The transmission voltage of high-voltage transmission lines is mostly above 10,000 volts, and the voltage of some lines is as high as 100,000 volts or 500,000 volts. If you want to insulate such lines, the thickness of the insulation layer of ordinary wires is far from enough. We Normally, the voltage of wires at home is only 220V. As long as they are wrapped with a thin layer of insulation to prevent contact with live wires, electric shock can be prevented. However, high-voltage equipment is different. People stand at a certain distance from high-voltage equipment, even if they are not. Contact may still cause electric shock.

Electric shock caused by high voltage can be divided into two types: step voltage electric shock and high voltage arc electric shock:

Step voltage electric shock means that if a high-voltage transmission line falls on the ground and current flows into the earth, the potential near the grounding point will gradually decrease toward the distance. Then there will be a voltage difference where the person's feet are standing, causing the current to flow through the human body. Electric shock, this is step voltage electric shock.

High-voltage arc electric shock occurs when a person approaches a high-voltage charged body to a certain distance, and a discharge occurs between the high-voltage charged body and the human body. The current flows through the human body, causing high-voltage arc electric shock.

The latest regulations define voltage levels above 10kV as high voltage. Nowadays, overhead lines in cities (the kind on street poles) are basically 10kV lines. Not surprisingly, they have been replaced with insulated wires. This is what the questioner refers to as "covered with an insulating layer." The thickness of this insulating layer is not high, so it has little impact on the cost. Since 10kV lines have more opportunities to come into contact with the public, insulated wires can improve operation efficiency. The security is well worth it.

However, if the lines of 110kV and above are made into insulated lines, the thickness of the insulation layer will be very large, which will result in a significant increase in cost and bring some technical problems. First, the heat dissipation is insufficient. Well, in order to reduce heat dissipation, we can only reduce its carrying capacity, which actually increases the cost. Secondly, the strength of such a heavy line will be greatly reduced, the span of the line will be reduced, and more towers will be needed. Thirdly, installation and construction Will it be greatly improved? In some places with impassable roads, construction may not be possible.

Therefore, if the lines of 110kV and above are changed to insulated lines, the cost will increase at least 3 to 5 times. The annual power investment is limited. If insulated lines are used, 3 to 5 times less lines will be built, which will have an impact on the country's development. Economic construction is very unfavorable. The so-called insulation layer plays the role of insulation and safety. This kind of insulator is just a decoration for high-voltage lines, because in the face of high voltage, air can break down conductivity, and insulators are even less powerful. It has no effect. Under normal circumstances, a high voltage of 10 kV can penetrate more than 1 cm of air to conduct electricity. According to national technical specifications, high-voltage transmission lines must be erected so that the wires are away from the ground or buildings, and the distance is at least several meters. Even tens of meters away, therefore, there is an air-filled space between the transmission lines and the ground or buildings, as well as places where people may appear.

Air itself is a good insulator, and its breakdown voltage is generally above 3 kV/mm, which is equivalent to the effect of ordinary resin insulating plastics. That is to say, for example, for a 110 kV high-voltage transmission line, theoretically, as long as the distance People are safe if they are above 40 mm, but the actual separation distance is generally 5 meters, that is, more than 5000 mm, or at least 2 meters. Under normal circumstances, there is no need to wrap any other insulators, as long as a certain spatial distance is maintained , air can play a good insulating role, and personal safety is fully guaranteed. If the high-voltage wires are wrapped with plastic insulators such as resin, the economic cost of wire manufacturing will be greatly increased, and the weight and weight of the wires will be increased. It is difficult to erect because the insulation effect of insulating plastic and air is similar. In the end, the safety of high-voltage lines has not been improved at all, so it is not worth the loss.

The only danger of exposed high-voltage wires is that if they break and fall on the ground or a building, it will cause a great risk of electric shock. Therefore, there are high requirements for the strength, erection technology and daily inspection of wires to prevent breakage and leakage. Danger, only when certain force majeure natural disasters, such as earthquakes, fires and floods occur, the power needs to be cut off in time to prevent possible leakage danger. If high-voltage wires are found to be broken and fall to the ground, the safe way is to keep them for at least 20 A distance of more than 1 meter is required to prevent electric shock accidents. As long as outdoor overhead lines are erected to a certain height and there are no buildings below or nearby the overhead lines, bare conductors are used regardless of high voltage or low voltage, which can reduce construction costs. With sufficient safety distance, the probability of electric shock accident is extremely small. In rural outdoor overhead lines, there is no need to use insulated wires.

High-voltage and low-voltage wires are generally bare wires. Near low-voltage overhead lines in old urban areas, where buildings are denser, wires with insulated layers are generally provided. Since high-voltage wires have high requirements for the insulation of the insulating layer, the construction process is complex and the cost is high. Generally, bare conductors are used, and the height of overhead lines is increased to prevent electric shock accidents. For the sake of beauty and safety, overhead lines are no longer visible in new urban areas. High-voltage and low-voltage lines are buried underground. In fact, there are also high-voltage line packages. The insulated layer is a high-voltage cable, which will not be used unless absolutely necessary. Its cost is 10 times that of ordinary overhead lines. For wires of the same cross-section, the current carrying capacity of the cable is still less than that of overhead lines. This is because the cable is made of copper. case (aluminum for overhead lines)

Due to the continuous improvement of power system systems, procedures and technologies over the years, electric shock accidents have been greatly reduced. The general public has few opportunities to be exposed to voltage levels above 10kV, and electric shock accidents with voltage levels above 10kV rarely occur. Therefore, this high voltage There is no need to use insulated wires for voltage level lines.

XZT 7111 High Voltage Circuit Breaker Tester