HEAVY-DUTY AND WATER-PROOF LINK BOXES FOR CROSS BONDING OF EXTRA

HIGH VOLTAGE CABLE SYSTEMS

Technical Field

The present invention relates generally to field of electric extra high voltage cable systems.

The invention especially relates to a heavy-duty and water- proof link box for cross bonding of metallic sheathes of extra high voltage cable system.

State of the Art

High voltage cables have a metallic sheath, along which a voltage is induced as a function of the operating current. In order to minimize the flow of circulating currents and also to limit the magnitude of sheath voltages, bonding and earthing of cable sheathes at cable joints and terminations is performed. Methods such as single-point bonding and cross bonding can be used respectively in short length and long length high voltage cables.

It is general practice to use link boxes in high voltage cable joints and terminations for accessing cable sheathes. Link Box can be viewed as protective housing safeguarding all the related components and bonding and earthing connections are made through removable links. This allows disconnecting the individual cable sheathes for sheath testing and also establishes the integrity of sheath. If required link boxes contain sheath voltage limiters to limit induced lightning or switching overvoltages of cable system.

Link boxes are commonly used devices in cable systems but ordinary link boxes cannot meet requirements of extra high voltage cable systems in extreme environmental conditions with an economical way. Extra high voltage cables and their accessories are expensive assets which require specially designed link boxes. For example, thermal and mechanical effects of very high short circuit level of extra high voltage cable systems will lead to failure of ordinary link boxes. Another condition which cannot be met by ordinary link boxes is withstanding against internal arc. When an internal arc occurs inside the ordinary link boxes, increased pressure of air inside the box will lead to explosion that may be dangerous to nearby equipment or persons. Another feature which is not available in ordinary link boxes is long-time resistance to submersion in water. Link boxes installed in underground manholes may be subjected to water immersion due to flood for example.

Moreover, there is another problem which is frequently encountered in ordinary link boxes when using high cross section coaxial bonding cables. Existing clamping systems of link boxes are not appropriate for high cross section coaxial bonding cables.

Other parameters such as cost, dimension and weight limitations also should be considered in optimal design of a link box. For example one can propose to use a very thick stainless steel body to reach internal-arc resistant link box. But it's not a practical solution because of increased weight and of course the cost.

Having been encountered as a result of the technical researches, the Application No. CN20158451 U relates to special connector for coaxial cable. Another application which has been encountered as a result of the technical researches is the Patent No. US5052946 which relates to a plug connector for high-voltage coaxial cables. However, neither of the applications have a novelty which aims to solve the aforementioned drawbacks.

As a result, due to the drawbacks mentioned above and the inadequacy of the existing solutions regarding the subject matter, it is required to make a development in the related technical field.

Objects of the Invention

The invention, configured by being inspired by the current conditions, aims to solve the above mentioned drawbacks.

The present invention has many features which make it special rather than ordinary link boxes:

• Its specially designed connection system of coaxial cables, extremely low-ohm and tight connections makes it resistant against thermal and mechanical effects of very high short circuit currents so it is appropriate for use in extra high voltage cable systems.

Special connection system of enclosure cover to enclosure body using some domed rivet nuts makes it internal-arc resistant.

Its special sealing mechanism enables it to operate normally even it submerged in water or exposed to dust for a long time. Sealing gasket of enclosure cover, O-ring of domed rivet nut and also sealing system of cable gland prevents ingress of dust or water into link box.

Special clamping system of coaxial bonding cables makes it easy to use of wide range and high-cross section bonding cables between 95-400 mm ² or 300-500 mm ² without any adjustment.

All of these features achieved with reduced thickness of stainless steel enclosure (only 2 mm). In addition to the above mentioned advantages, other features such as

• compactness,

• economically advantageous,

• lightweight and

• installation easiness

makes the present invention appropriate for use in industry.

To achieve the aforementioned objects, the present invention is a link box which provides cross bonding of metallic sheathes of extra high voltage cable system and comprises

• an enclosure body which all other components are placed inside and protects the all components from environmental effects,

• an enclosure cover which is upper part for the link box,

• supporting insulators which are fastened to the enclosure body and all internal components are mounted thereon and provide electrical isolation of energized components from the enclosure body,

• cable glands through which provide entering into enclosure body of earthing cable used to connect earthing busbar to earthing electrodes outside of the link box and coaxial bonding cables which are used to connect metallic sheathes of three-phase high voltage cable joint to the link box and including inner conductor and wire screen.

• disconnectable crossing bars which are used to provide a cross connection between inner conductor of coaxial bonding cable related to 1th phase and wire screen of coaxial bonding cable related to 2nd phase characterized in comprising;

• domed rivet nuts and a sealing gasket which provide sealed and tight connection between enclosure body and enclosure cover and prevent ingress of water or dust into link box even when it submerged in water and protect the integrity of link box when internal arc fault occurs,

• adjustable sealing plugs which provide sealing for cable gland and coaxial bonding and earthing cables and act as an interface between cable gland and coaxial bonding cables / earthing cable for water-proof penetration of coaxial bonding cables / earthing cable into enclosure body.

In another preferred embodiment of the present invention, said link box is comprising clamping system of coaxial bonding cables which provide fixing wide range and high-cross section coaxial bonding cables to enclosure body and also separating main inner conductor and wire screen and the clamping system comprises

· coaxial cable fixing clamps which connect to wire screen of coaxial bonding cable and

• cable end fixing clamps which connect to inner conductor of coaxial bonding cable.

According to another preferred embodiment of the present invention, the link box is comprising clamping system of earthing cable which provides fixing wide range and high- cross section earthing cables to enclosure body and comprises

• single cable fixing clamp which connects to conductor of earthing cable which provides connection to earthing electrode outside.

In another preferred embodiment of the present invention,

· said enclosure body, enclosure cover, sealing gasket and domed rivet nuts comprise fixing bolt holes fixing the enclosure cover to the enclosure body by means of fixing bolts on same axis

• said domed rivet nuts comprise an o-ring which prevents ingress of water from surface of enclosure body and a leaning surface which provides uniformly distribution of forces on enclosure body and protecting integrity of link box.

In another preferred embodiment of the present invention,

• said domed rivet nuts are made of stainless steel and sealing gasket is made from EPD . According to another preferred embodiment of the present invention,

• said sealing gasket is one-piece continuous structure and comprises embedded channels and embedded o-rings contact surface with domed rivet nut prevent ingress of water or dust

· said adjustable sealing plug are fixed to the coaxial bonding cables, earthing cable and cable gland by means of cable ties and

• said mastic tape is wrapped around junction points of adjustable sealing plug-cable gland and adjustable sealing plug-coaxial bonding cables or earthing cable which prevents ingress of water from surface of coaxial bonding cables / earthing cable also surface of cable gland into enclosure body.

The structural and characteristic features and all the advantages of the present invention will be more clearly understood thanks to the figures below and the detailed description written with reference to those figures, therefore; the evaluation needs to be done by taking said figures and the detailed description into consideration.

Figures for a Better Understanding of the Invention

Figure 1 is an exploded view of present invention

Figure 2 is an assembled view of present invention.

Figure 3 shows clamping system of coaxial cables.

Figure 4 shows earthing cable clamping system in detail.

Figure 5 shows cross-sectionai view of connection between enclosure cover and enclosure body.

Figure 6 shows sealing gasket of enclosure cover.

Figure 7 shows details of domed rivet nut with o-ring.

Figure 8 shows cross-sectional view of cable gland sealing system.

The drawings do not need to be scaled and the details that are not necessary for understanding the present invention may have been ignored. In addition, the elements that are at least identical to a great extent or at least have identical functions to a great extent are referred with the same number.

Description of the Part References

1. Enclosure body 2. Enclosure cover

3. Sealing gasket

3A. Embedded Channels

3B. Embedded O-ring

4. Adjustable sealing plug

5. Coaxial cable fixing clamp

6 Cable end fixing clamp

7. Single cable fixing clamp

8 Insulator

9. Disconnectable crossing bar

10. Earthing busbar

11. Surge voltage limiter

12. Domed rivet nut

12A. O-ring

12B. Leaning Surface

13. Base plate

14. Cable gland

15. Cable ties

16. Mastic tape

17. Heat-shrinkable tube

18. Coaxial bonding cable

18A. Inner conductor

18B. Wire screen

18C. Outer sheath

18D. Core insulation

19. Earthing cable

19A. Conductor

19B. Conductor insulation

20. Fixing bolt

21. Fixing bolt hole

100. Link box

Detailed Description of the invention In this detailed description, the preferred embodiments of the invention are described only for a better understanding of the subject without any limiting effect. The invention relates to a heavy-duty and water- proof link box (100) for cross bonding of metallic sheathes of extra high voltage cable joints.

Fig.1 is an exploded view of present invention. Present invention mainly includes of an enclosure body (1) which all other components are placed inside and an enclosure cover (2) which can be seen as upper part for the link box (100). All internal components are mounted on supporting insulators (8) which are used also to electrical isolation of energized components from enclosure body (1). These insulators (8) are fastened to enclosure body (1) via a base plate (13).

Fig.2 is an assembled view of present invention. Coaxial bonding cable (18) and single earthing cable (19) are assembled during installation of link box (100) on site. Three coaxial bonding cables (18) are used to connect metallic sheathes of three-phase high voltage cable joint to link box (100). One earthing cable (19) is used to connect earthing busbar (10) to earthing electrodes outside of the link box (100).

Fig.3 shows clamping system of coaxial bonding cables (18). Each coaxial bonding cable

(18) includes mainly of inner conductor (18A), outer wire screen (18B), outer sheath (18C) and core insulation (18D). When each coaxial bonding cable (18) enters into enclosure body (1) through cable gland (14), its wire screen (18B) is separated via a coaxial cable fixing clamp (5) and then inner conductor (18A) is connected to cable end fixing clamp (6). It can be seen that coaxial cable clamping system intended to fix the coaxial bonding cable (18) and also separating main inner conductor (18A) and wire screen (18B). Current clamping/separating mechanism allows to use wide range and high-cross section coaxial bonding cables (18). Also, cable end fixing clamp (6) made of hard alloy material provides a hard-soft connection between cable end fixing clamp (6) and inner conductor (18A).

As shown in Fig.2, disconnectable crossing bar (9) are used to provide a cross connection between inner conductor (18A) of coaxial bonding cable (18) related to 1th phase and wire screen (18B) of coaxial bonding cable (18) related to 2nd phase. One side of surge voltage limiters (11) is connected to disconnectable crossing bars (9) and another side is connected to common point of earthing busbar (10).

Fig.4 shows earthing cable (19) clamping system in detail. Each earthing cable (19) includes mainly of conductor (19A) and conductor insulation (19B). Conductor (19A) of earthing cable

(19) is connected to earthing busbar (10) via single cable fixing clamp (7) and then it will be ready for connection to earthing electrode outside. Current clamping system is suitable for wide range and high-cross section earthing cables (19). Also, single cable fixing clamp (7) made of hard alloy material provides a hard-soft connection between single cable fixing clamp (7) and conductor (19A).

Fig.5 shows cross-sectional view of connection between enclosure cover (2) and enclosure body (1). Connection between enclosure cover (2) and enclosure body (1) is made by a sealing gasket (3) as well as some domed rivet nuts (12) with o-ring (12A). These two components provide sealed and tight connection between enclosure body (1) and enclosure cover (2). This connection method prevents ingress of water or dust into link box (100) even when it submerged in water. Also, it plays a critical role during internal arc. Details of each component is discussed below.

Fig.6 shows sealing gasket (3) of enclosure cover (2). Sealing gasket (3) made from EPD (ethylene propylene diene terpolymer) plays an important role in enhancing water proof feature of present invention. Its one-piece continuous structure, flexibility of its material, embedded channels (3A) and embedded o-rings (3B) contact surface with domed rivet nut (12) prevents ingress of water or dust and also guarantees its long-term sealing performance. Also enclosure body (1), enclosure cover (2) and sealing gasket (3) have fixing bolt holes (21) which provide fixing the enclosure cover (2) to the enclosure body (1) by means of fixing bolts (20) on same axis. In addition to this, domed rivet nuts (12) are also mounted on enclosure body (1) thanks to fixing bolt holes (21).

Fig. 7 shows details of domed rivet nut (12) with o-ring (12A). Main two functions of this component includes: (i) along with sealing gasket (3) provides a water proof connection between enclosure body (1) and enclosure cover (2) (ii) provides tight connection between enclosure body (1) and enclosure cover (2) so link box (100) shall remain integrated during internal arc. First function is achieved with specially designed contact surface between domed rivet nut (12) and sealing gasket (3) as well as embedded o-ring (12A) inside domed rivet nut (12). Aforementioned o-ring (12A) prevents ingress of water from surface of enclosure body (1).

Concerning second function, domed rivet nut (12) plays a critical role during internal arc. When arc fault occurs inside the link box ( 00), temperature heats up and expands the air in the enclosure body (1). Increased pressure exerts severe mechanical forces on fixing bolt (20) upward causing force to domed rivet nut (12). Leaning surface (12B) of each domed rivet nut (12) causes to uniformly distribution of forces on enclosure body (1). Accordingly, integrity of link box (100) is maintained. Fig.8 shows cross-sectional view of cable gland (14) sealing system. Cable gland (14) sealing system provides a water-proof penetration of coaxial bonding cables (18) and earthing cable (19) into enclosure body (1). Note that surface of coaxial bonding cables (18) and earthing cable (19) made of plastic materials and cable gland (14) is made of stainless steel. This implies that special method is required to seal cable gland (14) and coaxial bonding and earthing cable (18, 19). Final sealing system should prevent ingress of water into link box (100) during submersion. First step includes insertion of an adjustable sealing plug (4) on both coaxial bonding and earthing cable (18, 19) and cable gland (14). Prior to this step, two ends of adjustable sealing plug (4) are cut according to coaxial bonding and earthing cable (18, 19) diameter. This component made from EPDM rubber and acts as an interface between bonding cables and cable gland (14). Two cable ties (15) are used to fix adjustable sealing plug (4) at two points. Then mastic tape (16) is wrapped around adjustable sealing plug (4)-cable gland (14) and adjustable sealing plug (4)-bonding cable (coaxial bonding cables (18) or earthing cable (19)) junction points. This filling mastic tape (16) prevents ingress of water from surface of bonding cables and also surface of cable gland (14) into enclosure body (1). Finally, a heat-shrinkable tube (17) with glue is used to cover all of the components.