Why are the wires of the power lines noisy

Why are the wires of the power transmission line humming? Have you ever thought about this? But the answer to this question can be by no means trivial, although completely unsophisticated. Let's look at several explanations, each of which has a right to exist.

Corona discharge

Most often give such an idea. An alternating electric field near the power line wire electrifies the air around the wire, accelerates free electrons, which ionize the air molecules, and they in turn generate corona discharge. And now, a corona discharge around the wire lights up and goes out 100 times per second, while the air near the wire heats up - cools down, expands - contracts, and in this way we get a sound wave in the air, which our ear perceives as a buzzing wire.

Vibrate veins

Still there is such an idea. The noise comes from the fact that an alternating current with a frequency of 50 Hz produces an alternating magnetic field, which forces individual conductors in the wire (especially steel wires in wires of grades like AC-75, 120, 240) to vibrate, as if they collide with each other, and we hear a characteristic noise.

In addition, wires of different phases are located next to each other, their currents are in the magnetic fields of each other, and according to Ampere’s law, forces act on them. Since the frequency of field changes is 100 Hz, the wires in each other’s magnetic fields vibrate from the Ampere forces at this frequency, and we hear it.

Mechanical system resonance

And such a hypothesis is found in some places. Oscillations at a frequency of 50 or 100 Hz are transmitted to the support, and under certain conditions the support, entering the resonance, begins to make a sound. The loudness and resonant frequency are affected by the density of the support material, the diameter of the support, the height of the support, the length of the wire in the span, as well as its cross section and tension force. If there is a resonance, noise is heard. If there is no resonance, there is no noise or it is quieter.

Vibration in the Earth's magnetic field

Consider another hypothesis. The wires vibrate at a frequency of 100 Hz, which means that they are constantly affected by an alternating transverse force associated with the current in the wires, with its magnitude and direction. Where is the external magnetic field? Hypothetically, it may be that magnetic field that is always underfoot, which guides the compass needle, - Earth's magnetic field.

Indeed, the currents in the wires of high-voltage power lines reach an amplitude of several hundred amperes, while the length of the wire lines is considerable, and the magnetic field of our planet, although relatively small (its induction in central Russia is only about 50 μT), it nevertheless acts everywhere on the planet, and everywhere it has not only a horizontal, but also a vertical component, which crosses perpendicularly both the wires of power lines laid along the lines of force of the Earth’s magnetic field, and those wires that are oriented across them or Posted in General by any other angle.

To understand the process, anyone can conduct such a simple experiment: take a car battery and a flexible speaker wire with a cross section of 25 square mm, at least 2 meters long. Connect it to the battery terminals for a moment. The wire will bounce! What is this if not the impulse of the Ampere force acting on a wire with a current in the Earth's magnetic field? Is that the wire jumped in its own magnetic field ...