Our sky is completely filled with a web of power lines, but only in some places, where there are a lot of high-voltage lines, can you hear a frightening hum, as if the person passing beneath them is about to be struck by lightning. However, you don’t need to let your imagination run wild: this sound generally does not signal danger.
Source of the Humming
You have probably noticed that not all high-voltage power lines hum. This phenomenon is mostly characteristic of lines with voltages above 100 kV.
High-voltage lines are designed to transmit electric current from transformer substations to consumers. There are several reasons why you might hear a crackling sound overhead. Let’s explain everything clearly.
What Causes the Humming of Wires?
What is a wire anyway? It’s an electrical engineering product consisting of a conductive core intended for carrying electric current, and insulation. Usually, this core is made of copper, aluminum, or steel wire. As the electric current passes through the conductor, it can sometimes start to crackle. Scientists explain this phenomenon in two ways.
Corona Discharge
This is a type of gas discharge that occurs in a highly non-uniform electric field when the field intensity exceeds a critical value. It is characterized by the formation of a glowing corona made up of ionized gas molecules. When too high a voltage is applied to a conductor, the magnetic field generated around it starts the process of air ionization, literally electrifying its particles.
This leads to the formation of a glowing sheath around the wire (have you ever seen power line towers glowing along their contours? If so, you have witnessed the process of corona discharge)
As a result of this phenomenon, there are sharp changes in air temperature: it heats up and cools down rapidly. These fluctuations generate sound waves, which can sometimes reach our ears.
Most modern power lines are designed to avoid this problem because, in some cases, it can be dangerous. Especially in rainy weather, when corona discharge can release toxic gases such as ozone.
Vibration of the Conductor
At the beginning of the article, we mentioned the conductive core. Some scientists believe that it is responsible for the humming of the wires. The fact is that high-frequency electric current literally “forces” the conductive cores to vibrate. As a result, they hit each other, creating a hum.
When the wires are surrounded by airflow (especially in strong winds), the sound can become even louder.
This explains why high-voltage power lines hum and crackle, making them sound eerie but usually not dangerous.