GB2067839A

GB2067839A - Arc extinction in circuit breakers

Info

Publication number: GB2067839A
Application number: GB8039895A
Authority: GB
Original assignee: HEINEMANN ELECTRIC SOUTH AFRICA Ltd
Current assignee: HEINEMANN ELECTRIC SOUTH AFRICA Ltd
Priority date: 1979-12-12
Filing date: 1980-12-12
Publication date: 1981-07-30
Also published as: GB2067839B

Abstract

A circuit breaker has a housing 10, 12 with de-ionizing means 16 inside and an aperture 28 is formed in the wall of the housing for venting to atmosphere de-ionized gas from the inside of the housing. The circuit breaker has an external terminal 20 connected to a contact inside the housing, and this terminal is shielded from gas passing through the vent aperture 28 by means of a shield 22 formed on the housing. A further projecting shield 24 may direct the gas away from a similar adjacent circuit breaker, not shown. <IMAGE>

Description

SPECIFICATION Arc extinction in circuit breakers This invention relates to the extinction of arcs in miniature and moulded case circuit breakers. In this specification "circuit breaker" includes a switch, an isolator and other switching mechanisms.

On the switching of a circuit breaker with a heavy fault current arcs are caused which in the interests of safety and reliability of operation must be extinguished. Generally a de-ion grid assembly is used to extinguish the arc and the de-ionised gases are expelled from inside the circuit breaker by the internal rise of pressure which results.

These gases are generally directed through an outlet which is located at the back of the circuit breaker as far as possible from any contacts which are located externally of the circuit breaker. This step is taken to prevent external arcing. An alternative approach is to force the arc products through a swirling vent, usually at the top of the breaker, in an effort to disperse the de-ionized gases.

Problems are however encountered with these approaches in that the hot de-ionized gases which leave the circuit breaker may cause external flash over in the vicinity of live terminals externally of the circuit breaker, the problems being pronounced when there are a number of terminals with different potentials.

It is an object of the present invention to provide a circuit breaker with an alternative arc extinction mechanism.

The invention provides a circuit breaker which comprises a housing, de-ionizing means inside the housing, an aperture being formed in the wall of the housing for venting to atmosphere de-ionized gas inside the housing, a terminal which is connected to a contact inside the housing, the terminal being located externally on the housing adjacent the venting aperture, and means shielding the terminal from gas passing through the aperture.

The shielding means may comprise one or more members, preferably consisting of formations on the housing, which prevent the gas which passes through the aperature from blowing directly onto the terminal.

The venting aperture may be located in the base of a channel-like formation on the housing.

The walls of the channel then form the shielding means.

A first wall may be adjacent the terminal and its upper surface may be substantially flush with an outer surface of the terminal.

The opposing wall may be substantially of the same height as the first wall so that when the circuit breaker is mounted adjacent a similar second circuit breaker the opposing wall is substantially flush with an outer surface of the terminal of the second circuit breaker, thereby shielding it.

The housing may consist of two interengageable shells with the venting aperture being defined by opposing wall portions of the shells.

The terminal and the first wall may be located on one shell and the opposing wall on the other shell.

The invention is further described by way of example with reference to the accompanying drawings in which: Figure 1 is a side view of one shell of a circuit breaker according to the invention, Figure 2 is a view in the direction of the arrow 2 in Figure 1 of an assembled circuit breaker according to the invention, and Figure 3 is a similar view of the circuit breaker of Figure 1 but taken in the direction of the arrow 3.

The drawings illustrate a circuit breaker according to the invention which consists of two shells 10 and 12 which form a housing 14.

Figure 1 iilustrates the shell 10 but the switching mechanism of the circuit breaker has been omitted for the sake of clarity. A de-ion grid assembly 1 6 is mounted inside the shell 10 near its upper end. A contact 1 8 is located at one end of the grid assembly and is connected to a terminal 20 located externally of the housing.

A first wall 22 is formed integrally with the shell 10 adjacent the terminal 20. It extends from the shell so that its upper surface is substantially flush with the upper surface of the terminal 20, see Figures 1 and 3. A second wall 24 is formed on the shell 12 opposing the first wall 22. The two walls are of substantially the same dimensions and, as shown in Figure 3, define a channel-like structure 26 adjacent the terminal 20. A venting aperture 28, see Figure 2, is defined in the base of the channel by opposing each edge portions of the two shells. The vent is adjacent the upper edge of the grid assembly 16.

The circuit breaker is provided with other contacts and a switching mechanism and formations for mounting the circuit breaker on a switchboard but these devices are all conventional and have been omitted as they are not necessary for an understanding of the invention.

The de-ion grid assembly 1 6 is used for cooling and de-ionizing the gasses which are generated by arcs established during switching of heavy fault currents inside the circuit breaker. The assembly is so placed that the arc products are deflected into the vent 28. The vent 28 is arranged on one side of the circuit breaker with the terminal 20 on the other side and the arrangement is such that the wall 22 prevents the arc products from being blown out of the vent directly onto the side or the top of the terminal 20. In addition the wall 24 shields the terminal of a similar circuit breaker which may be mounted adjacent the circuit breaker illustrated. The walls 22 and 24 are formed integrally with the shells and allow for complete shielding of the live terminal 20. This is achieved without any relative increase in the incidence rate of the external flash over. The extension of the arc is also faster due to the fact that the vent 28 opens directly to atmosphere and is not obstructed in any way by the shells 10 and 12 or the terminal 20.

Claims

1. A circuit breaker comprising a housing, deionizing means inside the housing, an aperture in the wall of the housing for venting to atmosphere de-ionizing gas inside the housing, a terminal which is connected to a contact inside the housing, the terminal being located externally on the housing adjacent the venting aperture, and means sheilding the terminal from gas passing through the aperture.

2. A circuit breaker as claimed in Claim 1, wherein the shielding means comprises a wall on the housing which prevents gas passing thrbugh the aperture from blowing directly onto the terminal.

3. A circuit breaker as claimed in Claim 2, wherein the wall is formed integrally with the housing.

4. A circuit breaker as claimed in Claim 2 or Claim 3, wherein the wall is adjacent the terminal, and the upper surface of the wall is substantially flush with an outer surface of the terminal.

5. A circuit breaker as claimed in any preceding claim, wherein the venting aperture is located in the base of a channel-like formation on the housing, so that the walls of the channel form the shielding means.

6. A circuit breaker as claimed in Claim 5, wherein the walls of the channel are substantially the same height so that when the circuit breaker is mounted adjacent a similar second circuit breaker, the wall remote from the terminal on the first circuit breaker is substantially flush with an outer surface of the terminal of the second circuit breaker, thereby shielding the terminal of the second circuit breaker.

7. A circuit breaker as claimed in any preceding claim, wherein the housing consists of two interengageable shells with the venting aperture being defined by opposing wall portions of the shells.

8. A circuit breaker as claimed in Claim 7, wherein the shielding means comprises a pair of walls, and the terminal and the first wall are located on one shell and the other wall on the other shell.

9. A circuit breaker substantially as herein described with reference to and as shown in the accompanying drawings.