Views:77 Author:Site Editor Publish Time: 2019-08-13 Origin:Site
Firstly, make full use of the natural grounding body to save investment. If the natural grounding resistance measured in the field has met the requirements of the grounding resistance value and meet the thermal stability conditions, there is no need to install a manual grounding device. Otherwise, a manual grounding device should be installed as a supplement.
The artificial grounding device should force the potential distribution around to be arranged uniformly as possible to reduce the contact voltage and the step voltage, in order to ensure personal safety.
The steel structure and steel bars of the building, the rails for driving, the buried metal pipes (except for the flammable liquids and the flammable and explosive gases), and the metal sheaths of the cables laid in the ground which not less than two, can be used as natural Grounding body. The substation can use its reinforced concrete foundation as a natural grounding body. When using a natural grounding body, be sure to ensure good electrical connections.
The artificial grounding body has two basic structural types: vertical burying and horizontal burying.
The commonly used vertical grounding body is a steel pipe with a diameter of 50 mm and a length of 2.5m or an angle steel of L50×5. In order to reduce the influence of external temperature changes on the flow resistance, the upper end of the vertical grounding body buried in the ground should not be less than 0.7 m from the ground.
As the grounding device laid in a highly corrosive place, anti-corrosion measures such as hot-dip tin plating and hot-dip galvanizing should be adopted according to the nature of corrosion, or the cross-section should be appropriately increased. When a plurality of grounding bodies are close to each other, the flow of the ground current is mutually displaced, and this effect is called a shielding effect. This reduces the utilization rate of the grounding device, so the space of the vertical grounding bodies should not be less than 5m, and the space of the horizontal grounding bodies should not be less than 5m.
The layout of the grounding grid should force the potential distribution around to be arranged uniformly as possible to reduce the contact voltage and the step voltage.
The equipotential bonding is a kind of measure that does not need to increase the protection electric appliance. With some connecting wires, the potential can be balanced and the contact voltage can be lowered to eliminate the electric shock hazard caused by the potential difference. It is economical and effective in preventing electric shock.
Equipotential bonding typically includes total equipotential bonding and supplementary equipotential bonding. The main purpose of total equipotential bonding is not to shorten the operating time of the protective device, but to make the potential between the exposed conductive portion and the external conductive portion that can be simultaneously touched by the human being approximately equal, that is, the contact voltage falls below the safe value. The safe voltage value is 50V under normal conditions and 25V in wet conditions. The total equipotential bonding is indispensable when using automatic power cutoff as a measure to prevent indirect electric shock.
The supplementary equipotential bonding is also called local equipotential bonding. The PE line or the PEN line is connected to all the exposed conductive parts and the external conductive parts in a localized range so as to be at the same potential in a local range. A supplement to the total equipotential bonding. The main purpose of the local equipotential bonding is to reduce the contact voltage below the safe voltage.