Circuit breaker having equalized poles

The circuit breaker includes two polarities each including two poles connected in parallel, each pole having a switch and a tripping device. Each of the polarities has an equalizer electrically connecting the link between the switch and the tripping device of a first pole and the link between the switch and the tripping device of the second pole.

The invention concerns a circuit breaker comprising two polarities each including two poles connected in parallel, each pole having a switch and a tripping device.

Some circuit breakers for direct current have poles in parallel, in order to increase the maximum use of current. Such a circuit breaker comprises two polarities each including two poles connected in parallel. Each pole has a tripping device, which can operate by overload and/or by short circuit, that is suited to detecting a current greater than half the total maximum current beyond which the circuit breaker is activated. Each pole likewise comprises a switch connected in series with the tripping device, this switch providing for the current to flow as a result of contact between conductive portions.

When two poles or more are connected in parallel, the current is distributed between these poles in a manner inversely proportional to the resistance of these poles. The resistance of a pole includes the resistance of all of the conductive portions and the contact resistance of the switch. The resistance of the conductive portions is very invariable, because it is dependent only on the resistivity of the materials, which has little scatter, and on the geometry of the portions, the tolerances of which are under control. The contact resistance, on the other hand, is subject to variations that may be substantial, owing to the electrical arcs that affect the surface of the fixed and mobile contacts both under continuous load and in the case of a short circuit. Therefore, the resistance of the two poles in parallel may be substantially different. A current of greater intensity will therefore naturally flow in the pole that has the lowest resistance, with the risk of causing the circuit breaker to trip for an excessively low total current value. The reason is that it is possible for the current flowing in the pole with the lowest resistance to exceed half the maximum current intensity, or the total current intensity is lower than the maximum current intensity. The circuit breaker therefore cannot perform its function satisfactorily and can cause untimely power cuts.

These are disadvantages that the invention aims to overcome by proposing a novel circuit breaker with poles connected in parallel, in which the distribution of the current in the poles is under better control and which avoids untimely tripping.

To this end, the invention concerns a circuit breaker comprising two polarities each including two poles connected in parallel, each pole having a switch and a tripping device. This circuit breaker is characterized in that each of the polarities has an equalizer electrically connecting the link between the switch and the tripping device of a first pole and the link between the switch and the tripping device of the second pole.

By virtue of the invention, the distribution of the current between the poles is affected in practice only by the difference in the resistance of the tripping devices. In point of fact, these tripping devices are made up of conductive portions of known resistance, and the resistance differences between the tripping elements are negligible in practice. The current imbalances between the poles connected in parallel are therefore small, which minimizes the risks of the circuit breaker tripping for excessively low total current values.

According to advantageous but non-obligatory aspects of the invention, such a circuit breaker can incorporate one or more of the following features, taken in any technically admissible combination:The value of the resistance of the equalizer is no more than at the same order of magnitude as the value of the resistance of the tripping devices.The value of the resistance of the equalizer is less than three times the value of the resistance of the tripping devices.The equalizer is a conductive bow.The conductive bow has two fixing lugs provided with holes.The conductive bow is fixed by screws.The equalizers are cables or braids of conductive wires.The equalizers are fixed to the conductive portions of the tripping devices that form the links between the switches and the tripping devices.The equalizers are fixed to the conductive portions of the switches that form the links between the switches and the tripping devices.The equalizer is a bow comprising lateral branches formed by conductive portions of two adjacent tripping devices, these conductive portions forming the links between the switches and the tripping devices.

FIG. 1shows a circuit breaker1. The circuit breaker1comprises a positive polarity PP and a negative polarity PN that are connected to a power source10. Each polarity includes two respective poles3and5. Each of the poles3and5comprises a tripping device7and a switch9. The tripping device7and the switch9are connected in series. The polarities PP and PN are connected to a load11that is connected to the tripping devices7. The poles3and5are connected in parallel by an electrical link L1on the source10side and by an electrical link L2on the load11side. InFIG. 1, the circuit breaker1is shown to be open.

The object of the invention is to prevent variations in the contact resistances of the switches9from causing imbalances in the intensity of the current in the tripping devices7of two poles of one and the same polarity. To this end, the poles3and5are connected, between the tripping device7and the switch9, by an equalizer13electrically connecting the link between the tripping device7and the switch9of the pole3, and the link between the tripping device7and the switch9of the pole5. The link between the switch9and the tripping device7of the pole3is represented by the point P1inFIG. 1. The link between the switch9and the tripping device7of the pole5is represented by the point P2inFIG. 1. The links represented by the points P1and P2are, in practice, connecting interfaces between the tripping devices7and the switches9, said connecting interfaces being formed by conductive portions belonging to the tripping devices7and to the switches9.

The equalizer13allows the potentials of the points P1and P2to be made equal. Thus, the distribution of the current in the switches9does not affect the distribution of the currents in the tripping devices7. Moreover, the resistances of the tripping devices7are equivalent to the resistances of the conductive portions making up the tripping devices7, and the resistance of these portions is known and well under control. The distribution of the intensity of the current in the respective tripping devices7of the poles3and5is therefore substantially equal, which prevents the circuit breaker1from tripping for intensity current values below the maximum tripping current value.

In theory, the resistance of the equalizers13must be zero for the balance of the intensities in the tripping devices7of the poles3and5connected in parallel to be perfect, but this condition is impossible to produce. In practice, it suffices for the value of the resistance of the equalizer13to be no more than of the same order of magnitude as the resistance of the tripping devices7of the poles3and5connected in parallel in order for the balance of the currents to be significantly improved. Same order of magnitude is intended to be understood to mean that the value of the resistance of the equalizer13is less than approximately three times that of the resistance of the tripping devices7. By way of example, if the resistance of the tripping devices7is 25 micro-Ohms, the resistance of the equalizers13must be less than 75 micro-Ohms. The lower the resistance of the equalizer13in comparison with the resistance of the tripping device7, the better the balance of the currents will be. Preferably, the value of the resistance of the equalizer13must be lower than the value of the resistance of the tripping devices7.

As shown inFIG. 2, the equalizer13can be implemented in the form of a conductive bow formed by a rigid mechanical portion comprising a central part135and two terminals formed by fixing lugs130and131provided with holes133. The conductive bow13can be fixed by screws, which are not shown. The conductive bow13can be produced by forging or by hot forming.

FIG. 3shows a bow13′ in accordance with a variant of the invention. The bow13′ can comprise a central part135made up of a conductive braid or a section of cable and fixing and connecting lugs130and131as a result of the folding of a metal plate, which are connected to the central part135, for example by welding or by crimping.

FIG. 4shows a bow13″ in accordance with another variant of the invention. The bow13″ is entirely made up of a metal plate that has been cut and folded.

FIG. 2shows the part of the circuit breaker1that comprises the tripping devices7. Four tripping devices7belonging to each of the poles3and5of the polarities PP and PN are grouped in parallel into a tripping block17.

In the embodiment ofFIGS. 1 and 2, the bows13are mounted on the tripping block17, that is to say on the conductive portions of the tripping devices7that form the links between the tripping devices7and the switches9. Each tripping device7comprises a fixing and connecting lug170, which is electrically connected to the conductive portions of this tripping device7, and which forms the electrical link to the switch9of the corresponding pole3or5. Each bow13is fixed to two adjacent lugs170belonging to the poles3and5, respectively. The fixing lugs170project outside the tripping block17, and the central part135of the bows13is outside the tripping block17.

A preferred embodiment of the invention is shown inFIG. 5. InFIG. 5, an upper cover172of the tripping block17ofFIG. 2has been removed, making the inside of the tripping block17visible. The bows13are mounted inversely in relation toFIG. 2, the central part135of the bows13being inside the tripping block17.

A second and a third embodiment of the invention are shown inFIGS. 6 and 7, respectively. In these embodiments, the elements that are similar to those of the first embodiment bear the same references and work in the same way. Only the differences in relation to the first embodiment are detailed below.

FIG. 6shows the part of a circuit breaker100in accordance with a third embodiment of the invention that comprises the switches9. The four switches9belonging to each of the poles3and5are grouped in parallel into a switching block19that is suited to receiving a tripping block similar to the tripping block17. The switching block19comprises a control192that toggles when the circuit breaker100is tripped, and which can be actuated manually by a person in order to reset the circuit breaker100and reapply voltage to the installation.

In the embodiment ofFIG. 6, the bows13are mounted on the switching block19, that is to say on the conductive portions of the switches9that form the links between the switches9and the tripping devices7. Each switch9comprises a fixing and connecting lug190which is electrically connected to the conductive portions of this switch9, and which form the electrical link to the tripping device7of the corresponding pole3or5. Each bow13is fixed to two adjacent lugs190belonging to the poles3and5, respectively.

In the embodiment ofFIG. 7, the equalizer13is formed by a bow having lateral branches formed by conductive portions70of two adjacent tripping devices7. In such a case, the equalizer13can be formed by a single metal portion, or even by the securing of two conductive portions70by a central part135that is attached, by way of example, by welding.

According to an embodiment that is not shown, the equalizers13can likewise be produced in the form of cables or of braids of conductive wires.

The features of the embodiments and variants described above can be combined in order to create new embodiments of the invention.