EP0431306B1 - Overvoltage limiting circuit breaker - Google Patents

Abstract

The subject of the invention is an overvoltage limiting circuit-breaker comprising for each phase at least one disconnection chamber consisting of a sealed insulating envelope filled with a gas of high dielectric strength and comprising fixed and moving main contacts and fixed and moving arc contacts, and a means of driving the moving contacts, characterised in that the said envelope (1) encloses a varistor (20) and means of insertion (32, 42) in order:   - on the opening of the circuit-breaker, to insert the varistor (20), in parallel with the contacts, on separation of the main contacts (3, 9) and to disconnect the varistor before the end of opening travel of the moving arc contact (11)   - on the closing of the circuit-breaker, to insert the varistor, in parallel with the contacts, before the contacting of the arc contacts (6, 11) and to short-circuit the varistor on contacting of the main contacts (3, 9). <IMAGE>

Description

The present invention relates to a surge limiter circuit breaker.

It is known to have in parallel on the breaking chamber of a circuit breaker a variable resistor with the voltage across its terminals, called a varistor. This varistor, generally based on zinc oxides, makes it possible to avoid priming on the contacts of the circuit breaker and thus prevent their premature wear; in the case where the circuit breaker is in series with an inductive circuit such as vacuum transformer, reactance or motor, the varistor protects such a circuit against overvoltages which may occur during the opening operation of the circuit breaker.

Such use of a varistor is described, for example, in the Engineering Techniques collection, Tome E 2110, Varistances, page 13 and in US Patent No. 4,831,487.

When the circuit breaker is used to protect a line, it is subjected to overvoltages which can be high, in particular when the lines are cut when idle or in phase opposition. To avoid almost permanent operation of the varistor, it is necessary to have a switch in series with it which isolates it from the circuit when the circuit breaker is in the "open" position. This measure results in the production of conventional and bulky additional devices for the conventional type.

An object of the invention is to economically produce a voltage limiting circuit breaker by varistor in which the insertion of the varistor is done automatically when the circuit breaker opens, its disinsertion also being done automatically.

Usually, a varistor associated with a breaking chamber of a circuit breaker is placed in an insulating porcelain column arranged parallel to the breaking chamber, in atmospheric air. This column is subject to pollution; the appearance of pollution on one or more places of the porcelain leads to a modification of the distribution of the potential, being able to create zones of stress and heating with possibility of thermal runaway and destruction of the varistor.

Another object of the invention is to provide a voltage limiting circuit breaker by varistor, in which the varistor is not subject to any pollution.

Another object of the invention is to produce a voltage limiting circuit breaker by varistor in which the size of the varistor is reduced compared to the size of the varistors of the prior art.

• à l'ouverture du disjoncteur, insérer la varistance en parallèle sur les contacts à la séparation des contacts principaux et déconnecter la varistance avant la fin de course du contact d'arc mobile,
• à la fermeture du disjoncteur, insérer la varistance, en parallèle sur les contacts, avant la mise en contact des contacts d'arc et court-circuiter la varistance à la mise en contact de ces derniers.

All the aforementioned objectives are achieved by a circuit breaker comprising for each phase at least one breaking chamber consisting of a sealed insulating envelope filled with a gas with high dielectric strength and comprising main contacts and arcing contacts, characterized in that that said envelope encloses a varistor and means for:

• when the circuit breaker opens, insert the varistor in parallel on the contacts at the separation of the main contacts and disconnect the varistor before the end of travel of the movable arcing contact,
• when the circuit breaker is closed, insert the varistor, in parallel on the contacts, before bringing the arcing contacts into contact and short-circuit the varistor when they come into contact.

• la figure 1 est une vue groupée en coupe axiale d'un disjoncteur selon l'invention représenté en position enclenchée,
• la figure 2 est une vue groupée en coupe axiale du même disjoncteur en position déclenchée,
• la figure 3 est une vue partielle en coupe de l'extrémité d'un bras d'insertion de varistance,
• la figure 4 est une vue partielle en coupe de l'extrémité d'un bras d'insertion de varistance selon une variante,
• la figure 5 est une vue schématique d'un dispositif d'accrochage du bras d'insertion selon une variante.

The invention will be better understood from the description of a preferred embodiment of the invention, given by way of nonlimiting example, with reference to the appended drawing in which:

• FIG. 1 is a group view in axial section of a circuit breaker according to the invention shown in the engaged position,
• FIG. 2 is a group view in axial section of the same circuit breaker in the tripped position,
• FIG. 3 is a partial sectional view of the end of a varistor insertion arm,
• FIG. 4 is a partial sectional view of the end of a varistor insertion arm according to a variant,
• Figure 5 is a schematic view of a hooking device of the insertion arm according to a variant.

The circuit breaker of FIG. 1 comprises an insulating envelope 1, preferably made of porcelain, delimiting an interior volume 2 filled with 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 connected mechanically and electrically by arms 4 to a socket 5 of the circuit breaker. 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 blowing 12. The blowing means, which are not part of the present invention, have not been shown. They are made in a manner well known to those skilled in the art. The moving part is connected to an operating rod, not shown. The movable electrical contacts are connected to a second outlet not shown.

According to one of the features of the present invention, a varistor 20 is placed inside the breaking chamber; this varistor is preferably formed by a stack of metal oxide pellets based on zinc oxide (ZnO). The stack is pressed, at the upper part of the chamber, by a spring 21 which also bears against a metal cover 22 closing the chamber and electrically connected to the socket 5. A metal braid 19 provides electrical continuity between the varistor 20 and the cover 22.

The pellets are held and guided in an insulating tube 23 closed at its lower part by a metal end piece 24.

The mechanism for inserting and de-inserting the varistor is now described. It comprises an axial guide rod 25, fixed to the part 24 and terminated by a stop 26 provided with a damper 27, for example an elastomer plate. This rod serves to guide a semi-mobile assembly comprising a slide 30 provided with several arms 31 (preferably two arms) serving to support a contact ring 32, preferably made of copper. Magnetic pads 33 are inserted into the ring 32. The slide 30 is pushed down the figure by a spring 35 pressing against the end piece 24. A metal rod 37 connects the end piece 24 and the stop 26. The slide 30 crosses this rod and carries sliding contacts 38 which allow the electrical connection between the varistor 20 and the arm 31.

The circuit breaker is completed by a ring 42 provided with magnet pads 43 and carried by metal arms 44 in electrical connection with the movable contacts.

By construction, the arms 31 and 44 have a length such that, when the circuit breaker is in the tripped position (FIG. 2), the distance B between the rings 32 and 42 is less than the distance C between the arcing contacts 6 and 11 .

The circuit breaker works as follows:

1 / Closing the circuit breaker

We will refer to figure 2.

When closing, the moving element is pushed upwards in the figure.

There is successive contact between the rings 32 and 42, then between the arcing contacts 6 and 11 and finally between the main contacts 3 and 9. During the closing stroke, the spring 35 is gradually compressed. On contact between the rings 32 and 42, the varistor is inserted into the electrical circuit and the current flows through the ring 42, the ring 32, the arms 31, the sliding contact 38, the rod 37, the end piece 24, the varistor 20, the braid 19, the cover 22 and the socket 5.

On contact between the arcing contacts 6 and 11, the varistor is short-circuited.

2 / Opening of the circuit breaker

When the circuit breaker opens, the moving assembly is pulled down on the figure.

The relaxation of the spring 38 and the attraction of the magnets 33 and 43 allow the arms 31 to follow the movement of the movable contact.

Thanks to the attraction of the magnets, the rest position, shown in Figure 1, is exceeded, so that the slide 30 reaches the damper 27 of the stop 26, pulling the spring 35. The circuit breaker is adjusted so that the slider 30-damper 27 contact takes place approximately two milliseconds before the end of the opening stroke. The moving part continuing its travel, the rings 32 and 42 separate and the slide 30 returns to its rest position (position shown in FIG. 2 under the action of the spring 35).

When the currents are cut, when the arc goes out on the arcing contacts, the restored voltage is then applied to the varistor 20. If this voltage exceeds the nominal operating voltage of the varistor 20, a current establish between the rings 32 and 42. On the other hand, if this voltage becomes lower than the nominal voltage of the varistor 20, the varistor no longer conducts and becomes insulating again.

When the slide 30 reaches its rest position (Figure 2), the distance between the rings 32 and 42 is sufficient to hold the applied voltage, without operating the varistor.

As shown in Figure 3, the magnets will be arranged in the rings 32 and 42 so that in contact with the rings, a slight space 49 remains between the magnets 33 and 43; in this way, the arc is rather established on the copper parts of the rings.

To increase the dielectric strength of the cut-off interval B, it is possible to create an overpressure in the space between the rings. For this, as shown in Figure 4, the ring 42 is made integral with an annular cylinder 50 which therefore moves with the movable assembly. A piston 51, linked to the fixed parts of the circuit breaker, makes it possible to inject, by holes made in the ring 42 and the magnet 43, jets of compressed gas.

Figure 5 shows another attachment device in the engaged position of the contacts.

The arm 44 is fixed a corona hood 73 carrying a pivot 72 on which is articulated a hooking finger 70 terminated by a tip 76. A spring 71 presses the tip against the ring 32 and thus ensures its attachment. A hoop 74 serves as a stop for the end piece 76.

Before the end of the opening stroke, an insulating rod 75 comes to bear on the finger 70 to move the end piece 76 away from the ring 32, thereby freeing the arms 31 which return to their rest position.

It should be noted that in the case of the breaking of passive circuits such as capacitor bank, reactance, vacuum transformer, in which the restored voltage does not exceed 1 pu, the breaking and isolation interval B will no longer be necessary. The rings 32 and 42 can be made integral with one another by replacing them with a single tube. The spring 35 and the damper 27 will no longer be necessary.

It is also possible to connect the end 24 directly and electrically to the socket on the mobile contact side, by a part formed by two arms 31 terminated by a tube enveloping the corona guard 10.

Putting the varistor in the dielectric gas under pressure and inside a metal casing 22 makes it possible to reduce the dimensions of the varistor, and to avoid atmospheric pollution.

The invention has the following advantages:

1 / At the break:

When switching off, the voltage appearing across the circuit breaker is limited to a predetermined value, for example 1.6 p.u. , i.e. 1.6 Un 2/3, Un being the nominal network voltage.

In report No. 146 of the International Conference of Large Electric Networks (CIGRE), session of 1958, the authors proposed to limit the overvoltage to 1.9p.u. using circuit breakers fitted with opening resistance.

We know that in the event of a three-phase fault, the first pole that cuts will have a transient recovery voltage which can reach 1.5 x 1.5 p.u. The varistor then limits any overvoltage above 1.6 p.u.

In phase opposition or when the line is cut off at no-load, the voltage restored at the terminals of the circuit breaker can reach 2 p.u. or more.

In reactance failure, the overvoltage may exceed 2 p.u.

In all cases, the presence of the varistor prevents the terminal voltage from exceeding 1.6 p.u. and avoids, in many cases, direct ignition on the arcing contacts, sources of wear and overvoltage with steep front on the network.

Another advantage of the presence of a varistor is that, when cutting a line in the O 0.3 s FO cycle, during the first opening, thanks to the operation of the varistor, the line remains charged only at a lower value equal to about 0.5 pu, instead of 1 pu

In this way, on closing occurring 0.3 seconds later, the "downstream" overvoltage is lower. Under certain conditions, the closing resistance usually used on very high voltage networks can then be eliminated or avoid synchronized closing.

In very high voltage, the circuit breakers are all multi-chamber in series. We are afraid to further reduce the overvoltage at the time of reclosing on the empty lines, by operating the varistors.

For this, we delay by about 1 to 2 milliseconds the closing of a room or two rooms depending on the number of rooms per phase, so that the varistor (or varistors) which is inserted last sees a tension applied high exceeding its nominal operating value.

A resistance is thus inserted into the circuit making it possible to reduce the overvoltage.

The insertion time of the varistor at closing depends on the difference in distance between B and C and on the switching speed of the movable contact.

2 / In the open position of the circuit breaker:

As the resistance to lightning shock or to the operating shock of the cut-off interval B is lower than the resistance of the arcing contacts, in the event of an overvoltage exceeding the normalized value, the presence of the varistor limits the overvoltage absorbing energy.

3 / Pollution:

The damage caused by the pollution of the porcelains used for the varistors of the prior art is eliminated.

Claims (18)

1. A surge limiting circuit breaker comprising, for each phase, at least one interrupting chamber constituted by a gastight insulating enclosure filled with a gas having high dielectric strength, and containing fixed and moving main contacts, and fixed and moving arcing contacts, together with drive means for the moving contacts, the circuit breaker being characterized in that said enclosure (1) encloses a varistor (20) and varistor insertion means (32, 42) for:
      inserting the varistor (20) in parallel with the circuit breaker contacts on separation of the main contacts (3, 9) when the circuit breaker is being opened, and disconnecting the varistor before the end of the stroke of the moving arcing contact (11); and
      inserting the varistor in parallel with the circuit breaker contacts while closing the circuit breaker and prior to bringing the arcing contacts (3, 11) into contact with each other, the varistor being short-circuited when the arcing contacts come into contact.
2. A circuit breaker according to claim 1, characterized in that said varistor (20) is disposed coaxially with said enclosure.
3. A circuit breaker according to claim 1 or 2, characterized in that said varistor (20) is disposed between the cap (22) of the enclosure and the fixed contacts of the circuit breaker.
4. A circuit breaker according to any one of claims 1 to 3, characterized in that said varistor (20) is constituted by a stack of pellets enclosed in an insulating tube (23).
5. A circuit breaker according to claim 4, characterized in that said stack is compressed by a spring (21) bearing against a metal cap (22) connected to a current terminal (5) of the circuit breaker.
6. A circuit breaker according to claim 4 or 5, characterized in that said insulating tube is closed at one end by a metal endpiece.
7. A circuit breaker according to any one of claims 1 to 6, characterized in that said insertion means comprise a first contact (42) mechanically fixed to the moving contacts and electrically connected thereto, and a second contact (32) which is semimoving relative to the fixed contacts and which is electrically connected to said fixed contacts.
8. A circuit breaker according to claim 7, characterized in that when the circuit breaker is in its open position, said second contact (32) takes up a rest position such that the distance (3) between said first contact (42) and said second contact (32) is less than the distance (C) between the arcing contacts (6, 11).
9. A circuit breaker according to claim 7 or 8, characterized in that said second contact (32) is carried by a slide (30) sliding on a guide rod (25) which is coaxial with the enclosure and which is fixed to said endpiece (24), a spring (35) being interposed between said slide and said endpiece (24).
10. A circuit breaker according to claim 9, characterized in that said guide rod (25) is terminated by an abutment (26) provided with a shock absorber (27).
11. A circuit breaker according to claim 10, characterized in that said slide (30) carries sliding contacts (38) co-operating with a rod (37) extending between said abutment (26) and said endpiece (24) and passing through said slide.
12. A circuit breaker according to any one of claims 7 to 11, characterized in that said contacts (32, 42) are rings carrying magnets (33, 43).
13. A circuit breaker according to claim 12, characterized in that a gap (49) is left between said magnets (33, 43) when said contacts (32, 42) are in contact with each other.
14. A circuit breaker according to any one of claims 7 to 13, characterized in that it includes injection means for injecting a compressed gas into the zone between said contacts (32, 42) during a circuit breaker opening operation.
15. A circuit breaker according to claim 14, characterized in that said injection means comprise a cylinder (50) fixed to the contact (42) which is connected to the moving contacts, said cylinder cooperating with a fixed piston (51).
16. A circuit breaker according to any one of claims 1 to 11, characterized in that at least one chamber of a phase has a closure instant which is retarded relative to the closure instant of the other chambers.
17. A circuit breaker according to any one of claims 1 to 6, characterized in that the insertion means comprise two connected-together fixed pieces linking directly and electrically the end (24) of the varistor to the moving contact side of the lower current terminal.
18. A circuit breaker according to any one of claims 7 to 11, characterized in that the moving contact (42) includes at least one pivoting finger (70) urged by a spring (71) and terminated by a latching abutment (76) for engaging the semimoving ring (32), a fixed rod (75) co-operating with said finger to enable the semimoving ring (32) to be released.

Images