EP0430123B1 - High-tension switch with variators - Google Patents

Abstract

The invention relates to a high-voltage circuit breaker. <??>The subject is a high-voltage circuit breaker comprising at least one cutoff chamber (1, 2) and, in parallel with this cutoff chamber, on the one hand a varistor (V1, V2) in series with a switch (I1, I2) and, on the other hand, a distributing capacitor (C1, C2), characterised in that a purely ohmic resistor (R1, R2), of value lying between 30 and 300 ohms, is inserted in series with the said varistor (V1, V2). <??>Application in particular to reactance circuit breakers. <IMAGE>

Description

The present invention relates to a high voltage circuit breaker with varistors.

There are 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 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. The higher the overvoltage, the greater the energy absorbed by the varistor.

The desired overvoltage limit is often in the range of 1.5 to 1.6 p.u.

For line circuit breakers fitted with varistors, there is an important problem to consider: on the one hand, we want to set the overvoltage threshold at 1.5 p.u .; on the other hand, the overvoltage in phase opposition can reach 2 to 2.5 p.u.

It has been proposed to place, in series with the varistor, an opening switch to avoid applying too high a voltage to the varistor; despite this arrangement, the varistor remains the seat of too much energy dissipation. Let us take the example of a phase opposition, at the cut-off; a tension of 2 p.u. approximately is applied to the varistors for 1 period (at 50 or 60 Hz) before the arc is definitively extinguished on the switch contacts.

We know that at a voltage of 2 pu, the current can reach a high value. For exemple:
at 1 pu, the current can be 5 / IO OOO ampere,
at 1.5 pu, the current reaches 1 amp,
at 2 pu, the current can exceed 2000 amps.

As the duration of application of the voltage between 1.5 pu and 2 pu lasts several milliseconds, the energy dissipated in the varistors reaches several thousand kilojoules.

It is necessary to reduce this energy, while ensuring proper operation at 1.5 p.u.

The case of voltage transfer across a multi-chamber circuit breaker, by partial strikes, in the event of a fault break or no-load line, can also lead to thermal overload of the varistors.

An object of the present invention is to provide a high voltage circuit breaker with varistors allowing the solution of this problem.

The subject of the invention is a high voltage circuit breaker comprising at least one breaking chamber and, in parallel on this breaking chamber, on the one hand a varistor in series with a switch and, on the other hand, a distribution capacitor, characterized in that a purely ohmic resistance, of value between 30 and 300 ohms, is inserted in series with said varistor.

In a particular embodiment, the resistor is formed by a first stack of discs arranged in an insulating tube in which the varistor is placed in the form of a second stack of discs, said tube being placed inside an insulating column filled with a gas with good dielectric properties.

As a variant, said resistor is formed by a stack of discs placed in an insulating tube, said tube being arranged horizontally and being connected mechanically and electrically, on one side to a column containing the main breaking chamber and, on the other side, to a column containing the varistor.

According to another variant, the resistance formed by rods and the varistor are housed side by side in the insulating envelope which overcomes the main breaking chamber.

According to another variant, the varistor is arranged in a column provided with a cover having a horizontal extension containing the associated resistance, the extension being closed by a bottom provided with current outlet.

Advantageously, the cover having an extension containing the resistance overcomes the main chamber.

The varistor material is chosen from compounds based on zinc oxides and silicon carbide.

• la figure 1 est une vue schématique d'un disjoncteur selon l'invention, à deux chambres de coupure,
• la figure 2 est une vue partielle en coupe axiale d'une colonne isolante contenant une varistance et sa résistance associée,
• la figure 3 est une vue partielle en coupe axiale d'une colonne isolante contenant une varistance, la résistance associée étant placée entre cette colonne et la colonne contenant la chambre de coupure principale,
• la figure 4 est une vue partielle schématique en coupe d'une autre variante de réalisation dans laquelle la varistance et la résistance sont disposées côte à côte dans la même colonne isolante,
• la figure 5 est une vue schématique d'un disjoncteur à deux chambres de coupure en série, dans lequel la résistance associée à une varistance est disposée dans un prolongement du couvercle de la colonne contenant ladite varistance.

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

• FIG. 1 is a schematic view of a circuit breaker according to the invention, with two breaking chambers,
• FIG. 2 is a partial view in axial section of an insulating column containing a varistor and its associated resistance,
• FIG. 3 is a partial view in axial section of an insulating column containing a varistor, the associated resistance being placed between this column and the column containing the main breaking chamber,
• FIG. 4 is a schematic partial sectional view of another alternative embodiment in which the varistor and the resistance are arranged side by side in the same insulating column,
• Figure 5 is a schematic view of a circuit breaker with two interrupting chambers in series, wherein the resistor associated with a varistor is arranged in an extension of the cover of the column containing said varistor.

In FIG. 1, the reference L designates a phase of a high-voltage line into which a circuit breaker is inserted comprising, for each phase, two interrupting chambers in series 1 and 2. For the simplicity of the drawing, there is no not shown the supports of the switching chambers, nor their operating mechanisms. The breaking chambers are, as is well known, made up of a insulating column filled with a gas with high dielectric strength such as sulfur hexafluoride, under a pressure of a few bars.

In parallel on each of the switching chambers are arranged insulating columns respectively C1 and C2; these columns contain a gas or a dielectric liquid and house a capacitor and intended for the distribution of the voltage between the two breaking chambers.

Each chamber comprises in parallel another column, respectively K1 and K2, inside which there are, connected in series, a varistor (V1, V2) and a switch (I1, I2).

According to the main characteristic of the invention, there is, in series in the circuit of columns K1 and K2, a resistance (R1, R2).

We will show on an example how we can calculate the value of additional resistors R1 and R2. The common ohmic value of the resistors R1 and R2 will be designated below by Ra.

It is desired that for an overvoltage U equal to 2 p.u., the current in the varistor does not exceed a threshold value Is.

A Is corresponds a threshold voltage Us of the varistor. The internal resistance of the varistor to this threshold is: $$\text{Rs = Us / Is}$$

If Ra is the value of the additional resistance making it possible to limit the current to Is, the following operating equation comes, neglecting the impedance of the circuit: $$\text{U = Is (Ra + Rs)}$$

Let's take a numerical example:
U = 900 kV peak
Is = 700 A peak
Us = 845 kV peak
Rs = 1207 ohms

We deduce Ra = 80 ohms, or 40 ohms for each of the resistors R1 and R2.

During the passage of the current of 700 Acrête, the tension on each resistance is 28 000 V peak.

The total duration of transition to 700 A peak in phase opposition can be estimated at 6 milliseconds.

These considerations make it possible to determine the dimensions of the resistors R1 and R2 which, in general, will be between 30 and 300 ohms

Returning to the previous example, the thermal energy dissipated by the resistor during operation in phase opposition will be approximately:
$$\frac{\text{40 x 700²x 6. 10⁻³}}{\text{2}}\text{, or about 60,000 joules}$$

It should be noted that in the event of a rapid temporary overvoltage (case of short-circuit cut, case of voltage transfer), exceeding 2 p.u. or exceeding the voltage threshold of a varistor element, the presence of the additional resistance Ra makes it possible to effectively reduce the current to an acceptable value momentarily, for example 1,500 amperes in short time with 2.4 p.u. The voltage across each resistor R1 and R2 is then 60,000 V peak.

At the end of the opening travel of switches I1 and I2, the varistors V1 and V2 are completely isolated from the circuit.

It should be noted that the use of additional resistors is not valid for the protection of phase-to-earth faults. Indeed, during a lightning strike on the line, the presence of additional resistors prevents the rapid flow of charges. A high overvoltage then occurs on the resistor, given the large intensity of the discharge current which can reach ten kiloamperes, and the high rate of increase of the current.

It should be noted that to avoid a significant voltage drop at the time of the voltage transfer which generates a high frequency, the connection between the resistor and the varistor must be as short as possible.

Several embodiments of the invention will now be described.

Figure 2 is a partial view in axial section of the column K1 containing in particular the varistor V1 and the resistor R1.

Inside the ceramic column K1 is placed a tube of insulating material 9 in which the varistor V1 and the resistor R1 are placed.
The varistor V1 consists of a stack of discs 10 based on zinc oxides or on silicon carbide (CSi); the top and the base of the stack are closed by metal discs, 11 and 12 respectively.

The resistor R1 consists of a stack of discs 13, for example made of conductive ceramic based on carbon. The stack is placed directly above the metal disc 11, and is in contact at its upper part with a metal disc 14. A spring 15 presses the disc 14 against the stack R1 by pressing on the inside of a cover metal 16 closing the column K1. A metal braid 17 ensures the passage of current between the cover 16 and the disc 14.

The reference 18 designates the fixed contact of the switch I1 and the reference 19 the end of the movable contact; as the embodiment of the switch is well known and goes beyond the scope of the present invention, the switch has not been shown in detail. A metal cover 20, surrounding the end of the tube 9 and part of the fixed contact 18, makes it possible to smooth the equipotential curves in this zone.

The cover 16 is electrically connected by a link 21 to the top of the main breaking chamber 1, not shown in FIG. 2, but shown diagrammatically in FIG. 1.

The interior of column K1 is filled with a gas with good dielectric properties promoting cleavage, such as sulfur hexafluoride, pure or mixed, under a pressure of a few bars.

FIG. 3 partially represents the columns 1 and K1, the resistor R1 being disposed this time outside these columns.

The varistor V1 always consists of a stack of discs 10, surmounted by a metal disc 25 pressed by a spring 28 bearing on a metal cover 27 closing the column K1. A metal braid 28 between the disc 25 and the cover 27 ensures the passage of current.

Resistor R1 is formed by a stack of discs 13 placed in an insulating tube 30, for example made of epoxy glass, which can be provided with fins 31, for example made of silicone.

The tube 30 is hermetically closed at its ends by metal plates 32 and 33; the discs 13 are pressed by a spring 34 bearing between the plate 32 and a metal disc 35 at the end of the stack; a metal braid 36, between the plate 32 and the disc 35, ensures the passage of current.

The tube 30 is arranged horizontally, between the columns 1 and K1, to which it is mechanically and electrically connected. For this, connections 37 and 38 respectively connect on the one hand the plate 32 and the metal top 39 of the column 1, and on the other hand the plate 33 and the cover 27.

Resistor R1 only sees current flow for a very short time. In the "open" or "closed" position of the circuit breaker, the connections 37 and 38 are at the same potential; there is therefore no permanent voltage on the resistor R1.

Under these conditions, the use of synthetic insulation products has no drawbacks.

The discs 13 can be formed in a single block and closed by molding in a synthetic envelope.

FIG. 4 illustrates an alternative embodiment, in which the varistor V1 and the resistor R1 are housed in the casing 1 containing the main breaking chamber.

The varistor V1 is formed by a stack of discs 10 placed in a tube 40 fixed to the cover 41 of the column 1. This cover is placed at the top of an insulating cylindrical envelope 42 provided with fins 43; this envelope, which surmounts column 1, may be made of porcelain or of insulating synthetic material.

As before, the stacking of the discs 10 is surmounted by a metal disc 44 serving to support a spring 45 which also bears against the cover 41.

The lower part of the tube 40, not shown, serves as a support for the semi-fixed contact for inserting the varistor, as has been described for example in French patent 2,512,267.

The resistor R1 is formed by one or more rods 70 of small diameter based on carbon (ceramic resistor), housed in insulating tubes 71 and fixed between the cover 41 and the socket outlet 51 of the chamber 1. The number of sticks depends on the energy to be absorbed.

Reference 52 designates the fixed contact tube for the passage of permanent current.

FIG. 5 illustrates another embodiment of the invention, for a circuit breaker with two interrupting chambers per phase. The elements common to FIG. 5 and to FIG. 1 have been given the same reference numbers or signs.

Varistors V1 and V2 are arranged in columns K1 and K2 respectively; they are held by insulating supports, 81 and 82, fixed to the metal covers 91 and 92 surmounting the columns K1 and K2.

The metal covers 91 and 92 have horizontal cylindrical extensions 91A and 92A in which the resistors R1 and R2 are housed respectively. The resistors R1 and R2 are fixed, on the one hand to the supports 81 and 82, on the other hand to metallic bottoms 91B, 92B closing the cylinders 91A, 92A. The bottoms 91B, 92B have current sockets 91C, 92C, connected by a connection tube 94 for placing the two breaking chambers 1 and 2 in series.

The columns K1 and K2 and the cylindrical extensions of the covers form watertight assemblies filled with dielectric gas. The varistor-resistance pairs, V1, R1 and V2, R2, are found in the same dielectric fluid.

Of course, the cover 91 with its horizontal cylindrical extension 91A can very well also be mounted on the insulating casing 1 of the main chamber.

The invention applies to high voltage circuit breakers and in particular to reactance circuit breakers.

Claims (7)

1. A high tension circuit breaker comprising at least one circuit-breaking chamber (1, 2) and, in parallel with said circuit-breaking chamber, firstly a varistor (V1, V2) in series with an interrupter (I1, I2), and secondly a tension-distributing capacitor (C1, C2), the circuit breaker being characterized in that a linear resistor (R1, R2) having a resistance lying in the range 30 ohms to 300 ohms is inserted in series with said varistor (V1, V2).
2. A circuit breaker according to claim 1, characterized in that the resistor (R1) is constituted by a first stack of disks (13) disposed in an insulating tube (9) in which the varistor (V1) is placed in the form of a second stack of disks (10), said tube being placed inside an insulating column filled with a gas having good dielectrical properties.
3. A circuit breaker according to claim 1, characterized in that said resistor (R1) is in the form of a stack of disks (13) placed in an insulating tube (30), said tube being disposed horizontally and being mechanically and electrically connected at one end to a column (1) containing the main circuit-breaking chamber and at its other end to a column (K1) containing the varistor (V1).
4. A circuit breaker according to claim 1, characterized in that the varistor (V1) and the resistor (R1) constituted by sticks (70) are housed side by side in an insulating casing (42) which surmounts the main circuit-breaking chamber.
5. A circuit breaker according to claim 1, comprising at least one circuit-breaking chamber, the circuit breaker being characterized in that the varistor (V1, V2) is disposed in a column (K1, K2) provided with a lid (91, 92) having a horizontal extension (91A, 92A) containing the associated resistor (R1, R2), the extension being closed by an end (91B, 92B) provided with a current terminal (91C, 92C).
6. A circuit breaker according to claim 5, characterized in that the lid (91) having an extension (91A) containing the resistor (R1) surmounts the main circuit-breaking chamber.
7. A circuit breaker according to any one of claims 1 to 6, characterized in that the varistors are made of a substance selected from silicon carbide and compounds based on zinc oxides.

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