Title of Invention

AN EXTINGUISHING CHAMBER OF A CIRCUIT BREAKER WITH SELF-EXTINGUISHING EXPANSION, AND A THERMOPLASTIC RESIN ENCLOSURE

Abstract

The insulating enclosure 12 is formed by end-to-end assembly of two half-shells 12A, 128 achieved by moulding of a thermoplastic resin. A protective shield 100, 102 made of plastic material is fitted onto all the internal faces of each half-shell 12A, 128 to protect the enclosure 12 against the effects of the arc, the plastic material of the shield 100, 102 having a higher thermal resistance than that of the thermoplastic resin of the half-shells 12A, 128. A joining frame 106 cooperates with the facing ends of the two shields 100, 102 to perform centring thereof with respect to the longitudinal axis of the enclosure 12 and to improve the mechanical strength of the coupling.

Full Text

The invention relates to an extinguishing chamber for a high voltage circuit breaker, housed in an enclosure filled with a high dielectric strength gas, and containing : - separable contacts, - an arc extinguishing device by self-expansion of the gas after the arc has been made to rotate due to the effect of a magnetic field generated by an electromagnetic coil, - means for the chamber to communicate with the outside of the enclosure during the self-expansion phase after the contacts have separated, - the insulating enclosure being formed by end-to-end assembly of two half-shells achieved by moulding of a thermoplastic resin, - and a protective device made of plastic material fitted onto the internal face of the enclosure to protect the latter against the effects of the arc, the plastic material of the protective device having a higher thermal resistance than that of the thermoplastic resin of the two half-shells. In circuit breakers with self-extinguishing expansion and rotating arc, described notably in the documents US-A-5,166,483 and EP-A-768,692, the occurrence of the arc when separation of the contacts takes place causes a high-speed pressure increase of the sulphur hexafluoride SF6 gas contained inside the enclosure, with formation of a gas outflow through the tubular channel of the movable contact. The internal volume of the enclosure, and the diameter of the communication channel are calculated to obtain an optimum gas flow enabling high-speed arc extinction. The insulating enclosure is generally made of a thermosetting resin, for example epoxide resin-based, preferably with the addition of charges or strengthening in the form of particles or fibres, and hardening agents. The nature of the resin and the weight composition must meet specific requirements of the behaviour of the SF6 gas in the presence of an arc. The enclosure must in particular withstand the influence of the arc and of the SF6 decomposition products in order not to suffer any damage or premature wear. Manufacture of a thermosetting resin enclosure is achieved by casting the mixture of resin and charges. The cost of such a moulding operation is very high. SUIVIIVIARY OF THE INVENTION The object of the invention is to achieve an extinguishing chamber for a self-extinguishing expansion circuit breaker, using an insulating enclosure having a low manufacturing cost. The extinguishing chamber according to the invention is characterized in that the protective device is formed by two shields made of plastic material, and that joining means cooperate with the facing ends of the two shields to perform centring thereof with respect to the longitudinal axis of the enclosure and to improve the mechanical strength of the coupling, said joining means comprising a centring element in the form of a frame arranged inside the enclosure in the mid-plane of the interface between the two half-shells. According to one feature of the invention, the thermoplastic resin of two half-shells is polycarbonate-based. The protective shield is formed by a previously cut and folded polytetrafluorethylene PTFE plate. The frame of the centring element is made of rigid plastic material and comprises a pair of positioning grooves for positioning of the two shields. Preferably, the polytetrafluorethylene plate of the shield has a uniform thickness chosen between 0.5 mm and 3 mm, and comprises a base joined to four lateral surfaces by folding lines. The base of the plate is provided with a circular orifice for operation of the shield on a boss anranged on the panel of the half-shells. BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features will become more clearly apparent from the following description of an embodiment of the invention given as a non-restrictive example only and represented in the accompanying drawings in which : ■ Figure 1 is a cross sectional view of the extinguishing chamber equipped with the enclosure according to the invention; - Figure 2 is a perspective view of the centring frame of the protective shields; - Figure 3 is an elevational view of the frame of figure 2; - Figure 4 is a cross sectional view along the line 4-4 of figure 3; - Figure 5 shows a polytetrafluorethylene plate cut to form a protective shield; - Figure 6 is a cross sectional view along the line 6-6 of figure 5; - Figure 7 is a detailed view, on an enlarged scale, of figure 6, representing the folding lines of the plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In figure 1, an extinguishing chamber 10 for a pole of a high voltage circuit breaker of the self-extinguishing expansion type comprises an enclosure 12 made of insulating material and filled with a high dielectric strength gas, notably sulphur hexafluoride SF6. The internal volume of the extinguishing chamber 10 contains a tubular movable contact 14 operating in conjunction with a stationary contact device 16 associated to an electromagnetic coil 18 for rotating the arc. The movable contact 14 is located at the end of an elongate tube 20 made of conducting material, which is able to slide tightly through one of the panels 22 of the insulating enclosure 12. The external end of the tube 20 is coupled to an operating mechanism (not represented) designed to move the movable contact 14 between a closed position (figure 1) and an open position (figure 2). The stationary contact device 16 is extended by a conducting stud 24 of cylindrical shape passing through the opposite panel 26 in the longitudinal direction of the enclosure 12, and connected to the outside by the connection strip 28 of the pole. The hollow tube 20 enables the extinguishing chamber 10 to communicate with the external volume of the enclosure 12 as soon as the contacts 14, 16 separate to enable self-expansion of the gas. The insulating enclosure 12 is formed by abutment of the two half-shells 12A, 12B each made by moulding from a polymer resin having a good mechanical strength. The electromagnetic coil 18 used for extinguishing the arc comprises an axial stacking of copper conducting turns adjoined to one another and electrically connected in series by means of fixing screws 30 with interposed intercalated parts made of insulating material. The front face of the coil 18 is provided with an arc migration track 32, said track 32 of annular shape having an internal diameter slightly greater than the diameter of the movable contact 14. The rear turn opposite the front face is connected to the conducting stud 24 by support arms 34 constituting copper spacers, which are separated from the internal stationary contact device 16 by insulating pads 36. Two steel washers 38, 40 are fixed by screws 30 to the rear face of the coil 18, after the interposition of insulating washers 41. The stationary contact device 16 of the self-extinguishing expansion circuit breaker comprises three contact fingers in the form of circular sectors, circumferentially arranged to form a cylindrical hollow contact. The internal diameter of this hollow contact corresponds appreciably to the external diameter of the movable contact 14, so as to allow telescopic sliding, respectively at the beginning of opening travel and at the end of closing travel of the movable contact 14. The two shells 12A, 12B of square cross section of the enclosure 12 are achieved by means of a thermoplastic resin, notably polycarbonate-based. To protect the internal surface of the enclosure 12 against the thermal effects of the arc generated inside the extinguishing chamber 10, a protective shield 100, 102 made of heat-resistant plastic material is incorporated in each half-shell 12A, 12B. The shield 100, 102 is preferably formed by a previously cut and folded polytetrafluorethylene PTFE plate to present a conjugate shape to the cross section of the shells 12A, 12B. With reference to figures 2 to 4, a centring element 104 is used for end-to-end assembly of the two shields 100,102 inside the enclosure 102. The centring element 104 is formed by a frame 106 made of rigid plastic material of square cross-section, provided with two positioning grooves 108,110 staggered along the two sides of the periphery of the frame 106. The cross section of the frame 106 is smaller than the square cross section of the enclosure 12. In figures 5 to 7, the polytetrafluorethylene PTFE plate of each protective shield 100, 102 has a uniform thickness of about 1 mm and comprises a base 112 of square cross section, to which four lateral surfaces 114, 116, 118, 120 are joined by folding lines 122.The base 112 of the pre-cut plate 111 is provided with a circular orifice 124 enabling the shield 100,102 to be positioned on a boss 126, 128 (figure 1) provided on the internal faces of the panels 22, 26 of the enclosure 12. The protective shields 100, 102 are fitted in the extinguishing chamber 10 in the following manner: The first shield 100, whose base 112 bears on the panel 22, is fitted in the half-shell 12A equipped with the conducting tube 20. The boss 126 then enters the orifice 124 and performs axial positioning of the shield 100. The four lateral surfaces 114, 116, 118,120 of the shield 100 extend along the internal faces bounding the square cross section of the half-shell 12A. The second shield 102 is fitted in the other half-shell 12B in similar manner after the assembly formed by the coil 18 and stationary contact device 16 has been fitted. The two shields 100,102 are joined to one another by means of the centring element 104 arranged inside the extinguishing chamber 10 in the mid-plane of the interface between the two half-shells 12A, 12B in the abutted position. The two half-shells 12A, 12B then simply have to be finally fixed by assembly screws (not represented) to form an efficient continuous protection on all the internal faces of the extinguishing chamber 10. The presence of the centring frame 106 in addition enables the connection between the two shields 100,102 to be strengthened. It is clear that the invention applies for any other cross section of the enclosure 12, in particular for a cylindrical cross section. The thickness of the polytetrafluorethylene PTFE plate can also be adapted to suit the breaking capacity of the circuit breaker, and can be comprised between 0.5 mm and 3 mm. WE CLAIM 1. An extinguishing chamber for a high voltage circuit breaker, housed in an enclosure (12) filled with a high dielectric strength, gas and containing: separable contacts (14, 16); an arc extinguishing device by self-expansion of the gas after the arc has been made to rotate due to the effect of a magnetic field generated by an electromagnet coil (18); means for the chamber (10) to communicate with the outside of the enclosure (12) during the self-expansion phase after the contacts (14, 16) have separated; the insulating enclosure (12) which is being formed by end to end assembly of two half-shells (12A, 12B) achieved by moulding of a thermoplastic resin; and a protective device made of plastic material fitted onto the internal face of the enclosure (12) to protect the latter against the effects of the arc, the plastic material of the protective device having a higher thermal resistance than that of the thermoplastic resin of the two half-shells (12A, 12B), wherein the protective device is formed by two shields (100, 102) made of plastic material and that joining means cooperate with the facing ends of the two shields (100, 102) to perform centring thereof with respect to the longitudinal axis of the enclosure (12) and to improve the mechanical strength of the coupling, said joining means comprising a centring element (104) in the form of a frame (106) arranged inside the enclosure (12) in the mid-plane of the interface between the two half-shells (12A, 12B). 2. The extinguishing chamber as claimed in claim 1, wherein the thermoplastic resin of the half-shells (12A, 12B) is polycarbonate-based. 3. The extinguishing chamber as claimed in claim 1 or 2, wherein the protective shield (100, 102) is formed by a previously cut and folded polytetrafluorethylene PTFE plate (111). 4. The extinguishing chamber as claimed in any one of the claims 1 to 3, wherein the frame (106) has a conjugate shape to that of the enclosure (12). 5. The extinguishing chamber as claimed in claim 4, wherein frame (106) of the centring element (104) is made of rigid plastic material and comprises a pair of positioning grooves (108, 110) for positioning of the two shields (100, 102). 6. The extinguishing chamber as claimed in claim 3, wherein the polytetrafluorethylene plate (111) of the shield (100, 102) has a uniform thickness between 0.5 mm and 3 mm and comprises a base (112) joined to four lateral surfaces (114, 116, 118, 120) by folding lines (122). 7. The extinguishing chamber as claimed in claim 6, wherein the base (112) of the plate (111) is provided with a circular orifice (124) for operation of the shield (100, 102) on a boss (126, 128) arranged on the panel (22, 26) of the half-shells (12A, 12B). 8. An extinguishing chamber for a high voltage circuit breaker, substantially as herein described with reference to the accompanying drawings.

Documents:

0039-mas-1999 abstract-duplicate.pdf

0039-mas-1999 abstract.jpg

0039-mas-1999 abstract.pdf

0039-mas-1999 claims-duplicate.pdf

0039-mas-1999 claims.pdf

0039-mas-1999 correspondence-others.pdf

0039-mas-1999 correspondence-po.pdf

0039-mas-1999 description (complete)-duplicate.pdf

0039-mas-1999 description (complete).pdf

0039-mas-1999 drawings-duplicate.pdf

0039-mas-1999 drawings.pdf

0039-mas-1999 form-19.pdf

0039-mas-1999 form-2.pdf

0039-mas-1999 form-26.pdf

0039-mas-1999 form-4.pdf

0039-mas-1999 form-6.pdf

0039-mas-1999 petition.pdf