Self-induction phenomenon - harm and benefit

The term induction in electrical engineering means the occurrence of a current in an electrical closed circuit if it is in a changing magnetic flux. Electromagnetic induction was discovered just two hundred years ago by Michael Faraday. Much earlier this could have been done by Andre Amper, who conducted similar experiments. He inserted a metal rod into the spool, and then, here's an ill luck, went to another room to look at the arrow of the galvanometer - and suddenly she would move. And the shooter was doing its job properly - was declining, but while Amper was wandering around the rooms - was returning to the zero mark. That's how the phenomenon of self-induction waited for another dozen years, until the coil, instrument and explorer are simultaneously in the right place.

The main point of this experiment was that EMF induction occurs only when the magnetic field passing through the closed circuit changes. But you can change it as you like - or change the value of the magnetic field itself, or simply move the source of the field with respect to the same closed loop. EMF, which occurs in this case, called "EMF mutual induction." But this was only the beginning of discoveries in the field of induction. Even more surprising was the phenomenon of self-induction, which was discovered by Joseph Henry at about the same time. In his experiments it was found that the magnetic field of the coil not only induced a current in another coil, but also with a change in the current in this coil, it also induced an additional EMF in it. Here it is something called EMF self-induction. In electric phenomena, the direction of the current is of great interest. It turned out that in the case of EMF self-inductance, its current is directed against its "parent" - the current caused by the basic EMF.

Is it possible to observe the phenomenon of self-induction? As they say, nothing is easier. We will assemble two electrical circuits: the first - a series-connected inductor and a light bulb, and the second - only a light bulb. We connect them to the battery through a common switch. When you turn on, you can see that the light in the chain with the coil lights up "reluctantly," and the second light bulb, faster "up", turns on instantly. What's happening? In both circuits, after switching on, the current begins to flow, and it changes from zero to its maximum, and just the current changes and an inductor that awakens the EMF of self-induction. There is an EMF and a closed circuit - that means there is also its current, but it is directed opposite to the main current of the circuit, which eventually reaches the maximum value determined by the parameters of the circuit, and ceases to grow, and if there is no current change, there is no EMF self-induction. It's simple. A similar picture, but with "accuracy to the contrary," is observed when the current is turned off. True to its "bad habit" to counteract any change in current, the EMF of self-inductance keeps it flowing in the circuit after the power is cut off.

Immediately became the question - what is the phenomenon of self-induction? It was found that the electromotive force of self-inductance is affected by the rate of change of current in the conductor, and it can be written:

E = L • dI / dt

From this it can be seen that the EMF of the self-induction E is directly proportional to the rate of change of the current dI / dt and the proportionality coefficient L, called the inductance. For his contribution to the study of the question of what the phenomenon of self-induction consists of, George Henry was rewarded by the fact that his name is the unit of measurement of inductance - Henry (HH). It is the inductance of the current flow circuit that determines the phenomenon of self-induction. One can imagine that inductance is a sort of "storehouse" of magnetic energy. In the case of an increase in the current in the circuit, the electrical energy is converted into a magnetic one, delays the current growth, and when the current is reduced, the magnetic energy of the coil is converted into an electrical one and maintains a current in the circuit.

Probably everyone had to see a spark when turning off the plug from the outlet - this is the most common version of the manifestation of EMF self-induction in real life. But in everyday life the currents are opened at a maximum of 10-20 A, and the opening time is of the order of 20 msec. With an inductance of the order of 1 GH, the EMF of self-induction in this case will be 500 V. It would seem that the question of what the phenomenon of self-induction consists in is not so complicated. And in fact, EMF of self-inductance represents a big technical problem. The bottom line is that when the circuit breaks, when the contacts have already parted, the self-inductance maintains the current flow, and this leads to the burnout of the contacts, because In the circuit circuit with currents of hundreds and even thousands of amperes commute. Here often it is a question of EMF self-induction into tens of thousands of volts, and this requires an additional solution of technical issues related to overvoltages in electrical circuits.

But not everything is so gloomy. It happens that this harmful EMF is very useful, for example, in ICE ignition systems. Such a system consists of an inductor in the form of an autotransformer and a breaker. The current is passed through the primary winding, which is switched off by the breaker. As a result of the termination of the circuit, EMF self-induction occurs in hundreds of volts (with the battery giving only 12V). Then this voltage is further transformed, and a spark of more than 10 kV is applied to the spark plugs.