FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"High Rupturing Capacity Fuse"
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: LARSEN & TOUBRO LIMITED,
L&T House, Ballard Estate, P. O. Box: 278, Mumbai 400 001, India
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

High Rupturing Capacity Fuse
Field of the invention
The present invention relates to electrical switches and more particularly, to a high rupturing capacity fuse as a semiconductor protection fuse.
Background of the invention
Over current protection devices such as fuses are essential in electrical systems to limit threats to human life and property damage. The fuse is a type of low resistance resistor that acts as a sacrificial device to provide over current protection of either a load or a source circuit. An essential component of the fuse is a metal wire or a strip that melts when too much current flows and interrupts the circuit in which it is connected. Short circuit, overloading, mismatched loads or device failure are the prime reasons for excessive currents. The fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented. Wiring regulations often define a maximum fuse current rating for particular circuits.
The time and current operating characteristics of fuses are used to provide adequate protection without needless interruption. Slow blow fuses are designed to allow harmless short term higher currents but still clear on sustained overload. Fuses are manufactured in a wide range of over current and voltage ratings to protect wiring systems and electrical equipment. Self-resetting fuses automatically restore the circuit after the overload has cleared and hence are useful in aerospace or nuclear applications where fuse replacement is impossible. However, the threshold for bursting strength of the prior art fuse is less and the fuse is damaged due to different degrees of thermal expansion of a solidified sand and a ceramic body. The melting fuses available in the market use the ceramic body having higher alumina content to avoid the problem of

damage to the ceramic body. However, such ceramic materials are relatively expensive.
Accordingly, there is a need to provide a high rupturing capacity fuse that improves bursting strength to effectively counteract the problem of damage caused under abnormal current conditions.
Objects of the invention
An object of the present invention is to counteract the problem of damage caused under abnormal current conditions.
Another object of the present invention is to improve bursting strength of a ceramic body.
Yet another object of the present invention is to improve robustness.
Still another object of the present invention is to produce the ceramic body having lower alumina content that facilitates cost effectiveness and simplicity in use.
Summary of the invention
Accordingly, the present invention provides a high rupturing capacity fuse. The high rupturing capacity fuse comprises at least two end plates, at least one fuse element and an insulating body. Each of the at least two end plates includes a knife type link fixed on an exterior side thereof. The at least one fuse element is attached between the knife type links.
The at least one fuse element is encapsulated in a cylindrical body. The cylindrical body is capable of breaking upon reaching a threshold internal

pressure. The cylindrical body is a glass tube filled with any of an air, a gas mixture, an elastic material and unconsolidated sand. The cylindrical body encapsulating the at least one fuse element is housed in the insulating body.
The insulating body includes a compacted sand filled therein and at least two terminals. The compacted sand surrounds the at least one fuse element in the insulating body. The compacted sand is a quartz that acts as an arc extinguishing agent. The at least two terminals are connected to each other by the fuse element. The insulating body is made up of a ceramic material having lower alumina content.
When the current flowing through the at least one fuse element exceeds a rated current under the abnormal current condition, the at least one fuse element melts increasing an internal pressure of the cylindrical body and generating an arc. The at least one fuse element then evaporates reflecting vapors of evaporation on a surface of the compacted sand that undergoes thermal expansion.
The compacted sand expands further due to release of an additional volume by breaking of the cylindrical body upon reaching the threshold internal pressure. The expanded compacted sand solidifies around the at least one fuse element to cool the arc thereby delaying/ preventing rupturing of the insulating body. The abnormal current condition is selected from any of a short circuit, an overload condition, a mismatched load, a device failure and a combination thereof.
Brief description of the drawings
Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawings:

Figure 1 shows a side view of a high rupturing capacity fuse with at least one fuse element encapsulated in a cylindrical body and housed in an insulating body, in accordance with the present invention;
Figure 2 shows a side view of the high rupturing capacity fuse of figure 1 showing the at least one fuse element without the cylindrical body and the insulating body;
Figure 3 shows a perspective view of the at least one fuse element encapsulated in the cylindrical body, in accordance with the present invention; and
Figure 4 shows a front view of the at least one fuse element of figure 1.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.
The present invention provides a high rupturing capacity fuse. The high rupturing capacity fuse has improved bursting strength and robustness to counteract the problem of damage to an insulating body. Further, the insulating body is made with a ceramic material having lower alumina content that facilitates cost effectiveness and simplicity in use.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures.

Referring to figures 1 to 4, a high rupturing capacity fuse (100) (herein after 'the HRC fuse (100);) in accordance with the present invention is shown. The HRC fuse (100) is a semiconductor protection fuse/ overcurrent protective device. The HRC fuse (100) comprises at least two end plates (10), at least one fuse element (30) and an insulating body (50).
Each of the at least two end plates (10) includes a knife type link (20) fixed on an exterior side thereof. The at least two end plates (10) keep the knife type links (20) as well as a fuse pop out indicator (not shown) intact. The at least two end plates (10) are used to pull out or push in the at least one fuse element (30) between fuse holders (not shown) using a fuse puller (not shown).
The at least one fuse element (30), alternately referred as a fuse link or a fusible conductor is attached between the knife type link (20) on the at least two end plates (10). In an embodiment, the at least one fuse element (30) is spot welded between the knife type link (20) to allow easy insertion and removal of the at least one fuse element (30). The number of the fuse element to be used for the HRC fuse (100) depends on a fuse rating.
The at least one fuse element (30) is encapsulated in a cylindrical body (40) (alternately referred as a bursting body) as shown in figure 3. The cylindrical body is capable of breaking due to an increase in an internal pressure to a threshold under an abnormal current condition such as a short circuit, an overload condition, a mismatched load, a device failure and a combination thereof. The internal pressure is dependent on geometry and wall thickness of the cylindrical body (40). In an embodiment, the cylindrical body (40) is a glass tube. The cylindrical body (40) is filled with any of an air, a gas mixture such as inert gases for example nitrogen and noble gases, an elastic material and unconsolidated sand.

The air, the gas mixture, the elastic material and the unconsolidated sand filled in the cylindrical body (40) improves the melting of the at least one fuse element (30). The air, for example compressed air filled in the cylindrical body (40) creates vacuum to provide an easy-to-implement and cost-effective way to improve the melting of the at least one fuse element (30) thereby aiding in faster arc quenching. The filling of the cylindrical body (40) with the unconsolidated sand provides an additional volume by impairing and limiting crushing of the cylindrical body (40) to a low value without affecting the accuracy of tripping of the HRC fuse (100).
The cylindrical body (40) encapsulating the at least one fuse element (30) is housed in the insulating body (50). The insulating body (50) is filled with a compacted sand (not shown) and includes at least two terminals. The at least two end plates (10) act as a wall to retain the compacted sand and the cylindrical body (40) within the insulating body (50). Specifically, the insulating body (50) is made up of a ceramic material having lower alumina content and good insulating properties.
The compacted sand surrounds the at least one fuse element (30) in the insulating body (50) and cools the arc generated upon melting of the at least one fuse element (30). Specifically, the compacted sand is a quartz/ silica sand grains that act as an arc extinguishing agent. However, it is understood that any other material can be used for extinguishing the arc. The at least two terminals are connected to each other by the at least one fuse element (30). The at least two terminals provide an electrical supply to heat the at least one fuse element (30).
When the current flowing through the at least one fuse element (30) exceeds a rated current under the abnormal current condition, the at least one fuse element (30) first melts to produce an electrically conductive plasma that increases the internal pressure of the cylindrical body (40) thereby generating the arc. The

heat developed due to the arc causes the at least one fuse element (30) to evaporate. When vapors of the at least one fuse element (30) are reflected on a surface of the compacted sand, the compacted sand in the insulating body (50) expands.
The cylindrical body (40) upon reaching the threshold internal pressure breaks to provide the additional volume required for further thermal expansion of the compacted sand in the insulating body (50). The expanded compacted sand solidifies around the at least one fuse element (30) to cool the arc thereby delaying/ preventing rupturing of the insulating body (50). In the sequence, the resistance increases in the interior of the HRC fuse (100) in such a way that the arc is extinguished finally.
Advantages of the invention
1. The insulating body (50) uses ceramic materials with low quality characteristics that are cheaper in price, cheaper to produce and easier to use.
2. The insulating body (50) uses ceramic materials having low alumina content for improved bursting strength and robustness of the at least one fuse element (30) and for reduced manufacturing cost of the HRC fuse (100).
3. The at least one fuse element (30) has higher strength and higher thermal expansion coefficient to counteract the problem of damage to the insulating body (50).
4. The HRC fuse (100) is capable of being used for high voltage applications.

5. The insulating body (50) and the compacted sand generally have different thermal expansion coefficient. The cylindrical body (40) provides the additional volume and increases the internal pressure and tension in the insulating body (50) that together with the temperature elevation due to the melting of the at least one fuse element (30) expands and solidifies the compacted sand more significantly.
6. The at least one fuse element (30) encapsulated in the cylindrical body (40) limits the heat generated in the insulating body (50) to a tolerable value. In this way, damage to the insulating body (50) due to stress cracks caused by the different degrees of thermal expansion of the solidified sand is avoided.
7. The additional volume causes the heated sand to expand further thereby delaying exertion of the pressure on the insulating body (50) and resulting in an increase threshold for the insulating body (50).
8. The at least one fuse element (30) welded on the knife type link (20) is easy to insert and remove as compared to that of bolted ones.
9. Prior art insulating body is made up of higher alumina content to achieve higher breaking/ bursting strength which is very expensive. Hence, the insulating body (50) with lower alumina content is used to achieve the same performance and same bursting strength in standard applications, and for difficult operating conditions, the insulating body (50) with lower alumina content is solidified by introducing the at least one fuse element (30) in the cylindrical body (40). The cylindrical body (40) burst to provide an additional volume for the compacted sand to expand further, thus having a cost effective solution without affecting performance.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not

intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.

We claim:
1. A high rupturing capacity fuse (100) comprising:
• at least two end plates (10), each of the at least two end plates (10) having a knife type link (20) fixed on an exterior side thereof;
• at least one fuse element (30) attached between the knife type links (10), the at least one fuse element (30) being encapsulated in a cylindrical body (40), the cylindrical body (40) being capable of breaking upon reaching a threshold internal pressure; and
• an insulating body (50) housing the cylindrical body (40) encapsulating the at least one fuse element (30), the insulating body (50) having a compacted sand filled therein for surrounding the at least one fuse element (30) and at least two terminals connected to each other by the at least one fuse element (30) to provide an electrical supply to heat the at least one fuse element (30), characterized in that the insulating body (50) being made up of a ceramic material having lower alumina content,
wherein, when the current flowing through the at least one fuse element (30) exceeds a rated current under the abnormal current condition, the at least one fuse element (30) melts increasing an internal pressure of the cylindrical body (40) and generating an arc and then evaporates reflecting vapors of evaporation on a surface of the compacted sand that undergoes thermal expansion and further expansion due to release of an additional volume by breaking of the cylindrical body (40) upon reaching the threshold internal pressure such that the expanded compacted sand solidifies around the at least one fuse element (30) to cool the arc thereby delaying/ preventing rupturing of the insulating body (50).
2. The high rupturing capacity fuse (100) as claimed in claim 1, wherein
the cylindrical body (40) is a glass tube.

3. The high rupturing capacity fuse (100) as claimed inclaiml, wherein the cylindrical body (40) is filled with any of an air, a gas mixture and an elastic material.
4. The high rupturing capacity fuse (100) as claimed in claiml, wherein the compacted sand is a quartz that acts as an arc extinguishing agent.
5. The high rupturing capacity fuse (100) as claimed in claiml, wherein the abnormal current condition is selected from any of a short circuit, an overload condition, a mismatched load, a device failure and a combination thereof.