Summary of electrical basic knowledge 89 cases
71. What are the motor insulation grades? What is the temperature?
A: Insulation grade points: A, E, B, F, H.
Where the A level allows the limit temperature of 105 ° C and the temperature rise to 60 ° C
E-level limit temperature of 120 ℃, the temperature rise of 75 ℃
Class B allows the limit temperature of 130 ° C and the temperature rise to 80 ° C
F-level limit temperature of 155 ℃, the temperature rise to 100 ℃
H-level limit temperature of 180 ℃, temperature rise of 125 ℃
72. What is the composition of hand-held electric tools?
A: By the drive part, drive part, insulation and mechanical protection part.
73. Lighting is generally divided into several?
A: (1) general lighting; (2) local lighting; (3) mixed lighting.
74. Lighting switch installation requirements?
A: (1) pull the switch from the ground height of 1.2-1.4m, from the door cabinet 150-200mm; (2) pull the switch is 2.2-2.8m, from the door cabinet 150-200mm; (3) concealed switch installed In the switch box, the switch box should have a complete cover.
75. Incandescent lamp, fluorescent lamp hanging section should not be less than how much?
A: should not be less than 0.75mm².
76. Three-phase asynchronous motor brake
A: (1) mechanical brake; (2) reverse braking; (3) energy consumption brake.
77. Motor bearing requirements for refueling?
A: For 3000 rpm, refueling to 2/3 weak is appropriate; on the 1500 r / min motor, refueling to 2/3 is appropriate; on the 1500 r / min motor, the general plus calcium nano Fat high-speed butter; on the 1000-rpm low-speed motor, usually add calcium nano-fat.
78. What is the difference between DC and AC?
A: DC referred to as DC, refers to the direction of the current does not change with time. In the constant resistance of the circuit, coupled with a constant voltage power supply, resulting in the size and direction are constant current. AC referred to as the exchange, refers to the size and direction of the cycle with the current changes in the current.
79. What are the common circuit protection devices?
A: Undervoltage protection, short circuit protection, limit protection, overload protection, chain protection.
80. What are the forms of the cable?
(5) common cable; (6) V-shaped cable; (7) bow pull line. (2) the four sides of the cable (3) on both sides of the cable (4)
81. What situation needs to be phased?
A: (1) the new input of the equipment; (2) two or more than two lines of cable lines; (3) two or more overhead lines; (4) two of them after the maintenance; (5) After the maintenance and parallel operation with another transformer.
82. How to distinguish between running lines and disabling lines?
A: (1) switch state; (2) whether the voltage indication; (3) signal display; (4) electroscope direct observation.
83. Equipment and lines common fault types?
(1) short circuit; (2) open circuit; (3) wrong wiring; (4) wrong operation.
84. What are the basic requirements for selecting wires?
A: (1) according to the allowable carrying capacity; (2) according to the allowable voltage drop selection; (3) by mechanical strength selection.
85. How many grounding methods? What role?
A: The way: to protect the ground, work grounding, shock grounding, then zero and repeated grounding. Role: is to protect the safety of personal and equipment, so electrical equipment need to take grounding measures.
86. What are the electric shock methods?
A: divided into single-phase electric shock, two-phase electric shock and step voltage electric shock.
87. What is the interstellar electric shock?
A: that is, when the human body and the earth insulation at the same time contact two different phase line or the body at the same time contact with different parts of the electrical equipment of the two charged parts, then the current from a phase through the human body to another phase line.
88. What is safe color?
A: The security color is to express the meaning of the security information, the expression of prohibited, warning, instructions, tips and so on. National security colors are red, blue, yellow, green four colors. Red forbidden, stopped; blue indicates instruction, must comply with the rules; yellow indicates warning, attention; green indicates indication, safe state, prevailing.
89. What is the line spacing?
A: The power lines above the communication line, high voltage lines above the low voltage line. The distance between the communication line and the low voltage line shall not be less than 1.5 m; the low voltage line shall not be less than 0.6 m; between the low voltage line and the 10KV high voltage line shall not be less than 1.2 meters; 10KV high voltage line and 10KV high voltage line shall not be less than 0.8 meters. 10KV line to the ground distance of not less than 4.0 meters; low-pressure sink line to the ground distance should not be less than 2.5 meters; low-voltage switch line across the opening of the street, the distance should not be less than 6 meters; across the difficult streets or sidewalks Should not be less than 3.5 meters. Direct buried cable buried depth should not be less than 0.7 meters.