FR2680043A1 - Circuit breaker with multiple cutoff equipped with varistors - Google Patents

Abstract

The present invention relates to a circuit breaker comprising, for each phase, at least two main cutoff chambers (1) each having a varistor (2) mounted in parallel with its terminals. Each varistor is sized so as to limit the voltage to 3 p.u, no distribution capacitor being mounted in parallel with the cutoff chamber terminals. Thus the problem of the high price of the capacitors is eliminated, in particular for very high-voltage circuit breakers.

Description

MULTI-CUT CIRCUIT BREAKER WITH VARISTORS

  The present invention relates to a circuit breaker comprising, for each phase, at least two main breaking chambers each having a varistor mounted in

parallel to its terminals.

  In French patent application 89 15713 filed on November 29, 1989 by the Applicant, a circuit breaker with two phase-breaking chambers is described. Each chamber is equipped with a varistor connected in series with a switch and a capacitor. The role of the varistor is to reduce the overvoltage and to distribute the recovery voltage during the shutdown of the main chamber The role of the capacitor is to distribute the recovery voltage on the main chamber and on the auxiliary chamber (or on the contacts of the device insertion of the built-in varistor) during power cut In the open position, the capacitor is used to distribute the voltage on each breaking element to ensure

dielectric strength.

  In French patent application 90 07426 filed on June 14, 1990 by the Applicant, there is described a standard circuit breaker equipped with distribution capacitors and comprising for each phase at least one varistor breaking chamber

  limiting the tension to 3 p u, without insertion device.

  However, it should be noted that in the case of very high voltage SF 6 circuit breakers (for example 420 k V or 550 k V with two interrupting chambers per phase), the price of the capacitors is

  high, given their dimensions.

  Thanks to the invention, it has been demonstrated that it is possible to eliminate the distribution capacitors in such circuit breakers fitted with varistors. In the case where the varistors are permanently mounted at the terminals of the breaking chambers, each varistor is dimensioned to limit the voltage to

  substantially 3 p u, no distribution capacitor being mounted in parallel at the terminals of the breaking chambers.

  In the case where each varistor is associated with an insertion device, each varistor being dimensioned to limit the overvoltage to approximately 1.2 pu, the insulating envelopes of the switching chambers are of a length5 proportional to the maximum distribution rate, none distribution capacitor not mounted in parallel to

breaking chamber terminals.

  Indeed, the voltage distribution with a point to ground does not exceed a certain percentage (or rate) for this

  which relates to circuit breakers having varistor insertion devices.

  The additional cost due to the lengthening of the insulating envelopes is lower than the price of the capacitor.

  According to a first variant, each varistor is housed with its insertion device in an auxiliary breaking chamber and the insulating jackets of the auxiliary chambers are also of a length proportional to the maximum distribution rate. According to a second variant, each varistor is housed

  with its insertion device in the corresponding main breaking chamber.

  The maximum distribution rate being of the order of 65%, the envelopes are elongated, more precisely, by a coefficient substantially equal to 1.3, compared to the case

  classic 50% 50% distribution.

  The invention is set out below in more detail with the aid of drawings showing only preferred embodiments. Figure 1 is a front view of a circuit breaker

  according to a first embodiment of the invention.

  Figure 2 is a front view of a circuit breaker according to a second embodiment of the invention, according to a first variant. Figure 3 is a front view of a circuit breaker

  according to the second embodiment of the invention, according to a second variant.

  Let us take the example of a 420 k V circuit breaker with two breaking chambers in series with varistors limiting the overvoltage to 3 p u without insertion device, and equipped with

  distribution capacitors. Generally, we have a distribution with a point to ground from 51% -49% to 52% -48%.

  Without distribution capacitor, as shown in FIG. 1, there is a distribution of 63% -37% to% -35% This distribution of 65% is applied to the interrupting chamber 1 most charged after the extinction of the current in the varistor The distribution on the two main chambers10 1, containing the main contacts 3 and of length L, is, during the breaking of the fault current, of the order of 50% -50% since it is ensured by two identical varistors 2. If the applied voltage is high (greater than or equal to 2 pu) and lasts several alternations, we will have the

  operation of the varistors at each alternation.

  In phase opposition at 2 p u, you must make sure that the varistors can hold the voltage for a few minutes. For applied voltages less than or equal to

  1.5 p u, the varistors can hold the tension indefinitely even with the distribution of 65% 35%.

  The use of two identical varistors 2 operating at 3 p u thus ensures the correct

  operation in the event of high voltage The capacitors25 can therefore be removed without the need to lengthen the porcelain enclosures of the breaking chambers 1.

  Let us now take the example of a circuit breaker with two breaking chambers 10, containing the main contacts 13,

  in series with a varistor 21 connected to an insertion device 30 in series and without distribution capacitor, as shown in FIG. 2.

  The varistor 21 and the insertion device 22 are housed in the auxiliary chamber 20 The voltage distribution is assumed to be 65% 35% .35 This distribution of 65% is applied to the breaking chamber 10 and to the auxiliary chamber 20 la more charged after extinction of the current in the varistor 21 The distribution over the two main chambers 10, after the fault current has been cut off, is in the order of% 50% since it is ensured by two varistors

identical 21.

  The restored voltage applied to the most charged auxiliary chamber 20 in the event of a three-phase fault cut-off is 1.5 (U / (f) * 0.65 = 0.975 (U / irf) o U / r J is the single tension or tension with respect to

Earth.

  It is therefore practically equal to the simple voltage and similar to the voltage obtained in the event of phase opposition cut In fact, in the case of phase opposition cut with two chambers, the distribution is 50% -50%, the total applied voltage being 2 * (U / f 3) By breaking chamber we therefore have

2 * (U / r 3) * 1/2 = (U / fl).

  The opening of the auxiliary switch 22 after the extinction of the current in the varistor makes it possible to isolate the

varistor 21 of the circuit.

  In the open position, each breaking chamber must hold dielectrically between contacts 65% of the test voltage. This is relatively easy with modern modern devices using SF 6 as the dielectric and breaking gas. For the external holding, it is necessary, compared to the classic case 50% 50%, to lengthen the porcelain envelope of the main chamber 10 and the auxiliary chamber 20 This elongation is equal to the ratio 65/50 = 1.3 called coefficient overload, i.e. L '= 1.3 * L. As shown in FIG. 3, it will be even more economical to incorporate the varistor il and the insertion device 12 into the main breaking chamber 10, containing the main contacts. 13 We thus only have the

master bedroom 10 to extend.

  In the case of circuit breakers with three interrupting chambers per phase, these application methods remain valid.

Claims (5)

  1) Circuit breaker comprising, for each phase, at least two main breaking chambers (1) each having a varistor (2) mounted in parallel at its terminals, characterized in that each varistor is dimensioned to limit the voltage to substantially 3 pu , no distribution capacitor being mounted in parallel with the terminals of the interrupting chambers.  2) Circuit breaker comprising, for each phase, at least two main breaking chambers (10) each having a varistor (11,21) mounted in parallel at its terminals and each varistor (11,21) of which is associated with a device insertion (12,22) and is dimensioned to limit the overvoltage to approximately 1.2 pu characterized in that the insulating envelopes of the breaking chambers (10,20) are of a length proportional to the maximum distribution rate, no capacitor distribution not being mounted in parallel with breaking chamber terminals.   3) Circuit breaker according to claim 2, characterized in that each varistor (21) is housed with its insertion device (22) in an auxiliary breaking chamber (20) and the insulating jackets of the auxiliary chambers (20) are also d '' a length proportional to the maximum distribution rate. 4) Circuit breaker according to claim 2, characterized in that each varistor (11) is housed with its insertion device (12) in the main breaking chamber   corresponding (10). 5) Circuit breaker according to any one of claims 2 to 4, characterized in that the envelopes are   elongated by a coefficient substantially equal to 1.3, compared to the classic case of a 50% 50% distribution. t OD Dh X A 12