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General knowledge of wire and cable
Mar 02, 2018

1, one-core cable sheath one end of the grounding method why must install a parallel cable laying along the Reflow line?

A: In the grounding cable line at one end of the metal sheath, in order to ensure that the inductive voltage in the sheath does not exceed the allowable standard, it is necessary to install a conductor that is laid parallel along the cable line, and the conductor is grounded at both ends, which is called the Reflow line. When a single-phase grounding fault occurs, the grounding short-circuit current can flow back to the center of the system through the Backflow line, because the magnetic flux generated by the grounding current of the backflow line offsets the magnetic flux generated by the grounding current of the cable conductor, thus reducing the inductive voltage of the sheath during short circuit failure.


2, cable engineering can be divided into several projects?

Secretary:

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

(2) Local engineering: Including road excavation, tunneling, channel construction, etc.

(3) laying works: including laying, middle head making, lifting cover, buried pipe, school tide, traction head production, etc.

(4) Both ends of the project: including support, suspension bridge frame and its foundation of the production and installation, the end of the production, oil pressure and signal installation, the name of the electrical performance test.

(5) Stopper works: including the production of oil-filled cable stopper, for fuel tank, automatic drainage and signal installation.

(6) Grounding engineering: including insulation joint, transposition box, protector, grounding box installation, etc.


3. What inspection should be carried out for the acceptance of cable line?

A: (1) Cable specifications should be in line with the provisions, arrangements should be neat, no damage, signs complete, correct, clear;

(2) The wiring of the cable's fixed bending radius, the distance and the metal protection layer of the single core power cable should meet the requirements;

(3) The cable terminal, the middle head does not leak oil, the installation is firm, the oil-filled cable oil pressure and the gauge setting value should meet the requirement;

(4) Good grounding;

(5) The cable terminal phase color is correct, the bracket and so on metal part paint is complete;

(6) The cable ditch and the tunnel, the bridge frame should be no sundries, cover the complete plate.


4. What are the requirements for measuring the positive sequence impedance of cable lines?

A: The AC resistance of the cable conductor and the three phase of the cable are sympathetic to the phasor and are called positive sequence impedance.

The positive sequence impedance of the cable line can be measured directly on the cable disk, generally used in the measurement of lower voltage, therefore, the need to use step-down transformers for Buck, Buck use star wiring, capacity generally more than 10kVA, there is a wide range of voltage regulation, the measurement of AC power should be more stable, To ensure that the current to meet the requirements of the measurement, the actual voltmeter reading value must be the voltage at the end of the cable, the test current is best close to the cable long-term allowable load flow, reading the value of each meter, close the current and read the values of three tables.


5, according to the "Electricity production safety regulations", electrical workers must have the conditions?

A: The following conditions must be met:

(1) The doctor has identified the health of the body without obstructing the work of the disease;

(2) have the necessary electrical knowledge, according to its position and the nature of work to master the relevant procedures, professional and technical and safe operation Technology, and pass the examination;

(3) familiar with the method of electric shock first aid.



6. What should be paid attention to during the transportation and loading and unloading of cables?

A: (1) in the transport loading and unloading process, should not make cable and cable disc damaged, the cable is strictly prohibited from the car to push down, cable-like should not be flat transport, flat storage.

(2) Transport or rolling cable disk, must ensure that the cable disk firmly, cable around tight, oil-filled cable to the pressure tank between the tubing should be fixed, no damage, pressure tank should be strong, pressure instructions should meet the requirements.


7. What are the measures for fire protection of cable?

A: (1) The use of flame-retardant cable;

(2) The use of fire-proof cable bracket;

(3) The use of fire retardant paint;

(4) Installation of fireproof partition and fireproof baffle in cable tunnel and interlayer exit;

(5) Overhead cables should avoid oil pipelines, explosion-proof doors, or should be taken to take part of the pipe or insulation fire prevention measures.

8, select the Power cable section from which aspects should be considered?

A: The following should be considered:

(1) long-term cable allowed to pass the working current;

(2) Thermal stability when short circuit;

(3) The voltage drop on the line cannot exceed the allowable working range.

9. What are the advantages of power cable and overhead line comparison?

A: (1) reliable operation, due to installation in the underground and other hidden places, less damage by external forces, fewer opportunities for failure, power supply security, will not cause harm to the person;

(2) The maintenance workload is small, does not need the frequent inspection;

(3) Do not need to erect towers;

(4) Help to improve power factor.


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