Porcelain insulator for high voltage ferroelectric tower. When it rains, there is water on the porcelain bottle. Why can't there be leakage?

Everyone has seen the high-voltage line tower, and everyone knows that the insulation between the high-voltage line and the tower is achieved by porcelain bottles, but in rainy days, a water film will form between the high-voltage line and the tower. High-voltage lines are as low as 10 kV, and hundreds of kV, even as high as 10 kV. Water is conductive, so why is there no leakage on the tower?

How do porcelain vases on high-voltage power towers isolate high voltage?

Everyone has seen porcelain bottles on high-voltage power lines. Some are generally cylindrical, some are umbrella-shaped, and some are one after another, forming a long string. This kind of material is mostly sintered ceramics, but there is also glass. Glass has two functions, one is heat insulation and the other is support!

High voltage insulator

According to the support mode, there are suspended insulators and post insulators. The structure of the two is somewhat different, because one is compressive support and the other is tensile support, but the principle is the same. For example, the suspension insulator has the following structure:

Connection between ceramic vases

The porcelain bottle is connected with the porcelain bottle hole through the metal rod, and the diameter of the end face of the metal pull rod is relatively large, which ensures that the tail of the inverted cone will not fall off before the porcelain bottle is broken!

Porcelain bottles are installed vertically.

How do porcelain bottles isolate high-voltage electricity?

First of all, the metal rods inside the porcelain bottle are not connected, so they are insulated in dry state and in rainy days. There are several ways to insulate porcelain bottles from high voltage electricity!

Porcelain bottles are hydrophobic and cannot form water films on their surfaces.

Porcelain bottles are umbrella-shaped and do not form a continuous surface.

The umbrella-shaped or corrugated surface of porcelain bottle has the function of arc breaking.

The surface of porcelain is inherently hydrophobic. Porcelain bottles on high-voltage lines will also be coated with dust-proof coatings, such as silicone oil 880 #, dimethyl silicone oil or paraffin wax. These materials will make it more hydrophobic and partially hydrophobic. The structure of porcelain bottles can't let these stains accumulate to form a continuous surface (dirt may reduce the insulation level).

Why are some insulators so short and some so long?

You should find that the porcelain insulator on the low-voltage tower is not long, but it will grow on the high-voltage tower. This is because the higher the transmission voltage of the high voltage tower, the higher the insulation level. Of course, insulators can be connected in series to achieve a higher insulation level!

Generally, the voltage borne by insulators is 10- 15kV. For example, there are three insulators for 35kV, seven insulators for 1 10kV and 25 insulators for 500kV. Want to know what voltage the transmission line is, just count the insulators! However, if the pollution is serious or important, the number of insulator pieces needs to continue to increase.

Can insulating porcelain bottles on high-voltage lines really be foolproof?

It sounds like high-pressure porcelain bottles are foolproof, but there are still many problems, because the actual environment is very complicated, such as heavy rain forming water flow, or freezing rain forming large areas of ice, which will cause very serious accidents!

These faults will form an arc. Let's take a brief look at this arc called flashover! General flashover refers to the phenomenon that when air or liquid around the insulator is broken down, it stays away from the insulator surface, just like climbing from one end to the other. When flashover occurs, it is mostly formed when the insulator surface is unclean, it rains or it is foggy in Mao Mao! At this time, the air humidity increases and the insulation level decreases, which will form this phenomenon of surface arc!

When the arc temperature is as high as 3000 degrees, a conductive path will be formed, and a loop will be formed between the high-voltage line and the tower to lead to the earth. At this time, the high temperature of flashover will ablate the surface and electrode of porcelain bottle. After the flashover accident, the high-voltage porcelain bottle must be replaced immediately, and other porcelain bottles must be cleaned!

In addition, when flashover occurs, the current will enter the high-voltage tower through the arc, and the high-voltage tower is grounded, so this current will be introduced into the earth. There is no problem in theory, but there is resistance in the earth, which may form areas with different voltage levels around the grounding point. If the voltage difference between the two ends of this area is too large, it may lead to step voltage electric shock, so please stay away from high-voltage towers in foggy or rainy days in Mao Mao.

There is also a kind of breakdown, mainly under the conditions of mechanical damage or aging, high voltage or ultra-high temperature. Insulators lose their original properties and form conductive channels. After flashover, the insulator may partially recover (need to be replaced immediately), but the breakdown is directly a short circuit, which is more serious.

Composite insulator

Electrical-grade materials used for ceramic insulation and glass insulators have excellent properties, but they also have several shortcomings, such as being too heavy, and the weight of ceramics and glass is well known. Secondly, they often need maintenance, such as painting with paraffin wax, and the insulation level will drop sharply under infiltration conditions, such as rain or fog in Mao Mao! In recent years, many ceramic insulators have been replaced by composite insulators.

Silica gel insulators generally use glass fiber rods or hollows to improve mechanical strength, and the shell adopts silicone rubber, EPDM, FRP or EPDM. It has excellent hydrophobicity, aging resistance, electric leakage resistance and electric corrosion resistance. Another point is that it is much lighter than ceramic or glass insulators, with the same size and interchangeability!