GB2200502A

GB2200502A - Electric insulator

Info

Publication number: GB2200502A
Application number: GB08729761A
Authority: GB
Inventors: Andrea Catanzano
Original assignee: FIP Formatura Iniezione Polimeri SpA
Current assignee: FIP Formatura Iniezione Polimeri SpA
Priority date: 1987-01-29
Filing date: 1987-12-21
Publication date: 1988-08-03
Also published as: JPS63193412A; IT8712410A0; FR2610448A1; IT1208237B; DE3743888A1; GB8729761D0

Description

2"' 0 0 5 0 2 ro r t1 A1 1 M&C FOLIO: 230P55369 INSULATOR WITH

THERMOPLASTIC RESIN COATING This invention relates to an insulator with a thermoplastic resin coating. It is known that medium-voltage insulators may consist of a bar of insulating material, to the ends of which two metal end pieces are fitted. In general. the end pieces may each be connected to electric cables. but in practice the insulator is normally used to suspend an electric cable with one end piece secured to a fixed. earthed structure and the other secured to a live electric cable. The bar of insulating material must have annular flan ges to prevent arcing and also to increase the surface electrical resistance of the insulator. particularly in a humid or wet environment; the insulators may be used out of doors, and therefore they must retain their characteristics even in the presence of driving rain. The annular flanges generally have the shape of a bell: this increases the length of the axial profie of the insulator, correspondingly increasing the surface electrical resistance. Furthermore, no air spaces may remain between the inner surfaces of the flanges and the outer surface of the bar, otherwise 1 2 the preferential path of the very -discharges which are to be avoided would be defined between the outer surface of the insulating bar and the inner surface of the through hole of the bell-shaped flanges.

It is therefore necessary, when the annular flanges are made separately, to insert a suitable adhesive sealant between the outer surface of the insulating bar and the inner surface of the through hole in the flanges themselves.

There are currently three main known systems for making insulators for electric, cables of the type described the first system -envisages the use of glass or porcelain bells, linked to one another in a chain.

More recently, said glass bells have been replaced by a bar of insulating material onto which, as stated above, bell-shaped holed flanges were inserted, after positioning a suitable adhesive between the two surfaces.

A third known process again envisages the use of a bar of insulating material, generally fiberglass-reinforced plastic, to the ends of which two terminals for connecting the electric cables are fixed. On the bar in, question said bell-shaped flanges are formed by direct moulding in one piece, using thermosetting material.

This invention applies to thermoplastic resins the hh 3 p; IS shrinkage of which is controllable, and it also envisages that the ends of said series of bell-shaped flanges be made in a single piece, with special connecting couplings arranged on the two ends, against the two metal terminals. The main characteristics of the invention are summarized and schematically described in the claims; its aims and advantages can also be seen from the following description referred to forms of embodiment chosen by way of example only and with particular reference to the attached drawings, in which: figure I is a side view of half an axial crosssection of an-insulator according to the invention; figure 2 shows, on an enlarged scale and with some of-the dimensions purposely out of proportion, a partial axial cross-section of the end of the metal end piece or terminal, which will be partly coated with thermoplastic resin. With particular reference to the above figures, the insulator according-to the invention envisages an -insulating bar 10 in fiber glass or other similar insulat ing materials having high quality mechanical characteristics.

At the two ends 11 and 12 of the insulating bar two end piece or /terminals consisting of metal cup-shaped bushings -13 i 1 4 and 14 are forcibly fixed.

The first of these metal bushings 13 is closed by an intermediate transverse diaphragm 15 which defines an axial cavity 17 opposing the cavity which houses the end 11 of the insulating bar.10. The supporting pin of the insulator, not shown in the figure, may be inserted in said cav ity 17.

Appropriate diametrically opposed holes l? and 1?.1 allow this supporting pin to be fixed to the terminal 13 by means of a suitable pin not shown in the figure.

other hand, has a threaded spigot 18 protrudes outwards, for connection to a subsequent terminal, not shown in the figure.

Obviously the ends of the terminals formed by the bushings.13 and -14 which face outwards may be either identical or made in any other way suitable for fixing to the traditional cable ends of metal conductors.

What distinguishes the insulator according to this invention from stateof-the-art insulators is a continuous coating 20 of the insulating bar 10 and the '@shape" of the coating at the ends-which cooperate with the metal bushings 13 and 14. - According to the invention said coating 20 consists of a sleeve 21, and a series of slanting or bell type The second metal bushing 14, on the visible bottom 16, from which a l.

h% 1 1 i C.

flanges 22 formed in a single piece together v., i t h the sleeve 21.

According to the invention said coating 20 (the sleeve 21 plus the bellshaped flanges 22) is formed by moulding in thermoplastic resin directly over the assembly consisting of the two metal bushings 13 and.14 and the insulating bar.10.

The natural sirin[..:age of the thermoplastic resin after moulding over the parts 10-13-14 as a whole prevents the creation of empty spaces between the inner surface of the sleeve 21 and the outer surface of the insulating bar 10.

In addition to this, according to the invention the t h e i r metal bushings.13 and 14 terminate, on edges facing towards the bar 10, in an annular enlargement 30, the radial surface of which 33 is shifted outwards as compared to the outer surface of the bar 10. In this way an annular space is formed which may be filled with the thermoplastic resin at the time of moulding the coating 20.

Furthermore, at the time of moulding the coating 20, the enlargement 30 is also coated externally by the thermoplastic resin.

It may therefore be said that the two ends of the sleeve 21 terminate in turn in enlargements 40 in the 1 6 shape of an annular channel, the arms of which 3-1 and 32 cover the enlargement 30 of the metal bushings 13 and 14.

This conformation is such that there are no metal parts of -the bushings '13 and 14 protruding outwards radially and thus the possibility of an undesired voltaic arc between radially protruding parts of the metal bushings -13 and 14 is further reduced.

In order to ensure proper contact between the inner surfaces of the annular groove of the enlargement 40 on the one hand and the out-er surfaces of the metal enlargement 30, the latter is shaped as illustrated in detail in figure 2.

The annular enlargement 30 is defined internally and externally by conical surfaces 33 and 34 widening out towards the end 35 of the enlargement 30.

In this way, the withdrawal of the thermoplastic resin of the enlargement 40 causes forcing of the surfaces in contact with the metallic enlargement 30 on one side and the thermoplastic resin enlargement 40 on the other side.

It is therefore-not necess?kry to use adhesive sealants even between the parts in contact with the coating 20 on the one hand and with the sleeve terminals 13 and 14 on the other.

Q 0 7 M&C FOLIO: 230P55369 Although for descriptive reasons this invention is based on the above descriptions and illustrations by way of example only with particular reference to the attached drawings. many changes and variations may be brought about in the embodiment of the invention.

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Claims

1. An insulator having an insulating bar to the ends of which two metal end pieces are fixed. an insulating thermoplastic resin coating with bellshaped flanges being moulded onto the insulating bar between the end pieces. the coating also covering the ends of the end pieces.

2. The insulator of Claim 1. wherein each end piece has an annular enlargement defined by two surfaces, the inner of which is spaced radially outside the insulating bar, the annular enlargement being covered, both on its outer surface and on its inner surface, by the thermoplastic resin of the coating. '

3. The insulator of Claim 2, wherein the outer and inner surfaces of the annular enlargement are conical.

4. The insulator of Claim 2 or 3, wherein the radial distance between the outer and inner surfaces of the annular enlargement increases in the direction of the centre of the bar so that. after the thermoplastic resin has coated the enlargement. the shrinkage of the freshly moulded thermoplastic resin created a compacting of the facing resin and metal surfaces.

I:

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5. An insulator. substantially as herein described with reference to, and as shown in. the accompanying drawings.

6. The insulator of any of the preceding Claims. one of whose end pieces is secured to an electric cable.

Published 1955 at The Patent OMce. State House. 66'71 High Holborr, London WClR 4TP Further copies may be obtaLried Lrom The Patent =ce, Sales Branch. St Mary Cray. Orpington, Kent BR5 3RD Printed by Multiplex techraques ltd. S Mary Cray, Kent Con. 1/87.