FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: A VARIABLE MAGNETIC RELEASE ASSEMBLY USING SOLENOID FOR MOULDED CASE CIRCUIT BREAKER
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
This invention relates generally to a moulded case circuit breaker (MCCB) and more particularly to a variable magnetic release assembly using a solenoid to sense the fault as per the pre-set fault level and giving signal for tripping the MCCB.
BACKGROUND AND THE PRIOR ART
A circuit breaker is a device used for the protection of circuits from faults ranging from marginal increase in rated current to very high current. The MCCB provides high current protection through repel opening of the contacts or through tripping of the mechanism on receiving signal from the magnetic release assembly or both i.e. repel opening as well as mechanism tripping completes the fault clearing process. The repel opening is due to repel forces developed because of the opposite direction of current in the contacts, forcing the movable contacts to move upward away from fixed contact. The repulsion force is further augmented by the presence of slot motor in the contact opening region.
The present invention has found its application in the magnetic release part for sensing the fault and transferring the signal to the mechanism for opening of the contacts. Different types of magnetic release assembly are used based on the ratings of moulded case circuit breaker (MCCB). In the present invention solenoid type of magnetic protection is used.
In US6201460 an undervoltage release device for a circuit breaker is disclosed having an operating mechanism, a trip bar, line and load terminals, and a cover. The device includes a housing, a solenoid, upper and lower actuators aligned with a plunger of the solenoid and in selective contact with the trip bar, plunger and actuator reset levers mounted upon the solenoid frame, and pair of terminals in electrical contact with the solenoid coil and line terminals of the breaker, wherein the force of the solenoid corresponds to the line voltage. Also disclosed is a method for tripping a circuit breaker when line voltage drops below a selected value, in a circuit breaker having an operating mechanism and a trip unit with an intermediate latch.

The method includes steps of closing the circuit breaker with the operating mechanism, installing the device in a cover of the circuit breaker, the device having a solenoid with a plunger and a plurality of actuators in selective contact with the plunger and the trip unit; and wiring the solenoid in parallel with the load circuit, wherein the magnetic force of the solenoid is proportional to the line voltage and maintains the plunger in contact with the actuators, and wherein the plunger is released by the solenoid when the line voltage drops below the selected value, thereby providing for at least one actuator to contact the trip unit and open the circuit breaker. However, the prior art does elucidate on a mechanism which could work at variable voltages.
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 magnetic protection through variable magnetic release assembly which can be adjusted for different fault levels based on the requirements.
Another object of the present invention is to provide a moulded case circuit breaker comprising the said variable magnetic release assembly.
Yet another object of the present invention is to provide signal to the Trip-p!ate to rotate on its axis, which is required by mechanism of the MCCB for opening the contacts.
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 a magnetic protection through variable magnetic release assembly which can be adjusted for different fault levels based on the requirements.
According to one embodiment of the present invention, there is provided a moulded case circuit breaker comprising the said variable magnetic release assembly.
Yet another embodiment of the present invention provides for signal to the Trip-plate to rotate on its axis, which is required by mechanism of the MCCB for opening the contacts.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 illustrates Different sub-assemblies of Moulded case circuit breaker in open state.
Fig. 2 illustrates Tripper on plunger and Trip-plate in detailed view with their proper alignment in the Moulded case circuit.
Fig. 3 illustrates Moulded case circuit breaker cut section depicting different components in the assembled state and detailed view of Magnetic release assembly.
Fig. 4 illustrates magnetic lines in the cut section of solenoid assembly.
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 moulded case circuit breaker in open state is shown. It shows housing, cover, contact assembly, mechanism assembly, magnetic release assembly, contacts, trip-plate etc.
Fig. 2 shows Tripper on plunger and Trip-plate in detail including moving plunger, extension spring, bracket etc.
Fig. 3 shows plunger with tripper on it, bobbin, compression spring, static core and box frame.
Fig. 4 shows magnetic lines in the cut section of solenoid assembly.
The invented system is thus a variable magnetic release assembly using a solenoid to sense the fault as per the pre-set fault level and giving signal for tripping the MCCB.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly the present invention provides for variable magnetic release used in the Moulded case circuit breaker.
Components used in the present system are as follows:
1 - Housing
2 - Cover
3 - Contact assembly
4 - Mechanism assembly
5 - Magnetic release assembly

6 - Moving contact (Upper contact)
7 - Fixed contact (Lower contact)
8 - Trip-piate
9 - Mechanism plate
10 - Tripper
11- Moving Plunger
12- Cylindrical surface of tripper
13- Extension spring
14- Bracket
15- Magnetic release assembly
16- Plunger assy, with tripper on it 17-Bobbin

18- Compression spring
19- Static core
20- Box frame
21- Magnetic field lines
22- Air-gap
MCCB consist of housing (1), contact assembly (3), mechanism assembly (4) & magnetic release assembly (5). Contact assembly consist of moving contact (6) and fixed contact (7), which mates to conduct the current in the system and separates to interrupt the current so as to disconnect electrical system.
Mechanism assembly is used for opening and closing of the main contacts. In the event of faults it receives tripping signal from magnetic release to open main contacts and thus isolates the electrical system from fault.
Magnetic release consists of bobbin (17) made up of insulating material, coil assembly which is part of main current carrying path and is wounded on bobbin, box frame (20) made up of ferromagnetic material, static core and moving plunger made

up of ferromagnetic material, compression spring, tripper made up of non magnetic material and connected to a moving plunger.
The static core is connected to box frame through screw thread type joint. The thread on static core enables the position adjustment for static core. The compression spring is locates in air-gap between moving plunger (11) & static core (19) and restrict the movement of moving plunger during normal operation when the current flowing through main circuit is below pre-set fault level.
The initial position of the trip-plate 8 is determined by the extension spring (13) which pulls trip-plate in anticlockwise direction.
The cylindrical face (12) of the tripper (10) rests on the surface of trip-plate & its downward movement causes rotation of trip plate in clockwise direction.
During ON operation of MCCB, the main latch of mechanism is held by trip plate. The rotation of trip plate in clockwise direction releases the main latch causing tripping operation of mechanism and thus separation of main contacts which interrupts main circuit.
Current flowing through the coil assembly produces magnetic field (21) as shown in figure 4. This magnetic field produces attraction force on moving plunger. In normal working condition, i.e. when current flowing through main circuit is less than the preset fault level, the attraction force acting on moving plunger is not adequate to move the plunger in downward direction as the compression spring (18) exerts force on moving plunger in opposite direction.
In the event of fault when fault current exceed the pre-set fault level the magnetic force generated by coil assembly becomes higher than the compression spring, causing downward movement moving plunger. As the tripper is connected to the moving plunger, this downward movement causes trip plate to rotate in clockwise

direction resulting in tripping operation of MCCB & hence interruption of the main circuit.
The attraction force acting on moving plunger is proportional to the magnetic field produced in the magnetic release. Higher magnetic field exerts higher force on the moving plunger large enough to overcome compression spring force, thereby pulling it in the downward direction. Higher magnetic field will be produce either by high current or by reducing the air-gap (22) between the static core & moving plunger. The thread provided on static core engages it with the box frame, avoiding its movement during normal operation & it also allows the initial adjustment of air-gap. With this arrangement the air-gap between moving plunger and static core can be adjusted to any value which will helps in setting different pre-set fault levels. The adjustment in air-gap allows moving plunger to move only when fault current threshold exceeds corresponding pre-set fault level.
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. A variable magnetic release assembly using solenoid for tripping a moulded
case circuit breaker having a housing (1), contact assembly (3), mechanism
assembly (4),the variable magnetic release assembly (5) comprising:
a bobbin (17) made up of insulating material;
a coil assembly which is part of main current carrying path and is wounded on the said bobbin (17);
a frame means(20) made up of ferromagnetic material;
a spring means (18);
a tripper (10) on plunger (16) made up of non magnetic material and connected to a moving plunger (11);
a trip plate (8).
2. A variable magnetic release assembly as claimed in claiml wherein the static core is adapted to be connected to said frame means through screw thread type joint.
3. A variable release assembly as claimed in claim 2 wherein the thread in static core enables the position adjustment for static core.
4. A variable magnetic release assembly as claimed in claim 1 wherein the spring means being located intermediately between said moving plunger (11) and static core (19) air gap thereby restricting movement of the moving plunger during normal operation when the current flowing through main circuit is below pre-set fault level.
5. A variable magnetic release assembly as claimed in claim 1 wherein the spring means is a compression spring.

6. A variable magnetic release assembly as claimed in claim 1 wherein the initial position of the trip plate (8) is determined by the extension spring (13) which pulls trip plate in anti-clock wise direction.
7. A variable magnetic release assembly as claimed in claim 1 wherein the tripper (10) comprising a substantially cylindrical face (12) resting on the surface of trip-plate and its downward movement causes rotation of the trip piate in clockwise direction.
8. Mechanism assembly (4) as claimed in claim 1 which in fault receives tripping signal from magnetic release open main contacts.
9. A variable magnetic release assembly using solenoid for tripping a moulded case circuit breaker as herein substantially described and illustrated with reference to the accompanying drawings.