1. What are the primary functions of insulation layer data for power cables?
Answer: It should have the following primary functions:
(1) High breakdown strength;
(2) Low dielectric loss;
(3) Relatively high insulation resistance;
(4) Excellent discharge resistance function;
(5) Has certain flexibility and mechanical strength;
(6) The insulation function remains stable for a long time.
2. What content should be indicated on the cable signboard? What are the requirements for writing?
Answer: The signboard should indicate the cable route planning number, cable model, standard, and starting point. Cables used in parallel should have a sequence number. Require clear handwriting that is not easily dropped.
3. What are the cable accessories?
Answer: Common electrical accessories include cable terminal junction boxes, cable center junction boxes, receiving and wiring terminals, steel plate wiring troughs, cable trays, etc.
4. What is a cable center joint?
Answer: The equipment that connects the conductors, insulation shielding layers, and maintenance layers of cables to connect cable lines is called the cable center joint.
5. What aspects should be considered when selecting the cross-section of power cables?
Answer: The following aspects should be considered:
(1) The operating current that the cable is allowed to pass through for a long time;
(2) Thermal stability in case of short circuit;
(3) The voltage drop on the line cannot exceed the agreed operating range.
6. What regulations should be followed when selecting the cross-section of power cables?
Answer: The selection of power cables should follow the following criteria:
(1) The additional voltage of the cable should be greater than or equal to the additional voltage of the equipment point power supply system;
(2) The continuous allowable current of the cable should be equal to or greater than the maximum continuous current of the power supply load;
(3) The cross-sectional area of the wire core should meet the requirements of stability in the event of a short circuit in the power supply system;
(4) Verify whether the voltage drop meets the requirements based on the length of the cable;
(5) The minimum short-circuit current at the end of the line should enable reliable operation of maintenance equipment.
7. What are the advantages of cross-linked polyethylene cables compared to oil paper cables?
Answer:
(1) Easy device, because it promises a small minimum bending radius and light weight;
(2) Not affected by line drop *;
(3) Good thermal function, promised high operating temperature and large transmission capacity;
(4) The cable accessories are simple and all of them are dry-type structures;
(5) Easy operation and maintenance, no oil leakage issues;
(6) Low price;
(7) High reliability and low defect rate;
(8) The manufacturing process is few, the technology is simple, and the economic benefits are significant.
8. What are the requirements for fixtures for fixed communication single core cables? Why?
Answer: The fixture should have no iron components to form a closed magnetic circuit. This is because when the cable core passes through an electric current, magnetic lines of force occur around it, which are proportional to the magnitude of the current passing through the core. If magnetic data such as iron components are used, according to electromagnetic induction, eddy currents will occur in the iron components, causing the cable to heat up and even burn out. So it is not possible to use iron as a fixed fixture for single core communication cables.
9. What are the biggest features and advantages of accessories for heat shrink cable heads?
Answer: The biggest feature of heat shrink attachments is the use of stress tubes instead of traditional stress cones. It not only simplifies the construction process, but also reduces the size of the joint terminals. The equipment is convenient, time-saving, labor-saving, functionally superior, and saves metal. The heat shrink cable accessory combines the advantages of both infusion and dry pack types.
10. What inspection tasks should be carried out before cable laying?
Answer:
(1) The bracket should be complete and the paint should be intact.
(2) The cable model, voltage, and standard are in line with the planning.
(3) The insulation of the cable is outstanding. When there is doubt about the sealing of the oil paper cable, it should be judged for moisture damage; Directly buried cables and small bottom cables should undergo DC withstand voltage testing and fail to pass; The oil sample of the oil filled cable should pass the experiment.
(4) The oil pressure of the oil filled cable should not be lower than 1.47MPa.
