电力知识三相电照明电（Electric power knowledge, three-phase electric lighting）.docVIP

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电力知识三相电照明电（Electric power knowledge, three-phase electric lighting）.doc

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电力知识三相电照明电（Electric power knowledge, three-phase electric lighting）

电力知识三相电照明电（Electric power knowledge, three-phase electric lighting） Protective earthing The metal casing of the electrical equipment is connected with the grounding body through the grounding wire, and the principle is the shunt principle Protective zeroing As the low voltage network (380V/220V) neutral point is not grounded, only individual occasions, such as mines, swimming pool, etc., and the general low-voltage power grid using neutral grounding three-phase four wire power supply system. A device in which the metal housing is connected to the zero line, i.e., the protective zero, is shown in figure 2. Zero protection purposes, but also to ensure safety, when a collision is caused by the equipment shell, single-phase short circuit, the protection device moves quickly, cut off the fault equipment. Zero protection should pay attention to the problem: (1) the circuit which is supplied by the same generator or the same transformer does not allow some equipment to protect the ground, and some equipment protect the connection to zero. (2) connect one or more points along the zero line, i.e., repeat ground. In order to ensure the reliable grounding device. But repeated grounding can only play the role of balanced potential, so the neutral line as far as possible to avoid breakage, the construction of neutral line requires careful attention to maintenance. The concept of three-phase electricity is that when the coil rotates in the magnetic field, the conductor cuts the magnetic lines to produce an induced electromotive force, and its change law can be represented by a sine curve. If we take three coils and place them at 120 degrees to three degrees apart in space, the three coils still rotate at the same speed in the magnetic field, which will induce the same induction electromotive force of the same frequency. Since the three coils are 120 degrees apart from each other in the space position, the current produced is also a three-phase sinusoidal change, called a three