A) TECHNICAL FIELD
[0001 ] The present invention generally relates to circuit breakers and particularly relates to Molded Case Circuit Breakers (MCCB). The present invention more particularly relates to contact systems providing a plug in type contact for the MCCB.

B) BACK GROUND OF THE INVENTION

[0002] Circuit breakers are the mechanical switching devices capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions. A circuit breaker basically consists of a pair of separable contacts and an interrupting medium. The function of the contacts is to conduct the electrical current, when the breaker is closed and withstand the arcs while interrupting. By making the moving contact to touch the stationary contact, an electric current flows and the breaker is closed. By driving the moving contact away from the stationary contact, an electric arc develops. By quenching It, the current flow stops and the breaker are open.

[0003] In the current scenario, one or more components are joined together through a spring force or the bolted joints. The components are joined together for maintaining an electrical connectivity between the components. The connections formed between the components are known as joints. A tremendous force is applied to join the one or more components. Even with high force, only few points of the contacts touch each other resulting in lower contact area. Further the lower contact area between the contacts leads to higher resistance thereby a circuit consisting of more joints will have higher resistance as compared to the circuit consisting of fewer joints. An increase in resistance in the circuit in turn increases the temperature.

[0004] Further as the number of joints increases in the circuit, the IR losses increases, due to which the temperature of the product also increases. The spring force is inversely proportional to temperature rise. In the existing technique, the upper limitation of the spring force is limited only by the dimensional space constraint to accommodate huge springs due to which an optimum force is selected.

[0005] One of the currently available techniques discloses that a high contact pressure is maintained between the one or more components by using huge springs. The hugeness of the springs results in dimensional constraints and also limits the contact pressure.

[0006] According to Holmz law, a force exists in the contact points. The force is called as Holmz force. The Holmz force is similar to that of the Lorentz's force except that the Holmz force occurs between the contact points. Further Holmz force occurs in contact regions due to only point contacts between the conductors. The electromagnetically created force opposes the contact pressure. The contact pressure is inversely proportional to the contact resistance. As the contact resistance increases, the temperature also increases. This leads to welding of the contacts and adversely affects the life and performance of the circuit breaker. In the existing scenario, the electromagnetic opposing force is overcome by using a heavy spring so that the required contact pressure is maintained.

[0007] Moreover, in the existing technique, t he temperature in the circuit is brought down to a satisfactory limit by using the contact systems with higher masses. Another technique discloses that a plurality of components is used in the circuit breaker to bring down the temperature thereby increasing the mass of the system.

Further due to the plurality of components used in the circuit breaker, the maintenance cost, the labor cost, assembling time and the material cost also increases.

[0008] Thus there is a need for a system to provide a plug in contact for the MCCB with minimum number of components.

[0009] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.

C) OBJECT OF THE PRESENT INVENTION

[0010] The primary object of the present invention is to provide a plug in contact system for the Molded Case Circuit Breaker with minimum number of components.

[0011] Another object of the present invention is to provide a plug-in contact system with additional surface area to dissipate heat generated in the circuit breaker.

[0012] Yet another object of the present invention is to provide a plug in contact system with less number of electrical contact joints.

[0013] Yet another object of the present invention is to provide a plug in contact system with lower mass.

[0014] Yet another object of the present invention is to enhance the contact pressure with a minimum spring force.

[0015] Yet another object of the present invention is to reduce the temperature rise of the plug-in contact systems in the circuit breaker.

[00I 6] Yet another object of the present invention is to develop a plug in contact in which the mechanical advantage is used to enhance the contact pressure with a very little spring force.

[0017] Yet another object of the present invention is to develop a plug in contact in which the elasticity of the copper material is also used to produce the required contact pressure.

D) SUMMARY OF THE INVENTION

[0018] The various embodiments of the present invention provide a contact arrangement for plug-in contact system in circuit breaker, such as a Molded Case Circuit Breaker (MCCB). According to one embodiment of the present invention, the plug-in contact system includes a fixed contact assembly, a moving contact assembly, a first spring pin, a second spring pin and a tensile spring. The tensile spring is provided to interconnect the first spring pin and the second spring pin. The fixed contact assembly is slotted at regular intervals for providing a plurality of contact points which in turn increases the contact area to reduce the resistance and hence to reduce heat generation.

[0019] According to one embodiment of the present invention, the moving contact assembly of the plug-in contact system includes a bolted joint. The fixed contact assembly of the plug-in contact system is made up of an elastic material to provide a uniform contact pressure. The elastic material is copper.

[0020] According to one embodiment of the present invention, the fixed contact assembly of the plug-in contact system includes two arms that are connected at one end and slotted at regular intervals to provide an extended surface area to dissipate heat. The two arms include a conducting portion and a non conducting portion. The two arms of the fixed contact assembly are tilted towards each other for providing generating contact pressure using the elasticity of the material.

[0021 ] According to one embodiment of the present invention, the fixed contact is assembled in a plug-in base with a bolted joint. The force generated is used to maintain the required contact pressure in the fixed contact assembly.

[0022] According to one embodiment of the present invention, the tensile spring interconnects the first spring pin and the second spring pin of the fixed contact assembly to provide a spring force for maintaining the contact pressure, when the moving contact assembly is inserted into the fixed contact assembly.

[0023] According to one embodiment of the present invention, the fixed contact assembly is designed to permit the air circulation through an inner surface of the fixed contact and an outer surface of the moving contact to improve the heat dissipation efficiency, when the moving contact is inserted into the fixed contact to make an electrical contact.

[0024] 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.

E) BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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:

[0026] FIG. 1 illustrates the perspective view of a fixed contact assembly of plug-in contact system, according to one embodiment of the present invention.

[0027] FIG. 2 illustrates the perspective view of the fixed contact assembly of plug-in contact system with a tensile spring, according to one embodiment of the present invention.

[0028] FIG.3 illustrates a top side perspective view of the Plug-in Contact system with the fixed contact assembly and moving contact assembly, according to one embodiment of the present invention.

[0029] FIG.4 illustrates a top side perspective view of the Plug-in Contact system with the fixed contact assembly before the insertion of the moving contact assembly, according to one embodiment of the present invention.

[0030] FIG,5 illustrates a top side perspective view of the fixed contact assembly, according to one embodiment of the present invention.

[0031 ] FIG.6 illustrates a front side view of the fixed contact assembly and the moving contact assembly, according to one embodiment of the present invention.

[0032] Although the 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

[0033] In the following detailed description, a 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.

[0034] The various embodiments of the present invention provide a contact arrangement for plug-in contact system in Molded Case Circuit breaker (MCCB). According to one embodiment of the present invention, the plug-in contact system includes a fixed contact assembly, a moving contact assembly, a first spring pin, a second spring pin and a tensile spring. The tensile spring is provided to interconnect the first spring pin and the second spring pin. The fixed contact assembly is slotted at regular intervals for providing a plurality of contact points which in turn increases the contact area to reduce the resistance and hence to reduce heat generation

[0035] According to one embodiment of the present invention, the moving contact assembly of the plug-in contact system includes a bolted joint. The fixed contact assembly of the plug-in contact system is made up of an elastic material to provide a uniform contact pressure. The elastic material is copper.

[0036] According to yet another embodiment of the present invention, the fixed contact assembly of the plug-in contact system includes two arms that are slotted at regular intervals and provide an extended surface area to dissipate heat. The two arms include a conducting portion and a non conducting portion. The two arms of the fixed contact assembly are tilted towards each other for generating contact pressure using the elasticity of the material.

[0037] According to one embodiment of the present invention, the fixed contact is assembled in a plug-in base with a bolted joint. The force generated is used to maintain the required contact pressure in the fixed contact assembly.

[0038] According to one embodiment of the present invention, the tensile spring interconnects the first spring pin and the second spring pin of the fixed contact assembly to provide a spring force for maintaining the contact pressure when the moving contact assembly is inserted into the fixed contact assembly.

[0039] According to one embodiment of the present invention, the fixed contact assembly is designed to permit the air circulation through an inner surface of the fixed contact and an outer surface of the moving contact when the moving contact is connected with the fixed contact.

[0040] FIG. 1 illustrates the perspective view of the fixed contact assembly of plug-in contact system according to one embodiment of the present invention, while FIG. 2 illustrates another perspective view of the fixed contact assembly of plug-in contact system with a tensile spring according to one embodiment of the present invention. With respect to FIG.1 and FIG.2, the fixed contact assembly 102 is connected to a bolted joint 104. The fixed contact assembly 102 is slotted in between and a plurality of slots 108 is created on the fixed contact assembly 102. The plurality of slots 108 on the fixed contact assembly 102 increases the number of contact points.
The slotted conducting part of the arm divides the current which in turn is the cause for lower Holmz force.

[0041 ] The Holmz force will be much larger than the Lorentz force. This can be understood by the following:

[0042] In the existing technique, the force is calculated using the equation:

[0043] In the present invention, the force calculated for the single conducting portion of the arm is given by the equation:

[0044] The total force of repulsion due to Holmz force is given by the equation:

[0045] The total force of repulsion due to holmz force according to the present invention is given by the equation:
Ftotal = Fold/ 6.

[0046] According to the above equation the magnitude of Holmz force is reduced 6 times. Further the attraction force does not get reduced as the region where the current flowing in the same direction is not slotted, thereby the attraction force is given by the equation:

[0047] In general, the holmz force is greater than the Lorentz force because the distance between the conductors in the case of Lorentz force will be in the order of millimeters while the distance between the contact points will be in nanometer or micrometer. As the force is inversely proportional to distance the Holmz force will be greater than the Lorentz force in a system.

[0048] The fixed contact assembly 102 is electrically connected to the moving contact assembly through the contact points. The contact points on the fixed contact assembly 102 provide a higher contact area. Further due to the higher contact area, the contact resistance is also reduced between the joints of the fixed contact assembly 102 and the moving contact assembly.

[0049] A tensile spring 206 is connected to a first spring pin 202 and a second spring pin 204 of the fixed contact assembly 102. A spring force is generated due to the connection of tensile spring 206 with the first spring pin 202 and the spring pin 204 of the fixed contact assembly 102.

[0050] The spring force generated by the springs 206 exerts a contact pressure between the joints of the fixed contact assembly 102 and the moving contact assembly. Further a heat is generated due to the contact pressure between the joints. The heat generated between the joints is dissipated through the arms 106 of the fixed contact assembly 102. The arms 106 acts as fin and provides an additional surface area for dissipating the heat generated between the joints.

[0051 ] FIG.3 illustrates a top side perspective view of the Plug-in Contact system with the fixed contact assembly and moving contact assembly according to one embodiment of the present invention, while FIG. 4 illustrates a top side perspective view of the plug-in Contact system with the fixed contact assembly before the
insertion of the moving contact assembly according to one embodiment of the present invention. With respect to FIG.3 and FIG.4, the fixed contact assembly 102 is electrically corrected to the moving contact assembly 302. When the moving contact assembly 302 enters into the plug-in contact system, the fixed contact assembly 102 opens up the arms 106 at the region of contact points. Further the arms 106 of the fixed contact assembly 102 come in contact with the moving contact assembly 302 and exert a contact pressure between the joints without using the spring force.

[0052] The fixed contact assembly 102 is designed in such a way that there is a free movement of air through the contact points when the moving contact assembly 302 is electrically connected to the fixed contact assembly 102. This design for the fixed contact assembly 102 provides a large surface area of the moving and fixed contacts for heat dissipation through convection.

[0053] The fixed contact assembly 102 is slotted in between and a plurality of slots 108 is created on the fixed contact assembly 102. The plurality of slots 108 constitutes the contact points 304 and the fixed contact assembly 102 is electrically connected to the moving contact assembly 302 through these contact points 304.

[0054] The heat generated between the joints 304 of the fixed contact assembly 102 and the moving contact assembly 302 is dissipated through the arms 106 of the fixed contact assembly. The heat is dissipated through a non conducting arm 106. The non conducting arm 106 provides an extended surface area for dissipating the heat generated.

[0055] Further the non conducting arm 106 does not add to the resistance of the circuit as there is no flow of current in this part of the arm. Thus the arms 106 of the fixed contact 102 decrease the heat generated in the circuit breaker.

[0056] The performance and life of the circuit breaker depends upon the working of the plug-in contact system during a faulty condition, such as a short circuit. A high current flows in the circuit breaker during the faulty condition that produces a high temperature rise and a high repulsion force.

[0057] The increase in the flow of current in the circuit breaker also increases the temperature of the product during the faulty condition as heat generation is proportional to the square of the current. The heat generation also depends on the time factor. When the circuit breaker is working normally then the faulty conditions are cleared within time duration of 10ms and hence the heat generation reaching to an alarming level is avoided.

[0058] FIG.5 illustrates a top side perspective view of the fixed contact assembly according to one embodiment of the present invention. With respect to FIG.5, the spring force generated by the springs exerts a contact pressure in the fixed contact assembly 102.

[0059] According to Lorentz's law when two current carrying conductors are placed nearby, a force is experienced between them. Further when both the conductors carry current in the same direction, the force of attraction exists between them. When both the conductors carry current in the opposite direction, force of repulsion exists between them. Consider let Ii be the current that is flowing in first conductor and I2 be the current that is flowing in second conductor.

[0060] The force in the first conductor due to second conductor is given by the equation:
F1= B2 * I1* sin θ
Where,
B2 = Magnetic flux density of second conductor in tesla.
LI = Length of the first conductor in meters.
θ = angle between the two conductors.

[0061] Considering both the conductors are cylindrical in nature and are placed in air, then the magnetic flux density of the second conductor is given by the equation:

Where,
r- Distance between the two conductors in meters.
µo- permeability of free space in H/m.

[0062] Considering both the conductors are cylindrical in nature having same length L and carrying same current I and are parallel to each other then the force experienced by at least one of the conductor with respect to other is given by the equation:

[0063] From the above equation the force is directly proportional to square of the current and is inversely proportional to the distance between the conductors.

[0064] The fixed contact is designed in such a way that the Lorentz's attraction force is higher compared to that of the Holmz repulsion force.

[0065] The repulsion force experienced by each of the slotted arm is given by the equation:

[0066] The total force generated due to the springs and the elasticity of the material is calculated using the equation:
Total force = Force due to spring + Force due to elasticity.

[0067] The force exerted due to springs for the fixed contact assembly 102 is calculated using the equation:

[0068] The applied force F2 depends on the ratio of Dl and D2. Further the applied force F2 is calculated from the above equation:

Where,
F1- is the required contact pressure in Newton.
F2 - is the applied force in Newton.
Dl and D2- is the distance measured in meters.

[0069] When the moving contact assembly 302 enters into the plug-in contact system, the fixed contact assembly 102 opens up the arms 106 at the region of contact points 304. This causes the arms 106 of the fixed contact assembly 102 to press against the moving contact assembly 302 thereby exerting contact pressures.

[0070] Further, the elastic nature of the material causes an expansion and accommodates the moved contact assembly 302 into the fixed contact assembly 102. The deflection of the fixed contact assembly 102 is caused due to the expansion of the material such as copper.

[0071] The deflection is maintained in such a way that elastic limit of the material is not exceeded. The arms of the fixed contact assembly 102 gets back to its original position, when the moving contact assembly 302 is removed from the fixed contact assembly 102. Thus the spring force is exerted using the elasticity of the material. The combination of the force exerted due to elasticity and springs provides the required contact pressure in the circuit breaker.

[0072] FIG.6 illustrates a front side view of the fixed contact assembly and the moving contact assembly according to one embodiment of the present invention. With respect to FIG.6, the fixed contact assembly 102 is Contact and the moving contact assembly 302 is Contact 2. The two contacts contact 1 and contact 2 are pressed against each other. But, all the points on the surface of both the contacts do not touch each other. Further to avoid this, the contact 1 is slotted in between and a plurality of slots 106 is created on the contact. The plurality of slots 106 increases the contact points and the contact 1 is electrically connected to the contact 2 through these contact points 304.

[0073] The fixed contact assembly 102 is designed in such a way that there is a free movement of air through the contact points, when the moving contact assembly 302 is electrically connected to the fixed contact assembly 102, thereby providing a large surface area of the moving and fixed contacts to improve the heat dissipation through convection.

[0074] The convection loss increases with increase in the surface area, heat and the temperature according to the equation for Convection loss:
Convection loss = H * A * ∆T
Where,
H - Heat transfer Coefficient.

A-Surface area of the system in meter2
∆T- Temperature difference.

[0075] Further, the arms of the fixed contacts are slotted for providing a large surface area for the current flow. The current flow in the large surface area reduces the resistance in the circuit. The reduction in resistance in turn decreases the temperature in the circuit.

G) ADVANTAGES OF THE INVENTION

[0076] The present invention provides a contact arrangement for plug-in contact system in Molded Case Circuit breaker (MCCB). The plug-in contact system includes the tensile spring connected at the edge of the arms. Further as the arm of the fixed contact assembly extends, the tensile springs also extends to a higher degree which in turn leads to providing a higher force. The arms provide an additional extension for the tensile spring. The heat is dissipated through the extended surface area provided by the extension of the arms.

[0077] The arms, in addition to acting as a fin, provide a means for leveraging. Further, the arms of the fixed contact assembly reduce the heat generated in the circuit breaker by providing an extended surface decreasing the temperature in the circuit.

[0078] The plug-in contact system, according to the embodiment of the present invention, exerts a lower spring force as compared to the essential contact pressure. The elasticity of the copper material and the designing of the fixed contact assembly minimize the number of components in the circuit breaker, which in turn decreases the temperature. The reduction in the number of the components in turn minimizes
the number of electrical contact joints in the circuit breaker. Thus the plug in contact of the present invention efficiently reduces the temperature rise of the Plug-in contacts thereby increasing the life and performance of the breaker.

[0079] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0080] 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.

CLAIMS
What is claimed is:
1. A plug-in contact system for circuit breakers, the plug-in contact system
comprising:
a fixed contact assembly;
a moving contact assembly;
a first spring pin;
a second spring pin;
a tensile spring provided to interconnect the first spring pin and the second
spring pin;
Wherein the fixed contact assembly is slotted at regular intervals for providing
a plurality of contact points which in turn increases contact area and the
increase in the contact area reduces resistance and heat generation.

2. The system according to claim 1, wherein the fixed contact assembly comprises two arms that are slotted at regular intervals and provide an extended surface area to dissipate heat.

3. The system according to claim 1, wherein the two arms comprises a conducting portion and a non conducting portion.

4. The system according to claim 1, wherein the conducting portion of the arms is
slotted to divide the current which in turn is the cause for lower Holmz force.

5. The system according to claim 1, wherein the two arms of the fixed contact assembly is tilted towards each other for providing contact pressure using the elasticity of the material.

6. The system according to claim 1, wherein the fixed contact assembly is assembled with a plug-in base by a bolted joint.

7. The system according to claim l, wherein the fixed contact assembly is made up of an elastic material to provide a contact pressure.

8. The system according to claim 1, wherein the elastic material is copper.

9. The system according to claim 1, wherein the tensile spring interconnects the first
spring pin and the second spring pin of the fixed contact assembly to provide a
spring force for maintaining the contact pressure, when the moving contact
assembly is inserted into the fixed contact assembly.

10. The system according to claim 1, wherein the fixed contact assembly is designed
to permit the air circulation through an inner surface of the fixed contact and an
outer surface of the moving contact, when the moving contact is connected with
the fixed contact.

11. The system according to claim 1, wherein the moving contact assembly comprises a bolted joint.