GB2172434A

GB2172434A - Circuit breakers

Info

Publication number: GB2172434A
Application number: GB08603117A
Authority: GB
Inventors: John Ceriog Evans; Herbert Robert Williams; Philip John Stott
Original assignee: General Electric Company PLC
Current assignee: General Electric Company PLC
Priority date: 1985-03-13
Filing date: 1986-02-07
Publication date: 1986-09-17
Also published as: GB8506498D0; GB8603117D0

Abstract

A circuit breaker for use on a D.C. system includes means 3, 4 for producing a pair of spaced unidirectional magnetic fields across the arc gap formed between the contacts 1, 2 when they separate. The magnetic fields are differently orientated so as to divert the arc in different transverse directions thereby increasing the arc length, leading to a more rapid arc extinction. <IMAGE>

Description

SPECIFICATION Circuit breakers This invention relates to circuit breakers of the kind having a pair of separable contacts disposed in a gaseous medium, for example air, and more especially to such circuit breakers designed for use on D.C. systems operating at up to 1200 Volts and with current ratings of up to 5000 Amps.

When the contacts of a circuit breaker separate under load conditions arc is formed between them, and it is desirable for the arc to be extinguished as rapidly as possible. It is known that in D.C. systems an arc tends to be more difficult to extinguish (particularly at low currents) than in A.C. systems of equivalent power ratings, and an object of the present invention is to provide a form of circuit breaker for use in a D.C. system which gives a particularly efficient arc suppression.

According, therefore, to the invention a circuit breaker for use on a D.C. system includes means for producing a pair of unidirectional magnetic fields across the arc gap which is formed between the contacts when they separate, and at spaced positions along the arc gap, the lines of force of the two fields being differently orientated so as to divert the arc in different transverse directions.

The effect of the magnetic fields, which are preferably provided by permanent magnets, is to produce a substantially wave-shaped arc, thereby considerably increasing the arc length, which results in a more rapid arc extinction.

This is particularly important at low currents when the current may have insufficient "self magnetic field" to drive it into the arc chutes. The strength of the magnets are chosen so as to complement the "self magnetic field" of the arc. For example at large currents, the "self magnetic field" is relatively strong and will cancel the effect of the field from the magnetics whilst still achieving arc extinction.

The permanent magnets may take any convenient form, and each magnetic field may be provided by two permanent magnets having an appropriate polarity disposition located on opposite sides of the arc gap.

Splitter plates are conveniently provided adjacent the arc gap into which part of the arc is driven by one or other of the magnets, this having the further effect of splitting the arc into a number of smaller arcs and thereby generating an additional anode/cathode voltage drop, as well as cooling the arc, and thus assists in the quenching of the arc.

One circuit breaker in accordance with the invention for use on a D.C. system will now be described by way of exmaple with reference to Figures 1 and 2 of the accompanying schematic drawing, in which Figure 1 represents a sectional side view of the circuit breaker in diagrammatic form, and Figure 2 represents a plan view of the circuit breaker also shown diagrammatically.

The circuit breaker comprises a pair of contacts 1, 2, the contact 1 being fixed in position and the contact 2 being movable from the position shown, in which it engages the fixed contact, to a further position, as indicated by the chain line 2', in which it is spaced from the fixed contact. On separation of the contacts under load conditions an arc will be drawn between them.

In accordance with the invention permanent magnets 3,4 are disposed so as to produce oppositely orientated magnetic fields across the arc gap formed between the separated contacts, near opposite ends of the arc gap. The effect of the magnetic fields is to cause an arc formed on separation of the contacts to be diverted in opposite directions, and accordingly with the current flowing in the direction indicated by the arrow A it will take up a waveform shape as indicated at 5 in Figure 1.

This substantially increases the arc length, leading to a rapid extinguishing of the arc. The arc extinguishing effect is enhanced by the provision, as at 6, of mutually insulated splitter plates into which part of the arc is forced by one of the magnetic fields, the splitter plates serving to cool the arc as well as generating an additional anode/cathode voltage drop.

It will be observed that if the flow of current between the contacts were to be in the opposite direction, the directions in which the arc is diverted will be reversed, the opposite end of the arc then being forced into the splitter plate assembly 6, so that the arc extinguishing effect acts equally well with either direction of current flow.

It will also be appreciated that the permanent magnets could in some cases be replaced by electromagnets arranged to provide unidirectional but oppositely directed magnetic fields.

The means for effecting the separation of the contacts can be of any convenient known form and have not been illustrated for simplicity. Furthermore the circuit breaker may be provided with main contacts which are arranged to carry the greater part of the current when the breaker is closed, together with arcing contacts to which current is momentarily transferred when the circuit breaker opens, and which separate at high speed following separation of the main contacts, the magnetic fields in such a case being associated with the arcing contacts.

For some applications more than two magnetic fields may be utilised to provide a further extension of the arc, by causing it to take up a multi-wave shape.

1. A circuit breaker for use on a D.C. system including means for producing a pair of unidirectional magnetic fields across the arc gap which is formed between the contacts when they separate, and at spaced positions along the arc gap, the lines of force of the two fields being differently orientated so as to divert the arc in different transverse directions.

2. A circuit breaker according to Claim 1 wherein the effect of the magnetic fields is to produce a substantially wave shaped arc.

3. A circuit breaker according to Claim 2 wherein the magnetic fields are produced by permanent magnets.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Circuit breakers This invention relates to circuit breakers of the kind having a pair of separable contacts disposed in a gaseous medium, for example air, and more especially to such circuit breakers designed for use on D.C. systems operating at up to 1200 Volts and with current ratings of up to 5000 Amps. When the contacts of a circuit breaker separate under load conditions arc is formed between them, and it is desirable for the arc to be extinguished as rapidly as possible. It is known that in D.C. systems an arc tends to be more difficult to extinguish (particularly at low currents) than in A.C. systems of equivalent power ratings, and an object of the present invention is to provide a form of circuit breaker for use in a D.C. system which gives a particularly efficient arc suppression. According, therefore, to the invention a circuit breaker for use on a D.C. system includes means for producing a pair of unidirectional magnetic fields across the arc gap which is formed between the contacts when they separate, and at spaced positions along the arc gap, the lines of force of the two fields being differently orientated so as to divert the arc in different transverse directions. The effect of the magnetic fields, which are preferably provided by permanent magnets, is to produce a substantially wave-shaped arc, thereby considerably increasing the arc length, which results in a more rapid arc extinction. This is particularly important at low currents when the current may have insufficient "self magnetic field" to drive it into the arc chutes. The strength of the magnets are chosen so as to complement the "self magnetic field" of the arc. For example at large currents, the "self magnetic field" is relatively strong and will cancel the effect of the field from the magnetics whilst still achieving arc extinction. The permanent magnets may take any convenient form, and each magnetic field may be provided by two permanent magnets having an appropriate polarity disposition located on opposite sides of the arc gap. Splitter plates are conveniently provided adjacent the arc gap into which part of the arc is driven by one or other of the magnets, this having the further effect of splitting the arc into a number of smaller arcs and thereby generating an additional anode/cathode voltage drop, as well as cooling the arc, and thus assists in the quenching of the arc. One circuit breaker in accordance with the invention for use on a D.C. system will now be described by way of exmaple with reference to Figures 1 and 2 of the accompanying schematic drawing, in which Figure 1 represents a sectional side view of the circuit breaker in diagrammatic form, and Figure 2 represents a plan view of the circuit breaker also shown diagrammatically. The circuit breaker comprises a pair of contacts 1, 2, the contact 1 being fixed in position and the contact 2 being movable from the position shown, in which it engages the fixed contact, to a further position, as indicated by the chain line 2', in which it is spaced from the fixed contact. On separation of the contacts under load conditions an arc will be drawn between them. In accordance with the invention permanent magnets 3,4 are disposed so as to produce oppositely orientated magnetic fields across the arc gap formed between the separated contacts, near opposite ends of the arc gap. The effect of the magnetic fields is to cause an arc formed on separation of the contacts to be diverted in opposite directions, and accordingly with the current flowing in the direction indicated by the arrow A it will take up a waveform shape as indicated at 5 in Figure 1. This substantially increases the arc length, leading to a rapid extinguishing of the arc. The arc extinguishing effect is enhanced by the provision, as at 6, of mutually insulated splitter plates into which part of the arc is forced by one of the magnetic fields, the splitter plates serving to cool the arc as well as generating an additional anode/cathode voltage drop. It will be observed that if the flow of current between the contacts were to be in the opposite direction, the directions in which the arc is diverted will be reversed, the opposite end of the arc then being forced into the splitter plate assembly 6, so that the arc extinguishing effect acts equally well with either direction of current flow. It will also be appreciated that the permanent magnets could in some cases be replaced by electromagnets arranged to provide unidirectional but oppositely directed magnetic fields. The means for effecting the separation of the contacts can be of any convenient known form and have not been illustrated for simplicity. Furthermore the circuit breaker may be provided with main contacts which are arranged to carry the greater part of the current when the breaker is closed, together with arcing contacts to which current is momentarily transferred when the circuit breaker opens, and which separate at high speed following separation of the main contacts, the magnetic fields in such a case being associated with the arcing contacts. For some applications more than two magnetic fields may be utilised to provide a further extension of the arc, by causing it to take up a multi-wave shape. CLAIMS

4. A circuit breaker according to Claim 3 wherein each magnetic field is provided by two permanent magnets having an appropriate polarity disposition located on opposite sides of the arc gap.

5. A circuit breaker according to Claim 3 or 4 wherein splitter plates are provided adjacent the arc gap into which part of the arc is driven by one or other of the said magnets.

6. A circuit breaker substantially as herein described with reference to Figures 1 and 2 of the accompanying drawing.