AN IMPROVED ARC CHUTE

Area of Invention:

The invention relates generally to the area of electrical engineering and more particularly embodiments of the invention relates to an arc chute in circuit breakers.

Object of Invention:

It is an object of the invention to provide an improved, dynamic arc chute that advantageously yields a low reluctance and produces the desired anode cathode drop required for arc to traverse through the chute. Further the invention also provides for a system that utilizes the said arc chute to enable an effective circuit breaker.

Prior Art:
Arc chute, as the name says its function is to quench the arc. Arc is a plasma state where the air breaks down and current continues to flow through the circuit. This Arc Chute concept is used wherever circuit
breaking is required.

A circuit breaker is designed to make, carry and break current during normal and abnormal conditions. Arc is formed under all circumstances (except for carrying) though the intensity of it varies in each case. Arc may also be formed during bouncing of contacts. Abnormal conditions that can normally occur during service conditions are overload and short circuit conditions. Short circuit has more adverse effects than overload as the fault current level is very much high and it is usually in the order of 50 kilo amperes or greater than that, whereas the overload current will be in the range of 3 to 6 times the rated current.

As the currents are of very high order, current flows through the circuit though the contact separates initially for some distance as the breakdown voltage is higher than the dielectric strength or breakdown voltage of air. This momentary conduction of current may cause damage to the circuit. So the arc must be quenched as soon as possible to save the system. So we go for arc chutes.
The essential functions of an Arc chute are:

1. To increase the voltage formed between two open contacts which is called as Arc voltage.

2. To absorb the arc as soon as possible from the main contacts button so that life of the button can be increased which in turn increases the life of the breaker.

Arc chute contribute to the arc voltage through anode and cathode drop and through the voltage drop In air between its plates. Arc is basically current which produces flux. These flux lines always chooses a low reluctance flux path to flow. Reluctance in magnetic circuit is analogous to resistance in electhcal circuit. So by reducing the reluctance in arc chute and provide a relatively low reluctance path than between contacts, arc can be attracted towards the arc chute. Air has very high reluctance when compared to mild steel (material of those stacked plates). So if we reduce air in a flux path, much of the reluctance can be reduced.

The intensity of the arc will be very high at the initial stage of opening of contacts when compared to the final stage. Intense arc at the initial stage produces more heat which may melt the contact buttons. So it is very important to remove the arc from the contact buttons as soon as possible.

A typical arc chute comprises of a number of plates stacked in columns, without any conducting path between each plate, for the formation of anode and cathodes.

In this concept, the number of plates and the thickness of each plate is designed employing a formula
Varc = N * Vac + (L- N * t) * Va
Refer fig 1.

Where, Varc = arc voltage in volts; N = no of plates 102; Vac = anode cathode drop (20 - 30 Volts); L = contact opening distance101, here 30 mm; t = thickness of each plate 103; Va = voltage drop in air between plates

When the contact completely opens, the plurality of plates arranged as described above produces arc voltage equal to or little greater than the system voltage.

If the arc chute is fully a solid block then it has low reluctance and can attract the arc quickly but it has a disadvantage of not producing the anode cathode drop. If the plates are stacked as in conventional type, the advantage is that we get anode cathode drop but the disadvantage is reluctance of the arc chute at all times will be constantly high so that pulling of the arc from the contact button is delayed.

Hence there is a need for a device that advantageously utilizes the stacking of plates to yield a low reluctance and produces the desired anode cathode drop required for arc to traverse through the chute. There is also a need for a system that utilizes the said arc chute to provide an effective circuit breaker.

Brief Description of Drawings:

Figure 1 shows the schematic diagram of arrangement of the plates in a typical arc chute generally employed in the circuits known in the prior art.

Figure 2 shows the schematic diagram of arrangement of the plates to provide a dynamic arc chute according to an embodiment of the invention.

Detailed Description of the Invention:

The invention provides an improved dynamic arc chute that advantageously utilizes the stacking of plates to yield a low reluctance and produces the desired anode cathode drop required for arc to traverse through the chute. Further the invention also provides for a system that utilizes the said arc chute to enable an effective circuit breaker.

In an embodiment of the invention, a dynamic arc chute is provided. The . said dynamic arc chute comprises of

a cup provided to hold the plates 201;

a plurality of stoppers 202;
at least two contacts, namely an upper contact 203 and a lower contact 208;

at least two plate holders 204, 207 and means for a mounting a plurality of such holders 205;
at least two fixed plates and

a plurality of plates 206 as shown in Figure2.

Dynamic arc chute's first plate is connected to 'first plate holder', which is projecting outwards for connection with the mechanism. The cup part which is connecting the contacts with the mechanism has two projections, called 'stoppers'. One of which is placed above the projection of the First plate holder and the other one below it. These stoppers are placed in such a way that lower stopper comes in to contact with the first plate holder only after the contact moves up for a distance of 16 mm, which is the solid length of the arc chute.

The first plate is connected with the remaining plates through a paper like thin insulating material, which can expand and contract at high speeds without breaking and can withstand high temperatures like fiber glass cloth.

During opening of contacts, the cup moves up along with the upper contact. Till the point the lower stopper reaches the solid length of arc chute, the plates remain stacked over one another. The plurality of plates are stacked successively such that the stack appears as a solid block when the contact
remains closed. When the contact opens and after it reaches a height equivalent to the solid length of arc chute the arc chute also opens along with contacts. In an example of the invention, the height to which the contact opens is equal to 16mm. At an instant when the contact just opens, the arc chute remains as a solid block until the height of 16 mm is reached. At this instant, the arc will be very intense. As the air gap is low, the reluctance in the arc chute will be low compared to the reluctance between the contacts, so it attracts the arc from the contact button much earlier thereby extending the life of the contact button.

Further, as the plates remain closed till this time the reluctance of arc chute is relatively low against the flux path between contacts. So the arc is pulled from the buttons to arc chute at the earlier stage. After opening the arc extinguishes as the arc voltage developed will be equal to system voltage as designed.

From here on the lower stopper would move the first plate holder to the remaining 14 mm as the total contact opening is 30 mm. When the contact opens fully, the plates as pre designed produce arc voltage when it opens to that distance. So the arc is quenched as in normal conventional types.

During closing of contacts, the cup moves downward which removes the support for the plate holder. So the plates start falling downward due to gravity. In the first plate holder there is a guide way against the casing which regulates its movement. But the contact system moves quickly than the plates falling due to its own weight. So the upper stopper comes into contact with first plate holder and drags it down to its solid length position.

Arc chute remains as a solid block when contacts are in a just open position, so that it attracts the arc from the button much quickly than in conventional type.

Embodiments described herein provides an improved dynamic arc chute which produces the synergistic effect of the advantages of both the types. Such an advantage results from the fact that the arc chute is almost a solid block at the time of opening and as the reluctance increases only after 16 mm opening, the arc is pulled away from the button much quickly. Further, when the contact fully opens, the anode cathode drop along with the voltage drop in air will increase to the system voltage.

The invention described in detail herein and as illustrated by the examples provides an improved dynamic arc chute device for effective circuit breaking in an electrical equipment.

The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Claims:
We Claim,

1. An improved dynamic arc chute comprising of a cup provided to hold the plates; a plurality of stoppers; at least two contact points, namely an upper contact point and a lower contact point; at least two plate holders and means for a mounting a plurality of such holders;

at least two fixed plates; and characterized in that a plurality of plates are provided to reduce the reluctance.

2. An improved dynamic arc chute of Claim 1, wherein the said plurality of plates utilized to provide the said reluctance are stacked successively to appear as a single unit.

3. An improved dynamic arc chute of Claim 1, wherein means are provided for the said stacking of the said plurality of plates to be dynamic.

4. An improved dynamic arc chute of Claim 1, wherein the said stacked plurality of plates appear as one block when the contact of the said arc chute is closed and appear as a distinct set of plates when the
contact of the said arc chute is open.

5. An improved dynamic arc chute of Claim 1, wherein the said stacking of the plurality of plates appearing as a single block during the said close position of the said contact enables reduction of