CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Chinese Patent Application No. 201210379806.7 filed on October 9, 2012 in the State Intellectual Property Office of China, the whole disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cold shrinkable termination to be mounted on an electric power cable in a pre-expansion manner, for preventing electric field concentration from being occurring at a connection termination of the electric power cable.

Description of the Related Art

Fig. l is a conventional cold shrinkable termination to be mounted on a high voltage electric power cable in a pre-expansion manner. As shown in Fig.l, the cold shrinkable termination mainly comprises an insulation body 1 , a stress control tube 2 and an end connection member 5.

Referring to Fig. l, the end connection member 5 is sealed on one end of the insulation body 1 and electrically connected to a conductor core of the electric power cable. The stress control tube 2 is disposed on an inner wall of the insulation body 1 near the other end of the insulation body 1.

The electric power cable mainly comprises a conductor core, an insulation layer covering the conductor core, a conductive shield layer covering the insulation layer, and a sheath covering the conductive shield layer. In order to terminate the electric power cable to other electric elements, a length of sheath of the electric power cable must be firstly removed to expose a length of conductive shield layer, and then a section of the exposed conductive shield layer is removed to expose a length of insulation layer, and then a section of the exposed insulation layer is removed to expose a length of conductor core.

After a section of conductive shield layer is removed from the electric power cable, it causes an electric field concentration on a region of the electric power cable on which the conductive shield layer has been removed. In order to decrease the electric field

concentration on the region of the electric power cable, in prior arts, as shown in Fig. l, a stress control tube 2 is provided to cover the region of the electric power cable.

However, in the prior arts, as shown in Fig. l , the stress control tube 2 only extends on the region of the electric power cable on which the conductive shield layer has been removed and does not extend onto and cover a part of the conductive shield layer of the electric power cable that is not removed. Accordingly, as shown in Fig.1 , when the cold shrinkable termination is mounted on the electric power cable, if an end surface (left end surface shown in Fig. l) of the stress control tube 2 is not abutted against an end surface (right end surface shown in Fig. l) of the conductive shield layer of the electric power cable that is not removed, there is a gap between the two end surfaces and a local electric field concentration occurs at the gap. Thereby, in the prior arts, the cold shrinkable termination must be mounted on the electric power cable in high position accuracy. However, it is difficult for an operator to accurately mount the cold shrinkable termination on the electric power cable.

Furthermore, as shown in Fig. l , in order to seal the right end of the cold shrinkable termination (the right end of the clod shrinkable termination is upward in use, and is also referred as a top end), the end connection member 5 is hermetically crimped on the right end of the cold shrinkable termination to prevent water or moisture from entering into the cold shrinkable termination.

A European patent application No. EP0944944B1 also discloses a cold shrinkable termination comprising a plurality of insulation material layers overlapped with each other and a stress control compound material lined within the cold shrink termination. The stress control compound material has a conformable dielectric constant to uniformly distribute the electric field. However, the stress control compound material generates a great amount of heat and causes a local high temperature in use; it accelerates the aging of the stress control compound material and shortens the service life of the cold shrink termination.

SUMMARY OF THE INVENTION

The present invention has been made to overcome or alleviate at least one aspect of the above mentioned disadvantages.

Accordingly, it is an object of the present invention to provide a cold shrink termination which permits there is a certain tolerance for the mounting position of the cold shrink termination on the electric power cable.

Accordingly, it is another object of the present invention to provide a cold shrink termination which can uniformly distribute an electric field and effectively prevent an electric field concentration on a connection termination of the electric power cable. According to an aspect of the present invention, there is provided a cold shrink termination for an electric power cable, comprising: an insulation body having a first end portion and a second end portion opposite to the first end portion; and a stress control tube disposed in the insulation body adjacent to the second end portion of the insulation body, wherein the electric power cable comprises a conductor core, an insulation layer covering the conductor core and a conductive shield layer covering the insulation layer, and wherein the stress control tube comprises a first portion directly overlapped on the insulation layer of the electric power cable and a second portion directly overlapped on the conductive shield layer of the electric power cable and extending a predetermined length thereon when the cold shrink termination is mounted on the electric power cable.

In an exemplary embodiment according to the present invention, the conductive shield layer is a metal conductive shield layer.

In another exemplary embodiment according to the present invention, the conductive shield layer is a copper wire conductive shield layer or a copper tape conductive shield layer.

In another exemplary embodiment according to the present invention, the electric power cable further comprises a semi-conductive shield layer between the insulation layer and the conductive shield layer; the stress control tube further comprises a third portion between the first portion and the second portion; the second portion has an inner diameter larger than or equal to that of the first portion; and when the cold shrink termination is mounted on the electric power cable, the third portion of the stress control tube is directly overlapped on the semi-conductive shield layer of the electric power cable.

In another exemplary embodiment according to the present invention, the stress control tube is molded or sprayed on the insulation body so that the insulation body and the stress control tube are formed into one piece.

In another exemplary embodiment according to the present invention, further comprising: a sealing compound disposed on an inner wall of the first end portion of the insulation body, the sealing compound is adapted to seal the first end portion of the insulation body on the insulation layer of the electrical power cable and a metal connection termination connected to the conductor core of the electrical power cable when the cold shrink termination is mounted on the electrical power cable.

In another exemplary embodiment according to the present invention, the sealing compound is pre-pressed on the inner wall of the first end portion of the insulation body by a pre-expansion tube before the cold shrink termination is mounted on the electric power cable. In another exemplary embodiment according to the present invention, the second end portion of the insulation body is sealed on a sheath at the outmost layer of the electric power cable.

In another exemplary embodiment according to the present invention, the cold shrink termination is pre-expanded by means of a pre-expansion tube before being mounted on the electric power cable; the pre-expansion tube comprising a first section having a first outer diameter and a second section having a second outer diameter larger than or equal to the first outer diameter; the second section of the pre-expansion tube is used to expand the second portion of the stress control tube and the second end portion of the insulation body, and the first section of the pre-expansion tube is used to expand the other portion of the cold shrink termination except the second portion of the stress control tube and the second end portion of the insulation body.

In another exemplary embodiment according to the present invention, the stress control tube is made of a semi-conductive silicon rubber.

In another exemplary embodiment according to the present invention, the

semi-conductive silicon rubber has a resistivity of 2 ohm · cm to 5000 ohm · cm.

In another exemplary embodiment according to the present invention, the insulation body is made of an insulation silicon rubber.

In another exemplary embodiment according to the present invention, the insulation silicon rubber has a resistivity of 10 ¹⁰ ohm · cm to 10 ¹⁸ ohm · cm.

In another exemplary embodiment according to the present invention, a plurality of umbellar protrusions are formed on an outer wall of the insulation body.

In another exemplary embodiment according to the present invention, the electric power cable is used to transmit a voltage below 1 lOkV.

In another exemplary embodiment according to the present invention, the second portion of the stress control tube has a length larger than 2mm and less than 200mm; and a total length of the first and second portions of the stress control tube is larger than or equal to 30mm.

According to another aspect of the present invention, there is provided a method of producing the above mentioned cold shrink termination, comprising:

S10: providing an insulation body;

S20: spraying a semi-conductive material on an inner wall of the insulation body to form a stress control tube, wherein the stress control tube and the insulation body are formed into one piece; S30: placing a sealing compound on an end of a pre-expansion tube; and

S40: pre-expanding the one piece on the pre-expansion tube on which the sealing compound has been placed, wherein the end of the pre-expansion tube having the sealing compound is disposed on an end portion of the one piece opposite to the stress control tube.

According to another aspect of the present invention, there is provided a method of producing the above mentioned cold shrink termination, comprising:

SI 00: providing a stress control tube;

S200: placing the stress control tube in a mold and injecting an insulation material into the mold to form an insulation body, wherein the stress control tube and the insulation body are formed into one piece;

S300: placing a sealing compound on an end of a pre-expansion tube; and

S400: pre-expanding the one piece on the pre-expansion tube on which the sealing compound has been placed, wherein the end of the pre-expansion tube having the sealing compound is disposed on an end portion of the one piece opposite to the stress control tube.

In various embodiments of the present invention, the stress control tube is designed to comprise an additional second portion having a predetermined length to extend onto and cover at least a part of a conductive shield layer that is not removed. Therefore, the stress control tube of the present invention can run from the insulation layer to the conductive shield layer of the electric power cable. As a result, the cold shrink termination of the present invention permits there is a certain tolerance for the mounting position of the cold shrink termination on the electric power cable. Accordingly, the present invention simplifies the mounting operation of the cold shrink termination and improves the safety of the cold shrink termination in use.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:

Fig.1 is a conventional cold shrink termination to be mounted on an electric power cable in a pre-expansion manner;

Fig.2 is a cold shrink termination for an electric power cable according to an exemplary embodiment of the present invention, wherein an insulation body and a stress control tube are molded into one piece;

Fig.3 is an illustrative view showing a sealing compound disposed in an end of the molded one piece of Fig.2;

Fig.4 is an illustrative view showing the cold shrink termination pre-expanded on a pre-expansion tube;

Fig.5 is an illustrative view of mounting the cold shrink termination on a processed connection termination of the electric power cable by means of the pre-expansion tube of Fig.4;

Fig.6 is an illustrative view of mounting a cold shrink termination according to another embodiment of the present invention on a processed connection termination of the electric power cable by means of the pre-expansion tube of Fig.4; and

Fig.7 is an illustrative view in which a stress control tube is sprayed on an inner wall of an insulation body according to another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE

IVENTION

Exemplary embodiments of the present disclosure will be described hereinafter in detail with reference to the attached drawings, wherein the like reference numerals refer to the like elements. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein; rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the concept of the disclosure to those skilled in the art.

Fig.2 is a cold shrinkable termination for an electric power cable 500 (see Fig.5) according to an exemplary embodiment of the present invention, wherein an insulation body 100 and a stress control tube 200 are molded into one piece.

In an exemplary embodiment of the present invention, the insulation body 100 may be made of, for example, an insulation silicon rubber having a resistivity of 10 ¹⁰ ohm · cm to 10 ¹⁸ ohm ^• cm. The stress control tube 200 may be made of, for example, a semi-conductive silicon rubber having a resistivity of 2 ohm · cm to 5000 ohm · cm.

As shown in Fig.2, the insulation body 100 having a first end portion 101 and a second end portion 102 opposite to the first end portion 101. In a normal use, the insulation body 100 is in a vertical state, therefore, the first end portion 101 becomes a top end and the second end portion 102 becomes a bottom end in the normal use. Referring to Fig.2, the stress control tube 200 is disposed in the insulation body 100 adjacent to the second end portion 102 of the insulation body 100.

In the embodiment of Fig.2, the insulation body 100 and the stress control tube 200 are molded into one piece. As a result, there are no air pockets and air bubbles in an interface between the insulation body 100 and the stress control tube 200, so that the insulation body 100 and the stress control tube 200 are solidly connected without any gap therebetween. In this way, it can effectively prevent an electric field concentration due to the air pockets and air bubbles in the interface.

Hereafter, it will describe the process of manufacturing the molded cold shrink termination of Fig.2.

Firstly, molding a separate stress control tube 200 with a semi-conductive material, for example, a semi-conductive silicon rubber; then, placing the stress control tube 200 in a mold and injecting an insulation material into the mold to form an insulation body 100. In this way, the stress control tube 200 and the insulation body 100 are formed into one piece.

Fig.3 is an illustrative view showing a sealing compound 300 directly disposed in an end of the molded one piece of Fig.2. But the present invention is not limited to this, the sealing compound 300 may be pre -placed on an end of a pre-expansion tube 400 (see Fig.4), and then the sealing compound 300 may be pre-pressed on the inner wall of the first end portion 101 of the insulation body 100 by means of the pre-expansion tube 400.

Fig.4 is an illustrative view showing the cold shrink termination pre-expanded on a pre-expansion tube 400.

As shown in Fig.4, the sealing compound 300 is pre-placed on an end of the

pre-expansion tube 400, and then the molded one piece of Fig.2 is expanded on the pre-expansion tube 400 on which the sealing compound 300 has been placed. In this way, the sealing compound 300 is pre-pressed on the inner wall of the first end portion 101 of the insulation body 100 by means of the pre-expansion tube 400.

Fig.5 is an illustrative view of mounting the cold shrinkable termination on a processed connection termination of the electric power cable 500 by means of the pre-expansion tube 400 of Fig.4.

As shown in Fig.5, after the molded one piece is expanded and supported by the pre-expansion tube 400, the processed connection termination of the electric power cable 500 is inserted into the pre-expansion tube 400. Then, the pre-expansion tube 400 is pulled out of the cold shrinkable termination step by step. After the pre-expansion tube 400 is completely pulled out of the cold shrinkable termination, the cold shrinkable termination shown in Fig.4 is shrunk on the processed connection termination of the electric power cable 500.

In the embodiment of Fig.5, the electric power cable 500 comprises a conductor core 501, an insulation layer 502 covering the conductor core 501, a conductive shield layer 503 covering the insulation layer 502, and a sheath 504 covering the conductive shield layer 503. In order to terminate the electric power cable 500 to other electric elements, an end of the electric power cable 500 must be processed in advance. That is, a predetermined length of sheath 504 of the electric power cable 500 must be firstly removed to expose a

predetermined length of conductive shield layer 503, and then a section of the exposed conductive shield layer 503 is removed to expose a predetermined length of insulation layer 502, and then a section of the exposed insulation layer 502 is removed to expose a predetermined length of conductor core 501.

As shown in Figs.3-5, the stress control tube 200 comprises a first portion 201 directly overlapped on the insulation layer 502 of the electric power cable 500 and a second portion 202 directly overlapped on the conductive shield layer 503 of the electric power cable 500 and extending a predetermined length thereon when the cold shrinkable termination is mounted on the electric power cable 500.

In exemplary embodiments of Figs.2-5, the stress control tube 200 is designed to comprise an additional second portion 202 having a predetermined length to extend onto and cover at least a part of the conductive shield layer 503 that is not removed. Therefore, the stress control tube 200 of the present invention can run from the insulation layer 502 to the conductive shield layer 503 of the electric power cable 500. In this way, the cut end surface of the conductive shield layer 503 is always covered by the lengthened stress control tube 200, and it can effectively prevent the electric field concentration at the cut end surface of the conductive shield layer 503. In other words, with the configuration of the stress control tube 200, the cold shrinkable termination of the present invention permits there is a certain tolerance for the mounting position of the cold shrinkable termination on the electric power cable 500. Accordingly, the present invention simplifies the mounting operation of the cold shrinkable termination and improves the safety of the cold shrinkable termination in use.

Considering the flexibility and strength of the silicon rubber for producing the stress control tube 200, in an exemplary embodiment of the present invention, the second portion 202 has an inner diameter larger than that of the first portion 201. But the present invention is not limited to this; the second portion 202 may have an inner diameter substantially equal to that of the first portion 201, if the silicon rubber has a good flexibility and strength.

In an exemplary embodiment of the present invention, the second portion 202 of the stress control tube 200 may have a length larger than 2mm and less than 200mm. A total length of the first and second portions 201, 202 of the stress control tube 200 may be larger than or equal to 30mm.

As shown in Figs.4-5, after the pre-expansion tube 400 is completely pulled out of the cold shrinkable termination, the sealing compound 300 pressed on the inner wall of the first end portion 101 of the insulation body 100 is shrunk on the insulation layer 502 of the electric power cable 500 together with the insulation body 100. As a result, the first end portion 101 of the cold shrinkable termination is sealed on the insulation layer 502 of the electric power cable 500, preventing water or moisture from entering into the cold shrink termination.

Further referring to Figs.4-5, after the pre-expansion tube 400 is completely pulled out of the cold shrinkable termination, the second end portion 102 of the insulation body 100 is shrunk on the sheath 504 of the electric power cable 500. As a result, the second end portion 102 of the insulation body 100 is sealed on the sheath 504 of the electric power cable 500, preventing water or moisture from entering into the cold shrink termination.

As shown in Fig.5, after the cold shrinkable termination is mounted on the electric power cable 500, the exposed conductor core 501 of the electric power cable 500 extends out of the cold shrinkable termination and is used to be electrically connected to another electric power cable or a connector (not shown).

In the embodiment of Fig.5, the conductive shield layer 503 may be a metal conductive shield layer, for example, a copper wire conductive shield layer, a copper tape conductive shield layer, or an aluminum armored shield layer.

In the embodiments of Figs.2-5, the stress control tube 200 may be made of a semi-conductive silicon rubber, and the insulation body 100 may be made of an insulation silicon rubber. In this way, the stress control tube 200 and the insulation body 100 can be molded together well to form one piece.

As shown in Figs.2-5, a plurality of umbellar protrusions 103 are formed on an outer wall of the insulation body 100 so as to increase the creepage distance.

In an exemplary embodiment of the present invention, the electric power cable may be an electric power cable used to transmit a high voltage below 1 lOkV, for example, an electric power cable for transmitting a voltage of 1 lOkV, lOkV or less.

In an exemplary embodiment of the present invention, the profile of the stress control tube 200 is optimized to decrease the electric field at the processed connection termination of the electric power cable 500. As a result, the electric field is distributed more uniformly at the processed connection termination of the electric power cable 500 without increasing the length of the insulation body 100 of the cold shrinkable termination. As shown in Fig.4, in an exemplary embodiment, the pre-expansion tube 400 may be a variable diameter tube including several sections having different diameters.

In an illustrative embodiment of Fig.4, the pre-expansion tube 400 comprises a first section 401 having a first outer diameter and a second section 402 having a second outer diameter larger than the first outer diameter. The second section 402 of the pre-expansion tube 400 is used to expand the second portion 202 of the stress control tube 200 and the second end portion 102 of the insulation body 100. The first section 401 of the

pre-expansion tube 400 is used to expand the other portion of the cold shrink termination except the second portion 202 of the stress control tube 200 and the second end portion 102 of the insulation body 100.

Although a variable diameter pre-expansion tube 400 is shown in Fig.4, the present invention is not limited to this; a constant diameter pre-expansion tube may be used to expand the cold shrinkable termination.

Fig.6 is an illustrative view of mounting a cold shrinkable termination according to another embodiment of the present invention on a processed connection termination of the electric power cable 500 by means of the pre-expansion tube 400 of Fig.4.

In the another embodiment of Fig.6, the electric power cable 500 further comprises a semi-conductive shield layer 505 between the insulation layer 502 and the conductive shield layer 503. During processing the connection termination of the electric power cable 500, a predetermined length of conductive shield layer 503 is removed to expose the

semi-conductive shield layer 505, and a predetermined length of exposed semi-conductive shield layer 505 is removed to expose the insulation layer 502.

In addition, as shown in Fig.6, the stress control tube 200 comprises a first portion 201, a second portion 202 and a third portion 203 between the first portion 201 and the second portion 202.

As shown in Fig.6, when the cold shrinkable termination is mounted on the electric power cable 500, the first portion 201 is directly overlapped on the insulation layer 502 of the electric power cable 500, the second portion 202 is directly overlapped on the conductive shield layer 503 of the electric power cable 500 and extends a predetermined length thereon, the third portion 203 is directly overlapped on the semi-conductive shield layer 505 of the electric power cable 500.

In addition, as shown in Fig.6, the cold shrinkable termination further comprises a metal connection termination 600. The metal connection termination 600 has an end extending into the first end portion 101 of the cold shrinkable termination and crimped on the exposed conductor core 501 of the electrical power cable 500. The other end of the metal connection termination 600 protrudes out of the first end portion 101 of the cold shrinkable termination to be electrically connected to another electric power cable or a connector. As shown in Fig.6, when the cold shrinkable termination is mounted on the electric power cable 500, the sealing compound 300 seals the interface between the first end portion 101 of the insulation body 100 and the insulation layer 502 of the electric power cable 500 and the interface between the first end portion 101 of the insulation body 100 and the metal connection termination 600.

Although it has described that the insulation body 100 and the stress control tube 200 are molded into one piece, the present invention is not limited to this, at least a part of the stress control tube 200 may be sprayed on the inner wall of the insulation body 100. For example, an insulation body 100 may be firstly molded, and then a semi-conductive silicon rubber may be sprayed on the inner wall of the insulation body 100, so that the insulation body 100 and the stress control tube 200 are formed into one piece.

Fig.7 is an illustrative view in which a part of the stress control tube 200 is sprayed on an inner wall of an insulation body 100 according to another embodiment of the present invention.

As shown in Fig.7, the second portion 202 of the stress control tube 200 may be formed in the insulation body 100 by spraying, and the other portions, for example, the first and third portions 201, 203 of the stress control tube 200 may be molded in the insulation body 100.

Although several exemplary embodiments have been shown and described, it would be appreciated by those skilled in the art that various changes or modifications may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.

As used herein, an element recited in the singular and proceeded with the word "a" or

"an" should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising" or "having" an element or a plurality of elements having a particular property may include additional such elements not having that property.