FR2679375A1 - CONTACTOR FOR CIRCUIT BREAKER. - Google Patents

Abstract

Electrical contact, usable as a mobile arcing contact in a self-blowing circuit breaker comprising a blowing volume and a blowing nozzle, characterized in that it consists of a metal tube (9) at the end of which is fixed an end piece (12) of insulating material.

Description

1 -

CONTACTOR FOR CIRCUIT BREAKER

  The present invention relates to an electrical contact usable to constitute the arcing contact

  a medium or high voltage circuit breaker.

  It is known that in self-blowing circuit breakers, the heat produced by the arc which is established at the separation of the arcing contacts is used to heat the gas by a volume called blowing volume or expansion volume Ce volume is defined at one end by a blowing nozzle; at the zero crossing of the current to be cut, the gas in the blowing volume expands through the neck of the

nozzle and blow the arc.

  It has been observed that the efficiency of the blowing, in particular for the blowing of the arc which occurs during the breaking of low currents (for example the intensity corresponding to the nominal value of the current in which the circuit breaker is inserted ), is not total, because the rise in pressure

  in the blowing volume is insufficient.

  An object of the present invention is to improve the contact so as to obtain a greater pressure in the blowing volume in particular

  for breaking low currents.

  This object is achieved by the contact of the invention, which can be used as a movable arcing contact in a self-blowing circuit breaker comprising a blowing volume and a blowing nozzle, and which is characterized in that it consists of a metal tube at the end of which is fixed a mouthpiece

insulating material.

  The invention will be clearly understood from the description

  of an exemplary embodiment with reference to the appended drawing in which: 2 - Figure 1 is a partial view in axial section of the breaking chamber of a self-blowing circuit breaker, shown in the engaged position, Figure 2 is a similar view after the separation of the arcing contacts, but before the arc blowing phase, Figure 3 is a similar view, at the time

of the arc blowing.

  The breaking chamber partially shown in axial section in FIG. 1 comprises a sealed casing 1 (made of porcelain for conventional circuit breakers, of metal for so-called metal grounded circuit breakers) filled with a gas with good dielectric properties such as sulfur hexafluoride under a pressure of

a few bars.

  Inside the chamber, there is a fixed assembly comprising a metal tube 2 electrically connected to a first outlet not shown and carrying a first metal tube 3 constituting the fixed main contact, a second metal tube 4 coaxial with the first and constituting the fixed arcing contact, and an insulating blowing nozzle, for example made of polytetrafluoroethylene (known for example under the registered trademark teflon) The tube 4 is provided at its end with a part 4 A of material resistant to the effects arc, for example carbide

of tungsten.

  The volume 6 delimited by the tube 2 and the nozzle 5

  constitutes the blowing volume of the circuit breaker.

  The tube 4 can be either plugged at its inner end (simple blowing), or open

(double blowing).

  The moving part of the circuit breaker comprises a metal tube 8 electrically connected by sliding contacts, not shown, to a second outlet for 3 - current. The tube is connected to an operating rod.

insulation not shown.

  The tube 8 has one end which opens out to carry a contact tube 9 constituting the movable arcing contact and contact fingers 10 forming the movable permanent contact The tube 9 is provided at its end with a part 9 A in resistant material

arc effects.

  The tube 9 is provided at its end with a nozzle 12 made of insulating material, which extends beyond the part 9 A This nozzle is secured to the tube 9 by

screwing or crimping.

  The material of the nozzle is advantageously polytetrafluoroethylene. The choice of this material is advantageous because it produces, when it is heated by the arc, fluorinated vapors which favor the breaking of the arc. This material can be charged, for example by

  fiberglass or resin.

  When the circuit breaker is in the on position, current flows through tube 2, the contact

3, fingers 10 and tube 8.

  When the circuit breaker trips, the main contacts 3 and 10 separate, and current flows through

arcing contacts 4 and 9.

  Upon separation of the arcing contacts (Figure 2), an arc 15 arises between the arcing contacts; the volume 6 gas heats up, which increases the pressure within this volume; thanks to the nozzle 12, the volume 6 remains practically closed although the end 9 A of the movable arcing contact 9 has exceeded the neck of the nozzle. In this way, the pressure in the volume 6 continues to increase because the gas of this volume can hardly escape through the weak annular passage

  existing between the nozzle 12 and the neck of the nozzle.

  It is only when the nozzle 12 exceeds the neck of the nozzle (FIG. 3) that the volume 6 is opened and that 4 - the blowing gas escapes through the neck of the nozzle. It is possible to calculate the length of the end piece 12, taking into account the speed of displacement of the contacts, in order to obtain, in volume 6, the overpressure making it possible to ensure cutting at

  moment of zero current crossing.

  Thanks to the invention, the breaking of low intensity currents (nominal current for example, as opposed to high currents such as short-circuit currents) is ensured, because the blowing effect

is used to the maximum.

  The invention applies to medium or high voltage circuit breakers, of the conventional type or to

metal shell to earth.

Claims (4)

  1 / Electrical contact, usable as a movable arcing contact in a self-blowing circuit breaker comprising a blowing volume and a blowing nozzle, characterized in that it consists of a metal tube (9) at the end which is attached a tip (12) made of insulating material.   2 / electrical contact according to claim 1, characterized in that the material of the tip (12) is polytetrafluoroethylene.   3 / electrical contact according to one of claims 1   and 2, characterized in that the end piece (12) is fixed to the tube (9) by screwing.   4 / electrical contact according to one of claims 1   and 2, characterized in that the end piece (12) is fixed to the tube (9) by crimping.   / Electrical contact according to one of claims 2 to 4, characterized in that the   polytetrafluoroethylene is loaded.