FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
Electro-Magnetic Actuating System for Circuit Breakers
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.

Electro-Magnetic Actuating System for Circuit Breakers
Field of the invention
The present invention relates to circuit breakers and more particularly, to an electromagnetic actuating system for low voltage circuit breakers.
Background of the invention
Circuit breakers provide protection to an electrical system from electric faults such as overloads and short circuits. Generally, circuit breaker incorporates a thermal trip device which responds to persistent low levels of over current and an electromagnetic trip assembly, alternatively electromagnetic actuator or magnetic release which responds to short time high levels of over current. Thus, the electromagnetic actuator must be designed to achieve fast tripping of the circuit breaker during short circuit faults, so as to ensure reliability and safety of the electrical system.
Conventional electromagnetic actuators consist of two cores- a moving core and a fixed core, a magnetic frame, a coil, a spring and a plunger for tripping the mechanism. The coil is energized with AC or DC supply depending on the application. The coil carries the current and the magnetic circuit formed by the frame, the moving core and the fixed core concentrates the magnetic flux in the direction of motion by giving low reluctance path.
Under normal condition, the electromagnetic actuator remains in open position and the circuit breaker mechanism remains latched. In a distribution system, the electromagnetic actuator system is used to sense the abnormal condition and give a trip signal to a tripping unit so that system reliability is assured. When abnormally

high current passes through the release coil, a magnetic field is produced. This exerts force on the moving core, which helps in overcoming the spring force. The moving core in the process of overcoming the high reluctance of air gap gets attracted towards the fixed core. The force developed by magnetic field holds the moving core and the magnetic frame together. The moving core while moving towards the frame moves/propels the plunger to give actuating signal to the circuit breaker mechanism to de-latch the mechanism thereby causing the circuit breaker to trip.
The conventional construction of the electromagnetic actuator has more number of components such as two cores which add to the cost of circuit breaker. In the conventional design if we opt for single core construction, the C shaped frame of the conventional electromagnetic actuator will result in producing forces in addition to operating forces. These forces which are not in the direction of motion might disturb the alignment of the moving core thereby causing friction. Thus, the moving core while moving has to overcome the frictional force that affects the tripping action.
Accordingly, there exists a need to provide an electro-magnetic actuator that overcomes drawbacks of the prior art.
Objects of the present invention
An object of the present invention is to eliminate a fixed core so as to reduce one component in an electro-magnetic actuating system thereby reducing cost thereof.
Another object of the present invention is to provide an improved frame design that nullifies forces other than operating forces thereby giving improved performance.

Yet another object of the present invention is to detect fault conditions and give trip signal to a circuit breaker to interrupt the current flow.
Still another object of the present invention is to provide a fast tripping action so as to isolate an electric system quickly thereby ensuring reliability and safety of the electric system as well as of the human.
Summary of the invention
Accordingly, the present invention provides an electro-magnetic actuating system for circuit breakers. The electro-magnetic actuating system comprises a moving core capable of moving linearly, a plunger capable of being propelled by the moving core for giving actuating signal for any abnormal condition to a tripping unit connected thereto, a spring attached to a lower end of the moving core, a magnetic frame having an upper bend and a lower bend, the lower bend connected to an external current carrying conductor and a coil welded to the upper bend. The magnetic frame is a U shaped magnetic frame that produces force only in the direction of an operation thereby guiding and accelerating the motion of the moving core and the plunger for tripping.
Brief description of the invention
Figure 1 shows a perspective view of an electro-magnetic actuating system, in accordance with the present invention;
Figure 2 is an exploded view of the electro-magnetic actuating system of figure 1;

Figure 3 shows an initial assembled view of the electro-magnetic actuating system of figure 1; and
Figure 4 is a view representing the electro-magnetic actuating system of figure 1 in close condition.
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 an electro-magnetic actuating system for a circuit breaker. The electro-magnetic actuating system eliminates a fixed core so as to reduce one component thereby reducing cost thereof. The electro-magnetic actuating system provides an improved frame design that nullifies forces other than operating forces thereby quickly detecting fault conditions and giving trip signal to the circuit breaker to interrupt the current flow thus resulting in an improved performance.
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 1 and 2, there is shown an electro-magnetic actuating system (hereinafter 'the system (100)') for a circuit breaker (not shown), in accordance with the present invention. Specifically, the circuit breaker is a low

voltage circuit breaker. The system (100) comprises a moving core (10), a plunger (20), a magnetic frame (30), a coil (40) and a spring (50).
The moving core (10) is capable of moving vertically. The moving core (10) is designed in such a way that the moving core (10) fulfils the requirement that magnetic gap enclosed by the coil (40) helps in flux linkage and also provides reduced effective magnetic gap keeping actual gap as required which reduces VA requirement. The moving core (10) rotates the plunger (20). The plunger (20) is capable of giving actuating signal for any abnormal condition or required specifications to a tripping unit (not shown) connected thereto when moved by the moving core (10).
The magnetic frame (30) includes an upper bend (22) and a lower bend (24). The
magnetic frame (30) is a U shaped magnetic frame that is optimally designed in such a way to act as a fixed core and produce maximum force only in the direction of motion. With the magnetic frame (30) (hereinafter "the U frame (30)"), the magnetic fluxes travel in two parallel paths through the U frame (30), each producing forces in opposite direction. These forces cancel out each other and there remains only the operating force. Thus, unlike the conventional C shaped frames, the U frame (30) even in the absence of the fixed core produces force only in the direction of operation, thus guiding and accelerating the motion of the moving core (10) and the plunger (20) thereby producing tripping.
The U frame (30) profile is designed in such a way that the upper bend (22) thereof gives proper space for easy welding of the coil (30) and the lower bend (24) is connected to an external current carrying conductor (not shown). Thus, the part of the U frame (30) between the upper bend (22) and the lower bend (24) also contributes in carrying current and hence the force generation. This helps in optimal

design of the coil (40) resulting in cost reduction. The U frame (30) includes the coil (40) welded thereto.
Specifically, the coil (40) is an electromagnetic coil. The coil (40) is welded to the U frame (30) in a space provided by the upper bend (22) of the U frame (30). The current path between the upper bend (22) and the lower bend (24) contributes in completing effective turn of the coil (40) as current flows there through. This is in turn helps in producing more flux and when current passes through the coil (40), a magnetic field is produced that attracts the moving core (10) thereby overcoming reluctance of the air gap. The magnetic field produced by fault current de-latches the circuit breaker mechanism causing the circuit breaker to trip.
The spring (50) is attached to the lower end of the moving core (10). Specifically, when the coil (40) is energized, the moving core (10) moves downwards in order to complete the magnetic flux path till the U frame (30) surface and links more flux with respect to the U frame (30) surface that helps in reducing active air gap.
Referring to figure 3, which represents an initial assembled condition of the system (100) wherein a magnetic gap is shown. The state of system (100) is de-energized and the moving core (10) and the U frame (20) are in open condition. As the coil (40) is energized, the moving core (10) moves downwards in order to complete the magnetic flux path until the fixed U frame (30) surface. Front profile of the moving core (10) is designed in such a way that as the moving core (10) moves downwards resulting in higher flux linkage with respect to the U frame (30) surface thereby producing higher force. The step in the moving core (10) helps in reducing active air gap but still maintains designed gap.

Figure 4 represents a closed condition of the system (100) wherein the moving core (10) is completely touching the surface of the U frame (20) such that the magnetic gap becomes zero. That is the magnetic flux completes the path through minimum reluctance, thus producing maximum force. This force overcomes the spring (50) force causing the moving core (10) and the plunger (20) to stay in that position till the coil (40) de-energizes, that is till the fault gets cleared.
Advantages of the present invention
1. The system (100) gives reliable performance, with the same efficiency but at reduced cost.
2. Introduction of the system (100) in the circuit breaker reduces manufacturing time and cost due to removal of the fixed core while giving efficient performance.
3. The U frame (30) design, unlike the conventional C shaped frame, produces force only in the direction of operation, thus guiding and accelerating the motion of the plunger (20) and the moving core (10), thus achieving efficient and fast tripping.
4. Single core design as against the conventional dual core magnetic release, reduces the manufacturing time and cost of one component.
5. The moving core (10) improves the flux linkage, gives benefit of effectively less magnetic gap and more actual gap for tripping hence giving more efficient performance.
6. The coil (40) design reduces the copper usage and hence the cost, while maintaining the performance requirement.
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. An electro-magnetic actuating system (100) for circuit breakers, the
electro-magnetic actuating system (100) comprising a moving core (10) capable of
moving linearly, a plunger (20) capable of being propelled by the moving core (10)
for giving actuating signal for any abnormal condition to a tripping unit connected
thereto, a spring (50) attached to a lower end of the moving core (10), a magnetic frame (30) having an upper bend (22) and a lower bend (24), the lower bend (24) connected to an external current carrying conductor and a coil (40) welded to the upper bend (22),
characterized in that the magnetic frame (30) is a U shaped magnetic frame that produces force only in the direction of an operation thereby guiding and accelerating the motion of the moving core (10) and the plunger (20) for tripping.