Grounding of electrical equipment is carried out by means of a grounding device. The grounding device is composed of a grounding body and a grounding wire. The metal body directly in contact with the earth is called a grounding body; the wire (or other conductor) connecting the electrical device and the grounding body is called a grounding wire.
The type of grounding body is the working ground. In order to meet the safe operation of the power system or electrical equipment, grounding a certain point of the power system is called working ground. For example, the neutral point of the power system is grounded.
The second is lightning protection grounding. Overvoltage protection grounding to prevent lightning overvoltage from harming people and equipment. Grounding such as lightning rods and lightning arresters.
The third is protective grounding. In order to prevent personal electric shock accidents caused by insulation damage of electrical equipment, the conductive part of the outer casing of the equipment is grounded, so that the voltage of the metal casing to the ground is limited to a safe voltage, which is called protective grounding. For example, 1 motor, transformer, lighting fixture, metal base and housing for hand-held or mobile appliances and other electrical appliances; 2 transmissions for electrical equipment; 3 disks (tables, cabinets) for power distribution, control and protection Frame; 4 AC/DC power cable frame, metal box of junction box and terminal box, metal sheath of cable and threaded steel pipe; 5 metal frame of indoor and outdoor power distribution device or steel bar of reinforced concrete frame and metal near electrified part Obstruction and metal door; 6 steel bars of the overhead line and the overhead ground wire on the tower, the equipment casing and bracket mounted on the tower; 7 bases or brackets for various electrical equipment of the power station; The metal casing of the resident electrical appliance, such as a washing machine, a refrigerator, etc., is grounded.
The fourth is to repeat the grounding. In the TN-C system of the low-voltage power distribution system, in order to prevent the grounding protection from being lost due to the neutral line failure, the electric shock hazard and equipment damage are caused, and the neutral grounding is repeated. The repeated grounding points in the TN-C system are: 1 the terminal of the overhead line and the appropriate part of the line; 2 the neutral line of the four-core cable; 3 the neutral line in the large workshop (straight-loop arrangement, and multiple grounding repeated )Wait.
The fifth is anti-static grounding. In order to eliminate the grounding caused by static electricity to the human body and equipment. Such as certain liquid or gas metal delivery pipes or the grounding of vehicles.
The sixth is shield grounding. In order to prevent electrical equipment from being affected by electromagnetic interference, the shielding equipment that affects its work or causes electromagnetic interference to other equipment is grounded.
Technical requirements for the grounding device Grounding device for the transformer (station): 1 The grounding body of the grounding device should be laid horizontally. The grounding body shall be made of round steel with a length of 2.5 m, a diameter of not less than 12 mm or an angle of not less than 4 mm, or a steel pipe with a thickness of not less than 4 mm, and connected by flat steel with a cross-sectional area of ​​25 mm by 4 mm. Close the ring, the corners of the outer edge should be curved. 2 The grounding body should be buried outside the wall of the transformer (station), with a distance of not less than 3 meters. The buried depth of the grounding grid should exceed the thickness of the local frozen soil layer, and the minimum buried depth should not be less than 0.6 meters. The main transformer of the 3 transformer (station) power station (station) should be connected to the artificial grounding grid respectively. 4 The lightning rod (wire) should be equipped with an independent grounding device.
Protective earthing of electrical equipment in inflammable and explosive places: 1 Inflammable and explosive electrical equipment and mechanical equipment" target=_blank>Mechanical equipment, metal pipes and metal structures of buildings should be grounded, and jumper wires should be laid at the pipe joints. 2. The connection point between the grounding trunk and the grounding body shall not be less than two, and shall be connected to the grounding body at both ends of the building. 3 In order to prevent the measurement of the grounding resistance from causing an accident caused by sparks, the grounding resistance shall be measured in a place where there is no danger of explosion. Carry out, or lead the measuring end button to a place other than a flammable and explosive place.
Grounding of DC equipment: Grounding of 1 pair of DC equipment, can not use natural grounding body as protective grounding wire or repeated grounding grounding and grounding wire, and can not be connected with natural grounding body. 2 The manual grounding body of the DC system should be no less than 5 mm thick, and the corrosion should be checked regularly.
Grounding of hand-held and mobile electrical equipment: The grounding wire of hand-held and mobile electrical equipment should be made of soft copper wire with a cross-sectional area of ​​not less than 1.5 mm2 to ensure sufficient mechanical strength. The connection between the grounding wire and the electrical equipment or grounding body shall be made of bolts or special clamps to ensure good contact and meet the requirements of dynamic and thermal stability under the action of short-circuit current.
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