What Electrical Knowledge about Transmission And Distribution Lines

Why are high-voltage transmission towers not charged?

1. The function of insulators:

High voltage transmission lines are fixed to iron towers through insulators (porcelain string). These insulators are capable of withstanding the voltage of the line and insulating it from the tower, thereby preventing direct current from passing through the tower.

The higher the voltage level, the longer the porcelain bottle string is used to maintain a necessary safety distance from the iron tower and increase the effect of electrical isolation.

2. A good grounding system for iron towers:

High voltage transmission towers have a good and reliable grounding system, which can eliminate induced currents and ensure that the tower itself is not electrified.

3. Security design:

The design of transmission towers takes into account safety and electrical isolation, so that the tower itself does not become a path for current.

4. Characteristics of iron towers with different voltage levels:

According to the different voltage levels, the size of the tower and the number of insulators also vary. For example, a 35kV wire uses 4 insulators, while a 110kV wire uses 7 insulators. This design is determined based on voltage level and insulation requirements.

5. Interference to radio broadcasting and communication:

Although the iron tower itself is not electrified, in adverse weather conditions, the dirt on the surface of the insulator may cause partial discharge, which can interfere with radio broadcasting and communication. But this interference does not come from the tower itself being charged.

What is the "sizzle" sound heard under the high-voltage transmission tower?

The "sizzle" sound heard under the high-voltage transmission tower is mainly caused by corona discharge. Specifically:

1.Definition of corona discharge:

When the surface electric field strength of the transmission line exceeds the free strength of air molecules (usually 20 to 30 kV/cm), air will ionize, resulting in discharge phenomenon, namely corona discharge.

2.The performance of corona discharge:

Corona discharge can be heard and seen. Under the high-voltage transmission tower, one can hear the discharge sound of the line, which is produced by the ionization of air.

At night or in rainy and foggy weather, a faint blue purple halo can sometimes be observed, which is a phenomenon of light generated by corona discharge.

3.Voltage level and corona discharge:

The higher the voltage level, the stronger the corona of the wire, and the greater the noise. For example, corona discharge is more likely to be observed near high-voltage transmission lines of 220 kV and 500 kV.

4.Urban distribution lines and corona discharge:

It is not easy to observe corona discharge in 10 kV and 35 kV distribution lines in urban areas, because most of these distribution lines use insulated wires that do not produce air ionization, and the voltage level is low, the corona intensity is weak, and they are easily covered by the background brightness and noise of the environment.

5.Influencing factors:

The intensity of corona discharge is influenced by various factors, including the electric field strength on the surface of the wire, air humidity, temperature, degree of pollution, etc.