ELECTRICAL CIRCUIT BREAKER

Abstract: An electrical circuit breaker (10) comprises an enclosure (12) filled with an insulating fluid. Within the enclosure (12) is a pair of opposing contacts (14 and 16) one of which is fixed and the other moves axially relative thereto. When the contacts (14 and 16) are separated an arc is drawn between them. The arc is rotated by a magnetic field generated by coil (18). A shield (20) prevents the arc short circuiting the coil (18) but also traps ionised gas particles and metallic vapours. To prevent the ionised gas and vapours building up a flow of purging gas is directed through channels (26 and 28) to region A. The purging flow of gas flushes out this region to prevent re-establishment of the arc.

Description: ELECTRICAL CIRCUIT BREAKER The present invention relates to an electrical circuit breaker and in particular to one in which an arc is rotated to assist in extinguishing the arc. Electrical circuit breakers are known which have a pair of opposing contacts located in an enclosure filled with an insulating fluid, for example sulphur hexafloride (SFg) gas. The contacts are capable of relative movement between a closed circuit position in which they engage with one another to pass a current therebetween and an open circuit position in which the contacts are separated. When the contacts are moved apart arcing of the current between the contacts occurs before the current is interrupted. The arc can seriously damage the contacts reducing the life of the electrical circuit breaker. To assist in the extinguishment of the arc and so prevent the contacts being damaged the arc is rotated. The arc is rotated by a Lorentz force produced when the current flowing through the arc cuts a magnetic field generated by a coil adjacent the contacts. The arc is rotated to remove it from areas were the gas has been ionised. If the arc is rotated faster than the gas can be ionised the arc will be extinguished. A problem with electrical circuit breakers in which the arc is rotated is that degradation of the gas in the region between the contacts where the arc is generated occurs and the arc may also short circuit the coil. The present invention seeks to provide an improved electrical circuit breaker in which the aforementioned problems are eliminated. According to the present invention an electrical circuit breaker comprises an enclosure filled with an insulating fluid, at least one pair of opposing contacts housed m the enclosure which are capable of being separated to draw an arc, the insulating fluid being purged from the area where the arc is drawn to assist in the extinguishment of the arc. In the preferred embodiment of the present invention a coil is located adjacent the contacts which generates a magnetic field to rotate the arc drawn between the contacts. Preferably the contacts are separated by relative axial movement. Relative axial movement between the contacts may be provided by at least one actuator. The actuator may have a piston mounted thereon which acts to compress a purging fluid, means being provided to direct the compressed purging fluid to the region where the arc is drawn. The purging fluid may be directed to the region where the arc is drawn via a passageway through at least one of the contacts or via at least one conduit. Preferably the purging fluid is sulphur hexafloride. A shield may be provided adjacent the coil which prevents the arc short circuiting the coil. The present invention will now be described with reference to and as shown in figure 1. Figure 1 is a cross-sectional view of an electrical circuit breaker m accordance with the present invention in an open circuit position. Referring to figure 1 an electrical circuit breaker, generally indicated at 10, comprises an enclosure 12 filled with an insulating fluid. In the preferred embodiment of the present invention the insulating fluid is sulphur hexafloride, SFg gas, under pressure. Located m the enclosure 12 are a pair of opposing electrical contacts 14 & 16. The contacts 14 & 16 extend through the enclosure 12 and are capable of relative movement between a closed circuit position and an open circuit position. The contact 14 is fixed and the contact 16 moves axially relative thereto. In the closed circuit position the tip of contact 16 is inside the fixed contact 14 to pass a current therebetween. In the open circuit position shown in figure 1 the contact 16 is withdrawn from the contact 14 by an actuator 22. The actuator 22 has a piston 24 mounted thereon and extends through a compression cylinder 25. A coil 18 is provided adjacent the fixed contact 14 and a shield 20 is fitted adjacent the coil 18. In operation when the electrical circuit breaker 10 is closed the main contacts 14 and 16 engage to carry one phase of the current supply. When the current is to be interrupted the actuator 22 moves the contact 16 axially relative to the fixed contact 14. The contacts 14 and 16 are separated and an arc is drawn between them. As the tip of the contact 16 passes through electrode 17 the arc transfers to between the contact 16 and the electrode 17. The electrical current path is then through the electrode 17 into the coil 18 and to the connection point 19. As the current passes through the coil a magnetic field is generated. The magnetic field is cut by the current flowing through the arc and a Lorentz force is produced which rotates the arc. The arc is rotated to remove it from areas where the insulating gas, SFg, has been ionised. If the arc is rotated faster than the gas can be ionised the arc will extinguish. The shield 20 provides an enclosure for the arc such that the arc is trapped and cannot short circuit the coil 18. The shield 20 also traps iomsed gas and metal vapours in region A. To prevent a build up of heat, metallic vapours and ionised gas, which cause electrical breakdown and prevent the arc from being extinguished, a purging flow of gas is supplied to region A. The purging flow of SFg gas is compressed in the cylinder 25 by the piston 24 mounted on the actuator 22 of the contact 16. As the contact 16 moves axially the piston 24 compresses the SFg gas. The pressure is relieved as the gas passes through a passageway 26 in the moving contact 16 and conduits 28 to region A. The purging flow of gas flushes out region A effectively dissipating the iomsed gases and metallic vapours which cause electrical breakdown. The purging flow of gas therefore assists in extinguishing the arc. The arc is extinguished by the combination of being rotated by the Lorentz force and the removal of heat, metallic vapours and ionised gas from region A. At low arc currents there is insufficient energy to rotate the arc at high speed. The arc may re-establish itself as it passes through the same ionised gas path. The purging flow of gas through the passageway 26 and the conduits 28 ensures that at these low arc currents the metallic vapours and ionised gases are dissipated to prevent re-establishment of the arc. An electrical circuit breaker in accordance with the present invention has particular efficacy at high voltages in the region above 72KV. However it will be appreciated by one skilled in the art that the use of a purging flow of fluid can be used in any electrical circuit breaker where removal of iomsed gas or contaminants is required from the region where an arc is drawn. It will further be appreciated by one skilled in the art that the purging flow of fluid may be any insulating medium and may be provided- from a separate supply controlled independently from the movement of the contacts.

Claims: Claims: 1. An electrical circuit breaker comprising an enclosure filled with an insulating fluid, at least one pair of opposing contacts housed in the enclosure which are capable of being separated to draw an arc, the insulating fluid being purged from the area where the arc is drawn to assist in the extinguishment of the arc. 2. An electrical circuit breaker as claimed in claim 1 in which a coil is located adjacent the contacts which generates a magnetic field to rotate the arc drawn between the contacts. 3. An electrical circuit breaker as claimed in claim 1 or claim 2 in which the contacts are separated by relative axial movement. 4. An electrical circuit breaker as claimed in claim 3 in which axial movement of the contact is provided by an actuator. 5. An electrical circuit breaker as claimed in claim 4 in which the actuator has a piston mounted thereon whereby in operation axial movement of the actuator causes the piston to compress a purging fluid, means being provided to direct the compressed purging fluid to the region between the contacts where the arc is drawn. 6. An electrical circuit breaker as claimed in claim 5 in which the means for directing the compressed purging fluid to the region between the contacts is a passageway extending through at least one of the contacts. 7. An electrical circuit breaker as claimed in claim 5 in which the means for directing the compressed purging fluid to the region between the contacts is at least one conduit. 8. An electrical circuit breaker as claimed in any preceding claim in which a shield is provided adjacent the coil to prevent the coil being short circuited by the arc current. 9. An electrical circuit breaker as claimed in any preceding claims in which the purging fluid is sulphur hexafloride gas. 10. An electrical circuit breaker as hereinbefore described with reference to and as shown in the accompanying drawing.

Inventors: HALL WILLIAM BEWICK, HALL, WILLIAM, BEWICK
Applicants: ELIN SERVICE B V, HALL WILLIAM BEWICK, ELIN SERVICE B.V., HALL, WILLIAM, BEWICK
Application year: 1998
Main classification: H01H33
IPC codes: H01H33, H01T1