Explanation principle (1) To 1) Electrically, the earth is an object with very low resistance and large capacitance, which has the ability to absorb infinite charges and can still maintain the potential after absorbing a large amount of charges. Therefore, it serves as a reference potential body in electrical systems. 2) The ground potential refers to a conductive body or group of conductive bodies that are in close contact with the earth and form electrical contact. It is usually made of round steel or angle steel, and can also be made of copper rods or plates. When the current flowing into the ground disperses in a hemispherical shape towards the ground through the grounding electrode, the resistance increases closer to the grounding electrode and further away due to the smaller spherical shape. The experiment proves that there is actually no resistance present at a distance of 20m from a single grounding electrode or contact point, and the potential at that point has approached zero. (2) Grounding ē D ì (1) [grounding; grounding; ground connection] [electricity] (2) [touchdown; ground contact] In the United States' power system, except for the hot line and neutral line, the pin with the middle round head is the so-called grounding pin. Connecting a part of the power system or electrical device to the grounding electrode through a grounding wire is called grounding. The wire connected to the grounding electrode is called the grounding wire. The grounding electrode and grounding wire are collectively referred to as grounding devices. Several grounding bodies are connected to each other in the ground to form a grounding network, and the grounding wire can be divided into grounding main lines and grounding branch lines. According to regulations, the grounding main line should be connected to the grounding grid at different locations using no less than two conductors. The grounding point in the power system is generally the neutral point. The grounding part of the electrical device is the exposed conductive part, which is the conductive part that can be touched in the electrical device. It is not charged normally, but may be charged in case of a fault. The external conductive part of the device, also known as the external conductive part, is not an electrical device and generally refers to metal pipes for water, heating, gas, air conditioning, and metal structures of buildings. (3) The main function of grounding is to prevent personal injury, damage to equipment and circuits, prevent fires and lightning strikes, prevent static damage, and ensure the normal operation of the power system. Grounding is an electrical safety measure taken to ensure the normal operation and personal safety of electrical equipment. It is achieved by connecting metal wires to grounding devices. Commonly used methods include protective grounding, working grounding, lightning protection grounding, shielding grounding, and anti-static grounding. The grounding device introduces the leakage current, static charge, and lightning current that may be generated on electrical equipment and other production equipment into the ground, thereby avoiding personal electric shock and potential accidents such as fire and explosion. 1) To prevent personal injury from electric shock, a good metal connection should be made between the normally uncharged metal parts of electrical equipment and the grounding electrode to protect human safety. For electrical equipment with grounding devices, when the insulation is damaged and the casing is live, the grounding current will flow through both the grounding electrode and the human body simultaneously. The current value flowing through each path will be inversely proportional to its resistance. The smaller the resistance of the grounding electrode, the smaller the current flowing through the human body. When the grounding resistance is extremely small, the current flowing through the human body approaches zero, thus avoiding the risk of electric shock. Therefore, in any case, it should be ensured that the grounding resistance is not greater than the grounding resistance value specified in the design or regulations. 2) To ensure the normal operation of the electrical system, the grounding of the power system is generally neutral point grounding, so the potential between the neutral point and the ground is close to zero. When the phase line collides with the shell or is grounded, the voltage of the other two phases to ground will increase to times the phase voltage in the neutral insulation system; In systems with neutral grounding, it is close to phase voltage. Due to the presence of a neutral grounding wire, the reliability of relay protection can be guaranteed. The DC power supply in communication systems generally adopts positive electrode grounding to prevent noise from entering and ensure the normal operation of communication equipment