FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION [See section 10, Rule 13]
PISTON CYLINDER ARRANGEMENT FOR CONTACT LOCKING;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA.
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
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FIELD OF INVENTION
This invention relates to the field of circuit breakers and more particularly to the field of current limiting circuit breaker with contact locking arrangement.
BACKGROUND
Circuit breakers usually are intended to protect a circuit from fault currents arising out of short circuit or other circuit faults. The current limiting circuit breakers are based on the principal of electromagnetic repulsion between elements carrying current in opposite directions. The ability of a circuit breaker to respond to a fault current decides its efficacy in protecting downstream equipments.
In addition to the quickness of the circuit breaker to react to the fault currents factors like re-striking contribute to the effective time taken by the circuit breaker to break a circuit. Usually, contact re-striking occurs as a result of reduced electromagnetic force of repulsion between the contacts, as the distance between the contacts increases. The extended arc time thus created may harm the downstream equipments and also the circuit breaker itself. Arc extinguishing methods employing ionized gases are thus used to suppress arc soon after its creation.
In order to overcome the problem of contact re-striking contact locking arrangements are designed. These contact locking arrangements aim to lock a moving contact in an open condition immediately after the parting of the contact elements, thereby avoiding the further movement of the moving contact. After the fault clearance the circuit breaker may be switched to normal operating condition either manually or by an automatic means.
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During the normal working of the circuit breaker the contact elements are required to be kept in constant contact by optimum contact pressure, allowing a continuous current path between the contact elements. An optimum value of contact pressure ensures that during normal condition at rated currents temperature rise of circuit breaker does not go high.
This causes complications in the design of the circuit breaker leading to increase in overall size and manufacturing cost associated. Additionally, this causes extra overhead during troubleshooting and replacement of parts.
Moreover, the position and arrangement of contact locking assembly usually exposes the assembly to ionized gases. Therefore, there is a need for a circuit breaker incorporating simple elements and their positioning, which is compact in size yet effective in working.
SUMMARY
The present invention provides a contact arrangement for circuit breaker. The contact arrangement provides for circuit limiting characteristics and avoids re-striking of contacts of a circuit breaker by providing a reliable locking mechanism.
The contact locking arrangement described can be applied to various types of circuit breakers such as for example single phase or multiphase circuit breaker. Further, the arrangement may be applied to a single or multiple contact arms.
Additionally, the arrangement provides for maintaining contact pressure on the contact buttons thereby providing uninterrupted current flow. This ensures that the temperature of the circuit breaker during closed condition is in agreement with the desired working thermal characteristics.
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The arrangement provides for a rugged and reliable locking mechanism. Also, the arrangement provided ensures reliable contact locking soon after contact arms part as a result of electromagnetic repulsion.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A contact arrangement for circuit breaker is described. The contact arrangement provides circuit limiting characteristics and avoids re-striking of contacts of a circuit breaker by providing a reliable locking mechanism.
The contact arrangement described can be applied to various types of circuit breakers such as for example single phase or multiphase circuit breaker. Further, the arrangement may be applied to a single or multiple contact arms. Also, the arrangement may be used in single pole, multi-pole low voltage current limiting
Fig. 1 shows a circuit breaker comprising a contact arrangement as per one embodiment of the invention. The contact arrangement comprises of a contact holder (1) pivoted about a first axis (3). A moving contact (5) may be attached or fixed to one end (7) of the contact holder (1). The moving contact (5) may hold electrical contact buttons (20, 21). Alternatively, the moving contact may be implemented in a single break configuration wherein the moving contact may hold a single contact button.
A driving shaft (30) may be provided which may be hinged to allow rotation about a second axis (32). The driving shaft may be operated manually or automatically by means of automatic actuators to bring the circuit breaker into a closed condition allowing uninterrupted current flow to downside
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equipments; or to bring the circuit breaker out of a closed condition leading to a normal open condition.
A cylindrical component (40) may be provided having one end (42) pivoted about the second axis (32) in the driving shaft (30). A piston component (50) may have one end (52) of the piston component (50) hinged to the other end (9) of the contact holder (1).
During the closed condition of the circuit breaker as shown in fig. 2 the contact buttons (20, 21) may be in contact with a pair of other contact buttons (22, 23) to allow for uninterrupted current flow. A biasing means (46) may be housed in a cylindrical component (40) such that one end (48) of the biasing means is in engagement with the other end (54) of the piston component (50). The biasing means may be a compression spring. Alternatively, various types of springs such as for example tension spring and leaf spring may be used with implied modifications. During the working of the circuit breaker in the closed condition, the biasing means (46) applies a force F1 (91) along the axis of the cylindrical component (40). The force F1 (91) tends to rotate the contact holder (1) about the first axis (3) thereby providing contact pressure between the contact buttons (20, 21) and the pair of other contact buttons (22, 23).
On occurrence of excessive current inflows in the circuit breaker the moving contact (5) repels away from the pair of other contact buttons (22, 23) causing the contact holder (1) to rotate about the first axis (3) as shown in fig.3, from the earlier closed condition of the circuit breaker. As the contact holder rotates the direction of force created by the biasing means shifts. As the direction of the force F2 (93) crosses the first axis (3) a reversal of
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effective force on the contact holder (1) takes place. The reversal of force causes the contact holder (1) to further open thereby causing motion away from the pair of other contact buttons (22,23).
The rotation of the contact holder towards the pair of other contact buttons (22,23) is avoided by the force F3 (95) created by the biasing means (46) which tends to keep the contact holder open thereby locking it in a blown open condition.
The contact arrangement provides a rugged arrangement for reliable contact opening and locking. Also, the arrangement provides for simple arrangement of the constituent parts, which makes the arrangement easier for assembling and replacement. Also, the locking feature of the arrangement provides for a reliable contact locking improving the reliability and performance of the circuit breaker.
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WE CLAIM
1. A contact arrangement for circuit breaker comprising:
a contact holder pivoted about a first axis to bring the circuit breaker into a closed condition or a blown open condition;
a moving contact at one end of the contact holder;
a cylindrical component having one end in a driving shaft rotatably hinged to bring the circuit breaker into the closed condition or a normal open condition;
a biasing means housed in said cylindrical component;
a piston component having one end pivoted at another end of the contact holder;
another end of the piston component in engagement with the spring means applying force about an axis of the cylindrical component to bring the circuit breaker into said blown open condition and providing contact pressure during the closed condition.
2. The contact arrangement as in claim 1, wherein the biasing means is a compression spring.
3. The contact arrangement as in claim 1, further comprising: a contact button on one end of the moving contact
4. A single-phase circuit breaker comprising the contact arrangement as claimed in claim 1.
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5. A multi-phase circuit breaker comprising the contact arrangement
as claimed in claim 1.

Dated this 4in day of December, 2006.

FOR LARSEN & TOUBRO LIMITED
By their Agent

(MANISH SAURASTRI) KRISHNA & SAURASTRI

ABSTRACT
A piston cylinder arrangement for circuit breaker is described. The contact arrangement provides for circuit limiting characteristics and avoids re-striking of contacts of a circuit breaker by providing a reliable locking mechanism.
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