FR2672424A1 - Fast circuit breaker for high currents - Google Patents

Abstract

This circuit breaker (1) comprises: - contact pieces (6-15) arranged in a stack in which each piece comes into contact with the adjacent piece, each of the end pieces (6, 15) being linked to one pole (19, 18) of the circuit breaker, - means (16) for guiding the pieces in translation along the direction of the stack, - actuator means (20), linked to one (6) of the end pieces, suitable for loading the stack in the direction of compression, and - means of triggering the circuit breaker, cooperating with the actuator means in order to: - in closed position, activate the latter so as to exert axial compression on the stack overcoming the axial forces resulting from the current forces produced by the current passing through the stack, and - in open position, release the latter so as to allow the various pieces to move apart axially from one another under the effect of the said ampere forces, thus forming, between the successive pairs of pieces, a plurality of arcs dissipating the switching energy in a distributed way.

Description

Fast circuit breaker for high currents
The present invention relates to a quick circuit breaker for high currents.

 By high currents we mean currents of a typical value of the order of megaampere and even more. At such current levels, it is difficult to achieve industrial circuit breakers that can react quickly enough. The transition from the conduction state to the non-conduction state must be done, in the easiest case, in a few tens of microseconds and, in the most difficult case, in a few tens of nanoseconds (these values do not are in no way limiting and very largely depend on the envisaged application).

 For quite a long time, devices have been used for breaking high currents, based on the self-destruction of an explosive wire crossed by the current of the circuit to be interrupted.

In these devices, when the current reaches a certain value, the stresses undergone by the wire under the effect of the crossing intensity produce a sudden explosive fragmentation of the latter. Then, in a second phase, the phenomenon is different, because there is the formation of an arc, then of a plasma between the different fragments, if at least the voltage applied to the terminals of the wire is sufficient; in the event that this voltage is insufficient, there is an interruption of the current at the end of the first phase.

 The first obvious drawback of such a device is its self-destructive nature, which prevents any repetitive operation, since the explosive wire must be changed after each opening of the circuit.

 Secondly, the precise instant of triggering of this circuit breaker cannot be precisely controlled since it will depend on the intensity traversing the wire; this device cannot therefore be controlled externally.

 Such explosive wires are described for example by Nasilovski in an article published in Exploding Wires (W.G. Chase, H.K. Moore editors), Vol. 3, Plenum, New York, 1964, under the title Unduloids and Stria tex Disintegration of Wires.

In an experimental attempt, exposed by Ruscak and Bruce in an article entitled Multi-Arc Generator and published in
IEEE Transactions on Plasma Science, Vol. PS 15, 1987, page 51, it has been proposed to avoid the destruction of the circuit breaker by replacing the wire with a segmented conductor of large diameter, the successive segments being made up of elements alternately of copper and aluminum arranged in a glass tube.

 This device, which only remained at the experimental stage, however has a relatively long switching time due to the formation of plasma between the segments, which tends to prolong the passage of current in the wire. In addition, as in the case of explosive wires, this device triggers as soon as a certain current threshold is crossed, without the possibility of precise external temporal control of the cut-off.

The most common technique currently is to use switches designed from the properties of plasmas. It has materialized in two main types of circuit breakers: plasma erosion opening circuit breakers called PEOS (Plasma Erosion Opening Switches) and plasma flow circuit breakers called PFS (Plasma Flow Switches). The state of the art can be found on these fast opening vacuum switches in the December 1987 issue of IEEE
Transactions on Plasma Science, Vol. PS 15, which is dedicated to them.

They are still currently the subject of various researches and are still laboratory products, either oriented towards the supply of propulsion circuits of the electromagnetic gun type, or towards obtaining plasmas for research in controlled fusion. In particular, PFS is derived from the device used for plasma focus experiments which have been and continue to be unsuccessful attempts at controlled fusion. Given its principle, the PFS does not allow a repetitive operation, at least in its usual form today, because its operation requires the explosion of a network of wires at the impact of the electromagnetic wave.

 The present invention provides a device which aims to obtain performances similar to those of PEOS, but according to a completely different principle. The circuit breaker object of the invention allows the transfer of currents of the order of megaampere without any destruction of the device - therefore with the possibility of recurrent tripping - the tripping being controlled externally regardless of the level of current flowing through the device. n also allows complete galvanic isolation between the circuit where the current passed before its operation and the circuit where it passes after its operation. The proposed device is thus a real switch.

 It will also be seen that the structure of the invention allows extremely fast switching, compatible with typical cut-off times of the order of a few microseconds or less than the microsecond.

 Finally, from an energy point of view, like any circuit breaker, the device of the invention will inevitably have to dissipate a certain amount of energy to cause the transfer of current to another branch of the circuit. However, as will be seen, in the case of the invention, this switching energy - and therefore the heat dissipation - is distributed over a large number of breaking arcs instead of being concentrated on a single arc as with classic circuit breakers. Thanks to this characteristic, the melting and erosion of the contact parts will be minimized, thus allowing operation during a greater number of cycles.

 The principle of the invention is based on the use of Ampere force between current elements.

This concept had been proposed in the last century (see in particular
A.-M. Ampère, Memoir on the determination of the formula which represents the mutual action of two infinitely small portions of voltaic conductors, read at the Académie des Sciences on June 10, 1822) on an empirical basis, but its existence n had not been supported by theory, especially given the fact that it had so far been believed to contradict Maxwell's laws.

Now the laws proposed by Ampère, which made it possible to explain the forces brought into play between current elements, have just proved to be perfectly compatible with the theory of Relativity (Lorentz force). The absence of contradiction - and therefore the probable reality of Ampère's forces - has just been recognized by
M. Rambaut and JPVigier as not contradicting Relativity, in three articles of Physics Letters A, one in volume 142, n "8-9 of December 25, 1989, page 447 and entitled The Simultaneous
Existence ofEM Grassmann-Lorentz Forces (Acting on Charged Particles) and Ampère Forces (Acting on Charged Conducting Elements)
Does not Contradict Relativity Theory, the other in volume 148, no. 5 of August 20, 1990 and entitled Ampère Forces Considered as Collective Non-relativistic Limit of the Sum of All Lorentz Interactions
Acting on Individual Current Elements :: Possible Consequences for
Electromagnetic Discharge Stability and Tokamak Behavior, and the third being scheduled to be released as
M. Rambaut and entitled Macroscopic Non-relativistic Ampère EM
Interactions between Current Elements Reflet the Conducting Electrons Accelerations by the Ion's Electric Field.

We can also refer on this subject to Peter's study.
Graneau entitled Ampère-Neumann Electrodynamics of Metallic
Conductors, published in Hadronic Press, Nonantum, Massachusetts, USA, 1985.

 As has been demonstrated in these documents, in a given conductor the force of Ampère produces a transverse attraction between elements of parallel currents and, above all, a longitudinal repulsion between elements of collinear currents. In particular, it is this latter effect which will be used in the device of the invention to produce, by purely electric means and without destruction of any element, a force capable of separating circuit elements to thereby produce the breaking of this circuit.

 More specifically, according to the invention, the circuit breaker comprises a plurality of contact pieces arranged in a stack where each piece comes into mechanical and electrical contact with the adjacent piece, each of the end contact pieces being electrically connected to a respective pole of the circuit breaker; means for guiding the contact parts in axial translation, in the direction of the stack; actuator means, connected to one of the end contact pieces, adapted to mechanically stress the stack in the direction of compression; and means for triggering the circuit breaker, cooperating with the actuator means so as, in the closed position, to activate the actuator means so as to exert on the stack sufficient axial compression to overcome the axial forces resulting from Ampere forces produced by the current flowing through the stack and, in the open position, releasing the actuator means so as to allow the different contact pieces to move axially apart from one another under the effect of said Ampere forces, thus forming, between the different successive pairs of contact parts, a plurality of arcs dissipating the switching energy in a distributed manner.

 Very advantageously, this circuit breaker comprises an envelope formed by two conductive cylindrical tubes placed end to end and separated by an insulating intermediate ring, each of the tubes being connected to a respective pole of the circuit breaker, and the envelope coaxially surrounding, distance from these, the contact pieces of the stack.

0
Other characteristics of the invention will appear on reading the detailed description below, made with reference to the accompanying drawings.

 FIG. 1 shows the equivalent circuit of a device according to the invention associating in the same device a member for opening the generator circuit and a member for closing the load circuit.

 Figure 2 is a sectional view of an embodiment of the circuit breaker of the invention.

0
At the outset, it should be noted that, although the invention is described below in the context of a supply circuit of a device of the cannon-rail type (railgun), this application is not however given that purely by way of illustration and the circuit breaker of the invention can find applications in extremely diverse fields, in particular whenever it is necessary to deliver high energy in the form of rapid pulses.

 This is the case of rail guns, water-arc guns, power circuits for radars, etc.

 The invention can also find applications as a safety device, whenever it is necessary to interrupt in a perfectly controlled manner large currents.

 In the circuit illustrated in FIG. 1, a generator G is used which is closed on an energy storage inductor L by means of a cut-off member K1 normally maintained in the closed state (circuit breaker). The diagram also includes, as illustrated, a switching member K2, normally maintained in the open state, in series with a load Z (user member with low impedance) to close the circuit of the latter (we will see later that the two members K1 and K2 are in fact associated in a single device 1 and operate simultaneously and suddenly the two switching operations) as well as, possibly, another closing member K3, which may be slow closing, in series with the inductor L.

 If the current flowing through the generator-inductance assembly can be quickly diverted to load Z by opening K1 and simultaneously closing K2, all of the stored energy will be transferred in the form of a rapid pulse to this load Z. In particular, the opening of K1 generates an arc or a series of arcs creating a relatively large reverse switching voltage having the effect of forcing the current to pass through the branch containing the low-impedance member, that is to say - say the charge Z.

 The generator G can in particular be a zero sequence generator, a device capable of delivering in a few tens of milliseconds, at high intensity and reduced voltage, energies of the order of a few tens of megajoules - characteristics which are perfectly suitable for a canon-rail accelerator. When the (direct) current flows in this generator-inductance loop, part of the energy is accumulated in the form of kinetic energy from the rotor, the rest being accumulated in the form of magnetic energy in the inductance.

 The circuit breaker proposed by the invention has the general structure illustrated in FIG. 2, where we find the generator G, the storage inductance L and the load Z, constituted by the gun-rail accelerator with a metal projectile 2 short-circuiting two longitudinal rails 3 and 4 forming slides.

 The main element of the circuit breaker 1 is a stack of cylindrical contact parts, of which there are ten in the example illustrated (parts referenced 6 to 15), and the transverse displacement of which is prevented by means of a rod. central unit 16 made of dielectric material, for example of alumina ceramic. The stack rests by the lower part 15 on a base 17 of metallic material, electrically connected to a first terminal 18 of the circuit breaker.

 The upper part 6 of the stack, for its part, is electrically connected to the other terminal 19 of the circuit breaker and mechanically connected to an actuator 20 allowing, by means of the rod or rod 21, to force this part upper 6 against the adjacent part 7 and, step by step, thus exerting stress on the stack in the direction of compression.

 The actuator 20 may be a pneumatic or hydraulic actuator, a mechanical cam actuator driven by a motor, or any other suitable known device making it possible to fulfill the desired function. A deformable region 22 allows the part 6 to be permanently electrically connected to the terminal 19 of the device.

 The contact parts are housed in a coaxial cylindrical conductive tube comprising an upper half 23 and a lower half 24 separated by a dielectric ring 25 forming an insulation barrier. The rails 3 and 4 of the barrel-rail are connected to these two respective tube halves 23, 24.

 The upper half 23 preferably comprises a peripheral lip 26 forming a stop, in order to limit the stroke of the upper contact part 6 displaced by the actuator by coming into contact with a shoulder 27 of this part.

 We will now describe the operation of this circuit breaker.

 Initially, the circuit breaker is in the position illustrated in FIG. 2, corresponding to an open state between the terminals 18 and 19. In fact, the upper contact part 6 is in the high position, therefore separated from the adjacent part 7 by an interval 28 appropriately sized (for example 1 cm in the intended application).

 The actuator 20 is then activated so as to lower the upper contact part 6, thereby bringing it into contact with the other parts of the stack and switching the circuit breaker to the closed state.

 The internal conductor constituted by the stack of contact parts 6 to 15 is isolated at all points from the upper part 23 of the coaxial conductive tube, and therefore from the rail 3 of the barrel-rail which is connected to it.

As the load current increases in the loop formed by the generator G, the storage inductance L and the circuit breaker 1, the Ampere forces, which are, as explained higher, longitudinal electrodynamic forces, will gradually increase and tend to move away from each other, in an axial direction, the various contact parts. It will be noted that the effect of the Ampere forces is all the more marked here since, due to the geometry of the stack, the streamlines are essentially parallel to the axis of the tube.
The pressure exerted by the actuator 20 on the stack is however sufficient to prevent the separation of the different contact parts under the effect of Ampère forces.

 Once the charging of the inductor L has been completed, a command is sent to the actuator 20 which will have the effect of eliminating the pressure exerted on the stack by the latter and even, very advantageously, of actively urging the upper contact piece 6 until it stops against the shoulder 26.

 This command can be carried out in an interval which, typically, can be of the order of 10 to 50 μls depending on the switching command. During this brief period, ten switching arcs will form (between each of the ten contact parts, and between the lower part 15 and the base 17) under the action of longitudinal Ampere forces.

 The collective effect of these arcs will be to establish a relatively high reverse switching voltage between the two terminals 18 and 19 of the circuit breaker, therefore to transfer the energy accumulated in the inductance (magnetic energy) and in the generator (kinetic energy) towards the low impedance charge Z constituted by the gun-rail, thus allowing the firing of projectile 2.

The speed at which the current transfer takes place depends essentially on the following three factors:
- the inductance of the supply circuit, forming storage of
inductive energy, as well as that of the circuit breaker, which will tend to
maintain a constant current therein,
- the own inductance of the load, which will oppose the transfer
current, and
- mutual inductance between the circuit breaker and the load, which
will oppose the development of f.é.m. self-induced in these
two circuit branches.

 Note that, with the proposed coaxial geometry, the f.é.m.

self-induced are largely canceled by f.é.m. mutually induced. And the low effective inductance of the coaxial structure of the device will allow a very fast current transfer.

 When the switching is complete, the arcs formed between the contact parts all go out and the stack returns to the position illustrated in FIG. 2. The circuit breaker remains in the fully open state, until reception of the command to next load applied to actuator 20.

 The complete operating cycle can be extremely short, which allows recurrence times as low as a few milliseconds, a value which is entirely compatible, in particular, with operation at a mains frequency of 50 or 60 Hz.

 In the case of such repetitive operation at a high rate, it may be necessary to provide suitable cooling systems, produced according to technologies in themselves conventional.

 It will also be noted that, from an energy point of view, the device of the invention makes it possible to distribute the switching energy over a large number of breaking arcs, between the various contact parts, instead of being concentrated on one single arc as with conventional spark gap circuit breakers. The erosion of the parts is thereby significantly reduced and the longevity of the device is increased accordingly.

Claims (4)

 distributed switching power.  of contact parts, a plurality of dissected arcs  Ampere forces, thus forming, between the different pairs  deviate axially from each other under the effect of said  so that the different contact parts can  in the open position, release the actuator means  and  Ampere forces produced by the current flowing through the empi  sufficient to overcome the axial forces resulting from  so as to exert an axial compression on the stack  in the closed position, activate the actuator means of  the actuator means so as to:  - circuit breaker release means, cooperating with  stacking in the direction of compression, and  end contact, suitable for mechanical stress  - actuator means (20), connected to one (6) of the parts  axial tion, in the direction of the stack,  - Means (16) for guiding the contact parts in transla  pectif (19, 18) of the circuit breaker,  end (6, 15) being electrically connected to a res pole  that with the adjacent piece, each of the contact pieces  where each part comes into mechanical and electrical contact  - a plurality of contact pieces (6-15) arranged in an empi  I. A fast circuit breaker (1) for high currents, characterized in that it comprises:  2. The circuit breaker of claim 1, comprising an envelope formed by two conductive cylindrical tubes (23, 24) placed end to end and separated by an insulating intermediate ring (25), each of the tubes being connected to a respective pole ( 19, 18) of the circuit breaker, and the envelope coaxially surrounding, at a distance from them, the contact parts of the stack.  3. The circuit breaker of claim 1, wherein said actuator means are double-acting means and said triggering means of the circuit breaker cooperate, when passing from the closed position to the open position, with these actuator means in activating these so as to actively urge the end contact part connected to the latter in the direction of the axial distance with respect to the other contact parts.  4. The circuit breaker of claim 1, wherein said guide means comprise a rod (16) of insulating material axially passing through the successive pieces of the stack.