In order to speed up urban development, beautify the urban environment, improve urban quality and vigorously promote urban infrastructure construction, many cities have carried out large-scale urban road reconstruction, and the cable entry of the original urban road overhead line into the ground. At the same time, with the development of the city, many new communities need power grid access, but the location and capacity of the high-voltage cabinet in the distribution substation is fixed, which can only change the cable line, so that the cable line can provide new power points for the new community. At the same time, large-scale subway construction also needs temporary changes of cable lines. In the process of large-scale power grid construction and transformation, many power cut cables are involved (the so-called cutting is to cut off the power cut cable for planning, so as to splice with another cable, so as to change the cable direction, extend the overall length of the cable or repair the damaged part of the cable). There are often multiple cables in the cable trench. How to accurately and quickly find the cable to be cut in multiple cables is the correct identification of power cables.

1、 Observation hand touch

Starting from the determined end of the cable, the eye will never leave the cable, and the hand will not leave the cable, and move along the cable to the part to be cut. This method is the observation hand touch method.

The advantage of observation hand touch method is relatively accurate and simple, but the disadvantage is that it is easy to make mistakes when the cable is long, the cables cross and overlap more, and the hands cannot intersect.

2、 Resistance method

First disconnect the three phase wires, ground wires and steel armor of the cable located in the power supply, and use the insulation resistance meter to measure that the resistance to ground of the steel armor should be megaohm high resistance (if the resistance is lower than 0.1 Ω, it should be measured with a multimeter, but the measuring instruments used on the site and the power supply side should be the same), and then go to the cable on site and pierce the protective insulation skin with a needle (enter the needle at the protruding position when the steel armor is overlapped, and the insulating skin is about 2mm thick) After contacting the steel armor, turn the needle left and right to make the needle tip pierce the paint skin on the steel armor so as to make good contact with the steel armor; then insert the probe of the insulation resistance meter into the wet land, and the other probe contacts the needle to measure the ground resistance. If the resistance is high, it is likely to be the cable to be found (because the steel armor of general cables is grounded, it should be low resistance).

In order to prevent poor grounding of the steel armor of other cables, measure the steel armor insulation to the ground of all cable shells in front and make records. If the steel armor insulation to the ground of only one cable is basically equal to the steel armor insulation on the power side of the cable, the cable is the cable to be found; if the steel armor insulation resistance measured on site is the same as that measured by the power supply If the high resistance is very different from the low resistance, the cable is not the cable to be found; if the insulation resistance values of the steel armor of the two cables are not very different, the method of intermittent grounding of the steel armor end of the cable to be found can be adopted, so that the phenomenon of alternating high and low of independent insulation resistance can be measured at the detection site, then it is the cable to be found.

1. The advantages of using resistance method to identify cables: it is economical, does not need to buy expensive special equipment, and is simple and easy.

2. Identify the disadvantages of cables by resistance method:

① It is necessary to pierce the cable sheath and touch the armor. The construction safety of 110kV and above cables needs to be further discussed.

② Waterproof work after skin puncture shall be considered.

③ The efficiency is not high. The steel armor grounding resistance of each cable must be measured and analyzed, which is time-consuming.

To be continued

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