CN101645548A - Method for grounding single-core high-voltage cable metal sheath - Google Patents

Abstract

The invention discloses a method for grounding the metal sheath of a single-core high-voltage cable. There is also a parallel connection ground wire between the ground box and the ground belt; one end of the parallel connection ground wire is connected to the original ground wire by a ground clamp, and the other end is connected to the ground belt by a ground bolt. Both clips and ground studs are sealed with waterproof tape. The invention effectively solves the problems that the grounding end of the metal sheath of the tunnel erected cable line is oxidized and corroded due to moisture, the resistance of the grounding point increases, resulting in an increase in leakage current, heating of the grounding point, and the need for maintenance and treatment of high-voltage cable power outages, and can be widely used It is applied to the operation and maintenance of high-voltage transmission lines.

Description

Grounding method of metal sheath of single core high voltage cable

technical field

The invention relates to the field of grounding protection for high-voltage cables of transmission lines, in particular to a metal sheath grounding protection method for single-core high-voltage cables.

Background technique

With the rapid development of the national economy and the rapid advancement of urbanization, high-voltage and long-distance cable lines in urban construction have grown rapidly, direct burial and tunnel cable erection methods have become the main direction, and high-voltage single-core power cables have been widely used.

In order to ensure the safety and transmission efficiency of the power network, high-voltage single-core power cables must be reliably grounded. The reason is that when an overvoltage or short-circuit fault occurs in the cable line, a high induced voltage will be formed on the metal sheath or the metal sheath, which will cause breakdown of the cable outer sheath insulation, so it should be used in a certain position of the metal sheath Special connection and grounding methods, and the installation of a sheath protector at the same time, limit the induced voltage and circulating current of the cable sheath with a reasonable grounding method, and ensure the safe operation of the cable line.

According to the national "Code for Design of Electric Power Engineering Cables" (GB50217-94), the metal sheath of AC single-phase power cables must be directly grounded, and the normal induced voltage at any point on the metal sheath that is not grounded must not exceed 50V. When touching the safety measures of the metal sheath, it shall not be greater than 100V. The grounding method of the metal sheath of the AC single-phase power cable can be grounded at one end of the metal sheath of the line, grounded at the middle point or directly grounded at both ends according to the length of the line. For longer cable lines, it is advisable to divide appropriate units and set insulating joints, so that the cable metal sheath is separated into three sections for cross-connection and grounding, so as to effectively reduce the induced voltage and circulating current of the metal sheath.

In the existing method of grounding the metal sheath of a single-core high-voltage cable, a coaxial cable is usually used to connect the cable metal sheath to the grounding box, cross-connection box or sheath protector, and the grounding box, cross-connection box or sheath protection The grounding terminal of the device adopts the grounding method of the grounding wire, and the main problems are: due to the single grounding wire grounding method, the grounding wire and the grounding belt or the return line are connected by cable terminals and bolt crimping, and the grounding point is connected for a long time. In the underground tunnels and direct burial environments exposed below the ground level of zero meters, the connection bolts will be oxidized and rusted for a long time due to the influence of underground seepage water and seasonal rainwater and moisture, and the resistance of the grounding point will increase, resulting in an increase in leakage current. Large, the grounding point is hot, and in severe cases, it is necessary to conduct power outage maintenance on high-voltage cables. The power outage operation and management procedures during maintenance are cumbersome, and the labor intensity of laborers is high.

The authorized announcement date was March 19, 2008, and the Chinese patent with the announcement number CN 201038515Y disclosed a "high-voltage single-core power cable cross-connection box", including a box body and a sheath protector, and the incoming cable passes through a plug-in head Its plug-in seat and the sheath protector adopt a plug-in wiring structure, which has the characteristics of easy installation, waterproof and moisture-proof, and is used for cross-connection of the metal sheath of high-voltage single-core power cables, which solves the problem of insulating joints. The metal sheath at both ends is connected waterproofly to the cross-connection box and the sheath protector via the coaxial cable, but the corrosion problem of the connection part between the cross-connection box and the grounding belt is not solved.

The date of authorization announcement was March 19, 2008. The Chinese patent No. ZL200720062875.X also disclosed "a grounding device for high-voltage single-core power cables", including a box body, a terminal post, and a grounding block. The column and the incoming cable are connected by plugging and unplugging. There is a connecting piece or a direct connection between the terminal and the grounding block. When the connecting piece is a sheath protector, it can be used as a grounding protection box. The terminal and the grounding block are directly connected. When connected, it is used as a direct grounding box. Although it solves the problem of convenient, fast and waterproof connection of the incoming coaxial cable, it still does not solve the problem of how the grounding block is connected with the grounding strip and the corrosion resistance of the grounding point.

Contents of the invention

The technical problem to be solved by the present invention is: the connection between the grounding wire of the secondary grounding terminal of the tunnel erection cable line and the grounding belt is prone to oxidation and corrosion due to moisture, the resistance of the grounding point increases, resulting in an increase in leakage current, heating problems at the grounding point, and It is necessary to overhaul and deal with the power outage of the high-voltage cable. The operation and management procedures of the power outage are cumbersome, and the labor intensity of the laborers is high.

The technical solution of the present invention is: a method for grounding the metal sheath of a single-core high-voltage cable, which includes first leading the metal sheath of the cable to the incoming line end of the grounding box with a coaxial cable, and then connecting the grounding end of the grounding box with the grounding wire to the grounding terminal. The ground connection is characterized in that a parallel connection ground wire is added between the ground box and the ground belt.

Further, one end of the parallel connection ground wire is connected to the original ground wire by a ground clamp, and the other end is connected to the ground strap by a ground bolt; both the ground clamp and the ground bolt are sealed with waterproof tape.

Compared with the prior art, the present invention has the following advantages:

1. The present invention reduces the leakage current value and the grounding resistance value of half of the existing grounding terminal due to the parallel connection method of the secondary grounding terminal of the cable, thereby ensuring the safe operation of the cable line.

2. The heat problem at the grounding point of the transmission line cable can be dealt with in an emergency without power failure of the high-voltage cable, which reduces the cumbersome power failure operation and management procedures.

3. The present invention is simple and easy to operate, and the number of operators for the grounding maintenance construction of the transmission high-voltage cable line can be reduced by half, and it can be adjusted to optimize the location that needs to be processed, so as to save labor and time, and reduce the trouble caused by excessive working distance. For various types of power outage work tickets that need to be processed, tunnel ventilation, and guards at wells in busy residential areas, the operators can easily master the construction and achieve safe and reliable operations.

4. Compared with the traditional grounding maintenance construction, the present invention greatly reduces the difficulty of operation, reduces the labor intensity of the staff, shortens the processing time, indirectly ensures safe production, and improves labor efficiency.

Description of drawings

Fig. 1 is a schematic diagram of the grounding principle of the grounding terminal of the grounding box of the present invention;

In the figure: 1-coaxial cable, 2-grounding box, 3-grounding wire, 4-grounding belt, 5-parallel connection grounding wire, 6-grounding clamp, 7-grounding bolt.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

In the schematic diagram of the grounding principle of the grounding terminal of the grounding box of the present invention in Fig. 1, the metal sheath (not shown in the figure) of the three-phase power cable is respectively led out to the incoming line end of the grounding box 2 with a coaxial cable 1, and the interconnection of the grounding box 2 The ground terminal or transposed busbar is connected to the ground strap 4 through the ground wire 3 .

For the high-voltage cable lines erected in tunnels, due to the different erection lengths, the grounding methods are also different, so the types of grounding boxes 2 are also different, which can be direct grounding boxes, cross-connected grounding boxes or grounding protection boxes (the box is equipped with cable sheath protection device), the metal sheaths of the three-phase power cables are respectively connected to the grounding box through coaxial cables, and the interconnection methods are also different.

When the cable line is short and the length is 500 meters or less, the metal sheath is usually connected with one end directly grounded and the other end grounded through the protector, so that the metal sheath does not form a loop and eliminates the circulating current on the metal sheath.

When the cable line is long and within 1000 meters, if the cable line is grounded at one end, the induced voltage of the metal sheath will not meet the requirements of the design specification, and the metal sheath of the cable can be connected at a single point at the midpoint of the cable line. Grounding, and the two terminals of the cable metal sheath pass through the protective ground, and ensure that the induced voltage of the cable metal sheath does not exceed 50 volts.

For example, when the cable length exceeds 1000 meters, the metal sheath of the cable is usually used for cross-connection grounding. It is necessary to divide multiple unit systems on the three-phase high-voltage transmission line, and each unit system should be divided into three equal-length divisions by insulating joints. In the section, the three-phase metal sheath at each insulating joint is led out with a coaxial cable and cross-connected through the cross-connection box and then grounded through the cable sheath protector. At the same time, the three-phase single-core high-voltage cables at both ends of each unit system The metal sheaths are connected to each other through the direct grounding box and then grounded.

Usually, the grounding wire 3 is led out from the interconnected grounding end of the grounding box 2 and connected with the grounding strap 4 by bolts. If the grounding wire 3 adopts a grounding cable, the terminal of the grounding cable can be crimped at first, and then connected to the grounding electrode or the grounding strap support by grounding bolts. However, after the long-term operation of the cable line, the grounding point and connecting bolts have been exposed to underground tunnels and direct burial environments for a long time, and are affected by underground seepage water and seasonal rainwater and moisture. The connecting bolts will be oxidized and rusted for a long time. The increase of resistance will lead to the increase of leakage current and heating of the grounding point. In severe cases, high-voltage cable power outages are required for maintenance. The maintenance and power outage operations and management procedures are cumbersome, and the labor intensity of laborers is high.

The present invention adds a parallel ground wire 5 between the ground box 2 and the ground belt 4, one end of the parallel ground wire 5 is connected to the original ground wire 3 outside the ground box, and the other end is connected to the ground belt 4. When the specific line is overhauled and installed, first determine the position according to the electric power maintenance regulations, hook up the temporary ground wire, and then install and connect the ground wire 5 in parallel along the original ground wire 3 . The parallel connection ground wire 5 can use a ground cable with an outer sheath whose material and cross-sectional area meet the design ground short-circuit capacity, and one end of it is connected to the original ground wire 3 with a ground clamp 6, and the outer sheath of the ground cable needs to be broken at the connection point. After installation, use waterproof tape to wrap and seal, and do a good job of waterproofing the connection point; between the other end and the grounding belt 4, use a crimping terminal and connect and fix it with the grounding bolt 7, then apply conductive paste, and also use waterproof tape to seal. . After the maintenance and installation work is completed, send and receive information, remove the temporary grounding device, and connect the ground wire and put it into use.

The secondary grounding end of the cable of the present invention adopts the method of grounding protection and connecting the ground wire, which reduces the leakage current value and grounding resistance value of the existing grounding end by half, and the grounding point is sealed with waterproof tape, which can effectively solve the long-term operation of the cable line Finally, the connecting bolts of the grounding point are oxidized and corroded due to the influence of underground seepage water, seasonal rainwater and moisture, resulting in increased leakage current and heating of the grounding point. This method is adopted in the maintenance of cable lines, and it can be operated and implemented without power failure of high-voltage cables. It is safe, reliable, simple and practical, and improves efficiency. At the same time, due to the implementation of parallel ground wires, the reliability of the cable grounding is ensured, avoiding the danger of misplaced positions in the process of wrong construction or maintenance personnel hanging the ground wires, and improving the safety of high-voltage power cable operation and personnel maintenance. It can be widely used in the operation, repair and maintenance of high-voltage transmission lines.

Claims (3)

1. A method for grounding the metal sheath of a single-core high-voltage cable, including first leading the metal sheath of the cable to the incoming terminal of the grounding box with a coaxial cable, and then connecting the grounding terminal of the grounding box to the grounding belt with a grounding wire. Its characteristics In that, a parallel connection ground wire is added between the ground box and the ground belt. 2. The method for grounding the metal sheath of a single-core high-voltage cable according to claim 1, wherein one end of the parallel connection ground wire is connected to the original ground wire by a ground clamp, and a ground bolt is used between the other end and the ground belt connect. 3. The method for grounding the metal sheath of a single-core high-voltage cable according to claim 2, wherein the grounding clamp and the grounding bolt are both sealed with waterproof tape.

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