F O R M 2
THE PATENTS ACT, 1970
(39 of 1970)

&

The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention - TRANSVERSE AXIAL MECHANISM FOR SWITCHING
DEVICE

2. Applicant(s)

(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 THE INVENTION

The present invention relates to a mechanism for switching devices. More particularly, the invention is concerned about a transverse axial mechanism for switching devices to avoid secondary bounce and to achieve higher breaking velocity of contact system.

BACKGROUND OF THE INVENTION

A contactor is composed of two different items such as contact system and magnet system. Contacts are the current carrying part of the contactor. This includes power contacts, auxiliary contacts, and contact springs. The electromagnet provides the driving force to close the contacts.
A basic contactor will have a coil input (which may be driven by either an AC or DC supply depending on the contactor design). When current passes through the electromagnet, a magnetic field is produced, which attracts the moving core of the contactor. The electromagnet coil draws more current initially, until its inductance increases when the metal core enters the coil. The moving contact is propelled by the moving core; the force developed by the electromagnet holds the moving and fixed contacts together. When the contactor coil is de-energized, a spring returns the electromagnet core to its initial position and opens the contacts.

For contactors energized with alternating current, a small part of the core is surrounded with a shading coil, which slightly delays the magnetic flux in the core. The effect is to average out the alternating pull of the magnetic field and so prevent the core from buzzing at twice the line frequency.

Magnetic blowouts use blowout coils to lengthen and move the electric arc. These are especially useful in DC power circuits. AC arcs have periods of low current, during which the arc can be extinguished with relative ease, but DC arcs have continuous high current, so blowing them out requires the arc to be stretched further than an AC arc of the same current.

Contactors are designed to be directly connected to high-current load devices. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, contactors are almost exclusively fitted with normally open contacts. Contactors are designed with features to control and suppress the arc produced when interrupting heavy motor currents.

A basic contactor has a linear arrangement of magnet system & contact system. While contactor is switched on, moving contacts start moving and when they touch fixed contacts, primary bounce appears on them, this bounce appears because contacts meet with certain velocity. This primary bounce occurs at very initial level of current rise. As the system current is lower, effect of this primary bounce can be neglected.

As moving contacts meet fixed contacts, contact spring comes in action while moving magnet covers over-travel region. After complete travel of moving magnet, it goes and hits the fixed magnet with certain momentum, which produces a shock wave which is in turn transferred to contact system since it’s connected with rigid connections on the linear axis of the magnet system. This shock wave creates a further bounce on the contact system. This bounce is called secondary bounce since it appears because of moving magnet hitting the fixed magnet. The effect of this bounce becomes detrimental for contact system as on the instant of bounce the current achieves its peak magnitude.

This secondary bounce affects the contacts surface because of the introduction of arc (since at higher currents if the contacts have micro gaps it leads them to have an arc on surface) which may deteriorate contact’s conduction properties over a period of time. Effect of this can affect the contactor’s performance.

The conventional practice in contactors is to employ a contact system which is assembled to follow the direction of motion of moving magnet system. The contact assembly is connected with moving magnet system along with the contact springs. The contact assembly moves in sync with moving magnet system until moving contacts touch the fixed contacts. The moment contacts touch each other, contact spring starts compressing further but at micro instant of contacts touching each other because of their moving mass (momentum) a bounce comes which is called as primary bounce, this bounce tries to repel contacts back but since moving magnet still has velocity and has not acquired its ultimate position, this bounce is recovered and contacts don’t get back further to this contact spring keeps on compressing to its final compressed condition. At primary bounce the device current is in initial level and hence primary bounce doesn’t affect the contact system.
As the compression of both return spring and contact spring ends for their final values, at this moment moving magnet hits the fixed magnet with certain velocity and since mass of magnet is too high as compared to contact system, a shock comes on magnet system, which in turn is transferred to the contacts system. Under the impact of shock, another bounce comes on to contacts which has a magnitude capable enough to give a separation to the contacts. As the contacts apart the current has already reached to its peak value. The separation between contacts at high current leads to an arc occurrence on contact surface. This erodes the contact surface and reduces its conducting properties. Since contactor is also used for applications where current switching frequencies are very high. In such application secondary bounce plays an important role in reducing contactor’s life exponentially. Hence contactors do not remain of economic use if secondary bounce is present. This phenomenon becomes fairly high in case of higher rated contactors where magnet system mass is very large as compared to contact system mass.

Another concern in contact system is to achieve higher breaking velocity to avoid arc during breaking operation at higher currents. If the return force of contact spring is not enough to provide sufficient velocity to the contact system arcing can happen which reduces contacts life even more as compared to secondary bounce. To avoid such phenomenon to happen contact spring forces can be increased sufficiently to provide a higher breaking velocity but with such configuration of contact system the magnetic coil rating has to improve also since electromagnet act against contact and return springs. This will give a higher energy consumption to electromagnet coil thus leads to economic consideration look up for contactor design and application.

Thus, there is a need to overcome the problems of the prior art. Therefore, present inventors have developed a transverse axial mechanism for contactor which would prevent contact system from secondary bounce and also would improve the breaking velocity of contact system.

OBJECTS OF THE INVENTION

An object of the present invention is to overcome the problems/disadvantages of the prior art.

Another object of the present invention is to provide a transverse axial mechanism for contactor.

These and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a transverse axial mechanism for switching devices, said mechanism comprising:

a contact system comprising plurality of contact means;
a magnet system comprising plurality of magnet means located so as to generate electromagnetic force along a predetermined vertical axis;
a connecting limb means;
wherein said contact system being operatively arranged along a predetermined substantially horizontal axis having perpendicular relationship with said vertical axis along which the electromagnetic force is established; and
wherein said connecting limb means having an appropriate angle adapted to establish a force component of said contact system along said electromagnetic axis; and
wherein said connecting limb means having an appropriate length such that said contact system acquires substantially the same velocity as that of the magnet system.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawings:
Figure 1 illustrates a perspective view of a transverse motion mechanism of electromagnetic switching devices.
Figure 2 illustrates an exploded perspective view of the contactor of figure 1.
Figure 2A illustrates an exploded perspective view of a portion of the contact system of figure 2.
Figure 3 illustrates an initial assembled view of a magnet and contact system.
Figure 4 illustrates a view representing contacts in just meeting condition with zero over travel
Figure 5 illustrates a view representing contacts and magnets in closed condition.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and illustrate the best mode presently contemplated for carrying out the invention. Further functioning of the mechanism has been discussed below to describe the way the mechanism operates. However, such description should not be considered as any limitation of scope of the present unit. 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.

According to the invention there is provided a transverse axial mechanism for switching devices. As shown in figure 1, a transverse motion mechanism of electromagnetic contactor 101 is shown in perspective view. The mechanism includes moving magnet 1, fixed magnet 2, return spring 11, connecting limb 5, return spring 10, moving contact 7, contact carrier 13, fixed contact 6, contact spring 10, side limb-left 3, side limb-right 4, holding pin 12 and contact button 9. This arrangement employs a unique way of placement of contact and magnet system. Both the contact and magnets assemblies are kept orthogonally. This way instead to a direct spring forces (which are fairly high in magnitude as compared to return spring forces) of contact springs against which the electromagnet has to work, only a component of spring force of contact spring (10), appears for electromagnet to counter act.

The present invention determines a particular angle of connecting limb (5) which connects the magnet and contact system. This placement of limb is the key for appearance of a component of force of contact spring which appears on magnet axis, other than return spring (11) electromagnet has to generate a force equivalent to this component of contact spring which is fairly low as compared to absolute vale of contact spring force at its final compression. This way for a given value of contact spring (10) lesser energy consumption coil of electromagnet can be used to achieve same performance.

The primary advantage of having such arrangement of magnet and contact system placement is the prevention of secondary bounce on contact system. The reason behind this is shock because of magnet closing doesn’t transfer on contact assembly as contact system being orthogonally placed the equivalent force component of shock vibration is zero in direction of contact system and contacts remain unaffected irrespective of moving mass of magnet system. This way the life of contacts can be increased significantly.

Figure 2 shows an exploded perspective view of the contactor of figure 1, displaying the moving magnet 1, fixed magnet 2, return spring 11, connecting limb 5, return spring 10, moving contact 7, contact carrier 13, fixed contact 6, contact spring 10, side limb-left 3, side limb-right 4, holding pin 12 and contact button 9.

Figure 2A shows an exploded perspective view of a portion of the contact system of figure 2, which includes fixed contact 6, moving contact 7, contact carrier 13, contact spring 10, holding pin 12, conducting block 8, and contact button 9.

Referring to figure 3, which represents the initial assembled condition of magnet system and contact system. This picture also shows the contact and magnet gap. The state of contactor is de energized and moving magnet 1, and moving contact 7 are in open condition. As electromagnet coil is energized the moving magnet 1, moves downwards in order to complete the magnet flux path until fixed magnet 2, surface. The length of connecting limb is chosen in such a way that contact system acquires the same velocity that of moving magnet 1. As the magnet moves downwards the angle between side limb 3 and 4 and connecting limb 5 reduces so that as the contact spring force starts appearing the component in vertical axis of magnet, starts reducing impacting lesser on magnet attraction force. The connecting limb 5 is substantially “T” shaped which is fixed to the moving magnet 1 in a substantially upright position. However, the connecting limb can also fixed to the moving magnet in an upside down position.

Referring to figure 4, which represents the moving contact 7, touching the fixed contact 6, till this travel of magnet and contact system, contact spring 10, doesn’t contribute towards contact pressure and moving magnet 1 is apart from fixed magnet 2, a distance equivalent to over travel of contacts.

Referring to figure 5, which represents the final positions of moving magnet 1 and moving contact 7, and final compressions of return spring 11, and contact spring 10 are achieved. In this closed condition a component of contact spring force Fx appears on magnet axis which depends on the value of angle pertaining between connecting limb and the contact horizontal axis and F is the absolute value of contact spring 10 at its final compression.
The present invention is concerned to a concept wherein contacts are kept on horizontal axis and magnet system on vertical axis. The arrangement explained in this concept can be interchanged i.e. contacts on vertical axis and magnet system on horizontal axis. With this change in arrangement it gives same advantages as explained above.

ADVANTAGES OF THE INVENTION

1. No Secondary Bounce on Contact System: The having said mechanism avoids contact system undergoing a secondary bounce. This secondary bounce appears because of moving magnet hitting the fixed magnet. The effect of this bounce becomes detrimental for contact system as on the instant of bounce the current achieves its peak magnitude and because of this bounce arc can take place between contacts. Since contact system being orthogonally placed the equivalent force component of shock vibration is zero in direction of contact system and contacts remain unaffected irrespective of moving mass of magnet system.

2. Higher breaking velocity: This is one more advantageous outcome of this concept. A high breaking velocity is required to minimize losses to contacts because of arc. So as in case of higher rated contactors where rating is high but the product size and its elements like copper volume, size of magnets and return/contact spring force value are constraints to provide quick breaking on high currents, all these are constraints against achieving higher breaking velocity. These limitations can be overcome by incorporating this concept. Since only a component of contact spring force appears on magnet axis against which the electromagnet has to counter act the absolute value of contact spring can be increased up to an extent where sufficient breaking velocity of contact system can be achieved without affecting the electromagnet coil consumption.

3. Better product life: The life of contactor mainly depends upon the physical condition of the contacts, the life of which reduces with frequent opening and closing of contacts on higher currents. If breaking is not efficient this may reduce contacts life exponentially. This can be eliminated by providing enhanced and efficient breaking system. This can be achieved by keeping the contact spring force values high, but at the same time closing and hold on conditions of contact system are affected as attraction force of magnet remains same. Using this concept for same magnetic/coil copper volume, spring forces can be increased without affecting the closing and hold on conditions of contact system. This provides better breaking system hence increasing contacts/product life.

4. Cost optimization: With this concept for achieving same performance of contact system, the coil copper volume and the size of magnet can be reduced substantially. This way cost saving can be done in this highly competitive environment.

5. Energy saving: A contactor is an electrically controlled switch used for switching a power circuit, and for switching contactor on the supply is given to the coil of magnet. The contactor has to carry current continuously to keep the power circuit healthy; in this manner continuous power consumption is required in the coil. Using this concept the coil parameters can be reduced and contactor requires lower energy to operate to give same performance level. Because of continuous operation of contactor the amount of energy saved even per hour is huge.

We Claim

1. A transverse axial mechanism for a switching device, said mechanism comprising:

a contact system comprising plurality of contact means;
a magnet system comprising plurality of magnet means located so as to generate electromagnetic force along a predetermined vertical axis;
a connecting limb means;
wherein said contact system being operatively arranged along a predetermined substantially horizontal axis having perpendicular relationship with said vertical axis along which the electromagnetic force is established; and
wherein said connecting limb means having an appropriate angle adapted to establish a force component of said contact system along said electromagnetic axis; and
wherein said connecting limb means having an appropriate length such that said contact system acquires substantially the same velocity as that of the magnet system.

2. Mechanism as claimed in claim 1, wherein said contact system is optionally arranged along a substantially vertical axis.

3. Mechanism as claimed in claim 1, wherein said magnet system is optionally arranged along a substantially horizontal axis.

4. Mechanism as claimed in claim 1, wherein said connecting limb means is substantially ‘T’ shaped.

5. Mechanism as claimed in claim 1 wherein said connecting limb means is operatively fixed to said moving contact in an upright position.

6. Mechanism as claimed in claim 1 wherein said connecting limb means is operatively fixed to said moving contact in an upside down position.

7. Mechanism as claimed in claim 1, wherein said connecting limb means comprising plurality of side limb means.

8. Mechanism as claimed in claim 1, wherein said plurality of side limb means being pivotally connected to said connecting limb means.

9. Mechanism as claimed in claim 1, wherein said plurality of side limb means being substantially symmetrically located on both sides of said connecting limb means.

10. A transverse axial mechanism for a switching device as herein substantially described and illustrated with the accompanying drawings.