CONTACT SYSTEM FOR MOLDED CASE CIRCUIT BREAKER
FIELD OF THE INVENTION
[0001] The present invention relates to molded case circuit breaker. More particularly to the contact system for molded case circuit breaker,
PRIOR ART [0002] IVlolded case circuit breaker are utilized as circuit protection devices to interrupts current flow in an electric power line upon detection of conditions which do not fall within predefined parameters. For example, if a short occurs within a power line, current flow can increase dramatically above that which is expected during normal operating conditions.
[0003] Normally a circuit breaker can have two kinds of contacts, one is main contact and other one is an arcing contact. Main contacts provide the electrical continuity in a circuit breaker and comprises of a pair of contacts. Further, the pair of contacts can both be fixed, movable, or one of them being fixed and other being configured moveably.
[0004] During normal operating conditions, the main contacts are in a closed, abutting relationship which allows current flow continuity between the contacts and through the power line. When the main contacts separate, current flow is interrupted. Such interruption may occur when circuit breaker trip unit which monitors power in the power line detects an operating condition which is not within predefined operational parameters.
[0005] The speed of opening of the moving contact influences the time for quenching of arc and has a great influence on arc dwelling time in the contact system. As the velocity increases the arc is quenched faster and it moves faster from the contact to the arc chute. This increases the performance and life of the breaker. The opening velocity can be increased by increasing the repulsion force between the two contacts. A increase in magnitude of current or a decrease in the distance between the conductors carrying current can result in increase of the force. [0006] The increase or decrease of the current depends on factors such as type of fault or location of breaker etc. There are devices know in prior art that employ

different types of contact, different methods of opening of the contacts for increasing the repulsive force. However, the above said types of contact or above methods for opening of contact does not significantly increase repulsive force in order to increase the opening time of the contact. Further, the different types of contact do not facilitate rapid quenching of the arc. Hence there is a need for a contact system that provides the larger opening veloci^ and remains open for a longer duration of time. There is also a need for a contact system that orovides a better quenching of the arc.
OBJECT OF THE INVENTION
[0007] An object of the invention is to provide a contact system for molded case circuit breaker that provides increase in the opening velocity. [0008] Another object of the invention to provide a contact system that remains open for longer duration of time to facilitate rapid quenching of the arc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. [0010] FIGURE I shows typical contact system in the prior art. [0011] FIGURE 2 shows the modified contact system. [0012] FIGURE 3 shows the 3D view of the modified contact system. [0013] FIGURE 4 shows the 3D view of the modified contact system.

DETAILED DESCRIPTION OF INVENTION
[0013] Various embodiment of this invention provide a contact assembly for a
circuit breaker. Examples of circuit breaker may include molded case circuit
breaker. The embodiments are not limited and may be implemented in connection
with low, high voltage power lines.
[0014] Figure 1 show contact assembly of the prior art with a lower contact 1 and a
upper contact 2. The lower contact is provided with a contact button la and the
upper contact is provided with the contact button 2a according to an embodiment
of the invention.
[0015] Figure 2 and 3 show an embodiment of a contact assembly 100 for a circuit
breaker (not shown) comprises a first contact 3 and a second contact 4. The first
contact 3 includes a contact end 3a. The second contact 4 includes a contact end
4a. A first step portion 5 is provided in the contact end 3a. A second step portion 6
is provided in the contact end 4a. The first step portion 5 includes a width Wis
substantially more then the width Wlc of the first contact 3, The second step
portion 6 includes a width W2s substantially more then the width W2c of the
second contact 4. A contact button 7 is provided in the contact end 3a. A contact
button 8 is provided in the contact end 4a.
[0016] The configuration, connection and materia] of the contacts (3, •^) and
contact buttons (7, 8) are kept as known to a person skilled in the art.
[0017] In an embodiment, the width of the step portions (Wis, W2s) and depth of
step portions are configured so as to maintain the same cross-sectional area as that
of the conventional contact assembly.
[0018] In one example the first contact 3 is stationary. In other example the first
contact 4 is movable.
[00J9] In an example the second contact 4 is movable. However other examples
may include stationary second contact 4.
[0020] Referring to Figure 4. it should be noted that the Lorentz force F generated
on the contact buttons (7, 8) is significantly increased due to the increase in the
widths (Wis, W2s) of the step portions (5, 6).

[0021] Referring to Figure 4, the first step portion 5 includes a proximal end 5p and a distal end 5d. The contact button 7 is provided at a location substantially close to the proximal end 5p such that a gap 9 is maintained between the contact button 7 and the distal end 5d. The second step portion 6 includes a proximal end 6p and a distal end 6d. The contact button 8 is provided at a location substantially close to the proximal end 6p such that a gap is maintained between the contact button 8 and the dista) end 6d.
[0022] It should be noted that the contact buttons (7, 8) are provided at locations substantially close to the proximal ends {5p, 6p) so as to maintain maximum perpendicular distance to the Lorentz force (F) such that the repulsive torque generated is possible maximum.
[0023] Moreover, it should be noted that the reduction in the distance between the two contacts (3, 4) along with the increased widths (Wis, W2s) of the step portions (5, 6) provides for a much higher repulsive force without increase in the cross-sectional area of the contact thereby improving the operational efficiency of the contact mechanism. Thus, for a given magnitude of the current flow through the contacts (3, 4), the resulting repulsive force is much higher as compared to the conventional contact mechanism.
[0024] Various specific embodiment of this invention provide a contact mechanism for a circuit breaker. Although various modifications that are obvious to a person in the art are possible, all such modification is deemed to be within the scope of the claim claimed herein under:

We Claim:
1. A contact assembly for a circuit breaker, comprising:
a. a first contact,
b. a second contact configured to move between contact
position and non-contact position relative to the first
contact, and
c. the first and the second contacts having first and
second contact ends characterized in that the first
contact end includes a first step portion and the
second contact end includes a second step portion
wherein a contact button is provided in each step
portion.
2. A contact assembly as claimed in claiml, wherein the first step portion includes a width substantially more then the width of the first contact.
3. A contact assembly as claimed in claiml, wherein the second step portion includes a width substantially more then the width of the second contact.
4. A contact assembly as claimed in claiml, wherein each step includes a proximal end and distal end wherein the contact button is provided in the step portion at a location substantially close to the proximal end.
5. A contact assembly as claimed in claim I, wherein the depth of the step is substantially equal to the difference between the width of the contacts and the width of the step portion.
6. A contact assembly as claimed in claim 1, wherein the first contact is fixed contact.

7. A contact assembly as claimed in claiml, wherein the second
contact is movable contact.
8. A contact assembly as claimed in claim !, wherein the circuit
breaker is molded case circuit breaker.
9. A contact assembly as claimed in any of the preceding claims and
as described herein the description and accompanying drawings.