EP0444568B1 - Circuit breaker assisted by varistor - Google Patents

Abstract

The subject of the invention is a circuit-breaker comprising, for each pole, an arc chamber with fixed contacts and a moving rig comprising moving contacts, and, in parallel with each pole, an assembly comprising a varistor and a switch in series, the said switch being open when the circuit-breaker is disengaged and closed when the circuit-breaker is engaged, characterised in that the said switch comprises a moving contact (54, 94) driven by the moving rig when the circuit-breaker performs an engage manoeuvre, the said moving contact being constrained to follow, with a certain delay, the motion of the moving rig when the circuit-breaker performs a disengage manoeuvre. <IMAGE>

Description

The present invention relates to a high-voltage circuit breaker fitted with resistors to limit overvoltages at cut-off.

We know, in particular from French patent n ° 81 06 444 and from French patent n ° 81 16 291 (FR-A-2512267), a circuit breaker according to the preamble of claim 1, the breaking chamber of which also contains a resistance , called closing resistance, intended to protect the circuit breaker against overvoltages during a closing operation. The closing resistor is connected for a short time during the closing of the circuit breaker by means of an insertion mechanism described in the aforementioned patent.

There are also known high voltage circuit breakers fitted with varistors, in particular for operating the shunt reactors of the electrical networks; the purpose of the presence of varistors, also called non-linear resistors or variable resistors or resistors depending on the voltage, is to reduce overvoltages.

It is known that the lower the operating threshold of the varistor, the more effective the overvoltage protection. To obtain a low varistor operating threshold, a small number of varistor elements must be combined in series; the drawback is that the energy absorbed by each varistor element is then high.

The overvoltage limit value which can be protected by varistor is currently around 1.6 p.u. (1 p.u. = Un x √2 / √3 at peak value, Un being the nominal phase voltage).

To limit the overvoltage below 1.6 p.u., it has been proposed to put in series with the varistor, a switch which separates the latter from the network after tripping of the circuit breaker.

An object of the present invention is to provide a circuit breaker based on this principle, the production of which is simple and economical, the object being achieved by a circuit breaker according to claim 1.

The invention applies equally to circuit breakers, of conventional or shielded type, in which the varistor is arranged, for each of the poles of the circuit breaker, in a column separate from that which contains the breaking chamber, as well as to circuit breakers in which the varistor is placed in the same column as the breaking chamber.

The invention applies to circuit breakers having several breaking chambers in series per phase, and in particular to circuit breakers having two breaking chambers per phase, arranged in T or V.

The flexible maneuvering arrangement according to the invention makes it possible to avoid any system of connecting rods, which makes the device particularly simple while being very reliable.

Advantageously, the switch and the varistor are arranged in a porcelain envelope filled with sulfur hexafluoride (SF6). The switch in series has a lower cut-off interval and tripping speed than those of the cut-out chamber.

Advantageously, said flexible hose is fixed, inside the column containing the breaking chamber, to a thrust arm, in the direction of the moving element, by a spring, said arm being able to be brought into contact with the moving element in the using insulating rods.

Said arm can carry a first cylinder provided with a flange defining with a second fixed cylinder provided with a flange a variable volume, said volume being maximum when the circuit breaker is in the on position, said volume being leak tight near and constituting a device retarder of the movement of said arm during a tripping operation of the circuit breaker.

Advantageously, one of said cylinders carries an adjustable valve.

According to a variant, said flexible hose is connected to the operating rod by means of a retarding member.

To limit the voltages on the varistors, advantageously resistive discs are inserted in the stacks of varistor elements.

The circuit breaker may further comprise, inside each breaking chamber, a resistor associated with a mechanism for its insertion for a brief instant when the circuit breaker closes.

According to another variant, the breaking capacity of the switch in series can be improved while retaining an acceptable voltage stress on the varistor when the circuit breaker is in the tripped position.

This is obtained by making the switch in series so that in the open position, it has a capacity of value between 0.6 and 1.1 times that of the varistor.

In a first embodiment, the means for conferring on the switch the desired capacity comprise first and second fixed metal frames facing each other, in electrical connection respectively with the movable contact and the fixed contact of the switch.

Said reinforcements have the form of rings or have a large flat facing surface.

In a second embodiment, the means for giving the switch the desired capacity comprise at least one cylinder of material with high dielectric constant, in electrical contact at its respective ends with fixed plates in electrical connection respectively with the movable contact and the fixed switch contact.

In a first embodiment, the material of the cylinders is araldite quartz.

As a variant, said cylinder is a commercial ceramic capacitor.

• la figure 1 est une vue partielle en coupe axiale d'un pôle d'un disjoncteur selon l'invention, dans lequel la chambre de coupure et la varistance sont disposées dans des colonnes distinctes,
• la figure 2 est une vue partielle d'un disjoncteur à deux chambres de coupure par phase, en T, selon l'invention,
• la figure 3 est une vue partielle d'un disjoncteur selon l'invention, à deux chambres de coupure par phase disposées en T,
• la figure 4 est une vue en coupe axiale de la colonne contenant la varistance et l'interrupteur en série, ce dernier étant muni d'anneaux,
• la figure 5 est une vue en coupe axiale de la colonne contenant la varistance et l'interrupteur en série, la valeur de la capacité de l'interrupteur étant ajustée au moyen de condensateurs en céramique.

The invention will be clearly understood in the light of the description given below of several embodiments of the invention, with reference to the appended drawing in which:

• FIG. 1 is a partial view in axial section of a pole of a circuit breaker according to the invention, in which the breaking chamber and the varistor are arranged in separate columns,
• FIG. 2 is a partial view of a circuit breaker with two T-phase cut-off chambers according to the invention,
• FIG. 3 is a partial view of a circuit breaker according to the invention, with two cut-off chambers per phase arranged at T,
• FIG. 4 is a view in axial section of the column containing the varistor and the switch in series, the latter being provided with rings,
• Figure 5 is an axial sectional view of the column containing the varistor and the switch in series, the value of the capacity of the switch being adjusted by means of ceramic capacitors.

The circuit breaker of Figure 1 is shown in the tripped position. It comprises an insulating envelope 1, preferably made of porcelain, enclosing the breaking chamber, and resting on an insulating column 100 of which only a part has been shown. The envelope 1 is closed at its upper part by a metal cover 1A.

The interior 2 of the envelope 1 is sealed and contains a gas with high dielectric strength, such as sulfur hexafluoride, under a pressure of a few bars.

The circuit breaker comprises a fixed main contact formed by a tube 3 mechanically and electrically connected by arms 4 to a first socket 5, in electrical contact with the cover 1A. The contact 3 is integral with a fixed arcing contact 6 also consisting of a tubular part; this contact 6 is electrically connected to contact 3.

The moving part of the circuit breaker comprises a movable main contact formed by contact fingers 9, protected by a corona hood 10 and cooperating with the tube 3. It also includes an arcing contact formed by fingers 11, cooperating with a nozzle 12. The means of blowing, which are not part of the present invention, have not been shown. The moving element is connected in a known manner to an operating rod, not shown. The movable electrical contacts are electrically connected to each other by a disc 13 itself fixed to a metal cylinder 14 electrically connected by sliding contacts not shown to a second socket 5A.

The varistor is arranged inside a sealed insulating column 20 closed at its ends by metal plates 21 and 22, electrically connected to the terminals of the circuit breaker by conductors 23 and 24. The interior of the envelope is filled with 'sulfur hexafluoride.

The varistor consists of varistor elements in the form of discs based on zinc oxides, stacked in two coaxial but separate piles 26 and 36.

The stack 26, made up of elements 26A, is placed inside an insulating cylinder 27 fixed under the upper plate 21; the cylinder 27 is closed at its lower part by a metal plate 28 extended by a cylindrical part 28A; the lower element of the stack 26 is in close contact with the plate 28 by virtue of the pressure exerted by a spring 29 resting on the one hand on a metal plate 30 situated at the top of the stack 26 and on the other hand on the plate 21. A metal braid 31 provides electrical continuity between the battery 26 and the plate 21.

The discs 26A of the stack 26 are pierced in their center with a hole so that the axis of the stack has a cylindrical channel in which a rod can slide, as will be seen below. Similarly, the cylindrical part 28A has a central bore for the passage of the rod.

The battery 36 is placed inside an insulating cylinder 37, fixed above the plate 22; elements 36A of the stack 36 do not have a central hole; to the upper part of the cylinder 37 is fixed a metal cover 38 provided with a cylindrical protuberance 38A intended to receive the rod which has been mentioned above. Between the lower element of the stack 36 and the plate 22, and separated by a metal washer 39 are disposed resistant disks 40 whose role will be explained later. The stack is clamped by a spring 41 resting on the one hand on the cover 38 and on the other hand on a metal plate 42 surmounting the battery 36. A metal braid 43 provides electrical continuity between the battery 36 and the plate 38.

The cover 1A carries, at its lower part, a metal cylinder 50 provided with lights in which slides a metal arm 51. To the arm 51 is fixed a first end of a metal hose 52 which passes through the cover 1A through an orifice of the latter ; the other end of the metal hose is connected to a rod 53, made of insulating material, which engages in the axis of the stack 26; the other end of the rod 53 is fixed to a metal rod 54 which passes through the cylinder 28A and cooperates electrically with the latter by means of sliding contacts 28B.

The hose 52 runs, outside of the columns 1 and 20, in a flexible sheath 56 connected in leaktight manner to the cover 1A and to the cover 21.

The arm 51 is pushed by a spring 57 bearing on the cover 1A. Insulating rods 58, fixed at one end to the arm 51, bear at their other end on the corona hood 10 of the circuit breaker.

The apparatus is completed by a device making it possible to delay the movement of the arm 51, when, the circuit breaker being in the latched position, a triggering suddenly drives the moving assembly towards the bottom of the figure. This device comprises a first cylinder 60 fixed to the cover 1A and provided with a flange 61 towards the outside, and a second cylinder 62, integral with the arm 51 and provided with a flange 63 facing inwards and placed above the flange 61; in this way, the cylinders and the flanges define a variable and tight volume 64, except for leaks; these leaks can be calibrated by a valve 65 placed for example on the cylinder 62.

The total length of the hose 52, the insulating rod 53 and the metal rod 54, and the distance between the batteries 26 and 36 are chosen so that, when the circuit breaker is in the tripped (open) position, the rod 54 is in its position furthest from contact 38A and that, when the circuit breaker is in the latched (closed) position, the rod 54 is in contact with contact 38A; this amounts to saying that the stroke A of the circuit breaker is equal to the stroke of the switch constituted by the rod 54 and the contact 38A.

The operation of the device is as follows.

In the engaged position, the moving element is in the high position; the rods 58 are pushed back by the cover 10, the arm 51 is in the high position, the spring 57 is compressed, the volume 64 is maximum, the switch 54-38A is closed. Varistor 26-36 is short-circuited by the circuit breaker contacts.

When the circuit breaker trips, the contacts separate very quickly. The cover 10 leaves the rods 58 which cannot follow the movement due to the delay device. As a result, the switch 54-38A remains closed for an instant, so that the varistor remains connected to the terminals of the circuit breaker; if an overvoltage occurs, the varistor works and plays its protective role; after a time which is determined and regulated by the leaks of the volume 64, the arm 51 moves under the action of the spring 57; the rod 54 leaves the contact 38A, which, after extinction of the arc formed, disconnects the varistor. It is observed that the cutting of the arc between the rod 54 and the contact 38A occurs at a time when the arc in the breaking chamber is already extinguished; the voltage between the rod 54 and the contact 38A is the transient recovery voltage which tends towards the single voltage; the current in the varistor being very weak, of the order of a few thousandths of amperes, the arc will extinguish by itself even when the rod 54 has finished its stroke.

The resistors 40 serve to reduce the voltage on the varistors 26 and 36 in the event of high restored voltage.

It will be noted that the varistor stack 26 can include, like the stack 36, resistive elements 40.

FIG. 2 represents an alternative embodiment of the invention, applied to a circuit breaker in which the varistor is placed in a column 20 distinct from column 1 enclosing the breaking chamber; but unlike Figure 1, the switch is operated by a mechanism directly connected to the operating rod of the circuit breaker.

In FIG. 2, where the elements common to this figure and to FIG. 1 have been given the same reference numbers, the insulating column supporting the breaking chamber and enclosing the insulating operating rod 121 has been designated by the reference 120. The latter is extended by a metal portion 122 connected to the movable element of the breaking chamber. It is also connected to a hose 123 fixed to the rod 154 of the switch, with the interposition of a delay mechanism 160, which can be similar to those previously described. The rod 154 of the switch cooperates with a contact fixed at the end of the stack of varistors 26. The hose is placed in an insulating sheath 123. The operation is identical to that described above.

FIG. 3 shows how the invention can be applied to a circuit breaker having two breaking chambers 201 and 202, arranged in a T shape.

The reference 203 designates an insulating column common to the two breaking chambers and placed on a metal frame 204 carrying an operating mechanism 205.

An operating rod 206, common to the two breaking chambers, ensures the opening and closing of the two chambers of the circuit breaker by means of a mechanism 207.

The interrupting chambers 201 and 202 are each associated with an insulating column; these columns are respectively referenced 211 and 212; they each contain a varistor in two batteries; only column 211 is shown in detail; column 211 contains a stack of varistor elements 216A without central hole, terminated by a contact 218 and a stack of varistor elements 236A, with central hole, supported by a metal cone 219 electrically connecting the end of the battery to a terminal of the breaking chamber 211. The elements 236A are traversed by an insulating hose 220 connected by a first end to the operating rod 206 by means of a delay mechanism 260. The second end of the hose is connected to a metal rod 221 cooperating with contact 218. The hose, outside the stack of elements 236A, is placed in a sheath 222.

Column 212 is similarly equipped.

The operation of the circuit breaker is completely identical to the operation of the circuit breakers of Figures 1 and 2.

It is possible to make a hybrid circuit breaker, protected both against overvoltage on closing and against overvoltage on opening, by having, in parallel to the terminals of the circuit breaker, a column containing a varistor with switch as it has been exposed opposite Figures 1, 2 and 3; in this case, the switch is actuated by a hose passing through the column of the circuit breaker and connected to the insertion mechanism mentioned above.

We know that under the permanent operating voltage, the varistor behaves like a capacitor. In the usual applications in the field of high-voltage circuit breakers, the varistor has a capacity of between twenty and thirty picofarads, the exact value depending on the diameter and the height of the varistor.

If the switch in series has its own capacity of the same order of magnitude, the voltage restored between its terminals will then be approximately half that applied to the breaking chamber which is connected in parallel on the varistor and switch assembly.

In case of phase opposition at 2 p.u. for example, the varistor will only be subjected to a voltage equal to 1 p.u.

In FIG. 4, first means have been illustrated for giving the series switch a capacitance having an order of magnitude close to that of the varistor.

To give the switch the desired capacity, it is fitted with a first frame 300, in electrical connection with the movable contact 54 via the contacts 28B and the block 28A, and with a second frame 301, in electrical connection with the contact 38A by the metal block 38.

The fixed and facing reinforcements can take the form of washers or any other shape provided that the reinforcements have a large planar facing surface.

It is easy to give the switch in the open position the desired capacity, by a suitable choice of the surface of the reinforcements and their distance.

If the reinforcements are plane surfaces of value S (in cm²) separated by a distance d (in cm), the capacity C (in picofarads) of the capacitor formed by the reinforcements is given by the known formula:
C = 0.139 KS / d, where K is a coefficient dependent on the gas of enclosure 20, and which can be taken equal to 1 for sulfur hexafluoride.

Note that when the circuit breaker is in the on position, the distance between the armatures is well determined; the varistor-armature assembly can be used to protect the line against high lightning strikes or high operating overvoltages. The priming between the armatures which act as spark gaps, operates the varistor, which absorbs all the energy of the lightning strike or the operating overvoltage.

The large value of the coefficient of non-linearity of the zinc oxide varistor and the presence of SF6 at a pressure of several bars makes it possible to easily interrupt the current of the switch.

It is a longitudinal protection to compare to the classic transverse protection (phase-to-earth) obtained with conventional surge arresters.

In Figure 5, there is shown another embodiment. The elements common to Figures 4 and 5 have been given the same reference numbers.

The value of the capacity of the series switch is adjusted by placing, between the plates 28 and 38, suitably enlarged, 310 cylindrical parts, made for example of araldite quartz or any other material having a high dielectric constant.

It is also possible to use one or more commercial cylindrical ceramic capacitors, of small diameter and of sufficient length to hold the voltage restored.

For example, a ceramic capacitor 40 mm long and 18 mm in diameter, could give a capacity of about 25 picofarads.

The invention finds application in the production of high-voltage line circuit breakers, conventional (with an insulating jacket) or shielded (with a metal jacket), as well as circuit breakers used to connect reactors or banks of capacitors.

Claims (14)

1. A circuit breaker comprising, for each pole, at least one first insulating case containing an interrupting chamber having fixed contacts and moving equipment including moving contacts, and in parallel with each interrupting chamber a series circuit comprising a resistor and a switch, said switch being open when the circuit breaker is disengaged and being closed when the circuit breaker is engaged, said switch comprising a moving contact (54, 94) driven by the moving equipment when the circuit breaker is performing an engagement operation, said moving contact of the switch being constrained to follow with a certain delay the movement of the moving equipment when the circuit breaker performs a disengagement operation, the resistor being disposed in a second case (20) distinct from the first case (1), said moving contact of the switch comprising a metal rod (54), with the resistor being constituted by a stack (36) of resistor components, one end of the stack (36) of components being provided with a female contact (38A) cooperating with said rod, the circuit breaker being characterized in that the resistor is a non-linear resistor, known as a "varistor", the resistor components being varistor components, and in that the varistor is constituted by two stacks (26, 36) of varistor components, the two stacks being separated by a distance not less than the isolation distance of the circuit breaker, the second (26) of the stacks having said moving contact passing therethrough, of which the metal rod (54) is fixed to a flexible metal drive member (52, 123) interconnecting the two cases (1, 20) outside the cases, said metal rod (54) being electrically connected to one end of the second stack (26).
2. A circuit breaker according to claim 1, characterized in that said flexible drive member (52) is fixed inside the first case (1) to an arm (51) which is urged towards the moving equipment by a spring (57), said arm (51) being capable of being put into mechanical contact with the moving equipment by means of insulating rods (58).
3. A circuit breaker according to claim 2, characterized in that said arm (51) carries a first cylinder (62) provided with a flange (63) co-operating with a second cylinder (60) which is fixed and which is provided with a flange (61) to define a variable volume (64), said variable volume being at a maximum when the circuit breaker is in the engaged position, said volume being closed, but leaky and constituting a device for delaying motion of said arm (51) during a circuit breaker disengagement operation.
4. A circuit breaker according to claim 3, characterized in that one (62) of said cylinders carries an adjustable valve (65).
5. A circuit breaker according to claim 1, characterized in that said flexible drive member (123, 222) is linked to the operating rod (121, 206) of the circuit breaker via a delay member (160, 260).
6. A circuit breaker according to any one of claims 1 to 5, characterized in that resistor disks (40) are inserted in the varistor component stacks.
7. A circuit breaker according to any preceding claim, characterized in that it comprises a resistance inside each interrupting chamber and associated with a mechanism for inserting the resistance briefly while the circuit breaker is being closed.
8. A circuit breaker according to any preceding claim, characterized in that it includes means (300, 301, 310) to give the series switch, when in the open position, a capacitance lying in the range 0.6 times to 1.1 times the capacitance of the varistor.
9. A circuit breaker according to claim 8, characterized in that said means comprise first and second facing fixed metal capacitor plates (300, 301) respectively in electrical contact with the moving contact (28) and with the fixed contact (38A) of the switch.
10. A circuit breaker according to claim 9, characterized in that said capacitor plates (300, 301) are in the form of a rings.
11. A circuit breaker according to claim 9, characterized in that said capacitor plates (300, 301) have large flat facing areas.
12. A circuit breaker according to claim 8, characterized in that said means comprise at least one cylinder (310) of material having a high dielectric constant, the cylinder being in electrical contact via its respective ends with fixed plates (28, 38) in electrical contact respectively with the moving contact (54) and with the contact (38A) of the switch.
13. A circuit breaker according to claim 12, characterized in that the cylinders are made of quartz Araldite.
14. A circuit breaker according to claim 12, characterized in that the said cylinder is a commercially-available capacitor.

Images