FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
Title of the invention - DECOUPLING OF EARLY BREAK ARCING
CONTACT BLOCK FOR CAPACITOR SWITCHING
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 a system for decoupling of early break arcing contact block in a capacitor switching contactor. More particularly, the invention relates to a decoupling/isolating system for early break arcing contact block in a capacitor switching contactor for sharp disengagement of releasable coupling after a sufficient over travel of main contact thereby improving the operating characteristics of the contactor reducing the over travel of the arcing contact while it is serving the purpose of dampening the inrush current and hence quenching the arc during closing operation.
BACKGROUND AND PRIOR ART
In a conventional capacitor switching contactor, the early make contacts closes first and then after suitable over travel of the arcing contact, the main contact closes with the desired over travel. The arcing contact bridge while switching in, inserts resistors connected in series with it. The resistor remains in the circuit even when the contactor is fully closed and carries the parallel path current, though in a very low level continuously throughout the closing operation. While breaking, the main contact breaks before the arcing contact and hence the entire arc voltage of the main contact appears across the resistors, which is permanently connected to the circuit which is very unhealthy to the resistor circuits. Presence of resistor in the circuit after dampening the inrush current is not desired. Figure 1 shows an arrangement in a capacitor switching
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contactor where the resistors are bypassed after the contactor is fully sealed.
In most of the existing technologies the third generation of Capacitor switching contactor follow the ancient method of early make contact with the heater wire resistor (in stretched or loop form) connected in series with it and hence suffers from the above said problem.
Reducing the grid resistor value used for dampening the sub -transient level inrush current up to a steady state is a known method. It has been practiced in the speed control of slip ring induction motor, whereby the inrush current is reduced by means of inserting resistors that reduce the heat loss of the winding during starting of the motor.
A patent US5323132 discloses a switch device using a main switch coupled to a monostable auxiliary switch through a releasable coupling. The releasable coupling consists of permanent magnet retained in one bridge, which is adhered to a magnetisable component of the other part of the bridge. Releasable coupling with magnetisable parts have the problem of inconsistent force, which varies with every operation of the contactor. Due to variation in the mating surface, the engagement and disengagement in the coupling is not reliable. Also, due to limitation in the space and volume, the permanent magnet has limited volume and thus is restricted by poor lifting force, which is unable to withstand the load of the opposing spring energy. Additionally for every operation, the airgap created during de - latching operation, restricts the usage of rare-earth type of permanent magnet with higher (BH) max. Inconsistent disengagement of the releasable coupling leads to
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breaking of arcing contact much earlier than the main contact closure thus reducing the life of contactor drastically.
To achieve a reliable and enhanced electrical life of both the resistor and contactor, an attempt is made to deploy the innovation of "Early Break Arcing Contact block" in a Capacitor switching contactor. By mean of this increases the electrical life of the contactor and resistor by double fold. Also there is substantial reduction in humming in the contactor and it would be possible to develop a contactor with noise free operation.
Thus there is a need to provide for a decoupling/isolating system for early break arcing contact block in capacitor switching.
The present inventors have found that the above problems of burning and insulation failure of the resistors of the contactors can be eliminated and sharp disengagement of the releasable coupling after a sufficient over travel of the main contact thereby improving the operating characteristics of the contactor reducing the chances of breaking of arcing contact before main contact closure can be achieved by an appropriate and desirable combination/integration in the contactors maintaining a desired contact gaps.
OBJECTS OF INVENTION
Accordingly, one object of the present invention is to provide a decoupling/isolating system for early break arcing contact block in capacitor switching contactors.
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Another object of the present invention is to provide sharp disengagement of the re leasable coupling after a suf f icie'nt over travel of the main contact.
Another object of the present invention is to provide reduction in inrush current at appropriate stage of operation.
Yet another object of the present invention is to provide bypassing of the resistor during breaking operation.
Yet another object of the present invention is to provide enhancement in the electric life of the capacitor.
Yet another object of the present invention is to provide a contactor with enhanced KVAR rating.
The other object of the present invention is to eliminate the humming sound in the contactor.
SUMMARY OF INVENTION
According to one aspect of the present invention there is provided a decoupling/isolating system for early break arcing contact block in capacitor switching contactors, said system comprising:
housing;
said housing including plural cover assemblies comprising side,
rear and front covers wherein
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side cover assembly comprises decoupling means so as to de-latch the front cover assembly from rear cover assembly for coil replacement;
said front cover assembly comprising arc interruption means, fixed contact assembly means for the main, a mobile assembly means carrying the bridge assembly means for the main contactor and moving magnet assembly means;
wherein said arc interruption means being placed in slotted rib provided in each pole of said front cover of the contactor;
wherein said bridge assembly means along with the mobile assembly means being secured and guided in the front cover of the contactor in a manner to travel along and across width of the contactor;
wherein said bridge assembly means comprises plurality of bridge means, said bridge means being bridge-I and bridge-II, wherein said bridge means being mechanically coupled with one another and made to rest in a predetermined position by a co-operating
means;
said co-operating means intermediately linking bridge means and a top block located on the bridge means in a manner that top block along with bridge-II is operatively interlocked with main bridge assembly of basic contactor comprising main contact and arcing contact having resistor means connected to it in a manner to be isolated from the circuit
for reducing the over travel of the arcing contact thereby dampening the inrush current hence quenching the arc.
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DETAILED DESCRIPTION OF INVENTION
The present invention avoids the arcing voltage to appear across the resistor during the breaking operation and eliminate the root cause for resistor burning. The present contactor provides an early breaking of the arcing contact while the main contact is still in closed condition so that the arc is not by passed through the resistor. This method improves the life of the resistor unit and hence that of capacitor switching contactor.
The contactor in the present invention comprises of two bridges:
1. De-Latch bridge that carries the arcing contact assembly and
2. Latch bridge that carries the electrical interlocking contact assembly
The two bridges are mechanically locked with respect to each other by means of a click-fit mechanism. The bridge assembly is held in its initial position by means of a torsion spring, which is fixed in between the bridge assembly and the housing of the top block. However, this spring does not restrict the scope of the invention and any other spring like compression spring, extension spring and the like can be used. The latch bridge, along with the top block assembly is mechanically interlocked with the main bridge assembly of the contactor. The desired contact gap of arcing contacts in the top block and that of the main contacts in the contactor is maintained through the return springs.
The operation of the contactor consists of three sequences:
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The first sequence represents the "OFF" condition of the contactor, at which the latch and de-latch bridge are positively locked with respect to each other and the whole bridge assembly is ready for a positive movement , along with the contactor closure.
In the second sequence, the early make arcing contact closes initially with certain over travel but the main contact and the magnet are not closed. Both the bridges {Latch and De-latch) have a positive locking between each other and the resistor connected in series with the arcing contact is inserted in the circuit for dampening of the inrush current.
In the third sequence, the main contact closes with an over travel. Before the magnet seals completely, the de-latch bridge carrying the early make and break arcing contact gets de-latched from the main bridge assembly and the resistor is isolated from the circuit permanently until the next closing operation. Thus, during breaking operation, the arc is quenched by the main contact and is not bypassed through the resistor.
Provision of the early break contact reduces the spring energy and hence the loading upon the prime mover (magnet system). This reduces the humming in the contactor.
The X component force ((Fx1 - Fi) x + (Fx - F2) x is responsible for compressing the two arm of the torsion spring along the inward direction for de-latching of bridge.
Where
Fi and F2 are the tensor due to the weight of the moving mass
"W" for arm -1
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and arm -2
Fs is the initial force of the spring
W is the weight of the moving.mass
6 is the angle between Fl and F2
p is the angle between Fs and Fl
Fext is the force exerted by the prime mover upon the arcing
contact block
Fx = Fx1 = (Fext + W) x COS (9/2)
Fy = Fy1 = (Fext ,+ W) x SIN (9/2)
(Fx1 - Fx )x = (Fx1 - Fi ) COS p
(Fx1 - Fi )Y = (Fx1 - Fi ) SIN j3
(Fx - F2 )x = (Fx - F2 ) COS P
(Fx - F2 )Y - (Fx - F2 ) SIN p
Force exerted on the spring
= (Fx1 - Fi )x + (Fx - F2 )x = (Fx1 - Fi ) COS p + (Fx - F2 )
COS p
Assuming (because of symmetrical arm length)
Fi = F2 = F11 . and Fx1 = Fx = Fx11,
The Force exerted by the prime mover on the spring to compress
it and to displace the two arm for de - latch operation of the
arcing contact block from the main bridge.
= 2 x (Fx11 - F11)' COS (3 = 2 x [{(Fext + W) x COS (9/2)} - {Fi} ] COS p
The present system can be applied for a capacitor switching contactor rated between 60 to 75 KVAR.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1 illustrates the circuit diagram of capacitor switching contactor.
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Figure 2 illustrates the isometric view of the decoupled arcing contact block in the OFF condition.
Figure 3 illustrates the isometric view of the> decoupled arcing contact block in the operational seguence-II condition.
Figure 4 illustrates the isometric view of the decoupled arcing contact- block in the operational sequence-Ill condition.
Figure 5 illustrates the force-stroke characteristics of said contactor
Fig - 6 illustrates the complete sectional view of the capacitor■ switching contactor with the innovative arrangement for "decoupling of. early break arcing contact block.
Figure 7 illustrates, a statistical representation of ■ the improvement in the electrical life of the resistor as well as the contactor.
Figure 8 illustrates a statistical ■ representation of the improvement in the KVAR rating.
Figure - 9a illustrates the free body diagram of the latched bridge along with a torsion spring resting along the arm of the latch bridge.
Figure - 9b- illustrates the arrangement of torsion spring in the latched bridge
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Figure - 10 illustrates the sectional view of the coupling between the latch and de-latched bridge
DETAILED DESCRIPTION OF ACCOMPANYING FIGURES
Figure - 1 illustrates a schematic diagram for a capacitor
switching contactor with a provision of early make and early
break arcing contacts with respect to the closure of main
contacts.
Figures - 2, 3 and 4 illustrate the coupling and decoupling of the latched and de-latched bridge during the closing operation of the capacitor switching contactor.
Figure 5 illustrates various sequences of operation of the system at different travel of the capacitor switching contactor. The shaded area marked as "A" indicates reduction in spring energy due to de-latching of the arcing contact from the main bridge assembly. The areas marked as "B" and "C" indicate the spring energy during the early make and main contact closing to de-latching of the bridge respectively.
Figure - 6 illustrates the assembly view of the device that essentially comprises of a top cover (13) with a click fit transparent lens for "ON" and "OFF" indication of the contactor, adjacent side cover (12) with a spring loaded button to de-latch the front housing assembly from the rear housing (2) assembly for coil replacement, , front housing (1) along with arc interruption components, a fixed contact assembly , for the main{7j , a mobile assembly carrying the bridge assembly for the main contactor (5) and moving magnet of a standard E - E type
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electromagnet assembly. The standard magnet assembly consists of a moving magnet (4), fixed magnet (3), and wounded coil (11), and return spring for the main. An add-on block carrying the resistor unit (14) via the early make and break arcing contact (21) for dampening the inrush current is attached with the main bridge of the contactor.
The front housing (1) consists of fixed contact assembly (7), at both the incoming and outgoing terminal and is supported between the insulated adjacent walls and screw fitment with respect to the base of the housing. Suitable arc interrupting device is placed in the slotted rib provided in each pole of the insulated front housing - of the contactor. The arrangement is done at both the incoming and outgoing terminal. The bridge (6) along with the mobile assembly is secured and guided in the front housing of the contactor along and across the width of the contactor.
Moving contact assembly (8) is placed inside the slotted window provided in the bridge (6) beneath the contact spring to provide the desired pressure. Bottom part of the mobile assembly consists of a moving magnet assembly (4), which is guided into the bridge assembly through a bridge strap (means of leaf spring). The whole of the mobile assembly (5, 4) along with the return spring (28), which is enclosing the middle limb and lying between the moving magnet and coil former, is suitably placed inside the coil.
The completed assembly as described above is placed inside the rear housing (2) . The insulated arc shield is placed upon the front housing through the blind hole provided in the front housing and arc shield through a self-tapping screw. As shown in the above figure, the circular insulated rib in the top cover
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(13) provides accessibility of the indicating and measuring probe to the incoming and outgoing terminals of the contactor. The cover is secured to the front housing (1) in a polarized manner by means of a click fit mechanism. Suitable insulated ribs, is provided in the side cover (12) for securing the bare conductor, to avoid undue flashover across the poles.
The add-on block consists of insulated top cover (16}, housing (17) for carrying, the fixed contact (22} and guiding the bridge assembly (18), which essentially consists of latch bridge (19), carrying the interlocking moving contact and de- latch bridge (20), which carries the arcing contact (21) with the desired contact pressure and a return spring (29) for opposing and positioning the de- latch bridge to its rest point after it gets de - latched from the latched bridge. The upward free movement of the de - Latch Bridge is restricted by means of a rubber bush (30) in between the top cover (16) and de - Latch Bridge. (20}
Figure-9b illustrates the latch bridge that consists of a torsion spring, which is rest on the adjacent arm of the bridge and the hook of the spring is fixed to the pinion point of the two adjacent arms. The angular deflection of the torsion spring, in the outward direction, ensures a correct click fit between the respective bridges. While closing, the force exerted by the prime mover upon the latch bridge via the main bridge of the contactor, gets transmitted to the respective arms of the de -Latch Bridge.
Figure-9a illustrates the free body diagram of the distribution of force in the event of closing operation of the contactor. The adjacent vector diagram, illustrates the vector distribution of the forces and there component along the 2 - dimensional
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direction. The X component force ( (Fxl - Fl) x + (Fx - F2) x is responsible for compressing the two arm of the torsion spring along the inward direction for de-latching of bridge.
Advantages :
1. Avoids Resistor heating, burning and flashover across the pole of the contactor.
2. Improves the Electrical life of the resistor as well as contactor suitable for capacitor switching duty(Refer Fig-1 for expected Electrical Life)
3. Reliability of the contactor increases.
' 4. Enhanced KVAR rating (Refer Fig -8 for projected KVAR rating)
5. Reduces spring energy load upon the prime mover of the contactor.
6. Reduces the humming and makes the contactor a noise free.
7. Improves the operating characteristics of the contactor.
8. Provides positive isolation for the arcing contact during "ON" condition of the contactor.
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
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details cited above. The spring as described above does not limit the scope of the present invention. The structure 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. h decoupling/isolating system for early break arcing contact block in capacitor switching contactors, said system comprising:
housing;
said housing including plural cover assemblies comprising side, rear and front covers wherein
side cover assembly comprises- decoupling means so as to de-latch the front cover assembly from rear cover assembly for coil replacement;
said front cover assembly comprising arc interruption means, fixed contact, assembly means for the main, a mobile assembly means carrying the bridge assembly means for the main contactor and moving magnet assembly means;
wherein said arc interruption means being placed in slotted rib provided in each pole of said front cover of the contactor;
wherein said bridge assembly means along with the mobile assembly means being secured and guided in the front cover of the contactor in a manner to travel along and across width of the contactor;
wherein said bridge assembly means comprises plurality of bridge means, said bridge means being bridge-I and bridge-II, wherein said bridge means being mechanically coupled
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with one another and made to rest in a predetermined position by a co-operating means;
said co-operating means intermediately linking bridge means and a top block located on the' bridge means in a manner that top block along with bridge-II is operatively interlocked with main bridge assembly of basic contactor comprising main contact and arcing contact having resistor means connected to it in a manner to be isolated from the circuit
for reducing the over travel of the arcing contact thereby dampening the inrush current hence quenching the arc.
2. System as claimed in claim 1, wherein the co-operating means selectively compromises return spring, compression spring, extension spring and the like.
3. System as claimed in claim 1, wherein the bridge means comprises de-latching bridge such that its upward free movement is restricted by means of bush means located between top cover and the de-latch bridge means.
4. System as claimed in claim 3, wherein the de-latch bridge means further comprises:
i) arcing contact co-operatively connected to a spring means;
ii) said spring means comprising return spring wherein the spring means co-operates with the contact such that desired contact pressure is generated thereby
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isolating resistors from the circuit permanently until next closing operation.
5. System as claimed in claim 1, wherein the bridge means further comprises a latching bridge.
6. System as claimed in claim 5, wherein the latching bridge comprises torsion spring such that angular deflection of the spring is adapted for correct click fit between the respective bridges.
7. System as claimed in claim 6, wherein the torsion spring comprising two arms adapted to receive compression force in accordance with
( (Fx1 - Fi) x + (Fx - F2) x
Where
Fi and F2 are the tensor due to the weight of the moving
mass "W" for arm -1
and arm -2
W is the weight of the moving mass
9 is the angle between FI and F2
(3 is the angle between Fs and FI
Fx = Fx1 = (Fext + W) x COS (9/2)
(Fx1 - Fi )x - (Fx1 - Fi ) COS [3
(Fx - F2 )x = (Fx - F2 ) COS P
8. System as claimed in claim 1, wherein the decoupling means
comprises spring loaded button.
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9. System as claimed in any preceding claims used for a capacitor switching contactor whose rating ranges from 60 to 75 KVAR.
10. A decoupling/isolating system for early break arcing contact block in capacitor switching contactors as herein substantially described and illustrated with reference to the accompanying figures.
^Iflfc^fc
tishek Sen Of S. Majumdar & Co Applicant's Agent
Dated this the 28th day of March 2007
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ABSTRACT
TITLE : DECOUPLING OF EARLY BREAK ARCING CONTACT BLOCK FOR CAPACITOR SWITCHING
The present invention relates to a decoupling/isolating system for early break arcing contact block in capacitor switching contactors. The system comprises housing (1) which includes plural cover assemblies comprising side, rear and front covers (2, 12) . The side cover assembly (12) comprises decoupling means so as to de-latch the front cover assembly from rear cover assembly for coil replacement. Front cover assembly comprises arc interruption means, fixed contact assembly means for the main, a mobile assembly means carrying the bridge assembly means for the main contactor and moving magnet assembly means. Arc interruption means are placed in slotted rib provided in each pole of front cover of the contactor. The bridge assembly means (6) along with the mobile assembly means (8) are secured and guided in the front cover. The bridge assembly means comprises mechanically coupled bridge-I and bridge-II and rest in a predetermined position by a co-operating means. A top block (13) located on the bridge means (6) in a manner that top block (13) along with bridge-II is operatively interlocked with main bridge assembly of basic contactor comprising main contact and arcing contact having resistor means connected to it in a manner to be isolated from the circuit for reducing the over travel of the arcing contact thereby dampening the inrush current hence quenching the arc.
Figure 6