Staying near high-voltage power lines, you can hear a buzzing sound. Why is there such an effect? It is not easy to answer this question, because you can use as many as four hypotheses to explain the fixed effect.
The reasons for the sounds of power lines
Sound makes air
Most often lead to the concept of corona discharge. It lies in the fact that near the power line wire the air is electrified by an alternating electric field. As a result, free electrons are accelerated. They already ionize air molecules, leading to the appearance of a corona discharge. Its frequency is about a hundred times per second! That is how many times it lights up and goes out near the wire.
At the same time, the air that dwells in the immediate vicinity is heated and cools, expands and contracts. The result is a sound wave, which is perceived by the human ear as a humming wire. The only thing that prevents it from unconditionally accepting is the corona discharge accompanied by a weak glow, which is not observed (perhaps it is simply not visible).
Core vibration
The following hypothesis is based on core vibration. It states that an alternating current with a frequency of 50 Hz can create an alternating magnetic field. It affects the individual conductors in the wires (this applies especially to steel grades), forcing them to vibrate, impacting them with each other. As a result of this, a characteristic noise is created.
The hypothesis does not end there.In the case of power lines, it must be taken into account that wires of different phases are located nearby. Their currents are in neighboring magnetic fields and, as Ampere’s law states, a mutual action of force is observed. The frequency of field changes is 100 Hz. Therefore, with the vibration of the wires, taking into account the neighboring magnetic fields, you can hear the sound near the high-voltage wires.
Mechanical system resonance
In addition to the answers discussed above, there are not such popular explanations of sounds near power lines. Of these, the two most probable and meaningless hypotheses will be considered. Another potential cause of buzz is usually called an imperceptible phenomenon - the resonance of a mechanical system. Oscillations with a frequency of 50/100 Hz are transmitted to the support.
If a number of conditions coincide, it can enter into resonance and begin to make a sound. Its volume, as well as the resonant frequency, is affected by the diameter, height and density of the support material. Additionally, the length and cross-section of the wire are important. And the last important parameter is the tension force. There is a hit in resonance by a combination of factors, which means that noise will be heard. And vice versa.
Vibration in the Earth's magnetic field
And the last hypothesis considered at the edge of the corner puts vibration in the Earth's magnetic field. Since the wires are in a state of vibration with a frequency of 100 Hz, this means that they are subject to a variable transverse force associated with the flowing current in the wires, its direction and magnitude.
Hypothetically, an external magnetic field that covers the entire Earth affects high-voltage wires.This assumption has a much more serious basis than it might seem at first glance. Currents flowing in high-voltage wires can reach amplitudes of several hundred amperes.
Moreover, the length of power lines ... very rather big. And the Earth’s magnetic field, despite a relatively small indicator (in the middle zone of the Russian Federation, its induction fluctuates around 50 microtesles), acts throughout the planet. It has a horizontal and vertical component. Here is the second component and allows them to cross the power lines, interacting and accompanying this process with an audible sound.
To understand the essence of the described process, everyone can conduct a small experiment. It is necessary to take a car battery and an acoustic flexible wire with a cross section of 25 square millimeters, the length of which will be at least 2 meters. It is worth connecting it to the battery terminals for a moment and the wire will jump. This will be an impulse of the Ampere force, which acted on a wire with a current in the Earth's magnetic field (or in its own, there is no exact answer).
Let's summarize all of the above. There is no exact answer to the question why high-voltage wires are buzzing. There are a number of hypotheses, among which the most popular and recognized are the assumptions about corona discharge and vibration of wire conductors due to competent scientific substantiation. Perhaps in the future, when researchers will understand the essence of the process, these hypotheses will be combined in one theory as complementary to each other.
