# Why does electricity make a humming sound?

Passing by a high-voltage power line or electricsubstation, you must have heard the characteristic hum. As a rule, it is not the most pleasant, and often makes people feel dangerous, as well as a desire to leave such a place as soon as possible. Sometimes the hum occurs even when household electrical appliances are turned on. This sound is commonly referred to as the “buzz of the network”. But have you ever wondered why electricity hums and whether this sound indicates any danger? In fact, not every type of electric current causes such a hum, but only alternating, or AC. It is called variable because it constantly changes direction. The alternation occurs within one second dozens of times. It is with the change of direction, you guessed it, that the sound of the network is connected. But why does it occur?

The hum of electricity is caused by an alternating current that changes direction at a frequency of 50 Hz

What is the relationship between network frequency and sound

Since the sound of the network is associated with a change of directioncurrent, its frequency also depends on the mains frequency. There are two frequency standards. For example, in the USA, Japan, South America, the network frequency is 60 Hz, that is, the current changes direction 60 times per second. In Europe and Russia, the network frequency is 50 Hz, respectively, the change of direction is 50 times per second.

According to experts, the frequency of sound is twiceexceeds the mains frequency. If, for example, this indicator in the USA is 60 Hz, then the frequency of the sound of the network here is 120 Hz. Musicians who tune their instrument with a tuner know that this sound is between A-flat and B-flat. In Russia, as well as throughout Europe, the network, respectively, emits sound at a frequency of 100 hertz. It is between A-flat and G.

The main reason for the hum of high-voltage power lines is corona discharge.

Why does the network hum

There are different reasons for the network hum.Even in the vicinity of high-voltage power lines, there are several sources of sound. The main reason for the characteristic buzz is that a powerful electric field arises near the surface of the high-voltage wire. In this field, free electrons that are present in the air are accelerated. Having accelerated, they ionize the air and lead to the emergence of the so-called corona discharge. This discharge flashes and goes out at a frequency of 100 Hz, that is, with the frequency of voltage rise and fall.

As a result of each such discharge, airheats up and expands, then cools down and contracts. According to experts, it is the constant compression and expansion of air that generates buzz. The volume of the sound depends on the weather, or rather, on the conductivity of the air. In addition, sound can cause sonic resonance. Oscillations with a frequency of 100 Hz are transmitted to the power transmission tower itself, as a result of which it also begins to buzz.

Power transmission towers can enter into sound resonance

There is another version according to whichwire strands vibrate. An alternating current with a frequency of 50 or 60 Hz forms a magnetic field. It causes the strands in some wires, especially steel wires, to vibrate and hit each other. Vibration can also be created by magnetic fields of wires of different phases that are next to each other. Since the frequency of the fields is 100 Hz, the wires that are in each other's magnetic field begin to vibrate at the same frequency. In addition, there is a version that the constant expansion and contraction of wires also creates sound. By the way, a material has already been created that conducts electricity, but does not heat up.

Why do electrical appliances hum

The reason for the buzzing of devices is completely different.Typically, the sound is produced by a magnetic element that is contained inside most devices. For example, power supplies often have a transformer that is used to reduce or, conversely, increase the supply voltage. It is an electromagnetic device that consists of an iron core around which a wire is wound. As a result of the change of polarity, that is, the constant switching on and off of the magnet, the transformer begins to vibrate and make a corresponding sound. For the same reason, transformer boxes are buzzing.

In electrical appliances, transformers are most often buzzing.

How dangerous is humming?As a rule, this sound accompanies the operation of absolutely serviceable electrical appliances, that is, it is a normal phenomenon. But if a characteristic hum at a frequency of 100 Hz appears suddenly in those devices that did not previously emit it, for example, in an air conditioner, this may indicate the failure of one or another of its elements. In this case, it is better to turn off the device and seek help from specialists.

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As for the sound of high-voltage power lines, it is notas safe as it might seem at first glance. During corona discharges, toxic gases, such as ozone, are produced that can be harmful to health. Therefore, when laying modern power lines, measures are taken to prevent or minimize corona discharges. Finally, I propose to read an interesting material about static electricity.