Composite insulator for an overhead power line with a protected leakage current detector

Abstract

A composite insulator (1) for overhead power lines comprises a rigid core extending axially between two attachment fittings (6) and having placed thereon a shell having sheds (5, 5) made of electrically insulating synthetic material. It includes a detector device for detecting surface leakage currents, which device includes an electrically conductive metal annular ring (7) surrounding the shell between an end shed (5) adjacent to one of the two fittings (6) and another shed (5) adjacent to the end shed (5) that extends radially over the ring (7). The ring (7) is connected by a conductive wire (8) passing through the end shed (5) to be connected to an electronic unit (9) of the detector device.

Claims

1. A composite insulator for overhead power lines, the insulator comprising a rigid core extending axially between two attachment fittings and having placed thereon a shell having sheds made of electrically insulating synthetic material, the insulator including a detector device for detecting surface leakage currents, the device comprising an electrically conductive metal annular ring surrounding said shell between an end shed adjacent to one of said two fittings and another shed adjacent to said end shed, said end shed extending radially over said ring, and said ring being connected to a conductive wire that passes through said end shed to be connected to an electronic unit of said detector device.

2. The composite insulator for power lines according to claim 1, wherein said ring is a removable band.

3. The composite insulator for power lines according to claim 2, wherein the insulator is provided with a number, N, of sheds defining a certain leakage current characteristic of the insulator, with said end shed being a shed that is additional to said N sheds.

4. The composite insulator for power lines according to claim 1, wherein the insulator is provided with a number, N, of sheds defining a certain leakage current characteristic of the insulator, with said end shed being a shed that is additional to said N sheds.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention can be better understood and other advantages appear on reading the following description and the accompanying drawing, in which:

(2) FIG. 1 is a diagrammatic view of a composite insulator for overhead power lines shown on a pylon for supporting an overhead power line;

(3) FIG. 2A is a diagram showing a portion of a composite type dielectric element;

(4) FIG. 2B is an axial section view of the portion of a FIG. 2A composite type dielectric element with an end shed fitted with a conductive annular ring; and

(5) FIG. 2C is a detail (enlarged) view in axial section of the end shed shown in FIG. 2B.

DESCRIPTION OF EMBODIMENTS

(6) FIG. 1 is highly diagrammatic and shows a composite suspension insulator 1 made up of a string of molded dielectric elements 5, 5 capable of suspending a high voltage overhead power line 2 in the air from a pylon P.

(7) As shown in FIGS. 2A and 2B, the insulator 1 comprises a core 3 in the form of a rod that is rigid and that extends between two metal attachment fittings 6, including the attachment fitting that is fastened to the pylon.

(8) The rod may be made of resin-impregnated glass fibers, giving the insulator 1 its mechanical strength.

(9) The insulator 1 has a shell 4 made of electrically insulating synthetic material that is placed on the rod and that forms sheds.

(10) The shell 4 may be made of cycloaliphatic resins, out of synthetic rubbers such as silicones or ethylene propylene diene monomer (EPDM), or indeed out of polytetrafluoroethylenes (Teflon).

(11) The shell 4 may be molded directly onto the rod or it may be threaded onto the rod.

(12) The insulator 1 shown in FIG. 1 in this example has seven sheds given the reference 5 and they are arranged in series so as to ensure the characteristic line of leakage for the insulator 1, together with an additional shed that is given the reference 5, which is at the end of the insulator 1 closest to the pylon P.

(13) This end shed 5 does not contribute to providing the characteristic leakage line for the insulator 1. This end shed 5 serves as an umbrella for an annular ring 7 of a device for detecting surface leakage currents that might flow on the outside surface of the shell 4.

(14) The ring 7 is an electrically conductive metal ring that is clamped around the shell 4 between the end shed 5 and the shed 5 adjacent thereto.

(15) The ring 7 is pressed against the bottom surface of the end shed 5 in order to intercept the surface leakage current (of a few milliamps) that passes towards the fitting 6.

(16) The end shed 5 thus extends radially, overlying the ring 7 like an umbrella.

(17) The ring 7 is connected by an electrically conductive wire 8 to an electronic unit 9 of the detector device, e.g. an electronic circuit for transforming the leakage current into a voltage, the electronic unit 9 subsequently supplying the voltage signal to a measurement unit that may be remote from the electronic unit 9 itself.

(18) As can also be seen in FIG. 2B, the end shed 5 has the wire 8 passing therethrough so as to run along the fitting 6.

(19) The ring 7 is a removable band of a band clamp, thus enabling it to be replaced during a maintenance operation, for example.

(20) As shown in FIG. 2C, the ring 7 may be square in section so as to present an inside peripheral surface that is directly in contact both with the cylindrical outside surface of the shell 4 between two sheds 5, and with the annular outside surface of the end shed 5.

(21) Because of the shaped outside peripheral edge of the end shed 5, rain water trickles naturally under gravity without reaching the ring 7, which is thus well protected.