GB2171255A

GB2171255A - Circuit breakers

Info

Publication number: GB2171255A
Application number: GB08525238A
Authority: GB
Inventors: John Ceiriog Evans; Herbert Robert Williams; Philip John Stott
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1985-02-15
Filing date: 1985-10-14
Publication date: 1986-08-20
Also published as: GB8525238D0; GB8503969D0

Abstract

In a d.c. circuit breaker having a splitter plate arc chute 5, the splitter plates 8 and other parts of the circuit breaker adjacent the contacts are formed of non-magnetic material, and means, other than a magnetic field, is used to drive the arc into the arc chute. This avoids the presence of a residual magnetic field which could drive a low current arc away from the arc chute in cases when the circuit is required to interrupt a current flow in the reverse direction. <IMAGE>

Description

SPECIFICATION Circuit breakers This invention relates to circuit breakers for use on D.C. systems, more especially, though not exclusively, for systems operating at up to 1200 Volts, and with current ratings of up to 5000 Amps.

When the contacts of such circuit breakers separate under load or overload conditions an arc tends to form between the contacts, and it is desirable for the arc to be extinguished as rapidly as possible.

It is known to provide an arc chute comprising an assembly of mutually insulated splitter plates adjacent the arc gap formed between the contacts as they separate, and to make use of electromagnetic forces generated by the arc current to drive the arc into the splitter plate assembly which, by virtue of the cooling effect of the plates and the increase in the anodel cathode voltage drop, together with the stretching of the arc, results in a rapid arc extinction. To achieve this the plates are commonly formed of a ferromagnetic material, so that on the formation of an arc between the contacts a strong magnetic field is produced within the arc chute splitter plate system, drawing the arc into the plates.

Under high current conditions such as may be experienced due to a short circuit fault this arrangement is highly effective, but is less efficient when breaking low currents.

If, however, the circuit breaker is now required to break a reverse current which is of insufficient magnitude to generate a magnetic field that will overcome the residual magnetic field within the arc chute, the forces acting on the arc, instead of forcing it into the arc chute region, can divert it in the opposite direction into the contacts and mechanism system, resulting in a failure of the circuit breaker to interrupt.

An object of the invention is to provide a circuit breaker in which this disadvantage is avoided.

According to the invention in a circuit breaker for use on a D.C. electrical supply system, having a splitter plate arc chute, the splitter plates and other parts of the circuit breaker adjacent the contacts are formed of non-magnetic material, and means, other than a magnetic field, is used to drive the arc into the arc chute.

The avoidance of the use of magnetic materials for the splitter plates and other parts of the breaker which could be magnetised by the passage of current, and thereby establish a residual magnetism which could drive the arc away from the splitter plates, ensures that the arrangement is effective to provide rapid arc extinction under both high and low current conditions, in both directions of current flow.

In general, the circuit breaker will incorporate, in known manner, main contacts and arcing contacts, the latter remaining initially closed after opening of the main contacts and then separating at relatively high speed, the arc being formed between the arcing contacts, thereby reducing the risk of damage to the main contacts by arc erosion, and in such a circuit breaker the arcing contacts conveniently carry diverging arcing runners extending towards and terminating closely adjacent the splitter plates.

In some cases also an air blast or other nonmagnetic means may be employed to divert or assist in diverting the arc into the arc chute.

One circuit breaker in accordance with the invention will now be described by way of example with reference to the accompanying schematic drawing.

The circuit breaker, which is shown in the closed condition, comprises two main contacts 1, 2 and two arcing contacts 3, 4. The contacts 2, 4 are movable away from the contacts 1, 3 activated by a solenoid-operated mechanism of any suitable construction shown only in part at 10 and are designed to function in air. The arcing contact 4 is pivotally mounted on the main contact 2 and is spring-loaded towards the other arcing contact 3 so that as the main contacts separate the arcing contacts 3, 4 are initially held in engagement, further movement of the actuating mechanism then causing the arcing contacts themselves to be separate at relatively high speed.

Springs as at 9 also bias the main contact 1 towards the contact 2 so as to ensure that these contacts are held firmly in engagement in the closed condition of the circuit breaker.

Above the arcing contacts 3, 4 there is located a splitter plate arc chute 5 and the arcing contacts are provided with arcing runners 6, 7 which extend divergingly upwards and terminate just below the lower edges of the splitter plates 8.

In accordance with the invention the splitter plates 8 of the arc chute 5 are formed of non-magnetic material, for example austenitic steel, and all parts of the circuit breaker adjacent the contacts and arc chute (that is to say in positions such that if formed of magnetic material they could retain residual magnetism which could divert a low current arc away from the arc chute) are similarly formed of non-magnetic material. By this means the pres pence of any residual magnetic field in the region of the arc gap is avoided.

Consequently, on the opening of the contacts 3, 4, the shape of the arcing runners 6, 7 and their close proximity to the splitter plates 8, causes the arc to be driven up into the arc chute, resulting in a rapid arc extinction due to the lengthening of the arc, together with the cooling effect of the splitter plates at all current levels and in both directions of current flow.

The spaces between the splitter plates 8 are open at the top in known manner, to allow the hot gases produced as a result of the arc to escape.

With a breaker used for voltages of up to 300 Volts D.C, and having a contact gap of about one and five-eighths inches, 28 splitter plates of austenitic steel having a thickness of approximately 0.125 inches, a spacing between them of approximately 0.125 inches, and a depth of about three inches has been found suitable.

A plurality of circuit breaker modules, each with a pair of separable contacts associated with splitter plates and other adjacent parts of non-magnetic material, may be arranged in series with each other to form a complete circuit breaker arrangement for use with higher voltage systems the pairs of contacts being arranged to be operated simultaneously; for example two modules can be used for voltages up to 600 Volts D.C. and so on. Such an arrangement has the advantage that the total arc energy is shared across the contact systems, and as a consequence of this the erosion of the contacts during short circuit interruption is much reduced compared with a single break operation which would be absorbing the total arc energy.

Furthermore the depth of the splitter plates in a multi-break arrangement can be made much less than those of a single-break arrangement designed to interrupt an equivalent current, as in the latter the arc will need to be driven further into the splitter plate assembly in order to dissipate the energy within the arc.

This has the advantage that a number of individual circuit breaker modules, together forming a single-multi-break arrangement, can be mounted side-by-side in a switch panel, so taking up less height than a single-break arrangement; consequently arrangements constituting two or three circuit breakers can be mounted one above the other, thus reducing the amount of space taken up by the switchgear.

Claims

1. A circuit breaker for use on a D.C. electrical supply system and having a splitter plate arc chute, wherein the splitter plates and other parts of the circuit breaker adjacent the contacts are formed of non-magnetic material, and means, other than a magnetic field, is used to drive the arc into the arc chute.

2. A circuit breaker according to Claim 1 in which the circuit breaker incorporates main contacts and arcing contacts, and in which the arcing contacts remain initially closed after opening of the main contacts and then separate at high speed, so that the arc is formed between the arcing contacts, wherein the arcing contacts carry diverging arcing runners extending towards and termianting closely adjacent the splitter plates.

3. A circuit arrangement according to Claim 1 or 2 including air blast means for diverting or assisting in diverting the arc into the arc chute.

4. A circuit breaker according to Claim 1, 2 or 3 wherein the splitter plates are formed of austenitic steel.

5. A circuit breaker according to any preceding Claim wherein the depth of the splitter plates does not exceed three inches.

6. A circuit breaker substantially as shown in and as hereinbefore described with reference to the accompanying drawing.

7. A circuit breaker assembly comprising a plurality of circuit breakers according to any preceding Claim connected in series with each other, the contacts of the circuit breakers being arranged to be operated simultaneously.