Grounding of electrical equipment for hydraulic structures
Grounding of electrical equipment for hydraulic structures Jia Hongjing, Wang Chao, Chen Yuxiao (Engineering Construction Management Department of Tongjiang Irrigation District, Tongjiang, Heilongjiang Tongjiang 156400) Failure to solve the safety problems of good electrical equipment will result in incalculable losses. The corresponding buildings produced unpredictable damage and even caused the operator to pay for the safety and life. Therefore, the safety of electrical equipment should be further valued by all parties involved in engineering construction. With the large-scale construction of water conservancy projects, electrical equipment has been further widely used, and the safety of electrical equipment has gradually emerged. In addition to the factors of electrical equipment itself, the idea of ​​artificial paralysis in construction is also an important reason. In itself, the water conservancy construction team lacks fully specialized electrical technicians, and there is no corresponding detection technology, making hydraulic electrical equipment more serious security risks. There are many aspects of the safety of electrical equipment: design, materials, production processes, installation, etc. But it is easy to be overlooked is the grounding of electrical equipment, which may be easily solved in the power system, but in the hydraulic construction is likely to be a production accident. The following talks about grounding related issues. 1 The main purpose of grounding of electrical equipment is to protect personal safety. When the current passes through the human body, the internal structure of the human body will have a complex effect. A large amperage of current passing through the human body will cause the body to suffer severe electrical burns, tissue carbonization and necrosis and other life-threatening injuries. A good electrical connection between a certain part of the electrical equipment and the soil is called grounding. The metal object that is in direct contact with the soil is called a grounding body. It is divided into artificial grounding body and natural grounding body. In the event of a fault, the current is dispersed hemispherically through the grounding body to the ground. At this point, Ie approaches zero at the fault 20m. Step voltages can occur within this range. 1.1 Classification grounding of electrical equipment grounding. The grounding to ensure the normal working requirements, such as the power supply neutral point directly grounded or arc-extinguishing ring grounding and lightning protection grounding. Protective grounding is called protective grounding to protect personal safety and prevent contact between the exposed conductive parts of the equipment. Repeatedly grounding, in the TN system where the power neutral point is directly grounded, in order to ensure that the public PE line or PEN line is safe and reliable, in addition to the work grounding at the neutral point of the power supply, it must be necessary at the following places of the PE line or the PEN line. Repeated grounding: 1 At the ends of the main lines and branch lines of the overhead lines and every 1 km along the lines; 2 The cables and overhead lines are introduced into the workshop or large buildings. 2 Grounding requirements and installation 2.1 Grounding resistance and its requirements Grounding resistance is the sum of the grounding body's resistance to flow and the resistance of the ground and grounding body. Since the resistance of the grounding wire and the grounding body is relatively small, it may be omitted. Therefore, it is considered that the grounding resistance means the resistance of the grounding body. 2.2 Installation of grounding device 2.2.1 - General requirements When designing and installing a grounding device, the natural grounding body should be fully utilized to save investment and save steel. If the resistance of the natural grounding body used in the field measurement can meet the requirements and these natural grounding bodies meet the thermal stability conditions, artificial grounding devices do not need to be installed. Otherwise, artificial grounding devices should be installed as a supplement. The arrangement of artificial grounding devices for electrical equipment shall be such that the potential distribution in the vicinity of the grounding device is as uniform as possible in order to reduce the contact voltage and step voltage and to ensure personal safety if the contact voltage and step voltage exceed the specified values, measures shall be taken. 2.2.2 The natural grounding body can be used as the natural grounding body: steel structures and steel bars for buildings, buried metal pipes, and reinforced concrete foundations for buildings. These methods are used in the pumping stations that are under construction or have already been built in Tongjiang City. However, there are three areas to pay attention to: 1 must ensure good electrical connection; 2 in the joints of the steel structure of the building, except for those who have been welded, where there are bolted or other connections must be used for cross-welding; 3 cross Wiring size must not be less than the specified value. 2.2.3 Installation of artificial grounding body There are two types of artificial grounding body, vertical and horizontal. The most commonly used vertical grounding body is a steel pipe with a diameter of 50 mm and a length of 2.5 m. If a diameter of 50mm is used, it is economically unfavorable and the shatter resistance does not become much smaller. In addition, in order to reduce the influence of external temperature changes on the shunt resistance, the upper end of the grounding body buried in the ground should not be >0.5m away from the ground. If the soil resistivity is high, the following measures may be adopted: 1 Use a multi-branch external grounding device. 2 If the underground soil rate is low, a deep-buried grounding body can be used. 3 Local use of soil replacement or soil chemical treatment. 4 According to the nature of corrosion, thermal tinning and hot dip galvanizing should be adopted. 5 Grounding body spacing 2 times the length of the grounding body. 6 artificial grounding body network should be closed. 7 The distance between the grounding body and the building foundation should be 1. 5m horizontal distance, generally 2~3m. In summary, in the electric construction, the design cannot be changed arbitrarily, or the electrical construction is changed for other projects. A small problem such as the shedding of solder joints and the breakage of the grounding strap will cause a large number of personal injury accidents, resulting in incalculable losses. Therefore, the issue of electrical safety should arouse the attention of our construction and construction personnel. Elimination of hidden dangers and control of accidents before they occur.
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