of an I-shaped movable core, according to an embodiment of this invention;
Figure 4 shows a perspective view of a CI electromagnet, according to an embodiment of this invention; and
Figure 5 shows a left side view of the C1 electromagnet, according to an embodiment of this invention.
Detailed description of the present invention

The foregoing objects of the 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.
Accordingly, the present invention provides an improved electromechanical actuator of CI type, which has significant improvement in the generated electromagnetic force as compared to normal CI type electromagnet and in particular that can be manufactured easily with reduced size.
Particularly the present invention enables reduction in size of the electromagnetic actuator in an optimized and compact form. Reduction in size of the actuator puts a limit to number of turns and the volume of magnetic material that can be accommodated. Due to reduction in number of turns the effective force generated in the armature may not be sufficient to trip the mechanism at the desired current level. This invention elaborates the innovative way of achieving the improved electromagnetic force on the armature for the same stroke movement in the given volume of space.
Referring now to figure 1, through 5, there is shown a mechanism for electromagnetic actuator (100), in accordance to various embodiments of the present invention.
The electromagnetic actuator (100) is an improved CI type electromagnet, best shown in the Fig 1. The electromagnetic actuator (100) includes a fixed core (2), a movable core (3), a coil (4), a spring locater (1), and a resilient expansion member (5).
In one embodiment of the present disclosure the fixed core (2) may be a C shaped fixed core (2), best shown in FIG. 2. Further, the movable core (3) may be an 1-shaped movable core (3). The movable core (3) may be made up of

commonly used magnetic material like MS, etc. In other embodiments of the present invention, the movable core (3) may be composed of any other magnetic material without deviating from the spirit of the invention. The movable core (3) is suitably placed on the inner edge of fixed core (201) as shown in Fig 2.
More specifically, the moving core (3) is adapted to be inserted diagonally into the fixed core (2) so that the outer edges (301, 302) of moving core (3) as shown in Fig 3 are engaged respectively with the inner edge (201, 202) of fixed core (2). A projected part (312) which is engaged with the inner surface (221) of fixed core (2) ensures the arrest of Y direction motion of the moving core (3). Similarly the surfaces (222, 223, 224 & 225) of the fixed core (2), as shown in Fig 4, are engaged with the surface (321, 322) of the movable core (3) to provide a restricted motion for the movable core (3) in Z direction depending on required stroke length.
The coil such as an insulated copper coil (4) of the electromagnetic actuator (100) is wound on fixed core (2). More specifically, as best shown in Fig 1, the insulated copper coil (4) of a predefined dimension and number of turns is wound over fixed core (2). Opposite ends (401, 402) of the insulated copper coil (4) are connected to upper and lower terminal of the main current path.
The spring locator (1) of the present invention is made up of non magnetic material, such as nylon. The spring locator (1) is fitted on the fixed core (2), as shown in figures.
Further, a resilient expansion member such as the helical expansion spring (5) made up of spring material, is connected between the spring locator (1) and the movable core (3).
The helical expansion spring (5) is connected between the spring locator (1) and the movable core (3) in such a fashion that one arm of the helical expansion spring (5) is hooked to the projected part of spring locator (1) and the second

arm is connected to the start of the projected part of the spring locator (1), as shown in Fig. 1.
The spring locator (1) is assembled to the fixed core (2) through interference fit in X direction. The Y & Z direction movement of the said body is arrested by the projected part (211, 212, 213 & 214) of fixed core (2) in engagement with the spring locator (1).
The connection of the helical expansion spring (5) with the spring locator (1) and the movable core (3) exerts a force on movable core (3). The resolved components of the spring force have higher magnitude in -X direction (horizontal) compared to vertical component (+Z direction). The engagement of surfaces (226, 227) with (323, 324) restrict the motion of moving core (3) in -X direction, so that at all times the edges (201, 202 & 301,302) are kept in contact. This acts like a hinge point for the moving core (3).
During the passage of over current therethrough, the insulated copper coil (4), generates an electromagnetic force in the movable core (3) which has components in +X and -Z direction. The Z axis & X axis component of electromagnetic force is comparatively higher & lower than the corresponding force component of retaining spring respectively, thus the resultant force has higher magnitude in -Z direction which rotates the moving core (3) with the said hinge point. The projected part of the moving core (311) which is connected to external trip point of circuit breaker (not shown), gives the signal to mechanism module of the circuit breaker 100 on abnormal condition to operate and to break the circuit.
In a preferred embodiment of the present invention, as best illustrated in FIG. 5, there exist two variable air gap between the movable core (3) and the fixed core (2). A variable air gap Al is between the surfaces (222, 223 & 321) and is indicated by the Fig 5 in front view as (a,b,c). The second variable air gap A2 is

between surfaces (228, 229 & 325,326) and it is indicated by the figure 5 in front view as (b,c,d,e). The projected part (211,212) of the fixed core (2) has an intentional profile geometry of increasing cross sectional area for providing variable air gap A2.
When the current starts to flow, magneto motive force is set up in the magnetic circuit which drives the flux tines across the magnetic circuit 1 & 2 through variable air gap Al and A2 respectively. The electromagnetic force generated in the movable core (3) acts along the direction so as to reduce the reluctance in magnetic circuit 1 & 2. In order to reduce the reluctance in magnetic circuit 1 & 2, an electromagnetic force is setup in the movable core (3) forcing it to move towards lower reluctance path. Profile of the projected part in fixed core (211, 212) is so arranged of increasing cross sectional area so that when the reluctance in magnetic circuit 2 reduces it complements the same by reducing the reluctance in magnetic cirucit 1, and a torque is generated on moving core (3) which is contributed by the electromagnetic force generated to reduce the reluctance offered in flux path 1 & 2. Due to leverage action principle the torque added to the body by the electromagnetic force generated in magnetic circuit 2 will be significantly higher during initial stages of motion. After breakeven point the torque contributed by the electromagnetic force generated in magnetic circuit 1 will be more predominant than the force generated in magnetic circuit 2 due to the reason that rate of change of reluctance in magnetic circuit 1 will be significantly more than the rate of change of reluctance in magnetic circuit 2 for per unit displacement. By this way, net torque acting on the moving core (3) is increased for the same current level.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to

best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We Claim:
1. An electromagnetic actuator comprising;
a fixed core,
a movable core associated with the fixed core such that an x and y direction motion of the movable core is arrested and a restricted motion of movable core is allowed, depending on a required stroke length;
a coil wound on the fixed core; ends of the coil being connected to terminals of main current path;
a spring locater fitted on the fixed core through interference fit;
a resilient expansion member connected to the spring locator and the movable core, the resilient expansion member exerts a force on the movable core and a resolved component of spring force has higher magnitude in horizontal direction compared to vertical component;
wherein, passage of a predetermined current through the coil generates an electromagnetic force in the movable core having components in a positive X and negative Z direction, the Z axis & X axis component of electromagnetic force is comparatively higher & lower than the corresponding force component of retaining spring respectively, thus the resultant force has higher magnitude in negative Z direction which rotates the moving core with the said hinge point to break a circuit of the circuit breaker.
2. The electromagnetic actuator as claimed in claim 1, wherein
outer edges of moving core are engaged with the inner edges of fixed core, a
projected part of moving core is engaged with the inner surface of fixed core and
surfaces of the fixed core are engaged with the surface of the movable core.

3. The electromagnetic actuator as claimed in claim 1, wherein the resilient expansion member is a helical expansion spring.