In the design of laboratory ground, the definition and characteristics of zero line and ground wire should be made clear. The zero line is the phase zero of three-phase alternating current. In the theoretical state, the angle between the phase angles of three-phase alternating current is pure 120 °. When the three-phase current is completely balanced, the neutral point to ground voltage is 0 V, and the zero sequence current is 0 a. However, if the zero line is ungrounded, the current of the zero line will be greater than 0 a due to the current imbalance, resulting in the neutral point drift. Therefore, there will be a certain voltage between the neutral point and the earth. This situation can be avoided by grounding the generator at the neutral point through the reactor.
In the laboratory decoration, the protective grounding is to ground the metal shell of the equipment to prevent the equipment and human body from being hurt by leakage and overvoltage. Considering the explosion-proof and equipment hazards, some special areas need to be grounded. The basic principle of anti-static grounding is to prevent the generation of static electricity. With static electricity, it can be quickly exported and directly discharged to the earth.
Lightning protection grounding refers to that the roof lightning protection belt is directly connected with the grounding system of the building, in the overhead line, it is connected with the ground through the lightning arrester, once the lightning is discharged directly to the ground; hybrid grounding is one of the most common grounding methods, which is to protect the grounding, equipment grounding, protective grounding, etc. into the same grounding grid, and the neutral point of the transformer is at the same potential.
The grounding device is a special part of the same protective grounding, but there are some more special, not all equipment grounding can do hybrid system, so some grounding equipment need to do independent grounding network, some equipment grounding resistance is higher than the traditional hybrid grounding resistance value, and some equipment grounding can only do circular single point grounding, forbidding ground cleaning. Through shielding grounding, there are also some grounding equipment needed by the reactor, such as UPS or generator, etc.
Equipotential grounding is to connect the metal parts of some equipment, such as metal shell or metal pipe elements, which are equivalent to the grounding main line together to make the same potential.
The network formed by connecting the metal shell group of the limited equipment with the metal pipes and components instead of the grounding main line is local equipotential.