FR2753833A1 - GENERATOR CIRCUIT BREAKER WITH VARIABLE DAMPING RESISTANCE - Google Patents

Abstract

Generator circuit breaker using resistance rods made of a polymer charged with carbon black, said rods being composed of resistance elements in series interposed by free spaces and connected by staggered electrodes.

Description

i Generator circuit breaker with variable damping resistor La

  the present invention relates to a circuit breaker

  generator with variable damping resistance.

  In the field of switchgear and, in particular, for generator circuit breakers protecting high power alternators, it is necessary to equip these circuit breakers with resistors of low ohmic value, or damping resistors, in order to greatly reduce the speed increase in transient voltage by

recovery when the power is turned off.

  The resistors used until now are often ceramic resistors based on carbon or graphite of constant value, in the form of discs.20 To greatly reduce the residual current to be cut by an auxiliary circuit breaker, it is necessary to have a

high value resistance.

  The first object of the invention is to propose a resistance increasing its initial value rapidly, passing, for example, from a few ohms to a few tens of ohms in 50 milliseconds in order to satisfy the two conditions simultaneously. A second object of the invention is to reduce the volume and

the weight of the resistance.

  Self-regulating polymer resistors are also known, used in industry in particular for heating water pipes in order to prevent freezing during winter.35 Indeed, at low temperature, the resistance formed from black charged polymer of carbon with a low ohmic value allows a larger current to flow, for example under a permanent voltage of 220V for a power absorbed

from 30 to 40 W / m.

  At higher temperature (in summer for example), the resistivity increases and the power consumed becomes much lower, i.e. less than 5 W / m. For more information on the principle of self-regulating polymer resistances, reference may be made to the article by F. Legros, A. Brault and G. Lorguilloux,

  "Self-regulating cables: principle and industrial use" (Acome Company, RGE n 11, December 1989).

  The solution proposed by the invention consists in using a variable resistor, consisting of polymer elements in a generator circuit breaker. Thus, the heating of the elements when they are traversed by a high current, will lead to an abrupt increase in their resistivity from a certain temperature threshold, 120 C for example. The present invention presents a particular architecture for variable resistance. Said resistance is in the form of a stick consisting of

  several resistive elements in series, separated by empty spaces. The assembly is covered with an insulating sheath and comprises flat copper electrodes which are mutually parallel and which have edges curved outwards.

  Other advantages and characteristics of the present invention will emerge from the description which follows.

  reference to the attached drawings in which: FIG. 1 represents a longitudinal section along the axis I-I of FIG. 2 of a resistance rod

  variable in polymer according to the invention. Figure 2 shows a sectional view of the same stick.

  Figure 3 shows schematically the overall arrangement of the generator circuit breaker implementing

  sticks of variable resistance.

  FIG. 4 shows a physical arrangement of the variable resistances around the breaking chamber of the circuit breaker.

  Figure 5 shows an alternative embodiment of the sticks of variable resistance.

  In FIG. 1, the rod 1 is formed of elements of variable resistance 2 of length L in series and presented in the form of a parallelepiped. The basic resistance element 2 consists of a resistance matrix 3 made of a polymer charged with carbon black and provided with two electrodes, 4 and 5, flat, parallel, curved on the two longitudinal edges, in

  tinned copper and spaced from each other by d mm. The purpose of the curvatures on the longitudinal edges is to avoid arcing at the corners.

  Resistor 2 advantageously has a resistivity of the order of a hundred ohms per centimeter, for example between 100 o.cm and 300 Q.cm. The basic element 2 is protected from the outside by a rigid cross-linked insulating sheath 6 which covers at the same time

  the other elements in series and the free spaces 9.

  The purpose of these free spaces is to prevent ignition under the effect of the potential difference between two

successive polymer elements.

  Preferably, the length 1 of these free spaces

is 10 mm.

  A small hole 10 drilled in the protective casing 6 at the free spaces 9 allows the heated air to flow into these free spaces. The electrodes 4 and 5 have lengths equal to 2L + l and

  are arranged in staggered rows within the rods 1.

  In Figure 3 which schematically shows the overall arrangement of the generator circuit breaker, the

  compartment 11 represents the main breaking chamber, and compartment 12 the auxiliary breaking chamber 5 used for breaking the residual current passing through the resistor 1 and for isolating it from the circuit.

  The auxiliary chamber 12 and the variable resistance rods 1 are in parallel with the main chamber 11.

  Several sticks of variable resistance can be

  mounted in parallel with each other via collectors 13 and 14.

  The connections 7 and 8 of the variable resistor are connected to the collectors 13 and 14 of the generator circuit breaker. 15 Figure 4 shows the arrangement of the resistor rods 1, in part, around the main chamber 11, in order to obtain a resistance initial of low value by paralleling said resistance rods 1

using collectors 13 and 14.

  This provision is of course not limiting.

  The device operates as follows: In normal operation, the interrupting chambers 11 and 12 are closed. The current flows through 11, that passing through the auxiliary breaking chamber 12 and through the resistor 1 being negligible. Element 1 has a low resistance, for example 5 ohms at room temperature of C.

  When the switch contained in the main chamber 11 is opened and the short-circuit current goes to zero

  circuit, the arc will extinguish in chamber 11 if there is a final cut. During the application of the transient recovery voltage across the main interrupting chamber 11, a resistive current flows through the auxiliary interrupting chamber 12 and the resistance rods 1. This current heats the polymer matrix 3 contained in each of the rods and greatly increases its value

  ohmic at each alternation of the residual current.

  About 50 ms after the opening of the main breaking chamber 11, the switch contained in the auxiliary breaking chamber 12 opens and cuts the residual current which, compared to its initial value, is reduced by about 10 times. The switch in room 12 therefore no longer has

  than a small resistive current to cut.

  The use of a variable polymer resistor thus makes it possible to be able to greatly reduce the breaking capacity of the switch 11 and also to reduce the volume and the weight of the damping resistor.15 The parallelepiped shape and small dimensions of the variable resistance rods 1 also makes it easier to parallel it around the main breaking chamber 11. As an example of an embodiment, the following values may be taken for a 17 kV network with an initial resistance of 5 ohms: - l spacing between the two electrodes is 10 mm; - the length h of each electrode is 15 mm; - the length 1 of the free spaces is 10 mm; - the length L of a resistance matrix is 50 mm; each resistance rod 1 is formed of 10 elements 2 in series; -40 resistance rods 1 are placed in parallel;

  The useful volume of the resistor is then approximately 7000 cm3 for a final resistance of 50 ohms.

  FIG. 5 indicates an alternative embodiment of the rods in which the electrodes 4 and 5 have been replaced by cylindrical copper conductors arranged one above the other. Envelope 6 and matrix 3 are also

  cylindrical in shape. The electrodes 4 and 5 have a diameter of the order of 4 mm, for a length L of the matrix 3 and a spacing 1 between the electrodes identical to those of the first embodiment. The equivalent volume is also 7000 cm3 - for a final resistance of 50 ohms.

  Although only two embodiments have been described, it is clear that any modification or improvement

  made to the present invention and which would be obvious to a person skilled in the art is included within the scope of the invention.

Claims (7)

  1) Generator circuit breaker using damping resistors comprising elements made of polymer charged with carbon black, characterized in that said resistors are arranged in the form of rods (1) comprising several resistance elements (2) in series interspersed with free spaces (9), in that said stick is protected by an insulating protective envelope (6) and in that said stick is provided with two   electrodes (4 and 5) mounted in staggered rows.   2) Circuit breaker according to claim 1 characterized in   that each of the resistance elements (2) has a resistivity between 100 Q.cm and 300 ú.cm.   3) Circuit breaker according to one of claims 1 to 2 characterized in that the rods (1) have a shape   parallelepiped and in that the electrodes (4 and 5) are flat, mutually parallel and have edges curved outwards.   4) Circuit breaker according to one of claims 1 to 2   characterized in that the rods (1) and the electrodes (4 and 5) have a cylindrical shape.   ) Circuit breaker according to one of claims 1 to 4 characterized in that a hole (10) is drilled in the casing   (6) at each of the free spaces (9) to allow the evacuation of heat.   6) Circuit breaker according to one of claims 1 to 5 characterized in that each of the resistance elements (2)   has a length (L) of about 50 mm.   7) Circuit breaker according to one of claims 1 to 6   characterized in that the length (1) of the empty space (9) is about 10 mm.   8) Circuit breaker according to one of claims 1 to 7   characterized in that the distance (d) between the two   electrodes (4 and 5) is approximately 10 mm.