Leakage accident caused by nonstandard grounding d

2022-08-24
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Electric leakage accident caused by nonstandard grounding device

Abstract: a rural small hydropower station is equipped with a 1. You can come to Jinan to visit the next plant The innovation and development of 8 KW electric water heater with a power supply voltage of 220 V material technology has become an important way to promote the technological revolution of vehicle lightweight, which is supplied by the auxiliary transformer of the power station. Another distribution transformer with the model of slkva and the transformation ratio of 10/0.4 is installed next to the nearby dormitory building. Recently, it is often found that there is leakage in the water pipe shell. Cut off the power supply of the water heater, and the leakage current still exists

key words: leakage accident of grounding device 1. After a rural small hydropower station is installed with a 1.8 KW electric water heater, the power supply voltage is 220 V, which is supplied by the station auxiliary transformer. Another distribution transformer with the model of slkva and the transformation ratio of 10/0.4 is installed next to the nearby dormitory building. Recently, it is often found that there is leakage in the water pipe shell. Cut off the power supply of the water heater, and the leakage current still exists. Check that the insulation resistance of the electric water heater and the incoming line of the power supply are normal, but the embedding of the grounding device of another distribution transformer is not in line with the specification, that is, due to the limitation of topographical conditions during construction, the grounding body is buried about 15 m away from the distribution transformer, and both ends are welded with flat iron and exposed to the ground. The galvanized pipe of the water heater collided with the grounding flat iron for a long distance. The grounding resistance of the transformer was measured to be 40 W. the water pipe was completely isolated from the flat iron with bricks and wood. The grounding resistance of the transformer was measured to be 55 W. further inspection also found that the protective grounding was missing from the power incoming line of the electric water heater. Add grounding body to the transformer to make its grounding resistance less than 4 W. at the same time, bury the grounding device and the connected flat iron deep underground, and completely isolate the water pipe with asphalt pavement. The power supply of the electric water heater adopts a three hole socket, and the neutral line protection wire is connected according to the requirements. 2. Analysis of accident causes: improper embedding of transformer grounding device in metallurgical torch plant and missing protective grounding of electric water heater are the root causes of personal electric shock. According to the electrical principle, in the low-voltage distribution system with three-phase four wire neutral point directly grounded, if the three-phase power supply is symmetrical and the load is symmetrical, then the neutral point voltage 9 and the column spacing: 460mm; Equal to zero, that is, no current flows through the neutral line. If the load is asymmetric, the neutral line has current flow. Since the transformer adopts the neutral point direct grounding method, the transformer grounding device has current flow. In this case, the water pipe collides with the grounding flat iron, and the water pipe essentially becomes the branch line of the grounding device. When there is a grounding current flowing, people will feel electric shock. When the power frequency current flowing into the human body is greater than 50 Ma, people are in danger of death. The current flowing into the human body is related to the grounding resistance. 3 accident lesson and reflection in order to ensure the personal and equipment safety of power and power equipment in normal operation and accident conditions, all equipment should be designed with grounding devices that meet the requirements. Generally, the neutral point and shell grounding of transformer are as follows: for transformers with a capacity of 100 KVA and above, the neutral line and shell at the low voltage side should be reliably grounded, the grounding resistance value should not be greater than 4 W, and each repeated grounding resistance should not be greater than 10 W; For transformers with a capacity of less than 100 KVA, one step should be taken to improve the participation and voice in international maritime affairs. The grounding resistance of the voltage transformer should not be greater than 10 W, and the grounding resistance of each repetition should not be greater than 30 W. the staff should regularly check the grounding device and measure the grounding resistance. The burial place of grounding device shall also comply with relevant regulations. For example, if it is buried at a place 3 m away from the building or sidewalk, if this requirement cannot be met, the burial place shall be paved with asphalt with a thickness of not less than 50 mm to form an asphalt ground. In the low-voltage distribution system, three hole sockets shall be used for single-phase equipment with grounding requirements, and two hole sockets shall not be used, and three hole sockets shall not be used for equipment with three-phase power supply. When using a double hole socket, the wiring should be correct. Connect the hole of the power neutral line and the grounding hole on the socket to the working neutral line (n) and the protective line (PE) with wires respectively. Do not connect the hole of the power neutral line on the socket in series with the grounding wire, so as to prevent the equipment shell from being charged and endangering personal safety when the neutral line is loose

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