FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: IMPROVED SOLENOID OPERATED CIRCUIT BREAKER TRIPPING ASSEMBLY
2. Applicants):

(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 switchgear applications. More particularly the present invention relates to an improved solenoid operated circuit breaker tripping assembly. This application is more relevant to solenoids which are designed for higher force in lesser space.
BACKGROUND AND THE PRIOR ART
In certain circuit breakers a solenoid is required for sensing electrical abnormalities. For example in internal accessories like UV & shunt release solenoid is required. Solenoid is an electromagnetic release which is used in switchgears for sensing electrical abnormal conditions and giving a mechanical output such as trip signal which will trip the breaker mechanism.
One of the prior art in the present field of invention is described below:
JP6243772 (A) provides a compact electromagnetic trip device for a circuit breaker. An actuator to slidingly move in a guide channel interacts with a contact point opening mechanism having a trip bar operable so as to close or open an electric contact point. A spring presses the actuator toward the trip bar. A solenoid arranged in a base part electromagnetically displaces a plunger along a straight line passage, and is also joined to a trigger having a locking surface to hold or release the actuator. The trigger is formed in an L shape, and pivotally moves with a pivot pin positioned between L-shaped two leg parts as the center. One among the two trigger leg parts is joined to the plunger, and the other has an engaging surface to move in the rear of a complementary-shaped surface so as to selectively stop motion of the actuator. A return spring presses the trigger toward a locking position.
Solenoids which are going along with the breaker have higher space constrains and also the solenoids which are used for continuous duty is required to be designed for lesser power consumption.
The present invention therefore provides for solenoids that requires fewer amperes turns, hence coil diameter is reduced, and thus solenoid becomes compact. Thus this invention

provides an improved solenoid operated circuit breaker tripping assembly that addresses space constraints, have less power consumption and offers higher output force. This application is more relevant to solenoids which are designed for higher force in lesser space.
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 solenoids which are used along with the breaker having higher space constrains.
Another object of the present invention is to provide solenoids adapted for continuous duty requiring lesser power consumption.
Another object of the present invention is to provide solenoid that offers higher output force in lesser space.
Yet another object of the present invention is to decrease remanence (residual magnetism).
SUMMARY OF THE INVENTION
There is provided an improved solenoid operated circuit breaker tripping assembly. This application is more relevant to solenoids which are designed for higher force in lesser space.
According to one embodiment of the present invention, there is provided improved solenoid operated circuit breaker tripping assembly, said assembly comprising a fixed core; a plunger; a coil assembly including a bobbin over which wire is wounded and placed inside a frame, said frame comprising a base plate, a side plate and a top plate; an opposition spring means located between said fixed core and said plunger for separating and forming an air gap between said fixed core and said plunger; wherein said fixed core, said plunger, said coil assembly and said frame together forming a magnetic circuit; wherein said fixed core riveted on said base plate and said moving core configured to move inside said bobbin between a

bobbin stopper portion and said fixed core; wherein said top plate having a slot on which bobbin projection is placed inside which plunger moves; wherein said coil is configured to overcome the oppositions offered by opposition spring and reluctance offered by the working air gap and radial air gap; wherein said solenoid adapted to provide higher force in lesser space; wherein said coil sense the electrical signal and gives mechanical trip signal as output.
BRIEF 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 compact solenoid 1, Plunger 2, Top plate 3, bobbin 4, opposition spring 5, working air gap 6, coil 7, fixed core 8 and side plate 9 are shown.
Fig 2 shows frame 10 formed with top plate 3, side plate 9, base plate 11, also it shows hole on top plate 3a & hole on base plate 1 la.
Fig 3 shows radial air gap 12 between plunger step 2a and top plate 3.
Fig 4 shows coil 7 wound on bobbin 4, plunger 2, plunger step 2a stopped by the bobbin stopper portion 4a and radial air gap 12. .
Fig 5 shows radial air gap and working gap.
The invented system is thus an improved solenoid for a moulded case circuit breaker.

DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention there is provided an improved solenoid operated circuit breaker tripping assembly. It consists of a fixed core, moving core or plunger, coil assembly and a frame which completes the magnetic circuit. The coil assembly is placed inside the frame as shown in figure 3 where the frame consists of base plate, side plate, and top plate as shown in figure 2.
In the present invention compactness is achieved by increasing the output force delivered by solenoid with less NI. For this magnetic circuit reluctance has been reduced at pickup by modifying top plate and better utilizing radial gap. Further to address the residual flux issues (remanence issue) radial air gap length and thickness as been maintain high at hold on. Because of this less NI requirement which means less turns, less conductor, less cost, less power consumption, less space and suitable to work in continuous duty. Top plate thickness will usually equal to side plate thickness, in this design top plate along with plunger has been modified to obtain the above said objective. (Refer Fig.5)
Force mentioned in this invention is the electromagnetic output force offered by solenoid at plunger, i.e. Pull force experienced by the plunger from fixed core which moves it. This invention is applicable for any type of mechanism which requires input from solenoid, which mean sensing an electrical signal but requires a mechanical output for actuation like sensing under voltage, over voltage, remote trip signal etc.
Reference numerals for the different components used are as follows:
• solenoid (1)
• Plunger (2)
• Plunger step (2a)
• Top plate (3)
• Top plate hole (3a)
• Bobbin (4)
• Bobbin stopper (4a)
• Opposition spring means (5)

• Working air gap (6)
• Coil (7)
• Fixed core (8)
• Side plate (9)
• Frame (10)
• Base plate (11)
• Base plate hole (11a)
• Radial gap (12)
• Radial gap length (12a)
• Radial gap thickness (12b)
The coil assembly consists of bobbin over which wire is wounded. The fixed core is riveted on the base plate and a plunger moves inside the bobbin between the bobbin stopper portion and fixed core. Top plate has a slot on which bobbin projection is placed inside which plunger moves. Also bobbin protects the plunger from touching the top plate.
The fixed core and moving core will be separated by an opposition spring which determines the operating point of the solenoid. The opposition spring is located between the fixed core and the step of the plunger as shown in the figure 1. Because of the opposition spring there will be an air gap between fixed core and plunger which is called as stoke or travel or working air gap. A radial gap is formed between the plunger step and top plate hole as shown in figure 3.
Solenoid coils are designed to overcome the oppositions offered by opposition spring and reluctance offered by the working air gap and radial air gap. In order to overcome this working gap, current and number of turns (Ampere turns) are the major parameters to produce the required pull force. So Ampere turns spent to overcome oppositions offered by opposition spring & working air gap are useful ampere turns which do the work required.
Apart from the working air gap, ampere turns which is spent to overcome the reluctance offered by radial air gap does not do any useful work. But the radial gap cannot be avoided because if it is zero it will affect the plunger movement, also it will affect drop off (plunger

not releasing issues) of a solenoid due to remnance. Also it cannot be too small due to the design constrains. Hence for an effective coil design, radial gap reluctance has been tuned to a lesser value.
Hence to have compact solenoid to address the space constrains and lesser power consumption, the magnetic circuit design should be done effectively. The size of side plate and base plate are decided by the saturation limits and strength hence it cannot be decreased. The size of plunger and fixed core is fixed based saturation flux density and force output requirement which are very critical and cannot be reduced in dimension.
The other component left for change is the coil. Coil dimensions are fixed by the total ampere turns requirement for generating the required force and safe current density for continuous operation. Hence there is a requirement of effective magnetic circuit design for generating higher force with minimum ampere turns. To have fewer amperes turns the reluctance of the magnetic circuit need to reduce. For air gaps and opposition springs are the main parameters which require higher ampere turns. Hence to have smaller coil diameter, there should be a need for fewer ampere turns requirement for offering same higher force.
The main factors affecting the reluctance of magnetic circuit are working air gap, opposition spring force and radial gap reluctance. Since the working air gap and opposition spring force are useful parameters the reluctance of the magnetic circuit is minimized by adjusting the radial gap reluctance. The radial gap reluctance is guided by two important parameters length of radial gap decided by inner and outer diameter, and thickness of radial gap. The radial gap reluctance can be decreased by having lesser gap length i.e. by having maximum inner diameter of plunger and minimum top plate slot diameter and by increasing the thickness of radial gap. Radial gap maximum inner diameter and minimum outer diameter are constrain by design parameters like minimum clearance, minimum plastic thickness etc., Hence in this invention, the thickness of radial gap has been increase between 1:1.5 to 1:4 such that the total reluctance of the magnetic circuit is decreases, hence the ampere turns requirement for the same higher magnetic force is decreased. Because of this the total copper consumption is decreased and also the total power consumption is also decreased. Hence the same output force is achieved with lesser copper and in smaller dimension than the conventional design.

The required higher radial gap thickness is achieved through increasing the top plate thickness, and to address the space constraints the side plate and base plate thickness are maintained at the minimum thickness considering strength requirements. Hence in this invention a compact solenoid has been made by effective design of magnetic circuit.
This invention requires fewer amperes turns, hence coil diameter is reduced, and thus solenoid becomes compact. Thus this invention addresses space constraints, have less power consumption and offers higher output force. The innovative feature in this invention is the variation in radial reluctance, i.e. having less radial reluctance during pickup and offers high reluctance during hold on. This feature has been obtained by modifying the top plate and plunger profiles which has been explained in the fig 5.
With regard to remanence, also called residual magnetism which is a property of soft magnets to retain the flux even after the supply or field has been removed i.e. Electromagnet will start to behave as permanent magnet holding moving and fixed core together. This will affect the basic functionality of solenoid to make it ready for next operation. The best solution to address the remanence is reversing the supply to coil, or recent trend in large magnets is to use ejector pins to separate cores, in some case permanent hole will be provided in the fixed core by compromise the magnetic force at pick up. All these methods will not be applicable in limited space requirement application like internal accessories. Remanence cannot be eliminated at the same time it should not be high hence there is a need decreased residual magnetism.
For remanence to be less at hold on condition i.e. when two cores are together, there should be some permanent air gap which provides high reluctance. In our case that reluctance has been provided by high radial air gap. But this high radial air gap will make the solenoid higher in size since to overcome working air gap and radial air gap the circuit will require more NI which in turn requires more copper increasing cost and power consumption. In current invention this reluctance offered by radial air gap has been reduced at the initial pickup by having thicker top plate, and plunger has designed to have a step in such a way that at hold-on the reluctance will be reduced to an optimum value to offer sufficient constant air gap to overcome residual magnetism. Figs 5 illustrate the condition at pick up and hold on.

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 solenoid operated circuit breaker tripping assembly, said assembly
comprising:
a fixed core;
a plunger;
a coil assembly including a bobbin over which wire is wounded and placed inside a frame, said frame comprising a base plate, a side plate and a top plate;
an opposition spring means located between said fixed core and said plunger for separating and forming an air gap between said fixed core and said plunger;
wherein said fixed core, said plunger, said coil assembly and said frame together forming a magnetic circuit;
wherein said fixed core riveted on said base plate and said moving core configured to move inside said bobbin between a bobbin stopper portion and said fixed core;
wherein said top plate having a slot on which bobbin projection is placed and providing for movement of said plunger;
wherein said coil is configured to overcome the oppositions offered by said opposition spring means and reluctance offered by the working air gap and radial air gap;
wherein said coil assembly configured to sense the electrical signal and gives mechanical trip signal as output.
2. Assembly as claimed in claim 1 wherein said air gap between said fixed core and said plunger is configured to determine operating point of said solenoid.
3. Assembly as claimed in claim 1 wherein said bobbin adapted to protect said plunger from touching said top plate.

4. Assembly as claimed in claim 1 wherein a radial gap is formed between a plunger step and a top plate hole.
5. Assembly as claimed in claim 1 wherein said radial gap thickness is kept substantially high by substantially increasing said top plate thickness.
6. Assembly as claimed in claim 1 wherein thickness of said side plate and said base plate are maintained substantially minimum considering strength requirements thereby addressing space constraints.
7. Assembly as claimed in claim 1 wherein said plunger is substantially a moving core.
8. An improved solenoid operated circuit breaker tripping assembly as herein described and illustrated with reference to accompanying drawings.