term induction in electrical engineering is the occurrence of an electric current in a closed circuit, if it is in a changing magnetic flux.Opened electromagnetic induction only some two hundred years ago by Michael Faraday.Much earlier it could make Andre Ampere, who conducted similar experiments.It is inserted into the coil metal rod, then that's bad luck, I went into another room to look at the galvanometer needle - and suddenly she stirs.A hand was doing his job properly - have been rejected, but until Ampere wandered from room to room - back to zero.That's self-induction phenomenon wait for another dozen years until the coil unit and a researcher at the same time will be in the right place.
The main point of this experiment was that the EMF induction only occurs when the magnetic field passing through a closed loop varies.But you can change it as you like - or change the value of the magnetic field, or simply move the source of the field relative to the same closed loop.EDS, which arises here, called the "emf of mutual".But that was only the beginning of the discoveries in the field of induction.Even more surprising was the phenomenon of self-induction, which was opened by Joseph Henry at about the same time.In his experiments, it was found that the magnetic field coil not only induce current in another coil, but also when the current in the coil, it induces in the additional emf.Here it's the call of self-induction EMF.The electrical phenomena of great interest is the direction of the current.It turned out that in the case of self-induction EMF its current is directed against its "parent" - current due to the main EMF.
And you can observe the phenomenon of self-induction?As they say, there is nothing easier.Putting the two circuits: the first - consistently included coil and light, and the second - just a light bulb.Connect them to the battery via the main switch.When enabled it can be seen that the light in the circuit with the coil turns "reluctantly" and the second lamp, the faster "uphill" starts immediately.What's happening?In both circuits after the current begins to flow, and it varies from zero to its maximum, and just waiting for changes in the current and inductor, which generates self-induction EMF.There EMF and closed circuit - means there and its current, but directed he opposite main current circuit, which eventually reaches a maximum value determined by the circuit parameters, and cease to grow, and if there is no current change - no self-induction EMF.It's simple.A similar pattern, but with the "exact opposite", observed when you turn off the current.True to its "bad habit" to oppose any change in the current, self-induction EMF supports its flow in the circuit after the power is turned off.
Immediately there was a question - what is the self-induction phenomenon?It was found that in the self-induction EMF affects the rate of change of current in the conductor, and can be written:
E = L • dI / dt
This shows that self-induction EMF E is directly proportional to the rate of change of the current dI / dt, and the coefficient of proportionality L, named inductance.For his contributions to the study of the question, what is the phenomenon of self-induction, George Henry was rewarded by the fact that his name is a unit of measurement of inductance - Henry (H).That inductance circuit current flow determines the phenomenon of self-induction.One can imagine that the inductance - is a kind of "storage" of magnetic energy.In the case of increasing the current in the circuit of the electric energy is converted into magnetic retards the growth of the current, and the current decreases when the magnetic energy is converted into electrical coil and maintains the current in the circuit.
Probably, everyone had to see when you turn off the spark plug from the wall socket - this is the most common form of manifestation of self-induction EMF in real life.But at home opens maximum currents of 10-20 A and trip time of about 20 msec.When the inductance of the order of 1 Mr EMF of self-induction in this case will be equal to 500 V. It would seem that the question of what is the phenomenon of self-induction, is not so complicated.In reality, the self-induction electromotive force is a large technical problem.The idea is that when the circuit when the contacts have separated, inductance maintains current flow and this leads to burnout of contacts, asin the art switching circuit currents in the hundreds and even thousands of amperes.There are often talking about self-induction EMF in the tens of thousands of volts, and it requires an additional resolution of technical issues associated with surges in electrical circuits.
But all is not bleak.It happens that this harmful EMF very useful, for example, the internal combustion engine ignition systems.Such a system consists of an inductor in the form of an autotransformer and chopper.It is passed through the primary winding current, which turns off a chopper.As a result, there is an open circuit emf of self-induction of hundreds of volts (the battery provides all 12V).Further, this voltage is further transformed, and the spark plug has a pulse of more than 10 kW.
