Basic knowledge of coal mine electricians

Coal mine electrical technology is only a small branch, but it is a specialized discipline with a wide range of expertise and special requirements. So how much do you know about coal mine electricians? The following is the basic knowledge of coal mine electricians compiled by me. I hope you like it!

Basic knowledge of coal mine electricians

1. The basic requirements for power supply for industrial and mining enterprises are reliable power supply, power supply safety, power supply quality and power supply economy.

2. The three major protections for coal mine power supply are protective grounding, overcurrent protection and leakage protection.

3. Voltage and frequency are the main indicators for measuring electrical energy.

4. The connection method of the power grid can be divided into radial power grid, main line power grid and ring power grid according to different load requirements.

5. In the three-phase power supply system, the neutral point operation mode of the power grid includes three modes: the neutral point is not grounded, the neutral point is grounded through the arc suppression coil, and the neutral point is directly grounded.

6. Bridge knotting is divided into three forms: full bridge, inner bridge and outer bridge.

7. In order to prevent fire, the underground substation must be equipped with sand boxes and fire-extinguishing equipment.

8. The underground mobile substation of a coal mine is usually installed in a trough 150-300 meters away from the working surface, and the working surface advances every 100-200 meters. The substation moves forward once.

9. The power distribution points of coal mine underground working faces are divided into two types: coal mining working face power distribution points and excavation working face power distribution points.

10. The power distribution point of the coal mine underground working face is generally 50-100 meters away from the coal mining face and 80-100 meters away from the excavation working face. The power distribution point of the working face moves with the advancement of the working face.

11. At present, electrical equipment is divided into three types according to the working system: long-time working system electrical equipment, short-time working system electrical equipment and intermittent working system electrical equipment.

12. There are three capacitor compensation methods: individual local compensation, decentralized compensation and centralized compensation.

13. Our country stipulates that two main transformers are generally used in mine substations.

14. The power loss of the transformer includes active power loss and reactive power loss.

15. In the three-phase power supply system, the basic types of short circuits are: three-phase short circuit, two-phase short circuit, two-phase ground short circuit, single-phase short circuit and single-phase ground short circuit, etc.

16. When short-circuited at the same point, Id(2) = 0.866 Id(3).

17. The effects of short-circuit current include electrodynamic effects and thermal effects.

18. If the voltage between the contacts of the electrical equipment is above 10-20 volts. When the current is above 80-100 mA, arcing will occur between the contacts. Its temperature can reach as high as 10,000 degrees.

19. The main forms of deionization are recombination and diffusion.

20. Switches (electrical appliances) with an alternating current rated voltage of 1200 volts and below or a direct current rated voltage of 1500 volts and below are low-voltage switches (electrical appliances).

21. The basic wiring methods of current transformers include one-phase wiring, star wiring and incomplete star wiring.

22. The main parameters of current transformer are rated voltage, rated current and accuracy level.

23. The main parameters of voltage transformer are rated voltage, accuracy level and rated capacity.

24. Explosion-proof measures commonly used in mining electrical equipment include explosion-proof enclosures, intrinsically safe circuits, advanced power-off and rapid power-off systems.

25. When the concentration of gas in the air is 8.2%-8.5%, it is most likely to explode. When the concentration of gas is 9.5%, the explosion pressure is the highest.

26. The explosion-proof enclosure of mining electrical equipment must have explosion-proof and explosion-proof properties.

27. The minimum energy required for a gas explosion is 0.28 millijoules.

28. The shortest time for an electric spark to ignite gas and coal dust is more than 5 milliseconds, while the power outage time of a general rapid power-off system is 2.5-3 milliseconds.

29. Mine electrical equipment is divided into two categories: general mining type and mining explosion-proof type.

30. QCZ83?120 (225) vacuum magnetic starter has overload, phase failure and short circuit protection functions.

31. Mine flameproof automatic feed switch can automatically trip when a short circuit or leakage occurs in the protected line.

32. In order to distinguish the phase sequence, the U phase of the three-phase AC bus is painted in yellow, the V phase is painted in green, and the W phase is painted in red.

33. Insulators can be divided into two basic types: high-voltage insulators and low-voltage insulators according to the voltage.

34. The selection of a complete set of power distribution devices is mainly to determine the model of the device, the primary circuit scheme and the selection and verification of electrical parameters.

35. Transmission lines are divided into two categories: overhead lines and cable lines.

36. According to different functions and positions, electric poles can be divided into straight poles, tension poles, corner poles, terminal poles, branch poles, spanning poles and transposition poles.

37. Power cables can be divided into three types according to insulation materials: paper insulated cables, rubber insulated cables and plastic insulated cables.

38. The installation position of the cross arm on the pole should be: the straight pole is installed on the load side, the corner pole, terminal pole, and branch pole should be installed in the opposite direction of the tension, and the tension pole Should be installed on both sides of the pole.

39. The requirements for relay protection devices are selectivity, quick action, sensitivity and reliability.

40. There are two ways to adjust the operating current of electromagnetic current relay: smooth adjustment and progressive adjustment.

41. Inductive relay is composed of two parts: induction system and electromagnetic system.

42. The hardware of microcomputer protection generally consists of three parts: data acquisition system, host computer and switching input/output system.

43. There are three common wiring methods for current protection devices: complete star wiring, incomplete star wiring and two-phase current difference wiring.

44. When a short-circuit fault occurs in the power supply system, its important characteristics are a sudden increase in current and a drop in voltage.

45. Overcurrent protection is generally divided into definite time overcurrent protection, inverse time overcurrent protection, non-time-limited current quick-break protection and time-limited current quick-break protection.

46. The setting of relay protection device includes the setting of operating current and operating time.

47. The insulation monitoring device of a general power grid consists of a three-phase five-column voltage transformer, three voltmeters and a voltage relay.

48. Selective grounding protection devices include zero-sequence current protection and zero-sequence power direction protection.

49. Large power transformers should generally be equipped with gas protection, longitudinal differential protection or current quick-break protection, overcurrent protection and overload protection.

50. Currently, there are three types of gas relays used in China: float type, baffle type and composite type.

51. When installing a transformer with a gas relay, it is required that the top cover of the transformer's oil tank has a slope of 1%-1.5% from the horizontal. There is a slope of *2%--4% between the connecting pipe leading to the oil pillow and the horizontal surface.

52. The unbalanced current in the differential protection of the transformer is mainly caused by: wiring method, current transformer type, current transformer ratio, transformer excitation inrush current and changing the transformer tap.

53. There are two types of operating power supplies: DC and AC.

54. There are three commonly used wiring methods for AC operation relay protection: direct action type, indirect shunt type and capacitor energy storage type.

55. According to different control locations, the control methods of relays can be divided into two methods: local control and centralized control.

56. Substation signaling devices include three categories: position signals of switches, action signals of protection and automatic devices, and central signals.

57. The central signaling device of the substation consists of accident signals and warning signals.

58. The microcomputer automatic monitoring system of the substation consists of a front-end monitoring unit, a back-end monitoring unit, a microcomputer protection unit and a reactive power compensation unit.

59. Electric shock is divided into two categories: electric shock and electric injury according to the degree of damage caused by electric current to the human body.

60. The types of grounding can be divided into working grounding, protective grounding, lightning protection grounding, anti-static grounding and repeated grounding according to the purpose and function of grounding.

61. Protective grounding is divided into three types: TT, IT and TN systems.

62. Grounding can be divided into two categories: natural grounding body and artificial grounding body.

63. The underground main grounding electrode is generally made of steel plates with an area of ??not less than 0.75 square meters and a thickness of not less than 5 mm.