AU661291B2

AU661291B2 - High voltage connecting terminal

Info

Publication number: AU661291B2
Application number: AU10131/92A
Authority: AU
Inventors: Jean-Paul Avocat
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-01-10
Filing date: 1992-01-10
Publication date: 1995-07-20
Anticipated expiration: 2012-01-10
Also published as: FR2671670A1; EP0494807B1; ATE136164T1; AU1013192A; EP0494807A1; DE69209325T2; DE69209325D1; FR2671670B1; ES2084298T3

Abstract

The invention relates to a high-voltage binding post for electrical apparatuses, such as a current or voltage transformer, having outsides moulded from insulating resin. The binding post comprises at least two portions, one of which, the head (1), is connected to a high-voltage line by means of a pin (2) and the other of which, the base (4), is connected to the earth of the apparatus. Both ends are separated by a tubular shedded insulator (5) which encloses a conduit (6) where the conductors connecting the head (1) to the output terminal of the apparatus are placed. According to the invention, the head (1) is covered with a metal layer (7) over its external portion and a metal ring (9) is interposed between the head (1) and the insulator (5). The invention concerns manufacturers of medium- and high-voltage electrical equipment. <IMAGE>

Description

P/00/01 1 ReguLation 3.2 AUSTRALIA 6612A 91 PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

0 04 0 TOB OLTDB PLCN Naeo plcn JA-ALAOA JENPUL0OA Adrs fo evc:9LIA A RE 7 ihSreKw 11 itra utai Inenio Til:"G OTG*CNETN9ENNL Th folwn ttmn4safl ecito fti netoicuigtebs ehdo pefrmn i nontom: la invention relates to a high-voltage terminal.-mee articularly suitable for current transformers for outdoor service and encapsulated in moulded resin. It is chiefly of interest to the manufacturers of electrical equipment.

A high voltage connecting terminal is a member designed to provide a junction with a high voltage outside line.

Although the present invention has been especially developed with a view to its application to current transformers, it is nonetheless perfectly applicable to other types of electrical apparatus.

To take the example of dry transformers, such transformers have windings wound around magnetic cores placed in a closed insulating mass moulded around the said cores.

Some of these windings are connected to an outside high voltage line, and the others to a low voltage secondary network.

The design of high voltage connecting terminals poses a number of construction problems. They are, in fact, generally made up of two portions, namely the. head, connected to the high voltage line, and the, base, connected to the equipment earth potential. These two portions are separated by a tubular insulator which encloses a conduit in which are placed the electric leads that connect the lower portion of the apparatus to the potential of the equipment earth 25 receiving the secondary output terminals and an upper portion Ia, carrying the parts for connection to the high voltage line.

Consequently, there is a very substantial potential difference between the head and the base and, given their proximity, this sets up intense electric fields which promote 30 the formation of electric arcs and ionizing discharges.

The insulator used is of the fin type, that is to say a series of peripheral discs are disposed on the outside of the insulator, the sides of the discs being downwardly inclined to prevent the occurrence of any stagnant moisture n the lower ski(ed wAsorteC iA i's felc( faces of the fins. The 4 man of th artp is familiar with j S

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2 numerous insulator profiles to lengthen the path from the high voltage portion to the earthed portion and to create leakage paths opposing the creation of electric arcs in order to prevent the passage of sparks and the striking of electric arcs along the insulator.

When it rains, or when more or less conductive atmospheric deposits form on the electrical apparatus, promoting electrolytic type conduction, the material of which the insulator is made has to have good spark and electric arc With tandAproperties. That is why use is made of porcelain, elastomers, synthetic resins or other similar materials to manufacture the insulator.

Furthermore, the active portions of the electrical apparatus formed, in the case of transformers, by magnetic circuits and low and high voltage windings, are encapsulated by strong moulded synthetic resin, the whole forming the body of the electrical applicance. This apparatus is thus divided into two portions, one being formed by the group of parts in contact with the high voltage, and the other portion being constituted by the group of parts in contact with the equipment earth at earth potential. The surface of the body of the electrical apparatus, which is naturally insulating, will be subjected to the electric field existing between the high voltage portion and the low vbltage portion connected to 25 earth. It will thus be the site, like the insulator, of creeping electrical discharges which can, in the long run, damage the apparatus and result in its destruction.

Indeed, the different regions on the surface of an insulating material are'.-brought to unforeseeable potentials 30 which are very difficult to determine and which depend, in particular, on the electric fields present in the vicinity.

When, as in the case of high voltage electric transformers, intense electric fields are present, these affect the surface of the insulating materials without it being possible, 'a priori', to determine the points in question, whence the

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Izi I ii t t< t f t 1 i "t S ItI ct r 1 i' L~ t t 3 occurrence of unanticipated electrical discharges which appear randomly on the surface of the insulating materials and are amplified through the effect of atmospheric moisture and the pollution of the insulator.

It has proved possible to solve this serious problem, which is liable to lead to the destruction of the electrical apparatus, by covering the body of the apparatus with a conductive metallic deposit. This is generally a relatively thick, solid layer of hot sprayed metal such as zinc, serving to form a conductive layer that equalizes the potential of the surface covered. The conductive layer is connected either to earth potential or to the high voltage terminal, depending on the arrangement chosen. In this way, the surface potentials are fixed and the influences of external electric fields are overcome. The risk of the formation of creeping electric sparks are completely eliminated. In addition, the conductive layer has to be capable of discharging the electric current due to possible arcing along the insulator.

The latter is then, in fact, exposed to the effect of 20 concentration of the high voltage line/earth electric field and, consequently, it is here that measures have to be taken t to reduce the risks of accidental failure, in the event of instantaneous overvoltage, of the external or internal insulation, through arcing, and, simultaneously, to prevent the formation of ionizing electrical discharges inside and in the vicinity of the insulator.

C, tt Uner these circumstances the conductive layer, which is SI" nonetheless thin, ends in a sharp edge opposite the insulator i which will generate spa ks in operation and arcing in the r event of overvoltages on the network, while the leakage currents along the insulator, which will form on the said edge, will gradually cause it to deteriorate by eating away the metallic layer.

The main object of the present invention is to provide a high voltage connecting terminal with improved insulation.

S b\ L A- -AI :I I ri -4- In this respect, improvement has been achieved in two areas. On one hand, as to the outside of the terminal, the surface of the head of the apparatus will no longer be a site for the formation of creeping sparks, and its useful life will be prolonged accordingly. Moreover, thanks to special constructional arrangements, the distribution of the electric field between the live parts and the equipment earth inside the insulator is completely mastered, so that there is no risk of any internal ionizing electric discharge.

In accordance with the present invention, therefore, there is provided a high voltage connecting terminal for electrical apparatus, said terminal comprising at least two portions, one of which is adapted to be connected to high voltage and the other to earth, said at least two portions being separated by a fin type insulator which encloses a conduit in which are placed leads connecting a head enclosing windings and a magnetic core to external portions of said apparatus, wherein said head is covered by a conductive metallic layer on the exterior surface thereof and wherein a metallic ring is interposed between said head and said insulator, said ring serving to protect said metallic layer of said head against deterioration caused by arcing/sparking.

In order that the invention may be more clearly understood and put into S practical effect reference will now be made to a preferred construction of a high voltage connecting terminal for electrical apparatus in accordance with the invention. The description is given by way of non-limitative example only and is with reference to the accompanying drawings, wherein: U figure 1 is a schematic cross-sectional view of the internal structure of a high voltage connecting terminal according to the present "25 invention; ,figure 2 is a detailed view of the connection between the ring and the high voltage pin; and i figure 3 is a schematic cross-sectional view of the internal structure of a high voltage connecting terminal, installed the other way round.

The present invention relates to a high voltage 715/95CS6323.SPU,4 It I

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connecting terminal for electric apparatus, such as a dry current or voltage transformer. It is chi,,efly of interest to the manufacturers of electrical equipment.

Although the present invention has been developed more particularly in connection with the construction of medium voltage current transformers, it can be extended to all medium and high voltage apparatus comprising components placed in an insulating housing or encapsulated in insulating resin.

High voltage connecting terminals are electrical components designed to be connected to an external high voltage line. In the* Proaon- example of he-current transformer the group of electrical components, that is to say the magnetic core and high and low voltage windings, are encapsulated in a moulded resin which takes the form of a head in figure 1. Through the head passes a pin (2) directly connected to the external high voltage line. The pin is fixed to a hollow insulating support which contains the different electrical components. This forms the 20 first portion of the apparatus, which is brought to the high voltage potential.

The other portion of the high voltage terminal is formed by the mounting base which is brought to earth potential. The low voltage output terminals of the apparatus are fixed to the base The head and the base are separated by a tubular insulator provided with fins, which encloses a conduit in which are placed the electrical connecting leads, not shown. There is a 'substantial potential difference, corresponding to the supply voltage of the electric apparatus under high voltage, between the head and the base The fin type insulator has to provide a leakage path sufficient to prevent the passage of the sparks due to the electric field present between the head and, the base When it rains, or when more or less conductive atmospheric 4 1 *I i~

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S11 h c;- 6 deposits form on the electric apparatus, the material used to form the insulator has to offer good creeping spark and electric arcA with tand capabilities. These electrolytic conduction phenomena are very dangerous and cannot be totally eliminated. Very special care has to be taken in the choice of the material to be used in the manufacture of the fin type insulator to ensure that it cannot be destroyed through the action either of electric arcs or of creeping sparks. For example, it is desirable to use porcelain, elastomer, synthetic resins or other materials of a natuy^o different from that used to form the encapsulation of the active portions of the apparatus.

These same live portions which, in the case of transformers, are formed by magnetic circuits and high and low voltage windings, are encapsulated in a strong moulded synthetic resin, the whole forming the body of the apparatus.

The surface of this'naturally insulating body will thus be subjected to the action of the external electric fields. By S• definition, the potentials of the different surface areas of these insulating materials will be floating and will vary according to structural geometry, the proximity of live S..conductors, and also atmospheric conditions. Under these :circumstances, completely uncontrollable electric fields will be seen to appear on the surface of the insulating materials.

Under certain conditions they can give rise to ionizing C discharges which, in the long run, can seriously damage the apparatus.

t It is precisely in order to -mbat this type of damage that constructors cover' the body of the apparatus with a relatively thick, strong, metallic deposit. The insulating surfaces are thus eliminated and the electric fields on the surfaces disappear. These conductive layers are connected either to the high voltage potential or to the equipment earth potential in order to define precisely the live parts and the earthed parts, and thus precisely locate the electric G! S 1 7 fields. In practice, the metallic surface deposits are formed by hot spraying zinc onto the resin to form a conductive layer that equalizes the potential of the surface covered.

In the chosen example in figure 1, the external portion CoVered of the head is veee4d by a conductive layer This conductive layer is connected to the potential of the pin and, consequently, to the high voltage line. Under these circumstances, the electric field in the external portion of the terminal is strictly confined to the portion located between the upper and lower ends of the fin type insulator The thickness of the conductive layer must be sufficient to support the discharge of an electric leakage current occurring between the pin and the base This arrangement initially gives the user satisfaction.

The conductive layer is, indeed, perfectly capable of meeting requirements and, in the event of accidental electric arcs forming, the creeping spark travels over the external surface of the fin type insulator from the lower portion S" of the layer that is to say the crown supporting the 0 20 head on 'the fin type insulator to the base The surface layer ends, precisely, at the sharp edge of n the crown supporting the head on the insulator The sharp edge favours the formation of sparks in operation and arcing in the event of overvoltages on the network. The leakage currents along the insulator will also occur at this edge and will gradually cause it to deteriorate by li eating away the metallic layer in this area.

t 'According to the present invention, a ring is L ,interposed between the 'head and the insulator as 30 iur e i greSe 30 illustrated in figure 1. UnderA=Pho conditions, the sharp edge of the crown supporting the head rests on the metallic ring and it is precisely this metallic ring (9) that will be the part closest to the base and at which the maximum electric field will be concentrated. In the event of arcing, the spark will form at the ring and travel to h| 8 the base and the sharp edge of the head will be completely protected.

Figure 2 is a detail showing how the ring is installed on the upper portion of the insulator This metallic ring has a profile with rounded edges. This restricts the creation of electric arcs, which tend to form on angular or pointed shapes, T arn eSePci (auy preterred eMbo/n;eAd 4e# -Te- outside diameter of the ring is greater than that of the crown supporting the head This makes it possible to protect the sharp edge of the metallic layer in the event of the formation of an electric arc the path of which must pass via the ring In order to ensure that the ring is at high voltage potential and can discharge a substantial current, the ring is advantageously connected to the pin by a braid or some other conductive element such as illustrated in figure 2.

Care must also be taken not to create, or at the very S" least favour, ionizing discharges which can lead to the S 20 formation of arcs inside the high voltage connecting terminal. For this purpose, one solution is to interpose an insulating shield (11) between the conduit and the ring The ring can also extend inside the insulator 25 via a cylindrical surface as illustrated in figure 1, i ending in a shoe (13).

An electrically insulating cylinder (14) can also be installed, extending the insulating shield (11) through the internal portion of the" insulator which is interposed 30 between the conduit and the ring provided with its extension (12).

To ensure tightness and, in particular, to prevent any communication to the outside environment of a liquid or gaseous dielectric bathing the interior of the insulator, a series of seals (15) are fitted between the insulating 7 i-.i

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cylinder (14) and the insulating portion (16) of the base The above two parts are coaxial, which enables part 14 to slide in part 16.

An O-ring can also be fitted in the ring to ensure tightness to gases or insulating liquids between the head (1) and the insulator In the example given in the preceding figures the different electrical components, such as the high voltage winding, the low voltage winding and the core, were eclosed in the body of the apparatus, that is to say the head of moulded resin placed on the upper portion of the apparatus.

However, it is perfectly possible to contemplate the reverse arrangement, as illustrated in figure 3, wherein the head (1) enclosing the different electrical components is located in the lower portion of the apparatus. In this case, the pin (2) for connection to high voltage is replaced by contacts (17 and 18) fixed to an insulating support (19) placed at the top of the insulator and connected to the head by electrical conductors introduced into the central connection 20 conduit The magnetic cores, the primary winding and the secondary winding are encapsulated in a moulded housing (3) placed in the head which is covered by an earthed 'i:nductive layer To prevent electric arcs from being able to form between the high voltage contacts (17 and 18) and the external surface of the head a ring is interposed between the insulator and the head at the base of the said insulator, as illustrated in figure 3. This ring is brought to earth potential and thus forms a protective shield for the conductive film Other embodiments of the present invention, within the oompetencc of a man-of the -art, could also- be cntemplated 4W**4 4 4 r 4 I *1r a *84 p,* 4* 4 i i I i i i i i i winu tlrrarin rm n ct_ mer m

Claims

1. A high voltage connecting terminal for electrical apparatus, said terminal comprising at least two portions, one of which is adapted to be connected to high voltage and the other to earth, said at least two portions being separated by a fin type insulator which encloses a conduit in which are placed leads connecting a head enclosing windings and a magnetic core to external portions of said apparatus, wherein said head is covered by a conductive metallic layer on the exterior surface thereof and wherein a metallic ring is interposed between said head and said inm;ulator, said ring serving to protect said metallic layer of said head against deterioration caused by arcing/sparking.

2. The high voltage connecting terminal according to claim 1, wherein said ring has a profile with rounded edges.

3. The high voltage connecting terminal according to claim 1 or claim 2, wherein said ring has an outside diameter greater than that of a crown supporting said head on said insulator.

4. The high voltage connecting terminal according to any one of claims 1 o to 3, wherein said ring is connected to a connecting pin of said head by a braid S" or other conductive element to the high voltage portion. t

5. The high voltage connecting terminal according to any one of claims 1 .t0041 to 4, wherein a screen is interposed between said ring and said conduit.

6. The high voltage connecting terminal according to any one of claims 1 to 5, wherein said ring is extended inside said insulator by a cylindrical surface ending in a shoe.

7. The high voltage connecting terminal according to any one of claims 1 to 6, wherein a seal is placed in a groove hollowed out in said metallic ring.

8. The high voltage connecting terminal according to any one of claims 1 to 7, wherein an insulating cylinder is interposed inside said insulator between said conduit and said ring and an extension thereof.

9. The high voltage connecting terminal according to claim 8, wherein said insulating cylinder has seals in the area of its connection by fitting over said insulating portion of a base. 1715195S6323.SPE,1O a No Legalization No Corporale Seal this 19th day of December 19 9 I A t" vfc-swri I W. 11(i mr Signature of Delaran Signature of Declarant To: The Commissioner of Patents. n iu ii-l 1 m 1 -UL -Tr .ir^ i, 3. -11- The high voltage connecting terminal according to any one of the preceding claims, wherein said electrical apparatus is a current or voltage transformer.

11. A high voltage connecting terminal for electrical apparatus, substantially as herein described with reference to the accompanying drawings. DATED this 17th day of May 1995. JEAN-PAUL AVOCAT By his Patent Attorneys: CALLINAN LAWRIE *1I661 I D C o 3 3 0 C C C (C (C CC 0 CC C Lr .~41 17/5/950S6323.SPB,1 I 12 ABSTRACT OF THE DISCLOSURE The invention relates ta a high voltage connecting terminal for electrical apparatus such as a current or voltage transformer for outdoor service encapsulated in moulded insulating resin. The terminal comprises at least two portions whereof one, the head is conn"cted to a high voltage line via a pin and the other, the base is connected to the earth of the apparatus. The two are separated by a fin type tubular insulator which encloses a conduit in which are placed the leads connecting the head to the output contact of the apparatus. According to the invention, the head is covered by a metallic layer on its external portion and a metallic ring is interposed between the head and the insulator The invention is of interest to the constructors of medium and high voltage electrical apparatus. FIG. 1 0 4 S4r 4 4*4 t 4 4 i 1 i I ts