FORM 2THE PATENTS ACT, 1970(39 of 1970)&The Patents Rules, 2003COMPLETE SPECIFICATION(See section 10; rule 13)
Title of the invention - AN IMPROVED CURRENT LIMITING CIRCUIT BREAKER SYSTEM FOR DETECTION AND DISCRIMINATION OF FAULTS
2. Applicant(a) NAME : LARSEN & TOUBRO LIMITED(b) NATIONALITY : An Indian Company(c) ADDRESS : L&T House, Ballard Estate, Mumbai 400 001, State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:


FIELD OF INVENTION
The present invention relates to an improved current limiting circuit breaker system for detection and discrimination of faults in power distribution lines. More particularly, the invention relates to a an improved current limiting circuit breaker system to detect and discriminate faults comprising means so as to combine actions of contact repulsion and contact acceleration and tripping enhancing breaking operation thereby improving performance with reduced number of constructive components thus providing simplicity in operation with a consequent benefit of cost.
BACKGROUND AND PRIOR ART
A current limiting circuit breaker consists of a housing, a cover, fixed contact secured in housing, moveable contact pivoted about the pivot point in an operating shaft which is connected to operating mechanism, arc chamber, thermal and magnetic releases and a trip unit which opens the contacts when a predetermined amount of current is exceeded. Operating mechanism is used to switch ON and OFF the circuit breaker. Breaker also has an intermediate position between ON & OFF, which is called TRIP position. This position is achieved when there is a fault or externally breaker is tripped.
Current limiting circuit breaker opens on fault condition when a current flow through it is of excessive magnitude. In case of fault, the moving contact responds to excessive magnitude current by electromagnetic repulsion between moving and fixed contacts, and rotates independent of operating shaft and operating mechanism. Performance need of circuit breaker reveals need of fast locking and mechanism arrangement, which
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responds to excessive magnitude current situation, opens it fast and keeps it in open on fault position.
The circuit breaker in vicinity of the fault location trips during faulted condition instead of upstream breaker thereby achieving discrimination in fault. This ensures maximum continuity of service, thereby coordination between protective devices.
Several techniques are used to ensure discrimination between two circuit-breakers during a short-circuit: that includes current discrimination, time discrimination, zone selective interlocking, energy-based discrimination.
The energy based discrimination system requires separate pressure trip system; the pressure that develops in the breaking unit of a circuit-breaker is a result of the energy produced by the arc. Above a certain fault current level, the pressure developed in breaking unit is used for detection of fault and tripping of circuit breaker. This is by directing the expanding gases in the unit toward a piston that trips the circuit-breaker. This reveals that for achieving discrimination the additional device is required in case of energy based discrimination of special pressure trip system is required and in electronic system addition zone selection facility is used. The discrimination system should be simple to implement and easy for discrimination.
EP0318274 discloses a method and apparatus for detecting and discriminating faults in transmission circuits. Particularly in transmission systems having a number of transmission lines carrying high voltages, it is important to ensure that any faults arising are detected so that the affected transmission line can be isolated from the system. Equally though, it is
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important to ensure that lines are not isolated unnecessarily. It would be possible to monitor the transmission lines at a number of individual locations at which associated circuit breakers are provided. However, this involves total reliance upon locally derived information and therefore does not possess any inherent discrimination properties. Therefore there is a high risk of unnecessary shut-downs occurring.
JP61111019 discloses extraction of current by a current detector 6 is inputted to a discriminator discriminating the presence of current. This discriminator starts operating with other electric quantity inputted together with a trip signal, confirms the input of the electric quantity from the said detector, uses the signal inputted to the discriminator in a prescribed time corresponding to a tA in figure after the trip signal is given so as to discriminate whether or not the signal inputted from the said current detector to the discriminator is consecutive. The high-order breaker is operated based on the result of discrimination. The time tA is a time when the success of interruption is discriminated in a time slightly longer than the time where a load circuit of the breaker is short- circuited. This reduces damages given to a load circuit or a load device and to miniaturize a thyristor element being a component of the titled breaker by supervising the quantity of current flowing from the interrupter in a prescribed time elapsed after an breaking command is given to the breaker so as to discriminate the success of current breaking thereby activating the high-order breaker.
Thus there is a need for an improved current limiting circuit breaker system for detection and discrimination of faults in power distribution lines with enhancement in the breaking operation.
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It has been unexpectedly found that a system comprising means profiled in a manner that provides improvement in the circuit breaker performance by way of combining actions of contact repulsion and contact acceleration with reduced number of constructive components resulting operational simplicity.
OBJECTS OF INVENTION
Thus one object of the present invention is to provide a mechanism for detecting and discriminating faults in power distribution lines.
Another object is to make a compact current limiting circuit breaker thereby limiting current cut off values and reducing let through energy in order to protect downstream equipments.
Yet another object is to provide mechanism tripping arrangement which overcomes the limitations of slow operating mechanism.
Another object is to provide improved breaker performance because of low let through energy, thereby reducing stresses on internal components of circuit breaker
Yet another object is to achieve higher breaking capacity through current limiting and holding arrangement
Yet further object is to implement inherent fault discrimination system thereby ensuring maximum continuity of service,
Another object is to provide co-ordination between protective devices during faulted condition without additional constructive components.
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SUMMARY OF INVENTION
Thus according to one aspect of the present invention there is provided an improved current limiting circuit breaker system adapted to detect and discriminate faults improving circuit breaker performance in power distribution lines, said system comprising:
housing;
fixed contact means and moving contact assembly wherein said
fixed contact means being mounted in said housing in a rigid
manner,
said moving contact assembly comprising moving contact and
rotatable means in co-operation with a cam means biased with
spring means so as to provide predetermined overtravel thereby
producing required contact pressure,
said cam means being provided with an undulating profile so as
to combine actions of repulsion between said fixed and moving
contact and moving contact acceleration and tripping thereby
providing directional flexibility in the moving contact
assembly thereby accelerating motion of moving contact
assembly.
Another aspect of the present invention is to provide a moving contact assembly comprising:
moving contact and rotatable means in co-operation with spring biased cam means so as to provide predetermined overtravel thereby producing required contact pressure,
said cam means being provided with an undulating profile so as to combine actions of repulsion between said fixed and moving contact assembly and moving contact acceleration thereby providing directional flexibility in the moving contact
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assembly thereby accelerating motion of moving contact assembly.
DETAILED DESCRIPTION OF INVENTION
In the present invention the system for detection and discrimination of faults in power distribution circuits comprises fixed contact rigidly mounted in the housing and moving contact assembly comprising a moving contact being pivoted about pivot point of rotatable means of the moving contact assembly inside the housing. The said rotatable means comprises operating shaft in co-operation with spring biased cam means so as to provide predetermined overtravel of the moving contact which is required to avoid hotspots on the fixed contact due to movement of the moving contact. This is achieved when after touching the fixed contacts, operating shaft rotates further in angular direction thereby generating the independent movement of moving contacts and generates required contact pressure between fixed and moving contacts, due to extra compression of spring means.
In another embodiment of the present invention the major component hereinbefore referred to as spring biased cam means comprises Of an undulating profile with predetermined slope of depression located approximately at the middle along the vertical surface of the cam means. The cam further comprises guide means provided with two modular limbs which pass through the spring means comprising compression springs so as to move the cam in a linear direction.
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Yet in another embodiment of the present invention the guide means comprises operating shaft profiled in a manner that during repulsion of the moving and the fixed contacts it would provide linear motion to the cam in a predetermined direction in order to accommodate moving contact motion.
In case of fault current high electromagnetic repulsive force is generated causing rapid separation of the moving and fixed contacts, which is rigidly mounted in housing comprising the mechanism and circuit breaker. The profile of the cam is such that on repulsion of the said contacts, the cam provides an accelerated motion to the moving contact. Because of profile of the cam, the compression spring generates the force in such a direction that produces required contact pressure during normal operation of circuit breaker, this arrangement ensures that the moving contact rotates in conjunction with operating shaft during normal operations.
In another embodiment of the present invention the moving contact is pivoted about the pivot point in the said operating shaft, which is operated by operating mechanism and thermal and magnetic releases, to avoid the overload and fault currents. This motion of cam is used to trip the operating mechanism thereby eliminating drawback of slow acting operating mechanism. During faulted condition breaker with accelerated contact opening and mechanism tripping arrangement co ordinates with upstream breaker with normal contact locking and mechanism tripping arrangement or upstream breaker without contact locking arrangement and achieves self discrimination. Fault is detected by rotation of the operating shaft at desired current values.
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BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1 illustrates side elevation view of the self
discrimination mechanism of the present invention with circuit
breaker in ON position. Enlarged view of the operating shaft
shown in figure IX.
Figure 2 illustrates side elevation view of the self discrimination mechanism of the present invention with circuit breaker in OFF position.
Figure 3 illustrates side elevation view of the self discrimination mechanism of the present invention with circuit breaker OPEN ON FAULT position.
DETAILED DESCRIPTION OF ACCOMPANYING FIGURES
In figures 1 to 3 fixed contact (1) is rigidly mounted in housing (2) and the moving contact (3) is pivoted about the pivot point (9) in operating shaft (4). The operating shaft (4) is operatively connected with the operating mechanism (6) and plurality of thermal and magnetic releases. One end of moving contact (3) comprises contact button (11) and the other end comprises slider pin (12), which slides on the profiled cam (10). The profiled cam (10) is guided in the slot (13) of the operating shaft (4). The compression spring (8) is biased with cam (10)
Figure 1 shows the mechanism in ON condition of circuit breaker. This condition of circuit breaker is achieved when energy is transferred from operating mechanism (6) to operating shaft (4). Moving contact (3) being coherent to operating shaft (4) rotates with the operating shaft (4) and
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touches the fixed contacts (1) . To avoid hotspots at contact, over travel is required. This is achieved when after touching the fixed contacts (1), operating shaft (4) (enlarged view shown in figure IX) rotates further in angular direction thereby generating the independent movement of moving contacts (3) and generates required contact pressure between fixed and moving contacts, due to extra compression of spring (8).
Figure 2 shows the mechanism in OFF condition of the circuit breaker. This condition of circuit breaker is achieved when the operating mechanism (6) is pulled back to the off position and mechanism spring pulls the operating shaft (4) to rotate it to the off position. In this condition moving contact being coherent to operating shaft (4) rotates with the operating shaft (4).
Figure 3 shows open on fault condition. This condition of circuit breaker is achieved when excessive magnitude of current flows through contact system. The speed of electromagnetic repulsion opening is fast as compared to contact opening by release operating mechanism (6) combination. The moving contact (3) and fixed contact (1) responds to electromagnetic repulsion prior to operation of operating mechanism (6). During such movement the slider pin (12) of moving contact (3) slides on the profiled surface (14) of cam and after a certain position, force coming on the moving contact (3) changes the direction with respect to the pivot point (11) of the moving contact (3), resulting in faster opening of the moving contact. This direction of force also prevents the moving contact (3) from coming down and hence results in locking of the moving contact (3) when moving contact (3) rotates fully.
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The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. Spring means as described comprises compression springs. But extension spring, leaf spring and torsion spring can also be used and still the invention can be performed. The improved system thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements which will still be comprised within its true spirit.
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WE CLAIM
1. An improved current limiting circuit breaker system
adapted to detect and discriminate faults improving
circuit breaker performance in power distribution lines,
said system comprising:
housing;
fixed contact means and moving contact assembly wherein said fixed contact means being mounted in said housing in a rigid manner,
said moving contact assembly comprising moving contact and rotatable means in co-operation with a cam means biased with spring means so as to provide predetermined overtravel thereby producing required contact pressure, said cam means being provided with an undulating profile so as to combine actions of repulsion between said fixed and moving contact and moving contact acceleration and tripping thereby providing directional flexibility in the moving contact assembly thereby accelerating motion of moving contact assembly.
2. An improved system as claimed in claim 1, wherein the rotatable means comprises operating shaft in co-operation with spring biased cam means so as to provide predetermined overtravel of the moving contact which is required to avoid hotspots on the fixed contact due to movement of the moving contact
3. An improved system as claimed in claims 1 and 2, wherein the cam means comprises undulating profile with predetermined slope of depression located approximately at the middle along the vertical surface of the cam means.
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4. An improved system as claimed in claims 1 to 3, wherein the cam means further comprises guide means having two modular limbs passing through the spring means so as to move the cam in a linear direction
5. An improved system as claimed in claim 1, wherein spring means comprises of compression springs so as to provide further rotation of the operating shaft in angular direction thereby generating the independent movement of moving contacts providing required contact pressure between fixed and moving contacts.
6. A moving contact assembly comprising:
moving contact and rotatable means in co-operation with a cam means biased with spring means so as to provide predetermined overtravel thereby producing required contact pressure,
said cam means being provided with an undulating profile so as-to combine actions of repulsion between said fixed and moving contact and moving contact acceleration and tripping thereby providing directional flexibility in the moving contact assembly thereby accelerating motion of moving contact assembly.
7. An improved current limiting circuit breaker system
adapted to detect and discriminate faults substantially
as herein described and illustrated with reference to the
accompanying figures.
Dated this the 20th day of June 2006
Abhishek Sen
Of S. MAJUMDAR & CO. (Applicant's Agent)
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ABSTRACT
TITLE : AN IMPROVED CURRENT LIMITING CIRCUIT BREAKER SYSTEM FOR DETECTION AND DISCRIMINATION OF FAULTS
The present invention relates to an improved current limiting circuit breaker system adapted to detect and discriminate faults improving circuit breaker performance in power distribution lines. The system comprises housing (2), fixed contact means (1) and moving contact assembly (3) rotatable means (4) in co-operation with a cam means (10) with an undulating profile and biased with spring means (8) so as to provide predetermined overtravel thereby producing required contact pressure and accelerating motion of moving contact assembly (3).
Figure 2
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