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Professional wire and cable FAQ

Information Source:Henan Huadong Cable Co., Ltd Release date:2014-03-12

Cable duct are required?
Answer: (1) row tube top to the ground distance, in the plant is 0.2m, the sidewalk was 0.5m, the general area of 0.7m;
(2) changes in the direction and the branch shall be discharge tube well pit, the length of more than 30mm should also be added to the pit;
(3) the pit depth is not less than 0.8m, manhole diameter not less than 0.7mm;
(4) exhaust pipe should tend to pit 0.5% ~ 1% drainage slope.

What are the requirements for electrical connection cable conductor?
Answer: requirements for resistance connection point is small and stable, the ratio of connection point of the resistance with the same length, the same cross-section of the conductor, the newly installed terminal head and middle head, should be less than 1; for the operation of the terminal head and middle head this ratio should not be greater than 1.2.

Design of cable joints and the head should meet the requirement?
Answer: should fulfill the requirements:
(1) high strength, good conductors;
(2) high mechanical strength, dielectric loss;
(3) has the advantages of simple structure, strong sealing.

What is cable fault? There are several types of common?
Answer: cable fault refers to the cable insulation breakdown or in operation in the preventive test, because the insulation breakdown, wire and cable force burning off the fault line outage. A common fault with fault, fault, fault, flashover fault and mixed failure etc..

How to deal with the cable line fault of single phase to ground?
Answer: cable line single-phase grounding fault in general, cable conductor damage is only partial, if belong to mechanical damage, and the fault point near the soil is dry, can be partial repair, add a dummy connector, not the cable core sawing, only the fault point insulation strengthening post sealing.

Power cable should be carried out which tests and inspections before being laid down?
Answer: before installation should check the cable type, specification and length to meet the requirements, if there are external injury, low voltage cable for 1000V megohmmeter telemetry insulation resistance, resistance is generally not less than 10M Ω, high voltage cable measured with 2500V megger shake resistance is generally less than 400M

The main plant in the laying of cables in general should pay attention to what?
Answer: in the main workshop in the laying of cables should pay attention to the general:
(1) control cable that leads to the control room should be laid overhead;
(2) the 6KV cable should be used in tunnel or pipe laying, the underground water level height can be elevated or pipe laying;
(3) the 380V cable ditch or row pipe at both ends of cable tunnel, at zero meter should, when one device in the end when, in part, be overhead laying, when underground water level was higher, appropriate overhead.

Power cable with the shielding layer and the outer shielding layers in what position? With what material? What is the role?
Answer: in order to make the insulating layer and the cable conductor has a good contact, to eliminate the increasing conductor surface is not smooth due to the conductor surface field strength, generally in the conductor coated with metal shielding layer of paper or semiconductor tape. In order to make the insulating layer and the metal sheath has good contact, generally in the insulating layer is wrapped in a layer of shielding layer. The outer layer and the inner layer of the same material, sometimes also bound with copper or copper ribbon.

The structure and properties of epoxy resin composites.
Answer: epoxy resin composites consisting of epoxy resin with hardener, filler toughening agent and diluent. Has the following properties:
(1) have sufficient mechanical strength;
(2) excellent electrical performance;
(3) stable electrical performance;
(4) there is enough and nonferrous metal adhesion;
(5) with good corrosion resistance;
(6) outdoor use, rain, light, heat resistance.

Single core cable sheath is grounded way why must be installed along a cable lay back line?
Answer: in the cable line grounding metal sheath end, in order to ensure the induction voltage protection sleeve does not exceed the permissible standard, must be installed along a cable lines laid parallel conductor, and the conductor grounded at both ends, the conductor called return line. When single-phase earth fault occurs, the short-circuit current can flow back into the system through the return line center point, because the return wire grounding current produces a magnetic flux offset magnetic flux a portion of the cable conductor earthing current generated, thus reducing the short-circuit fault induced voltage.

Cable engineering can be divided into several projects?
Answer: (1) site transportation: including engineering material from the warehouse to the construction of loading and unloading, transport and empty backhaul.
(2) the local engineering: including road excavation, tunneling, channel construction etc..
(3) laying project: including the laying head, middle production, cover lifting plate, pipe, school tide, traction head production.
(4): including the production team, two engineering bridge frame and the basic installation, terminal manufacturing, oil pressure and signal devices, a kind of electrical performance test etc..
(5) stop project: including oil filled cable stopper head production, automatic water supply tank, and a signal device installation etc..
(6) the ground project: including the insulating joint, transposition box, protector, grounding box installation.

Acceptance of cable line what checks should be carried out?
Answer: (1) the cable specifications should be consistent with the provisions, shall be arranged orderly, no damage, a full plate, correct, clear;
(2) connecting the metal shield cable fixed bending radius, relative distance and single core cables shall conform to the requirements;
(3) the cable terminal head, middle and no oil leakage, installation is firm, oil filled cable oil and meter setting value shall comply with the requirements;
(4) good grounding;
(5) the cable terminal phase color correct, metal parts such as paint complete bracket;
(6) the cable trench and tunnel, bridge should be no debris, the cover is complete.

What are the requirements for the positive sequence impedance measuring cable lines?
Answer: the phase volume conductor AC resistance and inductance of the cable three identical and known as positive sequence impedance. The positive sequence impedance of the cable can be directly measured in cable tray, the general use of voltage, low measurement therefore, need to buck with a step-down transformer, converter adopts star connection, capacity is more than 10kVA, voltage, wide adjustment range, measurement of AC power supply should be relatively stable, to ensure that the current reaches in accordance with the requirements of measurement, the actual voltage meter reading must be voltage cable end, close to the cable test current best long-term allowable ampacity, reading the meter value, close the current read at the same time three values.

According to the "electric power production safety regulations", what is electrical personnel must have the conditions?
Answer: must meet the following conditions:
(1) the doctors to identify the health of the body, not hinder the work conditions;
(2) basic knowledge of electrical necessary, according to the position and the nature of the work to master relevant rules, professional technology and safety operation technology, and pass the examination;
(3) Master shock first aid method.

Cable should pay attention to what the transportation loading and unloading process?
Answer: (1) in the transport and handling process, should not make the cables and cable trays are damaged, it is strictly prohibited to cable tray directly from the car down, cable like should not flat transport, horizontal storage.
(2) the transport or rolling cable tray, must ensure that the cable firm, an electric cable winding, oil filled cable to the pressure oil tank should be fixed, not damage, pressure tank should be firm, the pressure indication shall conform to the requirements.

Cable fire what measures?
Answer: (1) the fire retardant cable;
(2) adopts the fireproof cable bracket;
(3) the use of fire retardant paint;
(4) cable tunnel, interlayer exit setting fire wall, fire damper;
(5) the overhead cable should avoid the oil pipe, explosion-proof doors, or else should have to take local wear tube or fire insulation measures.

Section should choose power cable which a few respects?
Answer: should consider the following aspects:
(1) cable to allow long-term work through the current;
(2) once the thermal stability of short circuit;
(3) the voltage drop on the line can not exceed the permitted scope of work.

Power cables and overhead lines are what are the advantages?
Answer: (1) reliable operation, as installed in the underground shelter, damage by external forces, safety and less chance of failure, power supply, will not cause harm to the person;
(2) maintenance workload is small, do not need frequent inspection;
(3) do not need to set up the tower;
(4) helps to improve the power factor.

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