Issues Related To Cables

1. Briefly Describe The Composition And Properties Of The Epoxy Resin Compound

Answer: The epoxy resin compound consists of epoxy resin with a hardener, filler, toughener, and thinner. It has the following properties;

1. Sufficient mechanical strength
2. Excellent electrical properties
3. Stable electrical properties
4. Sufficient adhesion to non-ferrous metals
5. Good corrosion resistance
6. When used outdoors, it is resistant to rain, light and heat, and humidity

2. When Using A Single-Core Cable Sheath End Grounding Method, Why Must You Install The Cable Parallel To The Return Line?

Answer: A wire and cable conductor must be installed along the cable line laid in parallel in the metal sheath end of the grounded cable line to ensure that the induced voltage in the sheath does not exceed the acceptable standard.  The two ends of the grounded conductor are referred to as the return line.

When a single-phase ground fault occurs, the grounded short-circuit current can flow back through the return line to the system’s center. Due to the magnetic flux generated by the grounding current transmitted through the return line, a magnetic flux is caused by the grounding current of the cable conductor. This reduces the induced voltage in the wire and cable sheath during a short-circuit fault.

3. Cable Works Can Be Divided Into Several Projects. What Projects Are These?

Answer:

1. Site transport: involves loading and unloading engineering materials from the warehouse to the construction point, transportation, and empty backhaul.
2. Local works: includes road excavation, tunnels, trench construction, among others.
3. Laying works: involves laying cables, intermediate head fabrication, lifting of cover, the burial of pipes, tide proofing, and traction head fabrication.
4. Both ends of the project: include the production and installation of support and suspension bridges and their foundations, the output of terminal heads, the structure of oil pressure and signal devices, the electrical performance test of the name species, to name a few.
5. Plugging works: includes the production of oil-filled wire and cable sealing heads, the installation of oil supply tanks, automatic drainage, and signaling devices, among others.
6. Grounding works: includes insulation joints, transposition boxes, protectors, grounding box installation, to name a few

4. What Checks Should Be Carried Out For The Acceptance Of Cable Lines?

Answer:

• Cable specifications should be in line with the requirements of the project in question. The wire and table arrangement should also be neat, without damage, complete, and have correct and clear labeling
• The fixed bending radius of the cable, the distance concerned, and the wiring of the metal sheath of the single-core power cable shall comply with the requirements

• Wire and cable terminals, intermediate heads do not leak oil, firmly installed, oil-filled cable oil pressure and meter calibration values should meet the requirements

• Good grounding
• The cable terminal is correctly coloured, and the metal parts of the brackets should be painted completely
• Cable trenches and tunnels, bridges should be free of debris, complete cover

5. What Are The Requirements Of The Cable Line Positive Sequence Impedance Measurement Process?

Answer: The AC resistance of the wire and cable conductor and the phase sum of the three equivalent inductances of the cable is called positive sequence impedance.

The cable treasure application technology research institute revealed that the cable line positive sequence impedance could generally be measured directly on the cable tray.  Measurement typically uses lower voltage.  Therefore, there is a need to use a step-down transformer for step-down measurement.

A step-down transformer uses star-shaped wiring, and its capacity is generally 10kVA or more.  There is a wide range of voltage regulation. When carrying out measurement, the AC power supply should be more stable to ensure that the current achieves the specified requirements. The actual voltage meter reading value must be the voltage at the end of the cable. Ideally, the test current should be close to the cable’s long-term allowable load capacity and the measurement of the value of each meter close to the current after reading the value of the three meters at the same time.

6. According To The “Electrical Production Safety Regulations,” What Conditions Must Electrical Staff Meet?

Answer: For one to qualify as an electrical staff member, he or she must meet the following conditions;

1. Must visit the doctor for a check-up to ensure that they are in good physical health and not ailing from any diseases that might impair their working ability
2. They must have the necessary electrical knowledge. He or she must also master the relevant regulations on the particular area of wire and cable specialization and the professional technology and safety operation techniques. They must also have passed their electrical exams
3. Must be skilled in first aid methods of electric shock

7. What Should Be Noted In The Process Of Transporting And Loading Cables?

Answer:

In the process of transport loading and unloading, the cable and cable tray should not be damaged. It is strictly prohibited to push the cable tray directly from the car, and the cable should not be transported flat and stored flat.

Before transporting or rolling the wire and cable tray, you must ensure that the cable tray is firm. The cable winding should be tight. For an oil-filled cable, the pressure tank between the oil pipes should be fixed to avoid damage. The pressure tank should be firm, and the pressure indication should meet the ideal universal requirements.

8. What Measures Are Recommended For Cable Fire Prevention?

Answer:

1. Use of fire-retardant cables
2. Use of a fire-resistant wire and cable bracket
3. Use of fireproof paint
4. Set a fire partition wall and a fire baffle in the cable tunnel, mezzanine exit, and other similar high-risk places
5. For overhead cables, you should avoid oil pipes and install explosion-proof doors

9. Which Aspects Should Be Considered When Choosing A Power Cable Cross-Section?

Answer: You should consider the following aspects;

1. The long-term allowable working current through the cable
2. The thermal stability in the event of a short circuit
3. The voltage drop on the line should not exceed the permissible operating range

10. What Are The Advantages Of Power Cables Over Overhead Lines?

Answer:

1. Reliable operation plus the fact that external damage is slight, the chance of failure is less, there is optimum power supply safety, and they will not cause personal harm because they are installed underground
2. Less maintenance workload and no need for frequent wire and cable inspections
3. No need to erect poles.
4. It helps to improve the power factor