Summary of electrical basic knowledge 89 cases! Part Two

- Sep 08, 2017 -

Summary of electrical basic knowledge 89 cases

Part Two


40. What is the grounding wire and grounding device?

A: Connect the electrical equipment to the ground part of the metal conductor with the grounding body, called the ground wire. The grounding body and the grounding line are called the grounding device.

41. What is the protection of zero?

A: the electrical equipment is not charged with the metal part of the grid and the power grid connected to the zero line.

42. What is the role of protection?

A: The neutral point of the transformer or generator ground is called zero, and the zero-connected wire is called zero line. Protection is connected to the zero line is the electrical equipment under normal circumstances without electricity of the metal shell and the zero line connection. In the 1000V below the neutral point of the direct grounding of the power supply system, generally do not use the protection of the ground and the use of protection zero.

43. What are the key points to zero?

A: The following requirements should be met when connected to zero: (1) In the same system, it is strictly unsafe to place part of the electrical equipment and to connect another part of the electrical equipment to zero. (2) on the three-phase four-wire zero line, does not allow the installation of switches and fuses. (3) pay attention to the quality of zero line laying, in order to prevent the occurrence of zero line fault, should be installed enough ground grounding device, repeat the grounding resistance, should not be greater than 10 ohms. (4) All electrical equipment connected to the zero line, should be connected in parallel, in the pieces on the line or branch line. (5) The cross-sectional area of the zero line shall not be less than 1/2 of the cross-sectional area of the phase line.

44. What is a leakage protector?

A: electrical circuit or electrical equipment occurs when the single-phase short-circuit fault will produce residual current, the use of this residual current to cut off the fault line or equipment power protection device known as the residual current protection device, which collectively referred to as leakage protector.

45. What is the three-level protection mode commonly used for leakage protection?

A: overcurrent, ground, short circuit.

46. What is the cause of leakage? What are the consequences of leakage?

A: Cause: insulation damage (including aging, environment, machinery, toxic gases). Consequences: caused stray current, resulting in loss, loss of line loss.

47. What is the reason for the leakage of the lighting circuit and the method of checking the leakage method?

A: There are two ways to clean the line leakage: First, the insulation between the line of fire and the zero line damage, and the resulting line of fire and zero line leakage. Second, between the line of fire and the insulation damage to the formation of fire and earth leakage. The inspection procedure can be carried out as follows: (1) first determine whether the leakage. Use the shaking table to measure the size of the insulation resistance, or in the inspection of the building's general knife connected to a ammeter, remove all the lights, turn on all the light switch, if the ammeter pointer swing, then there is leakage. (2) to determine the line of fire between the line and the zero line, or between the line of fire and the earth leakage or both. Heart access ammeter check as an example: cut off the zero line, observe the current changes, ammeter instructions unchanged, is the line between the fire and the earth leakage. Ammeter indication is zero, is the line between the line of fire and leakage. Ammeter instructions become smaller, but not zero, then the line of fire for the zero line, between the line of fire and the earth are leakage. (3) to determine the leakage range. Remove the shunt circuit breaker or pull the knife, the ammeter indicates that the bus is the same, the ammeter instructions become smaller but not zero, then the bus and shunt are leakage. (4) to find the leakage point, according to the branch line, pull the switch, one by one investigation, find the leakage point and exclude.

48. What are the leakage protection methods?

A: The total protection of the whole network, refers to the low-voltage power supply at the installation of protective devices; for mobile power equipment, temporary electricity equipment and electricity of the family, should be installed last level protection; large low-voltage power grid multi-level protection. More than three kinds of protection, leakage protection device automatically cut off the power supply after the action.

49. What does electrical safety appliances include? What is the specific content?

A: electrical safety equipment by function: operating appliances and protective equipment. Operators include: electroscope, insulation rod, insulation clamp. Protective equipment including: insulated gloves, insulated boots, insulation pads, insulation Taiwan, shelter, climbing safety equipment.

50. What are the hazards of static electricity?

A: explosion and fire, electric shock, hinder production.

51. There are several measures to eliminate electrostatic hazards?

A: Grounding method, leak method, neutralization method and process control law.

52. What is a short circuit? What will cause short circuit?

A: The two power lines without direct contact with the load or touch, this phenomenon is called short circuit. Short circuit will cause electrical equipment overheating, and even burned electrical equipment caused by fire, while short-circuit current will produce a lot of electric power, resulting in electrical equipment damage. Serious short circuit accidents can destroy system stability and waste energy.

53. How does the safe voltage value specify?

A: China according to the specific environmental conditions, the safety voltage is defined as:

65 volts in buildings without high risk of electric shock;

There is a high degree of electric shock in the building for the 36 volts;

There are 12 electric shocks in buildings with special electric shocks.

54. What are the safety requirements for grounding?

(4) sufficient conductivity and thermal stability; (5) zero line to repeat the ground; (6) to prevent the use of (1) conductive continuity; (2) reliable connection; (3) have sufficient mechanical strength; Corrosion; (7) anti-mechanical damage; (8) underground installation distance to meet the relevant requirements; (9) grounding and then can not be connected in series.

55. To ensure that the normal operation of the transformer, including what?

A: Including observation current. Voltage. Power factor. Oil. Oil color. Temperature indication. Contact status is normal, observe the equipment and lines for damage, whether serious dirt, and observe the doors and windows. Fencing and other auxiliary facilities are intact, Listen to the sound is normal, pay attention to whether the discharge sound, smell with or without smell and other abnormal smell.

56. What is screen protection?

A: The screen is the use of screen protection device to control the insecurity, that is, using the cover. Shield. Cover. Box and other charged body with the outside world to isolate.

57. What is the main role of transformer oil?

A: The main role of transformer oil is cooling and insulation.

58. What is the role of automatic air circuit breakers?

A: Automatic air circuit breaker, also known as automatic switch, is a low-voltage distribution network in the important circuit on and off the device, with over-current limit protection, short-circuit instantaneous protection and loss of protection.

59. What are the high-voltage electrical equipment?

A: High voltage electrical equipment mainly includes high voltage fuses. High voltage isolating switch. High voltage load switch. High voltage circuit breaker. High voltage switchgear and power transformer.

60. What is the composition of the circuit?

A: The circuit is the current flow through the path, it consists of power, load, control electrical appliances and protection of electrical, wire composition.

61. What is Ohm's Law?

A: The current through the resistive element is proportional to the voltage across the resistor and is inversely proportional to the resistance, ie, I = U / R.

62. What is AC?

A: AC is the magnitude and direction of the electromotive force that changes cyclically over time.

63. What is the principle of asynchronous motor operation?

A: Asynchronous motor is to work with the magnetic field When the stator winding of the motor into the three-phase AC, with the stator windings in the three-phase current constantly changing, it produces the magnetic field is also in the space of continuous rotation, because The rotor wires cut the magnetic field lines during the rotation of the magnetic field. Since both ends of the rotor wires are connected together by two copper rings together, they constitute a closed loop. Thus, a rotor current is generated which is subjected to electromagnetic energy in the rotating magnetic field Force, then the axis of the formation of electromagnetic torque, so that the rotor along the direction of the rotating magnetic field and rotation.

64. What are the commonly used insulating materials?

A: mica, porcelain, asbestos, marble, glass and so on.

65. What are the commonly used organic insulating materials?

A: rubber, resin, quartz sand, silk and so on.

66. What is the importance of the FireWire switch?

A: When installing the lighting line, the lamp switch must control the FireWire, so that when the switch is disconnected, the lamp's lamp cap is not charged, the lamp is replaced or the lamp is not tripped.

67. What is the reason for the serious fever of the motor?

A: (1) the power grid voltage is too low or too high, drag the mechanical stuck or poor lubrication; (2) the motor ventilation is not good, the hood was gargled debris plug; (3) rotor broken; (5) stator and rotor rub; (6) stator winding with a small range of short-circuit or stator winding with local grounding.

68. What are the commonly used insulation tools?

A: There are insulation rods, insulation clamps, rubber insulated gloves and insulated boots, blankets and insulation platform.

69. What is the characteristic of the diode?

A: The characteristics of the diode is one-way conduction.

70. What are the common lightning protection devices?

A: lightning rod, lightning line, lightning network, lightning belt, arrester.


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