1, single core cable sheath end why must install a grounding method of along the cable backflow parallel line?
A: in the metal sheath grounding end of the cable line, the induced voltage in case really no more than promised to scale, must install a along the cable conductor, parallel to the line and the ends of the grounding conductor, the conductor is called back line。When single-phase earth fault occurs, grounding short-circuit current can pass back line flow back into the system the central point, because through the return line flux produced by the earth current offset a department cable wire grounding current generated by the magnetic flux, and thus can reduce the induction voltage of short circuit fault sheath。
2, cable engineering can be divided into several projects?
Transportation: (1) site including engineering materials from the warehouse to the ShiGongDian loading and unloading, transportation, and empty return.
(2) local engineering: including the excavation, tunnel, channel construction, etc.
(3) installation engineering: including installation, head, lift the cover plate, pipe laying, middle school tide, drawing head, etc.
(4) on both ends of the project: including suspension Bridges, and its basic installation, terminal head production, oil pressure and signal devices installation, chian electrical function test, etc.
(5) check project: including oil-filled cable plug check head production, tank, automatic drainage and signal devices installation, etc。
(6) grounding engineering: including insulation joint, switch box, protector, grounding box installation, etc.
3, which check the acceptance in cable line should be?
Answer: (1) cable specifications should comply with the defined, arrangement should be clean, no damage, the sign is complete, accurate and clear;
(2) fixed bending radius of cable, the interval and single-core power cable metal sheath wiring should conform to the requirements;
(3) the cable terminal, middle oil leakage, installation is firm, oil-filled cable oil pressure and the set values for the meter should comply with the requirements;
(4) the good grounding;
(5) cable terminal phase color accurate, bracket and other metal parts of the paint is complete;
(6) in cable trench and inside the tunnel, bridge rack should be without sundry, the cover plate is complete.
4, cable line in the process of positive sequence impedance measurement is there any requirement?
Answer: the ac resistance of cable conductors and cables three phasor and referred to as positive sequence impedance of the same impedance。
Positive sequence impedance of cable line generally can direct measurement on cable, measurement generally use the low voltage, therefore, need to be done with a step-down transformer step-down, step-down transformer USES the star connection, generally for more than 10 kva capacity, has a wide range of voltage regulation, measurement of ac power should be less chaos, to ensure that the current to achieve the requirement of the draw, when the measurement of actual meter reading values must be whole voltage cable, test current best close to the cable long promised to carrying capacity, read the meter measurement value, after close the current read at the same time, the value of three tables。
5, according to the electric power production safety defined, electrical work staff is the premise of must have?
Answer: must meet the following premises:
(1) the doctor healthy body, without getting in the way of work condition;
(2) the required electrical knowledge, according to its position and nature of work to grasp the related regulations, professional technology and safety control technology, and passed the examination。
(3) strong grasp the electric shock first-aid method。
6, cable should be pay attention to in the process of transportation loading and unloading?
Answer: (1) in the process of transportation loading and unloading, should not make the cable and the cable is damaged, it is strictly prohibited to directly pushed down by the car cable, the cable should not be flat transport, flat storage.
(2) transport or move before the cable tray, must ensure the cable is firm, cable wound tight, oil-filled cable to tubing shall be fixed between the pressure tank, shall not damage, pressure tank should be solid, pressure indicator should comply with the requirements。
What are the measures 7, cable fire?
Answer: (1) use flame retardant cable;
(2) use fire retardant cable bracket;
(3) use fireproof paint;
(4) the place such as cable tunnel, mezzanine export set fire partition, fire damper;
(5) repel and attack cable to avoid oil pipeline, explosion-proof door, or should have to take the local tube or heat insulation fire prevention measures.
8, and the choice of power cable cross section should consider which a few respects?
A: should consider the following aspects:
(1) the cable long promised by the working current of;
(2) once the short circuit when the heat is not confused;
(3) on a line voltage drop can't is beyond the agreed scope of work.
9, power cable and repel and attack line is what are the advantages?
Answer: (1) reliable running, because installed in underground shelter, such as damage by external force is small, the less chance of breakdown, power supply security, will not cause bodily harm;
(2) the maintenance workload small, does not need frequent inspection;
(3) does not need to set up tower;
(4) help to progress the power factor.