FORM 2
The Patents Act 1970
(39 of 1970) &
The Patent Rules 2003 COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
JAW FINGER DESIGN FOR JAW CLUSTER ASSEMBLY FOR AIR
CIRCUIT BREAKERS
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra . INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to circuit breakers and particularly to a jaw contact finger of jaw cluster assembly for electrical switchgear in air circuit breakers.
B) BACKGROUND OF THE INVENTION
[0002] The circuit breakers are used to protect equipments in an installation in case of a over current arising out of abnormal circuit conditions. A circuit breaker typically comprises a spring loaded contact system to carry, make, and break the current under normal and abnormal conditions involving a very high over-current.
[0003] Air circuit breakers use air as a medium to extinguish arcs in the circuit breakers used in industrial applications. The air circuit breakers are used for main power distribution in large industrial plants. The cradle assemblies connected to main power are used to enclose heavy and large circuit breakers.
[0004] Mechanical racking mechanisms are provided in the cradle assembly which can be operated manually or by using motors. The circuit breakers are provided with complimentary draw-out construction for easy installation and separation from the cradle assembly without disturbing main power connections. The circuit breakers can be tested

and serviced by mechanically moving it away from the cradle terminals coupled to the main power circuit.
[0005] The air circuit breakers are expected to operate to interrupt the fault current rapidly so as to minimize damage to the installations (downstream equipments) resulting from thermal and mechanical stresses. A currently available auxiliary fixing element such as a bolt can be provided for fixing arrangement in the circuit breakers. The bolt cooperates with a bore made in the body of the terminal and with a frame of the plug-in contact. This solution complicates assembly and disassembly operations. The rack-in contacts are however considered as wearing part which is capable of being inspected regularly and replaced, if required. With this type of device, maintenance operations are therefore complicated. However, the presence of an auxiliary fixing art increases the number of parts, which gives rise to extra cost. Hence, there is a need to provide an effective jaw cluster assembly at reduced cost,
[00061 A draw-out type air circuit breaker mainly comprises two parts. One part is a moulded circuit breaker housing assembly which consists of switching contact assemblies and mechanism such as a jaw cluster assembly. The other part is a fixed external frame called as a cradle assembly. The circuit breaker housing assembly mounted on the cradle assembly can be connected or disconnected from main power circuit by an axial withdrawal motion of the circuit breaker housing assembly. In the jaw cluster assembly, jaw cluster fingers are two halves of the same jaw cluster assembly and act as parallel conductors. As per the principle of electro-magnetism, when two parallel conductors


carry current in same or opposite direction, there is an electro-dynamic force of attraction or repulsion respectively between the two parallel conductors. As per the above mentioned principle, when the jaw cluster fingers in the two halves (geometrically upper and lower half of cluster assembly) carry the current from a cradle terminal to a breaker terminal , the jaw cluster lingers arc attracted towards each other because of the electro-dynamic force of attraction (Fa). Further, the jaw cluster springs are designed such that the spring force counterbalances the electro-dynamic force of attraction (Fa) between the jaw cluster linger sets during normal operating conditions of the air circuit breakers,
[0007) During abnormal operating conditions such as short-circuit and fault withstand, the value of fault current flowing through the jaw cluster assembly reaches a very high magnitude. Hence, the electro-dynamic force of attraction (Fa) overcomes the spring force of the jaw cluster assembly and leads to the separation of jaw cluster fingers from the cradle and/or breaker terminal . Due to the separation of electrical contact, a heavy arcing is produced at the gap between the jaw cluster fingers and the cradle and/or breaker terminal . This heavy arching erodes the contact surface and the persistent arcing at terminals may result in phase-fault and/or flash-over in absence of inter-phase barriers at the breaker terminal which may render the customer terminal to useless. The erosion of contact surfaces due to the arcing leads to excessive temperature rise at the customer terminal during normal operating conditions of the circuit breakers, which has the twin effect of deteriorating the cable insulation and high power loss in form of excessive heat. The demerit of very high value of spring force is a high-frictional force during rack-in


operation of the circuit breaker housing assembly, which is undesirable from customer point of view in field conditions.
[0008] The abovemenlioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
C) OBJECT OF THE INVENTION
[0009] The primary object of the present invention is to provide a jaw finger of jaw cluster assembly with an effective lever profile operation.
[0010] Another object of the present invention is to provide a jaw cluster assembly with semi-circular profile of jaw ftnger to retain on the cradle terminal after rack-out operation of the air circuit breakers.
[0011] Yet another object of the present invention is to provide a jaw cluster assembly with a mechanism to avoid undesirable contact breakings in the cradle terminal and the breaker terminal.
[0012] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.


D) SUMMARY OF THE INVENTION
[0013] The various embodiments of the present invention provide ajaw finger design for jaw cluster arrangement in the air circuit breakers. According to one embodiment of the present invention, a jaw cluster assembly has ajaw cage. Pluralities of jaw fingers are arranged inside jaw cage, The pluralities of jaw fingers act as solid conductive block between the cradle terminal and the breaker terminal adopter. The jaw fingers arc arranged in an upper hall'and in a lower half. The jaw finger in the upper half and the jaw finger in the lower half are connected to each other through a jaw spring to form a pair of jaw the jaw fingers are arranged so that the opening moment of one pair of jaw causes the closing moment of another pair of jaw. Each jaw finger has contact surfaces to mate with the cradle terminal and breaker terminal. The terminal contact surface has a semi circular profile. The jaw finger has a semi circular profile so that the jaw fingers remain in the cradle terminal after the complete rack out operation of the circuit breaker.
[0014] The jaw spring is designed to provide sufficient contact force to reduce the
temperature rise in the breaker terminals during normal operation. The jaw spring is
designed to provide counterbalance force to neutralize the electro-dynamic force of
attraction between the jaw fingers.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The other objects, features and advantages will occur to those skilled in the art
from the following description of the preferred embodiment and the accompanying
drawings in which:


[0016] FIG. 1 illustrates a side perspective view of an air circuit breaker according to one embodiment of the present invention.
[0017] FIG. 2 illustrates a top perspective view of a jaw cluster assembly according to one embodiment of the present invention.
[0018] FIG. 3 illustrates a schematic view of a jaw finger of the jaw cluster assembly according to one embodiment of the present invention.
[0019] FJG. 4 illustrates a schematic view of current path between the cradle terminal and the breaker terminal according to one embodiment of the present invention, when the breaker terminal is completely racked-in the cradle terminal.
[0020] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0021] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient


detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0022] The various embodiments of the present invention provide a jaw finger design for jaw cluster arrangement in the air circuit breakers. According to one embodiment of the present invention, a jaw cluster assembly has a jaw cage. Pluralities of jaw fingers are arranged inside jaw cage. The pluralities of jaw fingers act as solid conductive block between the cradle terminal adopter and the breaker terminal adopter. The jaw fingers are arranged in an upper half and in a lower half The jaw finger in the upper half and the jaw finger in the lower half are connected to each other through a jaw spring to form a pair of jaw the jaw lingers are arranged so that the opening moment of one pair ofjaw causes the closing moment of another pair of jaw. Each jaw finger has contact surfaces to mate with the cradle terminal and breaker terminal adopter. The terminal contact surface has a semi circular profile. The jaw finger has a semi circular profile so that the jaw fingers remain in the cradle terminal after the complete rack out operation of the circuit breaker.
[0023] The jaw spring is designed to provide sufficient contact force to reduce the temperature rise in the breaker terminals during normal operation. The jaw spring is designed to provide counterbalance force to neutralise the electro-dynamic force of attraction between the jaw fingers.


[0024] According to one embodiment of the present invention, the circuit breaker housing assembly of the air circuit breaker consists of E and/or F shaped breaker terminal protruding out parallel to an axis of breaker withdrawal. Each U-shapcd surface of the E and/or F shaped breaker terminal is designed to provide electrical contact for jaw cluster lingers of a jaw cluster assembly during rack-in operation of the circuit breaker housing assembly. The circuit breaker housing assembly can be connected or disconnected From main power circuit by an axial withdrawal motion of the circuit breaker housing assembly.
[0025] On cradle terminal, two parallel hollow cylindrical surfaces provide contact for the jaw cluster assembly and they also work as a pivot for rotation of jaw cluster assembly around the axis. The jaw cluster assembly rests on the cradle terminal while the breaker terminal moves along with the axis to make and break contact with the main power circuit. After complete rack-in operation of the circuit breaker assembly with the cradle terminal, the breaker terminal is connected to the cradle terminal via the jaw cluster assembly.
|0026| The jaw cluster assembly mainly consists of the jaw cluster fingers, a jaw cage and jaw cluster springs. The jaw cluster springs are designed such that the jaw cluster assembly offers a low fractional resistance during the rack-in operation of the circuit breaker housing assembly. After the complete rack-in operation of the circuit breaker housing assembly, the lever profile in the jaw cluster fingers acts as a solid link between


the cradle terminal and the breaker terminal, thus counterbalances the electro-dynamic force of attraction during short circuit fault condition.
[0027] The jaw cluster fingers are designed such that after complete rack-in operation of the circuit breaker housing assembly the two sets of jaw cluster fingers (i.e. upper and lower half of cluster assembly} in the jaw cluster assembly comes in mechanical contact {i.e. lever profile coming in contact) and the jaw cluster springs provide an adequate contact pressure to keep the temperature-rise to a lower value during normal operating conditions of the air circuit breakers. The opening moriient of one pair of jaw causes a closing moment of other pair of jaw by the lever effect about the lever profile of the jaw cluster fingers, After complete rack-in. operation of the circuit breaker housing assembly, the jaw cluster assembly acts like a solid conducting link between the cradle terminal and the breaker terminal . The temporary mechanical solidification of the jaw cluster assembly counter-balances the electro-dynamic force of attraction between the jaw cluster fingers during abnormal operating conditions. This avoids the negative consequences of separation of contact of jaw cluster fingers from the cradle terminal and the breaker terminal.
[0028] Further, the jaw cluster ringers have a semi-circular profile to retain the jaw cluster assembly on the cradle terminal even after complete rack-out operation of the circuit breaker housing assembly from the cradle terminal.


[0029] FIG. I illustrates a side perspective view of an air circuit breaker according to one embodiment of the present invention. With respect to FIG.l, the air circuit breaker mainly comprises two parts. One part is a fixed external frame assembly 1 called as a cradle assembly. The fixed external frame assembly 1 (cradle assembly) has a cradle top cross piece 3 and a cradle bottom cross piece 6 to support the air circuit breaker. Both the cradle top cross piece 3 and the cradle bottom cross piece 6 are arranged in parallel. A cradle terminal support 8 is mounted in between the cradle top and bottom cross pieces 3 and 6„ There are also one or more cradle terminal (s) 2 protruding out perpendicular to the axis of the fixed external frame 1. The cradle terminal 2 has two parallel hollow cylindrical surfaces to provide an electric contact for the jaw cluster assembly 4 and also to work as a pivot for rotation of the jaw cluster assembly 4 around the axis.
[0030] The other part of the air circuit breaker is moulded circuit breaker housing assembly 5 which consists of switching contact assemblies and mechanism such as a jaw cluster assembly 4 and one or more E and/or F shaped circuit breaker terminal (s) 7. The E and/or F shaped breaker terminal 7 is protruding out parallel to the axis of breaker withdrawal. Each E and/or F shaped breaker terminal 7 has a U-shaped surface to provide an electrical contact during a rack-in operation of the circuit breaker housing assembly 5.
[0031J FIG. 2 illustrates top perspective view of a jaw cluster assembly according to one embodiment of the present invention. With respect to FIG. 2, the jaw cluster assembly mainly includes a jaw cage 9, a set of jaw cluster fingers 10, and a set of jaw cluster


springs 11. The jaw cage 9 of the jaw cluster assembly has been designed to control the arrangement of the jaw cluster fingers 10 and the jaw cluster springs II. The jaw cluster fingers 10 are being in the form of two halves of the same jaw cluster assembly to act like parallel conductors. Also, the jaw cluster fingers 10 act like a conductive solid link between the cradk terminal 2 and the breaker terminal 7 (FIG. 1), The jaw cluster springs 11 have been designed such that jaw cluster assembly offers a low frictional resistance during the rack-in operation of the circuit breaker housing assembly 5 (FIG. 1).
[0032] FIG. 3 illustrates a schematic view of a jaw finger of the jaw cluster assembly according to one embodiment of the present invention. With respect to FIG. 3, each single unit of the jaw cluster lingers has surface contacts 12 and 13 for cradle side and breaker side respectively at their ends, a slot for the jaw cage 14, a set of slots for the jaw spring 16, and a lever profile 15.
[0033] FIG. 4 illustrates a schematic view of current path between the cradle terminal and the breaker terminal according to one embodiment of the present invention, when the breaker terminal is completely racked-in the cradle terminal. With respect to FIG. 4, after complete rack-in operation of the circuit breaker housing assembly, the jaw cluster assembly 4 acts as a conductive solid link between the cradle terminal 2 and the breaker terminal 7,
[0034] During normal operating conditions of the air circuit breaker, the spring force of the jaw cluster springs counterbalances the electro-dynamic force of attraction (Fa)

between the jaw finger sets. Also, after complete rack-in operation the two sets of jaw fingers (i.e. upper and lower half of the jaw cluster assembly) in a jaw cluster assembly come in a mechanical contact (i.e. lever profiles coming in contact) and the jaw cluster springs provide an adequate contact pressure to keep the temperature-rise to a lower value. The opening moment of one pair of jaw (i.e. right side of the jaw cluster assembly in FIG. 4) causes a closing moment of other pair of jaw (i.e. left side of the jaw cluster assembly in FIG. 4) by lever effect about the lever profile of jaw fingers. Hence, the temporary mechanical solidification of the jaw cluster assembly counter-balances the electro-dynamic force of attraction between the jaw fingers during abnormal operating conditions. This avoids the negative consequences of separation of jaw finger contact from cradle terminal and breaker terminal.
G) ADVANTAGES OF THE INVENTION
[0035] Thus the various embodiments of the present invention provide a jaw finger design for jaw cluster arrangement in the air circuit breakers. The jaw cluster finger design provides an effective lever profile operation in the jaw cluster assembly which acts as a solid conductive link between the cradle terminal and the breaker after rack-in operation of the air circuit breakers during short circuit fault condition to avoid undesirable contact breakings in the cradle terminal and the breaker terminal . The semi¬circular profile of jaw finger retains the jaw cluster assembly on the cradle terminal even after rack-out operation of the air circuit breakers.


[0036] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the ail to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.

[0037] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.
Date: March 30, 2009. RAKESH PRABHU
Place: Bangalore. Patent Agent

CLAIMS
What is claimed is:
1. A jaw cluster assembly for air circuit breaker assembly having breaker terminal
adopter and cradle terminal , the assembly comprising:
a jaw cage;
pluralities of jaw fingers arranged inside jaw cage;
wherein the pluralities of jaw fingers act as solid conductive block between the
cradle terminal adopter and the breaker terminal adopter.
2. The assembly according to claim 1, wherein each jaw finger has contact surfaces to mate with the cradle terminal and breaker terminal adopter.
3. The assembly according to claim 1, wherein the terminal contact surface has a preset profile.
4. The assembly according to claim I, wherein the terminal contact surface has a semi circular profile.
5. The assembly according to claim 1, wherein the jaw finger has a semi circular profile so that the jaw lingers remain in the cradle terminal after the complete rack out operation of the circuit breaker,
6. The assembly according to claim 1, wherein the jaw fingers are arranged in an upper half and in a lower half.


7. The assembly according to claim 1, wherein the jaw finger in the upper half and the jaw finger in the lower half are connected to each other through a jaw spring to form a pair of jaw .
8. The assembly according fo claim 1, wherein the jaw spring is designed to provide sufficient contact force to reduce the temperature rise in the breaker terminals during normal operation.
9. The assembly according to claim 1, wherein the jaw spring is designed to provide counterbalance force to neutralize the electro-dynamic force of attraction between the jaw fingers.
10. The assembly according to claim 1, wherein the jaw fingers are arranged so that the opening moment of one pair of jaw causes the closing moment of another pair of jaw.
Dated this the 30th day of March 2009

RAKESH PRABHU Patent Agent, ALMT Legal,
#2, Lavelle Road. Bangalore- 560 001
To,
The Controller of Patents, The Patent Office, Mumbai