Company: Henan Lubao Special Cable Co., Ltd.
Contact: Manager Su
Address: No. 13 Workshop B, Tiantan Venture Park, Huling Industrial Gathering District, Jiyuan City, Henan Province
1.Why must a parallel return cable be laid along the cable in the grounding method of one end of the single-core cable sheath?
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 in parallel along the cable line must be installed, and both ends of the conductor are grounded. This type of conductor is called a return line . When a single-phase ground fault occurs, the ground short-circuit current can flow back to the center point of the system through the return line. Since the magnetic flux generated by the ground current through the return line cancels out the magnetic flux generated by the ground current of the cable conductor, it can reduce the Induced voltage of the sheath during a short circuit fault.
2. Cable engineering can be divided into several projects
(1) Construction site transportation: including the loading and unloading of engineering materials from the warehouse to the construction site, transportation, and empty car return.
(2) Local engineering: including road surface excavation, tunnel, trench construction, etc.
(3) Laying project: Zhengzhou wire and cable includes laying, making of middle head, lifting cover plate, buried pipe, tide proofing, making of traction head, etc.
(4) Projects at both ends: including the production and installation of supports, suspension bridges and their foundations, the production of terminal heads, the installation of oil pressure and signal devices, and electrical performance testing of various types.
(5) Plugging works: including the production of oil-filled cable plug ends, the installation of oil supply tanks, automatic drainage and signaling devices.
(6) Grounding works: Insulation joints, transposition boxes, protectors, installation of grounding boxes, etc.
3. What inspections should be carried out for the acceptance of cable lines?
(1) The cable specifications should meet the requirements, the arrangement should be neat, no damage, and the signs should be complete, correct and clear;
(2) The fixed bending radius of the cable, the relevant distance, and the connection of the metal sheath of the single-core power cable should meet the requirements;
(3) There is no oil leakage at the cable terminal and middle head, and the installation is firm. The oil pressure and meter setting of the oil-filled cable 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 painted completely;
(6) There should be no sundries in the cable trench, the tunnel and the bridge, and the cover plates should be complete.
4. What are the requirements for the positive sequence impedance measurement of cable lines?
The ac resistance of the cable conductor and the cable's three inductive reactances are called positive sequence impedance.
The positive-sequence impedance of the cable line can generally be directly measured on the cable tray. Generally, a lower voltage is used for the measurement. Therefore, a step-down transformer is required for step-down. Wide voltage adjustment range. The AC power supply should be relatively stable during the measurement to ensure that the current reaches the specified requirements during the measurement. The reading value of the actual voltmeter must be the voltage at the cable end. For each meter, read the values of three meters at the same time after closing the current.
6.Precautions for cables during transportation
(1) During transportation, the cables and cable reels should not be damaged. It is strictly forbidden to push the cable reels directly from the car. The cables should not be transported and stored flat.
(2) Before transporting or rolling the cable tray, it must be ensured that the cable tray is firm, the cable is tight, and the oil pipe between the oil-filled cable and the pressure tank should be fixed without damage, the pressure tank should be firm, and the pressure indication should meet the requirements.
7. Fire prevention measures for cables
(1) Use flame-retardant cables;
(2) Adopt fireproof cable bracket;
(3) Adopt fireproof paint;
(4) Fireproof partition walls and fireproof baffles shall be set at cable tunnels and mezzanine exits;
(5) Overhead cables should avoid oil pipelines and explosion-proof doors; otherwise, there should be local pipe or thermal insulation measures.
8. Factors to consider when selecting a power cable cross section
(1) The working current that the cable is allowed to pass for a long time;
(2) Thermal stability in the event of a short circuit;
(3) The voltage drop on the line cannot exceed the allowable operating range.
9, the advantages of power cables compared to overhead lines
(1) Reliable operation. Because it is installed in a hidden place such as underground, it is less damaged by external forces, less chance of failure, power supply is safe, and it will not cause harm to people;
(2) The maintenance workload is small, and frequent inspections are not required;
(3) No need to erect poles;
(4) It helps to improve the power factor.