FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An improved ratchet and pawl based circuit breaker.
APPLICANT(S)
Crompton Greaves Limited, CG House, 6th Floor, Dr. Annie Besant Road, Worli, Mumbai - 400030, Maharashtra, India; an Indian Company.
INVENTOR(S)
Bagade Vishal Vijay of Crompton Greaves Limited, S3 R&D department Nashik, India; an Indian National.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to the field of mechanical engineering.
Particularly, this invention relates to mechanical assemblies and mechanical engineering with respect to switchgear equipment.
More particularly, this invention relates to closing and charging systems in circuit breakers.
Specifically, this invention relates to an improved ratchet and pawl based circuit breaker mechanism.
BACKGROUND OF THE INVENTION
The term 'switchgear', used in association with the electric power system, or grid, refers to the combination of electrical disconnects, earthing-switches and/or circuit breakers used to isolate electrical equipment and networks. Switchgear is used both to de-energize equipment to allow maintenance work to be done and to clear faults.
Switchgear equipment comprises circuit breaker mechanisms. Circuit breakers are crucial devices in an electrical substation. They are essentially switches that break (i.e., open) an electrical circuit manually or automatically to protect against faulty conditions. A circuit breaker has to open the circuit sufficiently fast to prevent damage to other major equipment in a substation (e.g., a transformer). Furthermore, if fault current flows through a circuit breaker for a long duration, there is a possibility of melting of contacts. A circuit breaker should also be able to connect the circuit back (i.e., close) after normal conditions are restored. This is achieved in circuit breaker mechanisms with the help of potential energy stored in opening and closing springs. This warrants quick closing and opening of the circuit breaker contacts. The operation of a circuit breaker mechanism is divided into three stages: 1) charging the closing spring; 2) closing the contact; and 3) opening the contacts. This disclosure deals with charging and closing operations.
Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using energy storage media such as springs or compressed air)

contained within the breaker is used to separate the contacts. Circuit breakers have coils to trip i.e. open and close the mechanism, and electric motors to restore energy to the springs.
A trip / close coil is a type of solenoid in which the moving armature delatches the opening / closing latching mechanism to open / close the circuit breaker.
In its working mode, if a power surge / fault occurs in the electrical system, signal is given to trip coil to delatch the opening latch mechanism so that the breaker will trip. This means that a breaker that was in the "on" position will flip to the "off position and shut down the electrical power leading from that breaker. Essentially, a circuit breaker is a safety device. When a circuit breaker is tripped, it may prevent a fire from starting on an overloaded circuit; it can also prevent the destruction of the device that is drawing the electricity.
A close coils is a coil which delatches the closing latch mechanism to close the circuit breaker electrically using an external voltage source when a specified voltage is applied across the coil. The operating mechanism, of a circuit breaker, consists primarily of two compression springs; 1) tripping spring; and 2) closing spring. The closing spring generates the required driving force to close the circuit breaker and charge the tripping spring. The tripping spring is directly connected to the circuit breakers link system. This means that the mechanical energy needed for the vital opening operation is always stored in the tripping spring when the circuit breaker is in closed position. In other words, a closed circuit breaker is always prepared for immediate opening.
Universal motor drives the spring charging gear, which automatically charges the closing spring immediately after each closing operation. The springs are kept in charged state by a latch that is released when the circuit breaker is being closed. This enables rapid reclosing of the circuit breaker after a pre-defined dead time interval.
Figure 1, of the accompanying drawings, illustrates a circuit breaker assembly wherein closing spring is discharged, opening spring is charged, and circuit breaker is in closed condition.
Figure 2, of the accompanying drawings, illustrates a circuit breaker assembly wherein closing spring is charged, opening spring is charged, and circuit breaker is in closed condition.

Figure 3, of the accompanying drawings, illustrates a circuit breaker assembly wherein closing spring is charged, opening spring is discharged, and circuit breaker is in open condition.
The list of numerals used in Figures 1, 2, and 3 are enlisted below:
10-motor
12-closing spring
14-ratchet wheel
16-pawl
18 - cam
20 - closing latch
22 - cam follower
24 - 3-phase lever (main shaft lever)
26 - 2-phase lever
28 - close coil
30 - closing trigger
32 - roller
34 - latch arm
36-trip latch
38 - roller for trip latch
40 - AL rod
42 - roller lever
44-trip trigger
46 - close hook
48-trip coil
50-opening spring
52 - damper
Operations performed by circuit breaker mechanism:
1) Closing spring charging -
This operation will result in storage of energy in closing spring (12).
A motor driven ratchet pawl mechanism is selected to transfer energy from motor (10) to spring.
Ratchet pawl mechanism enables high torque ratio in single stage.

Charging mechanism consists of ratchet wheel (14), two pawls (16), eccentric shaft. Pawls are referred as 'big pawl' and 'small pawl' considering the size. Big pawl and small pawl are rotatably mounted on eccentric shaft. Torsion springs (not shown in figures) are used to push pawls against ratchet wheel to maintain the contact between ratchet wheel and pawl tips. Ratchet wheel (14) is mounted on cam shaft on which cam (18) and crank are also assembled. Cam shaft is rotatably mounted on mechanism frame. Mechanism frame is fixed in housing, enclosure for assembly of mechanism and related components. Closing spring (12) is connected to crank through spring shoe and connecting rod forming a slider crank mechanism. Motor (10) drives the eccentric shaft, rocking motion of pawls (16) results in advancement of ratchet wheel (14). Advancement of ratchet wheel (14) results in rotation of cam shaft and crank. Rotation of crank causes linear displacement of spring shoe and compression of closing spring. This process continues till crank reaches top dead center position. Pawls (16) push ratchet wheel (14) beyond top dead center, typically, by 7.8 deg approximately. Closing spring (12) moving end always exerts downward force on spring shoe, causes anticlockwise torque on cam shaft center, to rotate the crank by next 1 deg approximately.
At this point, closing latch (20) stops roller on ratchet wheel. Closing latch rotation is prevented by closing trigger.
2) Closing operation -
Follower (22) is rotatably mounted on main shaft lever (24). Main shaft lever (22) is coupled to main
shaft which is rotatably mounted on mechanism frame. Two phase lever (26) which is rotatably
mounted on housing. Main shaft lever (22) and Two phase lever (26) are connected through adjuster
rod, which forms a four bar linkage.
On initiation of closing command, closing coil (28), which is electromagnet, actuates the plunger to
lift the closing trigger (30) which in turn enables the closing latch (20) to rotate in anticlockwise
direction. The contact between closing latch (20) and roller (32), on ratchet wheel (14), breaks.
Ratchet wheel (14) rotates in counterclockwise direction.
Therefore cam shaft, cam, and crank also rotate in same sense, counterclockwise.
Closing spring (12) displaces the spring shoe in downward direction to release the stored energy.
Cam (18) pushes the follower (22), which is rotatably mounted on main shaft lever, in clockwise direction. Clockwise rotation of main shaft lever results in counterclockwise rotation of two phase

lever (26) and upward motion of slide seal shaft which is connected to moving contact assembly in
i
interrupter.
Pawls fly off during counterclockwise rotation of ratchet wheel while closing operation and produce sudden shock on stopper screws. Impact of pawls on stopper screws results in heavy wear of screw heads. Torsion springs bring pawls back to maintain contact between ratchet wheel and pawl tip. Plain diameter of ratchet wheel is in contact with pawl tip while closing operation. Plain diameter of ratchet wheel creates impression on pawl tip. This further damages the pawl tip area which is beneficial for charging.
Damaged pawl tip area results in force transfer through high points on pawls which further results in deterioration of ratchet wheel teeth.
Prior art systems are riddled with problems and disadvantages, as listed below:
1) Failure of stopper screws for pawls which results in ratchet wheel teeth breakage while stopping the pawls which fly off during closing operation;
2) Wear of ratchet wheel teeth and pawl tips which results in no charging.
Hence, there is a need for an improved ratchet and pawl based circuit breaker.
PRIOR ART
US3689721 discloses a circuit breaker including ratchet and pawl spring charging means and ratchet teeth damage preventing means, it relates to a ratchet wheel which is free to rotate on cam shaft, has slot in radial direction. A disc with extrusion is fixed on cam shaft. While closing operation the extrusion moves in slot portion so the ratchet wheel is unaffected. Thus ratchet and pawl assembly is disengaged from closing mechanism. However, this patent requires the use of a bearing between the ratchet wheel and the cam shaft. Also, extra element i.e. disc with extrusion is needed.
US3689720 discloses a circuit breaker including spring closing means with means for moving a charging pawl out of engagement with a ratchet wheel when the spring means are charged. Here, extra pawl is provided on same shaft of charging pawl. At the end of charging a cam on cam shaft pushes the extra pawl which rotates the shaft on which the same is mounted, therefore the charging

pawl rotates to disengage it from ratchet wheel teeth. However, extra pawl, cam and shaft connecting two pawls are needed as additional elements in this patent.
US4705144 discloses a spring operating mechanism for a circuit interrupter. Here, a spring-loaded catch is used to hold the pawls after charging is completed. However, extra catch, torsion spring for catch and pin for mounting catch are needed as additional elements in this patent.
US4137436 discloses means for manually slow-closing a circuit breaker that has a spring-actuated operating device. A fixed cam profile pushes the pawl pin outside to disengage from ratchet teeth, which is further hold by a spring loaded catch at the end of charging operation However, extra element such as spring loaded catch is needed.
CA1109512 discloses a ratcheting mechanism for circuit breaker motor operator. Here, charging pawl and stopping pawl are held by a spring loaded latch while closing operation.However, extra element such as spring loaded latch is needed.
US5883351 discloses a ratcheting mechanism for industrial-rated circuit breaker. Here, handle driven four bar mechanism drives a pawl which advances ratchet wheel in counterclockwise direction. During Clockwise rotation of handle holding pawl stops the ratchet wheel clockwise rotation. Also, a fixed pin displaces driving pawl to avoid contact of pawl tip and ratchet wheel teeth during clockwise rotation of handle. However, the stopping pin provided in US5883351 provides single surface for stopping the driving pawl. After several operations, there is possibility of damage due to impact on same surface.
OBJECTS OF THE INVENTION
An object of the invention is to provide a ratchet pawl based circuit breaker wherein life of pawl and ratchet wheel is increased.
Another object of the invention is to provide a ratchet pawl based circuit breaker wherein there is no wear and tear of pawl tips and stopper mechanism for pawls.

Yet another object of the invention is to provide a closing and charging system for circuit breakers which eliminates problems arising due to pawl wear.
Still another object of the invention is to provide a closing and charging system for circuit breakers which is relatively less bulky.
An additional object of the invention is to provide a ratchet pawl based circuit breaker where closing speed is increased.
Another additional object of the invention is to provide a ratchet pawl based circuit breaker where charging time of circuit breaker is decreased.
SUMMARY OF THE INVENTION
According to this invention, there is provided an improved ratchet and pawl based circuit breaker comprising a ratchet and pawl based drive mechanism, said circuit breaker assembly comprises: i. at least a pawl assembly with a pawl tip and a projection extending tangential to said pawl and spaced apart from said pawl tip, said spaced apart manner of said pawl tip and said projection forming a substantially V-shaped groove, there between, where said projection juts out from said pawl and where said pawl tip juts out from said pawl mechanism; ii. at least a ratchet wheel adapted to be angularly displaceable in order to provide momentum for discharging, characterised, in that, there is a positive gap between a locus of high points defined by said pawl tip and a locus of high points defined by said ratchet wheel plain diameter (non-teeth zone); and iii. at least a roller assembly adapted to cooperate with said pawl assembly, said roller assembly being located at said V-shaped groove of said pawl assembly.
Typically, said pawl assembly comprises a big pawl and a small pawl located on an eccentric shaft.
Typically, said pawl assembly comprises a big pawl and a small pawl located on an eccentric shaft, characterised, in that, each of said pawls comprising a formed V-groove.

Typically, said pawl assembly comprises a big pawl and a small pawl located on an eccentric shaft, characterised, in that, each of said pawls comprising a formed V-groove, further characterised, in that, the angles of each of said V-grooves being designed such that the locus of points formed by the pawl tip in each of said pawls engage with the toothed surface of said at least a ratchet wheel but do not engage or touch the non-toothed surface of said at least a ratchet wheel.
Typically, diameter of said at least a ratchet wheel is decreased in such a way on its non-toothed part such that there is no friction of said pawls' tips on to said ratchet wheel.
Typically, said at least a ratchet wheel plain diameter is lesser that pitch circle diameter of the toothed portion of said at least a ratchet wheel.
Typically, start and end portions of reduced plain diameter circumferential portion of said at least a ratchet wheel are provided with tapered slant edge for gradual changeover for said pawl tip from contact to non-contact surface and from non-contact to contact surface.
Typically, said at least a roller assembly is an angularly displaceable roller assembly on a pin which is assembled in circuit breaker mechanism frame.
Typically, said at least a roller assembly comprises a first cylindrical shaft of a first diameter extending into a second cylindrical shaft of a second diameter.
Typically, said at least a roller assembly comprises a first cylindrical shaft of a first diameter extending into a second cylindrical shaft of a second diameter, characterised, in that, said first diameter being relatively lesser than said second diameter.
Typically, said at least a roller assembly roller assembly is a single machined element.
Alternatively, said at least a roller assembly roller assembly is made up of two separate elements abutted together.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1, of the accompanying drawings, illustrates a circuit breaker assembly wherein closing spring is discharged, opening spring is charged, and circuit breaker is in closed condition;
Figure 2 of the accompanying drawings, illustrates a circuit breaker assembly wherein closing spring is charged, opening spring is charged, and circuit breaker is in closed condition;
Figure 3, of the accompanying drawings, illustrates a circuit breaker assembly wherein closing spring is charged, opening spring is discharged, and circuit breaker is in open condition;
Figure 4 illustrates a charging assembly of the prior art;
Figure 5 illustrates ratchet pawl mechanism while closing operation, according to the prior art;
Figure 6a illustrates a ratchet wheel of the prior art;
Figure 6b illustrates a big pawl of the prior art;
Figure 6c illustrates a small pawl of the prior art; and
Figure 7 illustrates a stopper screw assembly of the prior art.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 8 illustrates a charging assembly;
Figure 9 illustrates ratchet pawl mechanism while closing operation;
Figure 10a illustrates a ratchet wheel;
Figure 10b illustrates a big pawl;

*
Figure 10c illustrates a small pawl; and
Figure 11 illustrates a roller assembly.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the prior art, a stopper screw mechanism was used for engaging with pawl(s). After about 1500 operations, stopper screw wears out, pawl tip wears out, and teeth of ratchet wheel wears out. Hence, charging operation in the circuit breaker is not performed as there is no engagement of the pawl tip with the teeth of the ratchet wheel.
Figure 4 illustrates a charging assembly of the prior art where reference numeral 14 refers to the ratchet wheel. Reference numeral 16a refers to a small pawl and reference numeral 16b refers to a big pawl. Reference numeral 19 refers to eccentric shaft. These are also seen in Figure 6a, 6b, and 6c of the accompanying drawings. Reference numeral 60 refers to stopper screw assembly whose isometric view is seen in Figure 7 of the accompanying drawings. Figure 5 illustrates ratchet pawl mechanism while closing operation, according to the prior art.
According to this invention, there is provided an improved ratchet and pawl based circuit breaker. Figure 8 illustrates a charging assembly.
Figure 9 illustrates ratchet pawl mechanism while closing operation.
Figure 10a illustrates a ratchet wheel.
Figure 10b illustrates a big pawl.
Figure 10c illustrates a small pawl.
Figure 11 illustrates a roller assembly.
In accordance with an embodiment of this invention, there is provided a pawl assembly (62, 64) with a pawl tip (66) and a projection (68) extending tangential to said pawl assembly and spaced apart

from the pawl tip. The spaced apart manner of the pawl tip and the projection is such that it forms a substantially V-shaped groove, there between, where the projection juts out from the pawl and where the pawl tip juts out from the pawl mechanism. Typically, there is big pawl (62) and a small pawl (64). Each of the pawls (i.e. small and big) (62, 64) have a formed V-groove. The angles of the V-groove, however, are not same. The angles of each of the grooves are designed such that the locus of points formed by the pawl tip in each of the pawls should engage with the toothed surface of the ratchet wheel but should not engage or touch the non-toothed surface of the ratchet wheel. The use of the roller assembly ensures that all surfaces of the roller assembly are uniformly used with the pawls, as the roller assembly is angularly displaceable. This ensures uniform wear and tear and does not load only a particular segment of the assembly. This decreases wear and tear, in general.
The big pawl and small pawl are located on an eccentric shaft.
In accordance with another embodiment of this invention, there is provided a roller assembly (70) adapted to cooperate with a pawl mechanism of the ratchet and pawl assembly that operates in the circuit breaker. Typically, the roller assembly comprises a first cylindrical shaft of a first diameter extending into a second cylindrical shaft of a second diameter. The first diameter is relatively lesser than the second diameter. The stopper assembly of the prior art is eliminated and the roller assembly is introduced. This roller assembly is rotatably mounted on a pin located at the V-shaped groove of the pawl (62, 64). The roller assembly may be one single machined element or two separate elements abutted together.
In accordance with yet another embodiment of this invention, there is provided a ratchet wheel (80) characterised, in that, there is a positive gap between the locus of high points defined by the pawl tip and the locus of high points defined by the ratchet wheel. Therefore, diameter of the ratchet wheel is decreased in such a way on the non-toothed part such that there is no friction of the pawls' tips on to the ratchet wheel. In other words, ratchet wheel plain diameter is lesser that pitch circle diameter of the toothed portion of the ratchet wheel. Also, start and end portions of reduced plain diameter circumferential portion of the ratchet wheel are provided with tapered slant edge for gradual changeover for the pawl tip from contact to non-contact surface and from non-contact to contact surface.

In its working embodiment, pawls (62, 64) pushed back due to momentum from ratchet wheel and stopped by roller assembly during closing operation. The roller assembly is rotatably mounted pin on the circuit breaker mechanism frame.
In accordance with a non-limiting exemplary embodiment of the current invention and prior art, after about 1500 operations, it was seen that the prior art mechanisms comprised a worn out pawl tip and damaged teeth of the ratchet wheel, while the current invention was functioning properly, without damage, (even after about 10000 operations which is minimal requirement of circuit breaker mechanism). Also, closing speed, in the current invention, increased by about 8% over the prior art. Furthermore, closing spring charging time decreased by about 10%.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. An improved ratchet and pawl based circuit breaker comprising a ratchet and pawl based
drive mechanism, said circuit breaker assembly comprising:
i. at least a pawl assembly with a pawl tip and a projection extending tangential to said pawl and spaced apart from said pawl tip, said spaced apart manner of said pawl tip and said projection forming a substantially V-shaped groove, there between, where said projection juts out from said pawl and where said pawl tip juts out from said pawl mechanism;
ii. at least a ratchet wheel adapted to be angularly displaceable in order to provide momentum for discharging, characterised, in that, there is a positive gap between a locus of high points defined by said pawl tip and a locus of high points defined by said ratchet wheel plain diameter (non-teeth zone); and
iii. at least a roller assembly adapted to cooperate with said pawl assembly, said roller assembly being located at said V-shaped groove of said pawl assembly.
2. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said pawl assembly comprising a big pawl and a small pawl located on an eccentric shaft.
3. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said pawl assembly comprising a big pawl and a small pawl located on an eccentric shaft, characterised, in that, each of said pawls comprising a formed V-groove.
4. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said pawl assembly comprising a big pawl and a small pawl located on an eccentric shaft, characterised, in that, each of said pawls comprising a formed V-groove, further characterised, in that, the angles of each of said V-grooves being designed such that the locus of points formed by the pawl tip in each of said pawls engage with the toothed surface of said at least a ratchet wheel but do not engage or touch the non-toothed surface of said at least a ratchet wheel.
5. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein diameter of said at least a ratchet wheel is decreased in such a way on its non-toothed part such that there is no friction of said pawls' tips on to said ratchet wheel.

6. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said at least a ratchet wheel plain diameter is lesser that pitch circle diameter of the toothed portion of said at least a ratchet wheel.
7. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein start and end portions of reduced plain diameter circumferential portion of said at least a ratchet wheel are provided with tapered slant edge for gradual changeover for said pawl tip from contact to non-contact surface and from non-contact to contact surface.
8. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said at least a roller assembly is an angularly displaceable roller assembly on a pin which is assembled in circuit breaker mechanism frame.
9. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said at least a roller assembly comprising a first cylindrical shaft of a first diameter extending into a second cylindrical shaft of a second diameter.
10. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said at least a roller assembly comprising a first cylindrical shaft of a first diameter extending into a second cylindrical shaft of a second diameter, characterised, in that, said first diameter being relatively lesser than said second diameter.
11. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said at least a roller assembly roller assembly is a single machined element.
12. The improved ratchet and pawl based circuit breaker as claimed in claim 1, wherein said at least a roller assembly roller assembly is made up of two separate elements abutted together.