AN IMPROVED CONTACT SYSTEM FOR A CIRCUIT BREAKER
Field of the invention
[0001] The present invention relates to circuit breakers (MCCB) and more particularly to the contact system used in such MCCBs.
Prior Art [0002] Molded Case Circuit Breakers (MCCB) are employed for current interruption. More particularly MCCBs are utilized to protect instruments from damage during adverse conditions prevailing during the operation of the circuit in which molded case circuit breaker is employed. During adverse conditions like short circuit, the current rises to an alarmingly high level. This high current may cause damage to the parts in the electrical system. Hence during these conditions the circuit has to be opened to protect the parts after the breaker. [0003] A circuit breaker has to carry, make and break during normal and abnormal conditions. An arc will be formed between contact buttons during current interruption. In order to provide efficient dampening of the arc, the contacts must be closed and opened (make and break) very quickly so that arc doesn't remain for longer time and destroy the contact button.
[0004] The knob movement should be sufficient to open and close the contacts at high speeds as well as to a greater isolation distance. Here the upper contact is made movable while the lower contact is fixed. So in order to make or break, the upper contact alone is moved. Here in this concept the upper contact is moved up and down linearly. Previously the contact system is opened at a degree (rotary type).
[0005] The upper contact should be moved away from the lower contact to a distance such that it provides isolation between the contact buttons. The minimum distance of separation between the upper and lower contact that can provide electrical isolation is called as isolation distance. This isolation distance should be designed in such a way that the insulator (air) has enough dielectric strength which can prevent the current to flow through it.

[0006] In the light of foregoing discussion, there is a need for a molded case circuit breaker, which has reduced constriction force and produces higher blow out force when an arc is produced while contacts are being separated. The molded case circuit breaker should provide greater opening between the upper and lower contacts and should be able to control short circuit withstanding time or current.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to provide an improved contact system for a
molded case circuit breaker. More particularly, it is an object of the invention to
provide a contact system capable of translational motion in a MCCB
[0008] It is also an object of the invention to provide an improved contact system
capable of translational motion in a molded case circuit breaker, which enables
greater opening between the upper and lower contacts.
[0009] It is a further object of the invention to increase the time for withstanding a
short circuit.
[0010] Accordingly, the present invention provides an improved contact system
capable of translatory motion for a molded case circuit breaker, comprising a
contact system having a stationary contact, a movable contact, and a spring-based
mechanism for enabling the coupling of the stationary and movable contacts,
wherein the spring-based mechanism is at an acute angle with the surfaces of the
contact buttons on the stationary and movable contacts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] 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.

[0012] FIG. 1 shows a contact system of a molded case circuit breaker in OFF
position
[0013] FIG. 2 represents the contact system of the molded case circuit breaker in
an ON position;
[0014] FIG. 3 shows the application of contact pressure utilizing tensile springs to
achieve override of the opening of the contacts.
DETAILED DESCRIPTION OF INVENTION
[0015] Various embodiments of the present invention provides an improved contact system for molded case circuit breaker which reduces the constriction force between the contacts and produces higher blow out force when an arc is produced while contacts are being separated. More particularly, the improved contact system provides for means with a spring biased mechanism for achieving the translatory movement of the contacts during the opening and closing of the said contacts. The improved contact system further enables greater opening between the upper and lower contacts and is able to control short circuit withstanding time or current.
[0016] We manually apply force on the knob to move it to a distance till the spring in the mechanism attains its maximum length point referred to herein as Dead center. Once the spring has reached its maximum load achieved due to maximum elongation, the spring will try to regain its original length. This sudden contraction of the spring is converted to the up and down movement resulting in a quick break and quick make of the upper contact through the links shown in the figure.
[0017] For same movement of the knob during breaking operation, this mechanism provides more isolating distance than the conventional type. In the conventional type, the upper contact opens at an angle to the lower fixed contact. Hence the linear distance of separation between the contacts is relatively low when compared to this mechanism.
[0018] In contacts, not all the points in the upper and lower contact button come into contact how much ever polishing is given. So the number contact points

should be increased so that area of contact is increased which reduces resistance and constriction force. So we give some force externally to the contact button so that the buttons remain in contact with contact pressure. [0019] Figure 1 shows the contact system when the knob 1 is in OFF position [0020] Figure 2 shows the contact system when the knob is in ON position [0021] In an embodiment of the invention, the tensile springs are used to provide the contact pressure. One end of the spring is connected to the rod placed above the upper contact inside the cup while the other end is connected to the rod placed below the upper contact outside the cup as shown in Figure 3, To provide the required pressure, the said cup part which is connected to the spring biased mechanism is allowed to move further down even after the upper and lower contact comes into contact. This extra distance moved by the cup is referred to herein as over ride. In an embodiment to the invention, this override distance is at least 5 mm. Further, the said movement of the spring through the said distance of at least 5mm is advantageously utilized for to produce a contact pressure of 6 kg. In an alternate embodiment of the invention, a plurality of springs are utilized to increase the contact pressure. Further, in an example of the invention, employment of four springs achieve a contact pressure of 24 kg for contacts in each pole. [0022] The contact pressure thus achieved by the advantageous employment of springs, is applied at the centre of the contact system. It is an established fact that if a force is applied in a simply supported beam at its centre, then the reaction force would be exactly half of the force applied as the algebraic sum of the vertical forces and horizontal forces should be zero. The improved contact system as described herein advantageously utilized the contact pressure to produce a reaction force would exactly be half of the contact pressure applied.
[0023] In an embodiment of the invention the contact buttons are tilted at an angle of 60° to the horizontal. So the reaction forces are resolved into vertical and horizontal components. In order to cancel out the applied force, the sum of the vertical component of the reaction forces should be equal to the applied force. If the vertical component alone is equal to 0.5 F, then the reaction force is exactly the

double of it (F). This results in the contact pressure in each button that is double than the conventional type.
[0024] The present invention, therefore, provides an improved contact system in a molded case circuit breaker, which reduces the constriction force between the contacts and produces higher blow out force when an arc is produced while contacts are being separated. The improved contact system for molded case circuit breaker of the present invention further enables greater opening between the upper and lower contacts and is able to control short circuit withstanding time or current. [0025] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

We claim:
1. An improved contact system for a circuit breaker comprising of a stationary contact, a movable contact, means provided on the said movable contact for housing a spring-biased mechanism to enable the coupling of the stationary and movable contacts at the contact buttons
2. An improved contact system according to claim 1, wherein the spring-biased mechanism comprises a cup, a shaft, a pin, and a plurality of springs, the cup holding the movable contact through the shaft and the pin, the pin restricting the horizontal movement of the movable contact with respect to the cup.
3. An improved contact system according to claim 1, wherein the said means provided on the said movable contact comprises of at least one rod and a slot provided for housing the said at least one rod and further wherein the said at least one rod is capable of movement within the said slot.
4. An improved contact system according to claim 1, wherein the lower face of the contact buttons on the movable contact are at a predetermined distance with respect to the lower face of the movable contact,
5. An improved contact system according to claim 1, wherein the said at least one rod provided on the said movable contact provides translatory motion during the opening and closing of the said contacts,
6. An improved contact system according to claim 1, wherein a plurality of said rods are provided on the said movable contact to house a plurality of said springs.
7. An improved contact system according to claim 1, the said improved contact system produces a predetermined contact pressure force at the contact buttons.
8. An improved contact system according to claim 1, wherein the said contact pressure force is achieved by the said movement of the said rods on the said movable contacts housing the said spring biased mechanism.

9. An improved contact system according to claim 1, further wherein the said movement of the said rods on the said movable contact is at least 5mm.