EP0275857A1 - Ultra-rapid circuit breaker assisted with semi-conductors - Google Patents

Abstract

Ultra-rapid circuit-breaker comprising an ultra-rapid cut-out mechanism provided with a repulsion disk equipped with moving contacts (7,7'), the said mechanism further comprising stationary contacts (9,9'), across the input and output terminals (1,3) of which is connected an assisting circuit (10) comprising a capacitor (21) and a choke (23) as well as a set of semiconductors (13,15,17,19), the choke (23) constituting in whole or in part the repulsion coil of the said ultra-rapid mechanism, characterised in that it comprises at least two parallel branches (CD, EF), a first branch (CD) comprising two opposed diodes (13,15) or the like, in series, each oriented in the blocking direction for the current entering the circuit, a second branch (EF) comprising two opposed thyristors or the like (17,19) each oriented in the passing direction for the current entering the circuit, and an LC oscillating circuit (21,23) which connects the point common to the two diodes (13,15) or the like and the point common to the two thyristors (17,19) or the like, the two thyristors (17,19) or the like being controlled remotely or via an incorporated current sensor (20) detecting the exceeding of a previously fixed triggering threshold which can be adjusted in the control electronics. <IMAGE>

Description

This invention relates to a hyper fast current limiting circuit breaker usable at medium voltage and although more particularly suitable for direct current electric traction in rolling stock or fixed equipment, can also be used in alternating current.

It is well known that DC networks in traction as in industry are becoming more and more complex and powerful. The design of switchgear must evolve to cut larger and larger currents and reduce maintenance costs. A new generation switchgear must be fast to limit the current and reduce the mechanical and thermal stresses of the entire installation as well as the wear of its contacts and its blowing box. Currently, switching devices, in traction network, include ultra-rapid mechanisms for opening the contacts and a blowing box in which the arc created is confined and cooled. These devices entail significant costs due to maintenance interventions and the replacement of wearing parts.

In European patent application ^No. 85 770 134.5 there is disclosed the combination of an ultra-rapid mechanism to maintain electromagnetic wherein the same element is both repulsion disk office and mobile contact bridge, with a circuit oscillating controlled by semiconductors and whose inductor is used as a repulsion coil in the cut-off mechanism. The assistance circuit described, connected to the terminals of the mechanism, comprises a capacitor, a choke (repulsion coil) and a thyristor, connected in series as well as a diode mounted in anti-parallel on the elements in series. The breaking device equipped with the assistance circuit of this type is however only suitable for cutting currents passing through said device in the given direction. Figure 6 of application 85.870 134.5 shows a similar assistance circuit intended for a bidirectional breaking device which makes it possible to cut a current in both directions. However, it appears that the cut-off efficiency in one direction of current flow is significantly better than that in the opposite direction. This is due to an asymmetry of the circuit from which it follows that the second current warhead produced by the capacitor, weaker than the first since already partially damped, must cut a short-circuit current which has had a long time to grow .

An object of the present invention is to provide a hyper fast circuit breaker assisted by semiconductors, which does not have the drawbacks of the devices known in the prior art as described above.

Another object of the present invention is to provide a super fast circuit breaker capable of breaking a direct current in both directions, with similar efficiency.

A complementary object of the present invention aims to provide a particularly efficient circuit breaker, inexpensive and not resulting in high maintenance costs.

According to the present invention, the circuit breaker comprises a super fast breaking mechanism provided with a movable contact bridge and fixed contacts, at the input and output terminals of which an assistance circuit is connected. The assistance circuit comprises at least two parallel branches, a first branch comprising two diodes opposite in series, each oriented in the blocking direction for the current entering the circuit, a second branch comprising two opposite thyristors, each oriented in the passing direction for the current entering the circuit, and an LC oscillating circuit which connects the point common to the two diodes and the point common to the two thyristors, the thyristors being controlled remotely or via an incorporated current sensor detecting the exceeding of a trigger threshold previously fixed and adjustable in the control electronics.

It can be seen that the combination of a hyper-fast cut-off mechanism with an assistance circuit of the aforementioned type using power electronics capable of high performance in transient conditions makes it possible to avoid the appearance and development of the arc electric between the contact terminals of the circuit breaker by very quickly opposing a calculable antagonistic voltage, whatever the direction of flow of the current to be cut.

• - la figure 1 représente le schéma de principe du circuit d'assistance conforme à la présente invention;
• - la figure 2 illustre le fonctionnement dudit disjoncteur;
• - les figures 3 à 4 représentent des variantes d'exécution particulièrement avantageuses du circuit d'assistance conforme à la présente invention.

Other details of the present invention will appear more clearly on reading the description given below in support of the drawings in which:

• - Figure 1 shows the block diagram of the assistance circuit according to the present invention;
• - Figure 2 illustrates the operation of said circuit breaker;
• - Figures 3 to 4 show particularly advantageous alternative embodiments of the assistance circuit according to the present invention.

In the figures, identical reference marks represent identical or analogous elements.

In the figures, there is shown the input 1 and output 3 terminals of the circuit breaker 5 comprising a quick cut-off mechanism represented only by the movable contact bridge 7, 7ʹ and by the fixed contacts 9, 9ʹ, as well as a assistance circuit 10 mounted in parallel on terminals 1 and 3.

With reference to FIG. 1, the assistance circuit 10 comprises two branches CD and EF mounted in parallel. The CD branch comprises two diodes 13 and 15 opposite and oriented in the blocking direction of the incoming current I. The EF branch comprises two thyristors 17 and 19 opposite and oriented in the passing direction for the incoming current I. The two branches CD and EF are connected by an LC type oscillating circuit comprising a capacitor 21 and a choke 23 which also serves as a repulsion coil for the repulsion disc (not shown) carrying the bridge of movable contacts 7, 7ʹ.

Suppose the device connected to a network so that direct current flows from A to B and is equal to its nominal value when a fault occurs.

The current increases and reaches at t = t₀ the value of the tripping threshold I _sd of the circuit breaker.

After a delay of a few micro-seconds specific to the electronics, at t = t₁, the latter gives an ignition order to the thyristor 17, following the information given by the sensor 20.

A current warhead arises in the tyristor 17-capacitor 21-self 23 circuit and splits in the diode 13 (HC circuit) and in the HD-3-8 circuit where it will evade the main current to quickly bring it- this to zero. It is quite obvious that the increase in the current warhead is of an order of magnitude at least greater than that of the maximum fault current in order to rapidly effect the cancellation of the current in the main contact 8.

As the inductance 23 also constitutes the repulsion coil of the super fast mechanism, it causes the opening of the contact 8, a hundred microseconds after the current warhead has been sent, at t = t₂.

As soon as contact 8 is open, the fault current finds a substitution path with 1-C-E-G-H-D, while the warp current follows the E-G-H-C circuit.

Consequently, the difference in voltage existing between terminals A and B is equal to the difference in the direct voltage drops of the diodes 13 and 15, therefore much less than the minimum voltage required to have an arc. across contact 8.

As long as the warhead current remains greater than the fault current, the situation is therefore as follows:
- Contact 8 is open and continues to run so that it can withstand significant tension. The current in contact 8 is canceled out at t = t₃ and the voltage across its terminals is almost zero. As there was no arc at the terminals of contact 8, the space between the terminals is not ionized and no wear is caused to the contacts.
- The current in the diode 13 is equal to the difference between the current in the external circuit and the warp current.
- The fault current continues to increase, but it has been transferred from contact 8 to the electronic assistance circuit.
-The upstream and downstream currents, i.e. the current supplied by the source and the current in the fault are identical.

This situation will persist until t = t₄ when the warhead current will equal the fault current for the second time. At this time the topology of the circuit will be modified; the voltage across the capacitor 21 is reversed and the latter is inserted in series with the network.

The fault current will therefore decrease, given the appearance of this antagonistic voltage.

Since the assistance circuit according to the present invention is substantially symmetrical, sumblable reasoning can be developed when the current flows from B to A.

FIG. 3 gives an advantageous embodiment of the circuit of FIG. 1 in which a freewheeling diode 24 and a nonlinear resistor 25 have been added. In fact, as soon as the fault current begins to decrease (instant t = t₄) the operations of the upstream and downstream circuits should be dissociated.

When the current in the downstream circuit decreases, the inductance of the circuit downstream of the circuit breaker polarizes the diodes 24 and 15 in the direct direction and can operate in freewheel mode to dampen with a time constant specific to said circuit.

The current in the circuit upstream of the circuit breaker decreases as the voltage across the capacitor 21 increases. In order to limit the voltage appearing at the terminals of the device to a reasonable voltage when the energy stored in the inductances of the upstream circuit is high, a non-linear resistor 25 has been provided to dissipate this energy and thus clip any higher overvoltage. to the advertised values.

In FIG. 4, it can be seen that said non-linear resistor 25 can also be mounted in parallel on the capacitor 21. In this case, it is however continuously energized, which can modify its service life.

At the instant t = t₅, the upstream current is canceled and the voltage at the terminals of the device will join the network voltage according to an oscillatory regime depending on the capacities and inductances present in the circuit.

Means can also be provided for galvanic isolation between the upstream and downstream circuits, which is actuated as soon as the current sensor 20 detects a zero current. Such a means can be mounted in branches 1-C and 3-D for example.

In the description of the figures, it has been assumed that the electronics triggers a thyristor, namely that which makes it possible to close the oscillating circuit and which is oriented in the passing direction for the main current. However, the two thyristors 17 and 19 can also be controlled simultaneously. In this case, however, the capacitor must be dimensioned differently since the warhead, in this case divided in two, must always be capable of surpassing the increase in fault current.

In the case described above, it may be advantageous to replace the two thyristors 17, 19 by two diodes 27, 29 and by a thyristor 31 mounted in the branch GH, as shown in FIG. 5.

It should be noted that the circuit breaker begins to fight against the short circuit at time t₄, that is to say less than a millisecond after the current has passed to its tripping value. The maximum value reached by the fault current is therefore of the same order of magnitude as the trip current even in the event of very violent short circuits.

In addition, at time t₄, a voltage appears at the terminals of contact 8, but this voltage does not reach its maximum value until later, that is to say when the inter-electrode distance is further increased.

Furthermore, the maximum value reached by the current and the speed of the cut-out means that the I²t in the event of a violent short-circuit is several orders of magnitude lower than the value relating to conventional devices.

As there is no arc formation, there is no projection of incandescent particles nor significant release of ionized gases. As a result, the isolation distances can be reduced.

The circuit breaker according to the present invention can cut all current according to the same principle. It is therefore characterized by the absence of a critical current.

It is obvious that the circuit breaker described above can also be used to cut a nominal current, by being controlled remotely, for example manually, rather than by a fault current reaching a tripping threshold.

The circuit breaker according to the present invention is particularly suitable as a current limiter usable at medium voltage and although more particularly suitable for electric traction with direct current, in rolling stock or fixed equipment, it can also be used in alternating current.

It can also be added that the means allowing galvanic isolation, advantageously mounted in branches 1-C and possibly 3-D or H-24 (see FIG. 3) consisting of suitable switches 33 and 35, can be used to carry out tests of line either to check the state of the line using a low current before switching it on, or to check the status of the insulators for example.

In the latter case of application, provision may be made for a command known per se of at least one of said switches, which allows it to be opened and closed according to a cycle at relatively low frequency of the order of 0.1 Hz in order to be able to work with a higher current, of the order of 5 A for example, without damaging the assistance circuit and while allowing good viewing of the insulators.

Claims (9)

1. Hyper-fast circuit breaker comprising a hyper-rapid breaking mechanism provided with a repulsion disk equipped with movable contacts (7, 7ʹ), said mechanism also comprising fixed contacts (9, 9ʹ), at the input and output terminals (1, 3) from which is connected an assistance circuit (10) comprising a capacitor (21) and a choke (23) as well as a set of semiconductors (13, 15, 17, 19), the choke ( 23) constituting in whole or in part the repulsion coil of said hyper-rapid mechanism, characterized in that it comprises at least two parallel branches (CD, EF), a first branch (CD) comprising two diodes (13, 15) or analogous, opposite, in series, each oriented in the blocking direction for the current entering the circuit, a second branch (EF) comprising two thyristors or the like, opposite (17, 19) each oriented in the passing direction for the current entering the circuit, and an oscillating circuit LC (21, 23) which connects the point common to the two diodes (13, 15) o u analog and the point common to the two thyristors (17, 19) or the like, the two thyristors (17, 19) or the like being controlled remotely or via a built-in current sensor (20) detecting the exceeding of a triggering threshold , previously fixed and adjustable in the control electronics. 2. Circuit breaker according to claim 1 characterized in that a freewheeling diode (24) is connected between the point common to the two opposite diodes (13, 15) and the earth. 3. Circuit breaker according to any one of claims 1 or 2 characterized in that it comprises a resistor, preferably a non-linear resistor (25), mounted in parallel on the assistance circuit (10). 4. Circuit breaker according to any one of claims 1 or 2 characterized in that it comprises a resistor, preferably a non-linear resistor, (25) mounted in parallel on the capacitor (23). 5. Circuit breaker according to any one of the preceding claims, characterized in that the current sensor or the remote control actuates the thyristor (17, 19) oriented in the passing direction for the incoming current. 6. Circuit breaker according to any one of claims 1 to 4 characterized in that the current sensor or the remote control actuates the two thyristors (17, 19) simultaneously. 7. Circuit breaker according to claim 6 characterized in that the two thyristors (17, 19) are replaced by two diodes (27, 29) oriented in the same direction and a thyristor (31) mounted in the oscillating circuit branch connecting the two parallel branches (CD, EF). 8. Circuit breaker according to any one of the preceding claims, characterized in that it comprises means (33, 35) allowing galvanic isolation between the circuits upstream and downstream of said circuit breaker, which is actuated as soon as the current sensor ( 20) detects a zero current, said means preferably being mounted in the branches connecting the assistance circuit (10) to the input and output terminals (1, 3) of the super fast mechanism. 9. Circuit breaker according to claim 8 characterized in that the means (33, 35) allowing galvanic isolation between the circuits upstream and downstream of said circuit breaker consists of at least one switch (33, 35), one switch (33) at less being provided with an opening and / or closing command according to a low frequency cycle.

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