1. The composition and properties of epoxy resin composites are briefly described.

 Epoxy resin composite consists of epoxy resin added with hardener, filler, toughener, and diluent. It has the following performance: ① Have sufficient mechanical strength; ② Excellent electrical performance; ③ Stable electrical performance; ④ Have sufficient adhesion to nonferrous metals; ⑤ Good corrosion resistance;  ⑥ When used outdoors, it is resistant to rain, light, and moisture.

2. Why is it necessary to install a return line running parallel to the cable in the way of grounding one end of the single core cable sheath?

 In a cable line where one end of the metal sheath is grounded, in order to ensure that the induced voltage in the protective sheath does not exceed the allowable standard, it is necessary to install a conductor laid parallel to the cable line, 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 of the system through the return line. The magnetic flux generated by the ground current flowing through the return line offsets the magnetic flux generated by a portion of the cable conductor ground current, thereby reducing the induced voltage of the sheath during a short circuit fault.

3. How many projects can cable engineering be divided into?

 (1) Site transportation: It includes the loading and unloading, transportation, and empty vehicle return of engineering materials from the warehouse to the construction site. (2) Local works: including road excavation, tunnel, trench construction, etc. (3) Laying works: including laying, intermediate head fabrication, lifting the cover plate, burying the pipe, tidal correction, traction head fabrication, etc. (4) Engineering at both ends: including the fabrication and installation of support and suspension bridge frames and their foundations, the fabrication of terminal heads, the installation of oil pressure and signal devices, and the electrical performance testing of various types. (5) Plug engineering: including the production of oil filled cable plug heads, installation of oil supply tanks, automatic drainage, and signaling devices. (6) Grounding works: including installation of insulated joints, transposition boxes, protectors, and grounding boxes.

4. What inspections should be conducted for the acceptance of cable lines?

 (1) The cable specification should comply with the regulations, the arrangement should be neat, without damage, and the labels should be complete, correct, and clear;(2) The fixed bending radius of the cable, the relevant distance, and the wiring of the metal sheath of the single core power cable should meet the requirements; (3) The cable terminal and intermediate head shall be free of oil leakage and firmly installed. The oil pressure of the oil filled cable and the setting value of the gauge shall meet the requirements; (4) Good grounding; (5) The phase color of the cable terminal is correct, and the metal parts such as the bracket are painted completely;  (6) The cable trench, tunnel, and bridge shall be free of debris, and the cover plate shall be complete.

5. What are the requirements for positive sequence impedance measurement of cable lines?

The AC resistance of the cable conductor and the phasor of the three same inductive reactances of the cable are called positive sequence impedance.  According to the "Research Institute of Cable and Cable Application Technology", the positive sequence impedance of a cable line can generally be measured directly on the cable reel, and a lower voltage is generally used for measurement. Therefore, it is necessary to use a step-down transformer for step-down. The step-down transformer adopts star connection, with a capacity of generally over 10kVA, and has a wide range of voltage regulation. During measurement, the AC power supply should be relatively stable to ensure that the current meets the specified requirements during measurement, The reading value of the actual voltmeter must be the voltage at the cable end. The test current should preferably be close to the long-term allowable current carrying capacity of the cable. When measuring and reading the values of each meter, close the current and simultaneously read the values of the three meters.