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Wire and cable common sense question and answer

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1. Why should a return line installed along the cable be installed in the grounding mode of the single-core cable sheath at one end?

Answer: In the cable line grounded at one end of the metal sheath, in order to ensure that the induced voltage in the sheath does not exceed the allowable standard, a conductor laid along the cable line in parallel must be installed, and both ends of the conductor are grounded. Streamlined. When a single-phase ground fault occurs, the ground short-circuit current can flow back to the system center point through the return line, and the magnetic flux generated by the ground current through the return line cancels the magnetic flux generated by the ground current of a part of the cable lead, thereby reducing The induced voltage of the sheath in the event of a short circuit fault.


2. Can a cable project be divided into several projects?


(1) Construction site transportation: including loading and unloading, transportation and empty return of engineering materials from warehouse to construction site.

(2) Local engineering: including road excavation, tunneling, and channel construction.


(3) Laying work: including laying, intermediate head making, shovel cover, buried pipe, school tide, production of traction head, etc.

(4) Both ends of the project: including the production and installation of the branch, the suspension bridge and its foundation, the production of the terminal head, the installation of the oil pressure and signal device, and the electrical performance test of the name.

(5) Stopping works: including the production of oil-filled cable plugs, the installation of fuel tanks, automatic drainage and signal devices.

(6) Grounding engineering: including insulation joints, transposition boxes, protectors, grounding box installation, etc.


3. What inspections should be carried out on the acceptance of cable lines?

Answer: (1) The cable specifications should meet the requirements, the arrangement should be neat, no damage, the signs are complete, correct and clear;

(2) The fixed bending radius of the cable, the relevant distance and the wiring of the metal sheath of the single-core power cable shall meet the requirements;

(3) The cable terminal and the middle head are not leaking oil, and the installation is firm. The oil pressure of the oil-filled cable and the setting value of the meter should meet the requirements;


(4) Good grounding;

(5) The color of the cable terminal is correct, and the metal parts such as the bracket are completely painted;

(6) There should be no debris in the cable trench, tunnel and bridge, and the cover is complete.

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