FORM 2
THE PATENTS ACT, 1970
COMPLETE SPECIFICATION
(See Section 10)
ASSEMBLY OF MOVING CONTACTS FOR SWITCHING
DEVICES
numbered as dated
INVENTORS:
1. ANANT KUMAR
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No 278,
Mumbai, 400 001, Maharashtra,
INDIA


ASSEMBLY OF MOVING CONTACTS FOR SWITCHING
DEVICES
A) TECHNICAL FIELD OF THE INVENTION:
[0001] The present invention relates to switching devices such as current limiting circuit breakers, and more particularly to the locking of the contact housing type current limiting circuit breakers and the moving contacts used therein.
B) BACKGROUND OF THE INVENTION
[0002] Electrical switching devices include circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers. These switching devices are used to protect electrical circuitry and equipment from damage due to abnormal condition, such as an overload condition or a relatively high level short circuit or fault condition. Extremely high currents, generated due to the short - circuiting of power supply sources, produce disastrous effect unless the high currents are interrupted by some means. Generally a circuit breaker interrupts such high currents by disconnecting the power supply source before the point of short circuit. The power supply is disconnected by physically separating two or more contacts in an insulating medium.


[0003] These switching devices typically have two positions corresponding to the status of the separable contacts. These positions would include an "ON" position, in which the separable contacts are closed and an "OFF" position in which the contacts are open. In few switching device there is a third state which would include tripped position in which the contacts are tripped open.
[0004] A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
[0005] Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. There are multiple types of circuit breakers currently available in the market. For example, the different types of circuit breakers available in the market are magnetic circuit breaker, thermal circuit breaker, thermo magnetic circuit breaker etc.
[0006] The magnetic circuit breakers are provided with a solenoid (electromagnet) in which the pulling force is increased proportionately with the magnitude of current. The contacts in the circuit breaker are held closed by a latch. When the current passed through


the solenoid increases beyond the preset rating of the circuit breaker, the latch is released by the pulling force of the solenoid to permit the contacts to be opened by a spring action. Some of the magnetic breakers have a hydraulic time delay feature to allow brief surge current beyond a preset level for starting motor or energizing electrical equipment. [0007] The thermal breakers use a bimetallic strip, which is heated and bent with increased current, and is similarly arranged to release the latch. Such thermal breakers are commonly used with motor control circuits. Thermal breakers often have a compensation element to reduce the effect of ambient temperature on the device rating.
[0008] The thermo-magnetic circuit breakers are found mostly in distribution boards. The thermo-magnetic circuit breakers include both an electromagnet that responds instantaneously to large surges in current (short circuits) and the bimetallic strip which responds with respect to less extreme but long -term over current conditions.
[0009] There are different technologies used in circuit breakers and they do not always fall into distinct categories. The commonly used circuit breakers in domestic, commercial and light industrial applications at low voltages (less than 1000 V) include a miniature circuit breaker (MCB) and a moulded case circuit breaker (MCCB).
[0010] A miniature circuit breaker (MCB) is used for a rated current of not more than 100 A., the trip characteristics are not adjustable normally. The MCB employs thermal or thermo-magnetic principles. The MCCB (Moulded Case Circuit Breaker) is used for a


rated current up to 1000 A. the MCCB uses the thermal or thermal-magnetic operation. The trip current may be adjusted in MCCB.
[0011] The circuit breakers for larger currents are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The circuit breaker comprises of various components and contact system forms one part of the same. When very high current flows through the system the contacts are so shaped that they repel because of current repulsion effect. The contact system of a switching device is spring loaded and when the contacts open it has a tendency to bounce back and re-make the circuit which gives rise to stresses in the system and damages the circuit breaker particularly the contacts.
[0012] The EP patent No.0569650 Bl discloses a phase and neutral circuit breaker provided with a modular housing having magnetic and thermal tripping circuits to permit the release of interlock and to separate the contacts.
[0013] The US patent No. 4656444 discloses a circuit breaker provided with a force generating shunt having folded back portions to generate a repulsive magnetic force to press the closed contacts together and to expedite the opening of the contacts.
[0014] In US 5310971, contact locking for switching devices is described. In this each spring is on one hand, anchored to the contact bridge, and on the other hand anchored to a


rod housed in a notch of the bar. The contact bridge bears on its edge cam surfaces which, at the end of opening travel, engage the anchoring rods to move them in the notches in the elongation direction of the tension springs. The cam profile ensures latching of the contact bridge in the open position.
[0015] In US 6259048 Bl, there is a provision of a link connection between a contact housing assembly and a movable contact arm to improve the performance of a circuit breaker during contact separation as well as contact closure. The arrangement of at least one expansion spring between the link and the associated contact housing provides the optimum contact force by compensating for component tolerance and contact erosion and wear while maintaining a reliable means for locking the contact arm open in the event of an over current condition.
[0016] The US Patent No. 6232570 discloses a rotary double-break circuit breaker which includes a case defining a circuit breaker enclosure with a rotatable bridge and contact arm arrangement. The contact arm has movable contacts, which is rotatable between a closed position and an open position. A pair of stationary contacts co-operates with the movable contacts, and a conductor is operatively connected to each of the stationary contacts for current input.
[0017] The US Patent No.5030804 discloses a contact arrangement, particularly intended for current-limiting low voltage circuit breakers. The contact arrangement has a double


break movable contact arm with the central portion attached to an insulating shaft which is rotatably moved in elongated holes in stand parts on each side of the contact arm. In the closed position of the arrangement, the movable contact arm is pressed against two U-shaped fixed contact arms with the aid of two torsion springs.
[0018] When the circuit breaker is closed the contacts are held together. When the breaker opens, the moving contact separates from the fixed contact and the arc is established at these contacts. When very high current flows through the system the contacts are so shaped that they repel because of current repulsion effect. The contact system of a switching device is spring loaded and when the contacts open, it has a tendency to bounce back and re-make the circuit which gives rise to stresses in the system and damages the circuit breaker, particularly the contacts. The contact bouncing generally occurs in a circuit breaker when high current flows through the circuit or during the circuit breaker closing operation hence resulting in burning of the contacts. During bouncing the moving contact moves away from the fixed contact. The moving contact while moving away from the fixed contact acquires a certain amount of velocity and momentum and releases that in the form of kinetic energy to the fixed contact. Since the contact mechanism is flexible and spring loaded, it has the tendency to bounce back. After bouncing the contact tends to close again as a result during bouncing, the circuit is never broken between the contacts. Hence the contact may bounce back and the process may be repeated until the circuit is closed. Hence there is a need to develop a system and


method for locking the moving contact of the circuit breaker and to prevent it from bouncing back and re-making the contact.
[0019] Prior art discloses a provision to link the connection between a contact housing assembly and a movable contact arm to improve the performance of a circuit breaker during contact separation as well as contact closure. None of the prior art discloses a proper provision for locking the moving contact of the circuit breaker to prevent it from bouncing back and re-making the contact. Hence there is a need to develop a system and method to enclose the moving contact assembly in housing to prevent the bouncing of moving contacts with respect to the fixed contacts.
[0020] While the conventional solutions are advantageous for their intended purposes, the existing state of the art generally does not provide adequate solutions for locking mechanism in switching device that can provide better and stable solution for contact arm moving and locking mechanism. The locking mechanism should not let the moving contact arm to mate with the fixed contact arm once the contacts repel open due to high currents flowing through the circuit. It should also be capable restoring its original position when the contact housing is moved with respect to it. Also the locking mechanism must be able to provide the necessary contact pressure when the contact mates.


C) OBJECT OF THE INVENTION:
[0021] The primary object of the present invention is to provide a circuit breaker in which a moving contact is assembled in a housing to prevent the moving contact from bouncing back and making the contact during over load conditions.
[0022] Yet another object of the present invention is to provide a circuit breaker including a locking means to prevent the spring loaded moving contact from bouncing back and making the contact during over load conditions.
[0023] Yet another object of the present invention is to lock the circuit breaker moving contact using a latch.
D) SUMMARY OF THE INVENTION:
[0024] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
[0025] The various embodiment of the present invention provide a provision for locking the moving contact of the circuit breaker when it opens due to high current flowing through the circuit and prevents it from bouncing back and re-making the contact.


According to one embodiment of the present invention a spring loaded contact housing type circuit breaker is provided with moving contact assembled in housing, wherein the entire assembly of moving contact can rotate and move with respect to the housing.
[0026] The breaker moving contact according to the present invention comprises of a latch, a notch (C) in a Latch, two pairs of extension spring, contacts, ground body, housing with notch (A) and pins. The two pairs of extension spring are attached at one end to the contact housing and the other end to the movable contact. The spring is connected to the contact housing with the help of a pin which is fixed to the contact housing. The other end is fixed and is connected to the movable contact with the help of a pin which passes through the slot in the movable contact. Locking of the contacts is affected by trapping the pin that is connected to the contact in the notch or other such arrangement in the latch.
[0027] According to another embodiment the extension springs used in the present invention serve the twin purpose of providing contact pressure and resetting the contact system to original position once the fault is cleared and the latch can be used as an indicator for contact position.
[0028] The latch according to one embodiment of the present invention comprises of a longer limb (B), Notch (C), smaller limb (D) and Hole (E). When the breaker is switched ON, the longer limb(B) of the latch presses against the pin and when the contacts are


repelled open the pin moves on the surface of the latch and finally get locked in the notch(C) provided in the latch, holding it in repelled position.
[0029] To unlock the contacts a notch (A) in the contact housing pushes against the smaller limb (D) of the latch which moves and frees the pin and hence the contact from the latch. The contacts get back to the original position because of the extension springs which are used to provide the contact pressure. Hence the threshold angle at which the locking should take can be altered by using a latch. Since the latch is used for locking the moving contacts the unlocking cannot be done unless the latch is removed. The contact pressure can also be varied for different application without affecting any other parameters. The present invention can be used with both single finger as well as multi finger contacts and for the latch either of the extension, compression or torsion spring can be used.
[0030] Other objects, features and advantages of the invention will be apparent from the drawings, and from the detailed description that follows below.
E) BRIEF DESCRIPTION OF THE DRAWINGS:
[0031] 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:


[0032] FIGURE.l Illustrates front view of the assembly of the movable contact system without the springs.
[0033] FIGURE.2 Illustrates front view of the complete assembly of the movable contact system with the springs.
[0034] FIGURE.3 illustrates the isometric view of the arrangement.
[0035] FIGURE.4 illustrates the isometric view of the arrangement.
[0036] FIGURE.5 illustrates the exploded view of the arrangement.
[0037] FIGURE.6 illustrates the latch used in the arrangement.
F) DETAILED DESCRIPTION OF THE INVENTION:
[0038] 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.


[0039] The various embodiment of the present invention provide a provision for locking the moving contact of the circuit breaker when it opens due to high current flowing through the circuit and prevents it from bouncing back and re-making the contact. According to one embodiment of the present invention a spring loaded contact housing type circuit breaker moving contact is assembled in housing, where in the entire assembly of moving contact rotates and moves with respect to the housing.
[0040] When very high current flows through the system the contacts are so shaped that they repel because of current repulsion effect. The contact system of a switching device is spring loaded and when the contacts open it has a tendency to bounce back and re-make the circuit which gives rise to stresses in the system and damages the circuit breaker. According to one embodiment of the present invention a movable contact enclosed in housing is locked by using a latch. The movable contacts include an extension springs, a single finger or multi finger contacts and a latch enclosed in housing between a pair of flat ground body.
[0041] According to one embodiment of the invention the movable contact is locked by using a latch when ever the contacts open due to magnetic repulsion. The latch enclosed in housing can be moved vertically up and down (or the notch (C) in the latch can be moved) for locking and unlocking the moving contact, hence the threshold angle at which the locking should take place can be altered using the latch without affecting other parameters. A latch comprises of a longer limb (B), Notch (C), smaller limb (D) and Hole


(E). When the breaker is switched ON, the longer limb(B) of the latch presses against the pin and when the contacts are repelled open the pin moves on the surface of the latch and finally get locked in the notch(C) provided in the latch, holding it in repelled position.
[0042] To unlock the contacts a notch (A) in the contact housing pushes against the smaller limb (D) of the latch which moves and frees the pin (6) and hence the contact from the latch. The contacts get back to the original position because of the extension springs (4) which are used to provide the contact pressure. The threshold angle at which the locking should take can be altered by using a latch without affecting other parameters. Since the latch is used for locking the moving contacts the unlocking cannot be done unless the latch is removed. The contact pressure can also be varied for different application without affecting any other parameters by changing the spring design of the extension spring (4).
[0043] According to another embodiment of the present invention extension springs are used to provide contact pressure and for resetting the contact system to original position once the fault is cleared.
[0044] FIGURE 1 illustrates the assembly of the movable contact system in front view without the springs. It shows a ground body (1) with two contacts (2) made separately as they can be manufactured easily in case of high capacity circuit breakers. The assembly of the moving contact with the contacts (2), a pair of latches and the springs is


enclosed in housing (3). The spring in this view is omitted for clarity. The moving contact assembly includes a pair of latch (7) with a longer limb (B), notch (C), smaller limb (D) and hole (E). FIGURE 1 shows the functioning of the movable contact assembly in OFF state. The movable contact (2) is locked once it opens due to the magnetic repulsion. The latch (7) in the present invention uses torsion springs (5) which are attached at one end to the pin (8) and other end to the ground body. The torsion spring (5) keeps the latch (7) pressed onto the pin (6) between the contacts and when the contacts (2) repel open the latch holds it onto this pin (6). Pin (8) passes through the hole (E) in the latch (7) and through the ground body (1) and the other end fixed to the latch (7). Pin (9) is fixed to the contact housing (3) and pin (6) to which the spring is attached in the contact housing. [0045] FIGURE 2 illustrates the complete assembly of the movable contact system in the front view with the springs in OFF state. When the moving contact opens due to high current flowing through the circuit, the pin (6) in the moving contact assembly interlocks with the notch (C) in the latch (7). Hence it prevents the moving contact from bouncing back and making the contact with the fixed contact. Hence it prevents the moving contact from making the contact again. The present invention uses two pair of extension springs (4) which are attached at one end to the contact housing and the other end to the movable contact. The spring is connected to the contact housing with the help of a pin (9) which is fixed to the contact housing. The other end is fixed and is connected to the movable contact with the help of a pin (6) which passes through the slot in the movable contact.


[0046] FIGURE 3 illustrates an isometric view of the moving contact assembly. A moving contact housing (3) is placed in-between the ground body (1) on either side. When high current flows through the circuit breaker, the moving contacts (2) move away from the fixed contact to break the contact. Since the moving contact arrangement is spring loaded it has a tendency to bounce back and remake the contact. The entire moving contact assembly with the contacts (2), extension springs (4) and latch(7) is enclosed in housing (3). Pin (8) passes through the hole (E) in the latch (7) and connected between the ground body (1). When the breaker is switched on, the longer limb(B) of the latch(7) presses against the pin(6) and when the contacts(2) are repelled open the pin(6) moves on the surface of the latch(7) and finally get locked in the notch(C) provided in the latch(7), holding it in repelled position. To unlock the contacts (2) a notch (A) in the contact housing(3) pushes against the smaller limb(D) of the latch which moves and frees the pin(6) and hence the contact(2) from the latch(7). The contacts get back to the original position because of the extension springs (4) which are used to provide the contact pressure.
[0047] FIGURE 4 illustrates the isometric view of the contact system. The springs, latch, contact housing and the contacts are visible in this view.
[0048] FIGURE 5 illustrates the exploded view of the moving contact assembly. It shows the various components like the body of the contact housing (3), movable contact (2), pin (9) fixed to the contact housing and pin (6) to which the spring is attached. Pin (7) to


which the latch (7) and the torsion spring (5) is fixed and a notch (A) in the contact housing (3).
[0049] The contact housing (3) as shown in the figure includes a notch (A) on either side of the housing. The contacts (2), extension springs (4), a latch (7) and a pin (6) are enclosed in housing as shown by the extended dotted lines. Pin (8) external to the housing (3) passes through the latch hole (E) should be connected between the ground body (1). Pin (9) is fixed to the contact housing and pin (6) to which the spring is attached. Since the entire assembly is mounted in the housing, it prevents the moving contact from bouncing back and making the contact, hence prevents the circuit breaker from being damaged. The moving contact can rotate and move freely in the housing. When the circuit breaker is switched 'ON' the longer limb (B) of the latch (7) presses against the pin (10) and when the contacts (2) are repelled open the pin (6) moves on the surface of the latch (7) and finally get locked in the notch (c) provided in the latch (7) holding it in repelled position. It includes Pin (8) to which the latch (7) and the torsion spring (5) are fixed. The torsion spring (5) keeps the latch (7) pressed on to pin (6) between the contacts.
[0050] According to one embodiment to unlock the contacts of the circuit breakers, a notch (A) in the contact housing pushes the smaller limb (D) of the latch which moves and frees the pin (6) and hence the contact from the latch. The contacts get back to the original position because of the extension springs which are used to provide the contact pressure. Hence the threshold angle at which the locking should take can be altered by


using a latch without affecting other parameters. Since the latch is used for locking the moving contacts the unlocking cannot be done unless the latch is removed. The contact pressure can also be varied for different application without affecting any other parameters. This invention can be used with both single finger as well as multi finger contact as shown in the figures and for the latch either of extension, compression or torsion spring can be used.
[0051] FIGURE 6 shows the latch used in the arrangement. The features of the latch like the longer limb(B), notch(C), shorter limb(D) and the hole(E) that fixes the latch to the pin(8) are visible. The latch (7) can be used as an indicator for contact position. The latch (7) uses torsion springs (4) which are attached at one end to the pin (8). Pin (8) passes through the hole (E) in the latch (7) and through the ground body (1) and the other end fixed to the latch (7). The torsion spring (5) keeps the latch (7) pressed onto the pin (6) between the contacts and when the contacts (2) repel open the latch holds it onto this pin (6). When the breaker is switched on, the longer limb (B) of the latch (7) presses against the pin (6) and when the contacts (2) are repelled open the pin (6) moves on the surface of the latch (7) and finally get locked in the notch (C) provided in the latch (7), holding it in repelled position.
[0052] To unlock the contacts (2) a notch (A) in the contact housing (3) pushes against the smaller limb (D) of the latch which moves and frees the pin (6) and hence the contact (2) from the latch (7). The contacts get back to the original position because of the


extension springs (4) which are used to provide the contact pressure. The extension spring (4) is used in the present invention to maintain the contact pressure and to reset the contact system to original position once the fault is cleared.
[0053] Thus the various embodiment of the present invention provide a provision for locking the moving contact of the circuit breaker when it opens due to high current flowing through the circuit and prevents it from bouncing back and re-making the contact. A spring loaded, contact housing type circuit breaker is assembled in housing, where in the entire assembly of moving contact can rotate and move with respect to the housing. Since the design is based on locking the contacts using a latch, it is very compact. Hence it avoids the links used for actuation of the contacts as earlier. The present invention can be used with both single finger as well as multi finger contact for the latch. The springs such as either of extension, compression or torsion spring is used in the present invention.
[0054] Since the latch is used for locking the moving contact of the circuit breaker unlocking cannot be done unless the latch is removed. The threshold angle at which the locking should take place can be altered by moving the latch vertically up and down without affecting other parameters. Contact pressure can also be varied for different applications by changing spring design without affecting other parameter.


CLAIMS:
WHAT IS CLAIMED IS:
1. A contact arrangement for electric switching devices, comprising:
a housing with a notch;
a ground body to house entire assembly;
assembly of movable contacts,
two latches;
pair of pins;
two extension springs; and
two torsion springs;
2. The contact arrangement of claim 1, wherein said latch further comprises of; a long limb; small limb; a notch; and a hole.
3. The contact arrangement of claim 1, wherein said latch is attached to one of the pins through said torsion springs at one end and the other end of said latch is attached to said ground body.
4. The contact arrangement of claim 1, wherein each said extension springs is attached at one end to said contact housing and the other end to said movable contact.


5. The contact arrangement of claim 1, wherein said movable contact enclosed in said hosing is locked by using said latch whenever the contacts open due to magnetic repulsion.
6. The contact arrangement of claim 1, wherein said latch enclosed in said housing is capable of moving vertically up and down for locking and unlocking said moving contact.
7. The contact arrangement of claim 6, wherein threshold angle at which the locking takes place can be altered using said latch without affecting other parameters.
8. The contact arrangement of claim 1, wherein said longer limb of said latch presses against said pin when said breaker is switched ON.
9. The contact arrangement of claim 1, wherein one of the said pins gets locked in said notch provided in said latch to hold it when the contacts are in repelled state.

10. The contact arrangement of claim 1, wherein said torsion spring provide necessary pressure to keeps said latch pressed onto said pin between said contacts.
11. The contact arrangement of claim 1, wherein said notch provided in the contact housing pushes against said smaller limb of said latch to unlock the contacts, wherein said smaller limb of said latch moves and gets separated from said pin to unlock said movable contact from the latch.


12. The contact arrangement of claim 11, wherein said extension springs provide necessary contact pressure to said movable contacts when contacts are in ON position.




ABSTRACT:
The embodiments provide a spring loaded contact housing type circuit breaker with moving contact assembled in housing, wherein the assembly of moving contact can rotate and move with respect to the housing. The assembly comprises of a latch, a notch in the latch, a pair of extension spring, a pair of torsion springs, moving contacts, ground body, housing with notch and pins. The extension springs provide contact pressure and reset the contact system to original position once the fault is cleared. The latch comprises of two limbs, a notch and a hole. When the contacts are repelled open, the pin gets locked in the notch provided in the latch, holding it in repelled position. To unlock the contacts, a notch in the contact housing pushes against the smaller limb of the latch which moves and frees the pin.
12 Claims, 6 Drawing Sheets