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:
THERMAL MAGNETIC RELEASE ASSEMBLED AS A SINGLE POLE MODULE FOR TRIPPING A CIRCUIT BREAKER

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:

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a thermal magnetic release assembly and more particularly, the invention relates to a thermal-magnetic release assembly used for tripping a circuit breaker.

BACKGROUND AND THE PRIOR ART

A circuit breaker is a mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those of short circuit (Short circuit is an accidental or intentional connection, by a relatively low resistance or impedance, of two or more points in a circuit which are normally at different voltages). The main function of any electrical switching apparatus is to carry the rated current. Therefore the current carrying capacity of any circuit breaker is so important that if the unit fails to carry the rated current it will cause damage to itself as well as to the electrical equipment to which is being protected.

Circuit breakers have three positions corresponding to the status of the separable contacts. For example, these positions would include an ON position, in which the separable contacts are closed, an OFF position in which the contacts are open and Trip position in which the contacts are tripped open with mechanism in de-energized condition. These circuit breakers / switching devices are usually installed in an enclosure so as to have all the control and distribution network laid in form of metallic sheets and or cable wires inside and all operating means from outside so as to prevent access to high voltage and thus a potential hazard. When a circuit breaker is in ON condition and a short circuit fault condition arises, high amount of fault current flows through the circuit and in response to this the circuit breaker tries to move the separable contacts to open position after sensing the fault condition through short circuit sensing mechanism (such as magnetic arrangement). The time taken from a fault condition initiation and the fault current being interrupted by circuit breaker determines the let through energy / arc energy passed by the circuit breaker to the downstream equipments. A circuit breaker is said to be more efficient when the let through energy is minimal.

Let through energy of circuit breaker depends on many parameters, one among them being the time required to sense the fault and send signals to the mechanism for separating / opening of the contacts from closed condition. The overload and short circuit sensing mechanism (generally called as Thermal-Magnetic Release Assembly) of circuit breaker involves mechanical elements in between and thus takes a definite time for sensing and giving a trip open signal to the mechanism which in turn separates contacts. The time taken by the mechanism of circuit breaker to separate the contact decides the let through energy. More the number of components more will be the time and hence more will be the let through energy.

Therefore there is a need for a system having least number of components so that the let through energy is less. Also there is a need to sense the fault and send signals to the mechanism for separating/opening of the contact in less time. The present invention provides a Thermal-Magnetic release assembly which is assembled as a single pole module used for tripping a circuit breaker during abnormal electrical conditions. The tripping operation is done by pushing a trip bar which is a part of mechanism of circuit breaker by the module’s thermal magnetic actuation system.

US 6646529 provides for an electromagnetic release drive particularly suitable for a residual current circuit breaker which includes a plunger loaded by a spring in a release direction, a permanent magnet configuration, a coil and a yoke. The electromagnetic release prevents sticking to the greatest possible extent, so that a release can be used readily even in a residual current circuit breaker for unlatching a switching mechanism.

US 6437670 provides for a magnetic release system wherein the release lever is preloaded during the withstand current level. Thus when the short circuit current level has been reached and the magnetic release system trips the circuit breaker, the release lever moves in a quick snapping action. In the prior art, the magnetic release operates independently of an operating mechanism to latch and un-latch first contact structure and second contact structure. However, in the prior art document it is not found that the magnetic release gives signal to main operating mechanism to de-latch the mechanism thereby separating the contact system.

US 4316163 provides a toggle and heart circuit breaker having a practical and economical over-current release device including thermal and sensitive magnetic release means. The bimetal carries a pivoted latch lever, and is surrounded by a core and armature unit adjacent its secured end, for operating the latch lever in response to high over-currents.

US 3936780 provides for a means for detecting overcharges by means of bimetallic strips and short circuiting by means of mobile magnetic plates effecting independently from each other the controlling of the switching off of a circuit breaker for the protection of a circuit. The thermal safety means operate through a mechanical power amplifier comprising a cage with uprights, a rotating catch dependent on the thermal phase detectors and a plunger transmitting the power of a spring to effect the switching off.

However, the mechanism as described in the above prior art documents are found to be complex in construction using large number of components assembling and dismantling of which also takes long time and involvement of a skilled personnel. Such mechanism are not at all cost effect and user friendly.

Presently in the circuit breakers, thermal-magnetic release is assembled in cassette type construction. The main drawback of this type of construction is the time and cost required to assemble the system due to a large number of components. The thermal-magnetic systems may be assembled without cassette type construction. The time required to assemble these systems are lesser compared to cassette type construction.

OBJECTS OF THE INVENTION

A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.

Another object of the present invention is to provide a thermal magnetic release assembled as a single pole module.

Another object of the present invention is to use least number of components so as to reduce the inter-dependency between components and hence faster response.

Another object of the present invention is to provide a thermal magnetic release assembly which can be assembled in isolation from rest of components of circuit breaker including mechanism.

Another object of the present invention is to save assembly time and ease production.

Another object of the present invention is to reduce the let through time.

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

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

There is provided a thermal-magnetic release assembly used for tripping a circuit breaker.

According to one embodiment of the present invention, there is provided least number of components so as to reduce the inter-dependency between components and hence faster response.

Other embodiment of the present invention provides for a thermal magnetic release assembly which can be assembled in isolation from rest of components of circuit breaker including mechanism.

Other embodiment of the present invention provides for saving assembly time and ease production.

Yet other embodiment of the present invention provides for reducing the let through time.

Additionally the present invention requires least energy to operate the thermal magnetic protection system and therefore provides for very high efficiency. The arrangement improves the life span of the circuit breaker.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the appended drawings:
Fig 1 illustrates the top and front view in with hidden lines and without hidden lines.
Fig 2 illustrates the front view in wireframe.
Fig 3 illustrates one isometric view with hidden lines and without hidden lines.
Fig 4 illustrates another isometric view with hidden lines and without hidden lines.
Fig 5 illustrates the exploded view with numbers.
Fig 6 illustrates the moving magnet.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.

Reference is first invited to Fig 1 wherein top and front view of the circuit breaker with the thermal magnetic protection system having least number of components is shown.

Fig 2 shows the front view of the assembly and the arrangement of different components.

Fig 3 and 4 shows different isometric views of the system.

Fig 5 shows each component of the system separately. It shows current carrying conductor, pin, spring, bimetal, screw attached to bimetal, non magnetic bracket for holding moving magnet, moving magnet, fixed magnet, plastic housing and rivet each separately.

Fig 6 shows the moving magnet and grooves to adjust tension on spring. The tension in the spring can be increased by just placing the end on the grooves provided on the moving magnet itself.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly the present system is designed with least number of components. As the number of components increases, the inter-dependency between these components increases and hence mechanical losses increases to rotate the trip bar system. To achieve faster response to the unhealthy electrical conditions it is necessary to remove all the inter-dependency which causes delay in signal transmission by using only components required for functioning of the thermal-magnetic system of the circuit breaker. This has also helped in reducing assembly time and ease of production.
This invention is an improvement to existing single pole modular thermal magnetic type trip units used with MCCB. It doesn’t involve any part of the MCCB’s mechanism. The other types of single pole modular thermal magnetic trip unit however may involve some part of the MCCB’s mechanism.
Some features of the present invention are listed below
a. Assembled for a single pole
b. Can be separately assembled without MCCB
c. Assembles with MCCB as a module
d. Saves assembly time of MCCB
e. Includes only thermal and magnetic actuation system of MCCB
f. Doesn’t involve any of the MCCB’s mechanism parts.
g. Can be separately calibrated and tested before assembly with MCCB
h. Can be replaced with another module easily
i. Simple arrangement of parts.
j. Components can be reduced further by removing plastic casing and incorporating the similar features of plastic casing in housing of circuit breaker.
The present invention relates to assembly of thermal-magnetic protection system with least number of components without compromising the quality of intended function while minimizing the delay between the generation of signals and response of mechanism, Least the energy required to operate the thermal-magnetic protection system, maximum is the efficiency of the system and maximum is the life span of the circuit-breaker.
There are various parameters which determine the performance of the circuit breaker mechanism. One of them is trip force required to trip the mechanism of circuit breaker. It is important to have optimum trip force at trip plate where the tripping signals are received to avoid any kind of delay between the generation of signals and response of mechanism.
In present circuit breakers, as shown in Figure 1 to 6, components of thermal-magnetic system are arranged to achieve the intended function.
Please refer Figure 6 for exploded view of thermal-magnetic protection system. Parts number and name for components shown in Figure 5.
1. Moving Magnet
2. Plastic housing (module)
3. Tension spring
4. Bimetal
5. Fixed magnet
6. Calibration screw of bimetal
7. Current carrying component
8. Fixing screw for fixing fixed magnet to current carrying component through plastic casing
9. Calibration screw of moving magnet

The thermal overload protection is achieved through a bimetal and screw arrangement attached to a current carrying conductor (called as heater) through electrically conductive joint. This bimetal bends during overload condition due to heat produced by the current carrying conductor and pushes the trip bar of mechanism and trips the circuit breaker.
The short circuit protection or magnetic actuation system consists of fixed magnet attached to the same current carrying conductor through screws or rivets and a moving magnet arrangement which gets attracted towards the fixed magnet whenever any short circuit condition occurs. The moving magnet is placed in the slot provided on plastic case.

The attraction force on the moving magnet arrangement is produced by electromagnetic effect due to current flowing in the current carrying conductor. The exact current threshold is set by the opposing force of tension spring attached to the moving magnet and fixed magnet. The movement of the moving magnet pushes the trip bar in the MCCB’s mechanism thereby tripping the MCCB. The tension in the spring can be increased by just placing the end on the grooves provided on the moving magnet itself. (Please refer Figure 6)
The total assembly of the thermal and magnetic actuation system is assembled as a separate single pole module with the help of housing. This can be assembled in isolation from rest of components of circuit breaker including mechanism which conventional designs lack. The modules can be separately calibrated and tested before assembling in circuit breaker. This will reduce the testing time and damage to contacts of circuit breaker caused during the tests and also reduces overall assembly time of circuit breaker.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.
Advantages
The present invention has following constructional and functional advantages:
1. Simple profile with Least number of components
2. Can be separately assembled without MCCB.
3. During rework at factory, defective module can be replaced with another module easily.
4. Assembles with MCCB as a module.
5. Saves assembly time of MCCB
6. Doesn’t involve any of the MCCB’s mechanism parts.
7. Can be separately calibrated and tested before assembly with MCCB
8. Can be replaced with another module easily
9. Simple arrangement of parts.
10. Components can be reduced further by removing plastic casing and incorporating the similar features of plastic casing in housing of circuit breaker.

WE CLAIM

1. A thermal-magnetic release assembly for use in circuit breakers comprising a thermal overload protection mechanism having a bimetal and screw arrangement attached to a current carrying conductor through electrically conductive joint and a magnetic actuation mechanism having fixed magnet attached to the same current carrying conductor through screws or rivets.
2. System as claimed in claim 1 wherein the bimetal bends during overload condition due to heat produced by the current carrying conductor and pushes the trip bar of mechanism thus tripping the circuit breaker.
3. System as claimed in claim 1 wherein the magnetic actuation mechanism further comprises a moving magnet arrangement which gets attracted towards fixed magnet during short circuit.
4. System as claimed in claim 1 wherein the moving magnet is placed in the slot provided on plastic case.
5. Magnetic actuation mechanism as claimed in claim 1 further comprising a trip bar for tripping operation on pushing.
6. System as claimed in claim 2 wherein the exact current threshold is set by the opposing force of tension spring attached to the moving magnet and fixed magnet.
7. System as claimed in claim 3 wherein the movement of the moving magnet pushes the trip bar in the moulded case circuit breaker’s mechanism thereby tripping it.
8. System as claimed in claim 6 wherein the tension in the spring can be increased by just placing the end on the grooves provided on the moving magnet.
9. A thermal-magnetic release assembled as a single pole module as herein substantially described and illustrated with reference to the accompanying drawings.