Views: 0 Author: Site Editor Publish Time: 2018-08-03 Origin: Site
11. What are magnets, magnets and poles?
Answer: The object has the property of attracting iron, cobalt and nickel. The magnetized object is called magnet. The magnet has the two most magnetic regions called magnetic pole, one called the north pole (N pole) and the other called the south pole. (S pole).
12. How is the direction of the current specified? Is the direction of free electrons the direction of current?
A: The current direction is defined as: the direction of positive charge motion is the direction of current. The direction of free electron movement is opposite to the direction of current motion.
13. What is AC and what is sinusoidal AC?
A: The current whose magnitude and direction change with time is called AC. In an AC circuit, when the magnitude and direction of the electromotive force, voltage, and current change with time according to a sinusoidal function, it is called sinusoidal alternating current.
14. What types of power transformers are classified according to structure and purpose?
Answer: The power transformer is divided into two winding transformers, three winding transformers, multi-winding transformers and autotransformers according to the structure. According to the use, there are step-up transformers, step-down transformers, distribution transformers, and tie transformers.
15. What measures should be taken if the high voltage equipment needs to be patrolled?
Answer: The indoors should not be within 4 meters of the fault point, and the outdoor room should not be within 8 meters of the fault point; those entering the above range. Insulated boots must be worn and insulated gloves should be worn when touching the outer casing and frame of the equipment.
16. What data can be measured by the multimeter?
Answer: The universal meter can measure DC current, AC and DC voltage, DC resistance, etc. The higher level can also measure the inductance, capacitance, audio voltage, audio power, level of the AC, and the DC amplification factor HFz of the transistor.
17. What are the uses of the test pencil?
A: The purpose is:
(1) It is possible to measure whether any wires in the low-voltage line are in phase or out of phase.
(2) It is possible to distinguish between alternating current and direct current.
(3) It can judge the positive and negative poles of DC.
(4) It can be judged whether the DC is grounded.
18. What parts does the asynchronous motor consist of?
Answer: Stator part: stator stator winding, stator core; rotor part: rotor core, rotor winding, fan, bearing; other parts: end cover, junction box, etc.
How is the phase-to-phase short circuit protection of a 19.380 volt low voltage motor achieved?
Answer: The structure of phase-to-phase short-circuit protection of low-voltage motors is divided into two types according to their switching devices:
(1) An electric motor using a low-pressure automatic air switch whose phase-to-phase short-circuit protection is realized by an overcurrent release of a low-pressure automatic air switch.
(2) The motor using the combination of the fuse and the contactor or the magnetic starter is connected. The phase-to-phase short-circuit protection is realized by the fuse being blown during the short circuit, and the cut-off capacity of the fuse is required to be appropriate.
20. What is primary protection?
Answer: It refers to the basic requirements that can meet the stability of the system and the safety of the equipment when a short-circuit fault occurs. Firstly, the protection of the protected equipment and the fault of the whole line is selectively removed by tripping.
