Everyone has seen high voltage pylons. Everyone knows that the insulation between high voltage wires and pylons is made with porcelain bottles. However, when it rains, a layer of water film forms between the high-voltage wires. wires and tension turns. High voltage wires It ranges from 10 kilovolts to hundreds of kilovolts, and even ultra high voltage transmission of tens of millions of volts is conductive, so why doesn't the tower leak electricity?
How do porcelain bottles on high voltage pylons insulate high voltage?
Everyone has seen porcelain bottles on high voltage wires. Some are roughly cylindrical, others umbrella-shaped, and some are connected one after the other to form a long series. Most of the time this material is. sintered ceramic. But there is also glass, which has two functionsions, one is to insulate and the other is to withstand the force!
High voltage insulators
According to the support method, there are suspension insulators and pillar insulators. The structures of the two are somewhat different, as one is a compression support and the other is a compression support. is a traction support, but the principle is the same. For example, the structure of a suspension insulator is as follows:
Connection between porcelain bottles
Porcelain bottles are connected by metal. porcelain bottle stems and holes. The diameter of the end face of the metal clamp rod is relatively large, so the reverse taper tail ensures that it will not fall off before the porcelain bottle breaks!
Porcelain bottles are installed vertically
How do porcelain bottles insulate high voltage electricity?
First of all, the metal rods insideThe porcelain bottle is not connected, so it is insulated when dry and insulated in rainy days. There are several ways porcelain bottles can insulate high voltage electricity!
The porcelain bottle is hydrophobic and cannot form a water film on its surface
The porcelain bottle is umbrella-shaped and will not form a continuous surface< /p>
The umbrella-shaped or wavy surface of the porcelain bottle It has the function of breaking arcs
The surface of porcelain is inherently hydrophobic. Porcelain bottles on high-voltage lines are also covered with anti-dust coatings, such as 880# silicone oil, dimethyl silicone oil, or paraffin. These materials will have better water-repellent properties and will also have partial stain-resistant functions. The structure of the porcelain bottle cannot allow accumulationion of dirt to form a continuous surface (. dirt can reduce the level of insulation)
Why are some insulators so short and others very long?
You may have noticed that the porcelain bottle on a low voltage line tower is not very long, but the porcelain bottle on a very high high voltage line tower will be very long. This is because the higher it is. The higher the high voltage line tower, the higher the transmission voltage. Insulators with higher insulation levels are then required. Of course, insulators can be connected in series to achieve higher insulation levels!
Generally, an insulator can withstand a voltage of 10 to 15 kV. For example, 3 insulators are used for 35 kV, 7 insulators are used for 110 kV and 25 are used for 500 kV. to find out what voltage it is. For transmission lines, you pYou can probably get a rough idea by counting the insulation! However, if the pollution is serious or significant, the number of insulators must continue to increase.
Can porcelain insulated bottles on high-voltage lines really be foolproof?
It seems that the high pressure porcelain bottle is foolproof, but in fact there are still many problems because the actual environment is very complex, such as the formation of heavy rain. If the flow of the water is blocked or if freezing rain causes widespread icy conditions, this will cause very serious accidents!
The faults mentioned above will form arcs. Let's briefly understand what's going on with this arc called flashover! Generally speaking, flashover refers to the phenomenon of electric discharge away from the surface of the insulator when the medium such as air or liquid around the insulator is broken down, just like ramper from one end to the other when the flashover phenomenon occurs. it is usually caused by dirt or mist on the surface of the insulation or formed in foggy conditions! At this time, the humidity in the air increases and the insulation level decreases, which will form this surface arc phenomenon!
The temperature of the arc can reach more than 3,000 degrees. It will form a conductive path, forming a loop between the high voltage line and the tower and leading it to earth. the high flashover temperature will cause the surface of the porcelain bottle and the electrode to be ablated, causing flashover. The high pressure porcelain bottle should be replaced immediately after the accident and the other porcelain bottles should be cleaned!
Also, when flashover occurs, current enters the high voltage power tower through the arc. The high voltage power tower is putto earth, this current will therefore be directed towards earth. , this is not a problem, but there is resistance in the ground, which can cause areas with different voltages to form around the grounding point. If a person passes through this area and the voltage difference is too great, it may cause an electric shock due to. step voltage. Therefore, stay away from high-voltage power line towers in foggy or rainy weather.
There are also breakdowns, which are mainly caused by mechanical damage or aging, excessive voltage or ultra-high temperature. The insulation loses its original performance and forms a conductive channel. After a bypass, the insulation loses its original performance. performance and forms a conductive channel. It is possible that the insulation can be partially restored (needs to be replaced immediately), but a breakdown is a direct short circuit,which has serious consequences.
Composite insulators
Ceramic and glass insulators use electrical grade materials with excellent performance, but they also have several disadvantages, such as being too heavy . Everyone has the weight of ceramics and glass. From experience, the second is that it requires frequent maintenance, such as applying paraffin wax and other coatings, and the other is that the insulation level will drop sharply in humid conditions, such as drizzle or thick fog! Causes large-scale faults in the power grid. In recent years, many applications of ceramic insulation have been replaced by composite insulation!
Silicone insulators typically use fiberglass rods or hollow cores to improve mechanical strength. The outer shell is made of silicone rubber, EPDM rubber,fiberglass or EPDM rubber. It has very good hydrophobicity, anti-aging, resistance to leakage and electrical corrosion. Another point is that it is much lighter than ceramic or glass insulators, and is the same size and interchangeable!