GB2052869A - Electrical circuit breaker - Google Patents

Abstract

In order to increase the life and operational reliability of high-capacity circuit breakers, a current is commutated on breaking, to a resistive conductor line 16 connected in parallel to a fixed contact A and a mobile contact B. Due to the magnetic field which then arises, a blow-out effect is produced which expands the arc 30 and drives it under acceleration to arc splitters 14 in an arcing chamber 13. To increase the dynamic repulsion forces between further contacts A', B', an electrically conducting lever 16b is pivoted about a point of rotation 24, and is electrically connected at 17, 18 to the end of a straight-line portion 16d of the conductor line 16 at one end and to a contact bridge 2'' at the other end. The lever 16b and portion 16d are traversed by the same current i, and as a result the lever 16b strikes an abutment 24 on the contact bridge 2'', whereby contact separation between contacts A' and B' is accelerated. An arc runner 9' transfers the arc 30 to an arc horn 19 connected to the contact A. <IMAGE>

Description

SPECIFICATION Electrical circuit breaker The present invention relates to an electrical circuit breaker, in particular a direct current high-capacity circuit breaker comprising a break chamber formed from at least two moulded plastics walls, in which a mobile contact bridge is disposed together with at least two fixed contacts disposed at a determined distance apart, wherein the contact surfaces of the fixed contacts and the mobile contact bridge are fitted at least approximately symmetrical to the direction of movement of the contact bridge, and wherein the points of contact between the two fixed contacts and the contact bridge are connected in series when in the closed state.

Very high-speed circuit breaking devices must be used in order to protect electrical power supply systems, generators, transformers etc. from overloads or short circuits. As mostly high breaking capacities are involved here, the circuit breaker construction must satisfy high requirements.

Double break contacts for high-speed circuit breakers are known (see DOS 27 23 624), in which a bridge contact is moved by means of an operating rod, and corresponding points of contact are thus opened or closed at choice.

These arrangements comprise a relatively low magnetic blow-out field, whereby the switching arc remains for a relatively long time in the contact region, and corresponding contact pitting is caused. Moreover, in the case of high short-circuit currents, the low dynamic repulsion forces between fixed and mobile contacts are a disadvantage, leading on the one hand to slow contact separation, and on the other hand to additional increase in the time for which the switching arc remains in the contact region.

The object of the invention is therefore to obviate the aforesaid drawbacks, and to provide an electrical circuit breaker in which the arc is quenched rapidly by simple technical means, so increasing the contact breaker life.

According to the present invention, there is provided an electrical circuit breaker, comprising a break chamber in which a mobile contact bridge is disposed together with at least two fixed contacts disposed at a determined distance apart, wherein the contact surfaces of the fixed contacts and the mobile contact bridge are fitted approximately symmetrical to the direction of movement of the contact bridge, and wherein the points of contact between the fixed contacts and the contact bridge are connected in series when in the closed state, and wherein one of the points of contact is bridged by a parallel connected conductor path which extends outside the break chamber and which has a resistance greater than the contact resistance at said point of contact.

A contact breaker constructed in this manner produces a strengthening of the magnetic blow-out field immediately after contact separation due to the parallel connected low resistance current path (conductor line).

With respect to known methods, the method according to the invention requires little or no expense in terms of additional conductors, and gives rise to no additional identifiable resistive losses at rated current operation due to voltage drop across the contact breaker. The aforesaid effects already occur just after the first contact separation.

The current then commutates completely into the secondary path formed by the conductor, as a result of the arc voltage.

Advantageously, the contact bridge may be loop shaped, with a portion projecting between the fixed contacts in the direction of the bridged point of contact This results in a rapid displacement of the switching arc in the direction of the arcing chamber, and facilitates the jumping-over of the arc root into the arcing chamber.

The conductor path may be in the form of a magnetic blow-out loop, allowing a desirable accelerated expansion of the arc by designing the magnetic blow-out loop to almost any desired shape.

An embodiment in which the conductor path is in the form of a single or multi-layer blow-out coil leads to an increased magnetic field, and thus strengthens the blow-out effect.

If two blow-out coils are used, connected in parallel and lying opposite each other laterally to the contact zone, the blow-out magnetic field is concentrated uniformly in the arcing chamber.

A further embodiment described below has the advantage of delaying contact opening on one side only, whereby the magnetic blow-out field builds up completely in the conductor line before the second point of contact is opened.

A breaker in which one bridge contact is in the form of a spring can be constructed particularly economically.

Connecting the bridge non-symmetrically and hingedly to a switching arrangement produces delayed contact opening on one side only, and requires only a very simple form of contact bridge.

An advantageous embodiment uses the electrodynamic force occurring in the conductor line in the form of a mechanical impulse for the initial acceleration of the contact bridge to be opened.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a direct current high-speed circuit breaker, in the open state, comprising a conductor line in the form of a blow-out loop disposed outside the break chamber, Figure 2 is a part section through the direct current high-speed circuit breaker of Fig. 1, in its closed state, Figure 3 shows a modification of a direct current high-speed circuit breaker with a contact bridge, in which part of a contact strip projects in a direction between the contacts bridged by the parallel connected conductor line.

Figure 4 is a plan view of the direct current high-speed circuit breaker of Fig. 3 without the arcing stack, and Figure 5 is a modification of a direct current high-speed circuit breaker comprising an electrically conducting lever in the conductor line in order to accelerate the opening of a point of contact.

Fig. 1 shows two fixed contact blocks 1 disposed symmetrically to a mobile contact bridge 2. The contact blocks 1 each comprise on their facing sides a trapezoidal projection 3 with contact surfaces 4. The contact bridge 2 is provided on that side facing the trapezoidal projections 3 with inclined contact surfaces 5, which match the contact surfaces 4 of the projection 3. The contact bridge 2 is connected to a known switching arrangement S-E, not shown, by means of a switching rod 6. Copper contact strips 7, 7' are fixed by screws 8 to the fixed contact blocks 1 at the level of the contact bridge 2. The contact strips 7, 7' have the same shape as the projections 3, and are disposed at a small uniform distance apart therefrom. Contact strips 9, 9' are fixed by screws 8 to the respective sides of the contact bridge 2 which face the contact blocks 1.The contact strips 9, 9' extend for a further distance upwards parallel to and at a short distance from the contact surfaces 5 of the contact bridge 2.

The contact strips 7, 7' and 9, 9' are provided on their opposing inclined surfaces with contact plates 11, 11 'a of a high silvercontent silver-cadmium oxide alloy. Insulation plates 1 2 are disposed at the level of the screws 8 in the free spaces between the contact bridge 2 and the lower parts of the fixed contact blocks 1. The upper end faces of the fixed contact blocks 1 are covered by further insulation plates 12'. Above these there is an arcing chamber 1 3 with a rectangular cross-section and in the form of a stack 15. Arc splitters 14 are located in the arcing chamber 1 3 for dividing the arc which occurs on closing or opening.A current path in the form of an electrical connection conductor line 1 6 between the contact strip 7 and the mobile contact bridge 2, and additionally comprising corresponding bent portions 1 6a, emerges from the stack 15, which at its front end is illustrated by a perspectively drawn side wall portion 1 5a. The conductor line 1 6 is connected to an arc splitter 14 lying thereover.

The conductor line 1 6 is constructed from individual straight copper bars, and comprises corresponding metallic connections. The mobile contact bridge 2 is metallically connected to a mobile copper stranded wire 1 7 by means of two stranded wire connectors 10 formed from screws.

In the subsequent figures, the same reference numerals are used for like components.

Fig. 2 shows the described circuit breaker in part section in its closed state. The side wall portion 1 5a is not shown, and accordingly the spacial form of the conductor line 1 6 with its bent portions 1 6a is clearly visible. Its metallic connections 1 8 are also shown.

Fig. 3 shows a direct current high-speed circuit breaker of the same type as in Figs. 1 and 2, but with a different form of mobile contact bridge 2'. The contact strip 9 lies as a form-fit on a contact surface 5' of the contact bridge 2', i.e. it cannot spring. In contast, the contact strip 9' is resiliently mounted, and its end portion projects in the direction of the left hand contact surface 4, which as in the case of Figs. 1 and 2 is connected to one end of the conductor line 16.

This extended contact strip 9' on the one hand takes up the arc which occurs during the switching function, aids commutation to the secondary path, and allows its desirable rundown in the direction of the arcing chamber 13.

In the plan view of Fig. 4 in which the arcing chamber 1 3 is removed, the individual components can be seen in the direction of their width. The bent portion 1 6a of the conductor line 1 6 can be clearly seen. As a further modification to the preceding embodiments, the conductor line 16' is shown dashed here in the form of a second two-layer blow-out coil.

The geometrical arrangement of the conductor line 1 6 can be optimised as desired to give maximum blow-out action, as it represents only a secondary current path which is advantageously arranged mainly outside the arcing chamber. This conductor line 1 6 can thus have its geometrical shape matched to the respective circuit breaker by an experimental approach. The criterion for determining this shape is that the arc is driven into the arcing chamber 1 3 as rapidly as possible. A particular advantage of this is the high current density which is possible, as the conductor line 1 6 has to be dimensioned only for the short time of the pulse-type contact separation and subsequent commutation of the arc.

In dimensioning the conductor line 16, its resistance R3 must be smaller than Au/f, where Au is the arc root voltage at the corresponding point of contact 11 a, 11 b, and î is the maximum current on contact separation.

As a practical example, it can be assumed that the arc root voltage Au is 25 Volts and the current î is 10 kA. This then gives a resistance Rs of 2.5 m corresponding to a copper conductor line 16 of 25 mm2 crosssectional area and a length of 3 m.

The circuit breaker arrangement shown diagrammatically in Fig. 5 corresponds in its operation substantially to the previously described figures. The contact pads are indicated by A, A', B, B'. Arcing horns 1 9 and 20 are included instead of fixed contact blocks. The power supply conductors and connection bars for the positive pole of a direct current power supply are indicated by 21 and 22. The current direction is indicated by I in the main path and i in the secondary path. An arc springing from the contact strip 9' to the arcing horn 20 is indicated by 30. The loopshaped mobile contact bridge 2" comprises an abutment 24 for a stop 23 on a lever 16b in the conductor line 16, this lever being pivoted at a point of rotation 25.A return spring 26 with two travel limit stops is fitted in the region of one end of the lever 16b. Arc splitters 14' are disposed in the region of the contacts A-B.

The operation of this arrangement is as follows: The contact bridge 2" is firstly moved by operating the switching rod 6, whereby the contacts A, B of the left hand contact point open. The inherent resilient force in the contact strip 9' ensures that the contacts A', B' still remain closed at the right hand contact point. The current i can now flow along the conductor line 1 6 firstly through the curved portion 16c, whereby a blow-out loop effect occurs. The current i flows parallel to and in the same direction as the current I in the connection bar 22. This current i is then transferred by way of a stranded wire 1 7 to a mobile lever 16b which is pivoted about a point of rotation 25.The lever 1 6b is pulled by the return spring 26 against the lower travel limit stop, so that when the circuit breaker is in its closed state, the stop 23 on the lever is spaced apart from the abutment 24. The current is now taken from the lever 16b by way of the stranded wire 17' and transferred to the contact bridge 2". By this means, in addition to the blow-out loop, a portion of the conductor line 1 6 is traversed twice by the same current, once through the level 16b in one direction, and once by way of the contacts B', A' and through the portion of the connection bar 22 parallel to the lever 16b in the other direction.The result of this is that these two conductor paths become pushed away from each other, and the stop 23 on the lever 16b hits against the abutment 24 with an impulse, by which the initial spring stress in the contact strip 9' is overcome, and the contacts A', B' are rapidly opened.

The arc splitters 14' serve for aiding the quenching of the arc which occurs on opening the left hand contact point.

Although in the embodiments described above, the contact bridge 2 had been connected symmetrically to the switching arrangement S-E by means of switching rod 6, it is possible for the contact bridge to be connected to the switching arrangement nonsymmetrically and hingedly. This could be done by using, for example a ball joint or a cylindrical joint. Such an arrangement produces delayed contact opening on one side only, resulting in increased commutation into the induced current path.

Obviously the individual embodiments can be constructively combined with each other as required. The considerations given for example with respect to a direct current high-speed contact breaker are also valid for alternating current contact breakers. In addition, the inductive conductor line 1 6 or the corresponding blow-out coil could also be fitted with an iron core for local intensification of the magnetic field.

Claims (11)

1. An electrical circuit breaker comprising a break chamber in which a mobile contact bridge is disposed together with at least two fixed contacts disposed at a determined distance apart, wherein the contact surfaces of the fixed contacts and the mobile contact bridge are fitted approximately symmetrical to the direction of movement of the contact bridge, and wherein the points of contact between the fixed contacts and the contact bridge are connected in series when in the closed state, and wherein one of the points of contact is bridged by a parallel connected conductor path which extends outside the break chamber and which has a resistance greater than the contact resistance at said point of contact.

2. An electrical circuit breaker as claimed in claim 1, wherein the contact bridge is loop shaped and a portion thereof projects between the fixed contacts in the direction of the point of contact bridged by the parallel connected conductor path.

3. An electrical circuit breaker as claimed in claim 1 or claim 2 wherein the conductor path is in the form of a magnetic blow-out loop.

4. An electrical circuit breaker as claimed in claim 1 or claim 2 wherein the conductor path is in the form of a single or multilayer blow-out coil.

5. An electrical circuit breaker as claimed in claim 1 or claim 2 wherein the conductor path is in the form of two magnetic blow-out coils connected in parallel and lying opposite each other outside the break chamber laterally to the contact zone.

6. An electrical circuit breaker as claimed in claim 1, wherein the contact bridge comprises a non-symmetrical holding-down spring, which in the region of one point of contact is higher than in the region of the other opposite points of contact.

7. An electrical circuit breaker as claimed in any preceding claim wherein at least one contact of the contact bridge is in the form of a spring.

8. An electrical circuit breaker as claimed in any preceding claim wherein the contact bridge is connected non-symmetrically and hingedly to a switching arrangement.

9. An electrical circuit breaker as claimed in claim 1, wherein the conductor path comprises a lever rotatably pivoted about a point of rotation, and provided with a stop which is associated with an abutment on the contact bridge.

1 0. An electrical circuit breaker as claimed in claim 1, wherein a swiveling lever is disposed laterally to a connection bar and is connected metallically on the one hand to the conductor path and on the other hand to the contact bridge and is provided at its outer swiveling end with a stop which cooperates with an abutment on the contact bridge.

11. An electrical circuit breaker as claimed in any preceding claim, wherein the break chamber is formed from at least two moulded plastic walls.

1 2. An electrical circuit breaker substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.