Inductive reactance in an alternating current circuit

Resistance in electrical circuits can be of two types - active and reactive. Active is represented by resistors, incandescent lamps, heating spirals, etc. In other words, all the elements in which the flowing current directly performs useful work or, in a special case, causes the desired heating of the conductor. In turn, reactive is a general term. It is understood as capacitive and inductive resistance. In the elements of the circuit with reactive resistance, various intermediate energy transformations occur during the passage of the electric current. The capacitor (capacitance) accumulates a charge, and then gives it to the circuit. Another example is the inductive resistance of a coil, in which part of the electrical energy is converted into a magnetic field.

In fact, there are no "pure" active or reactive resistances. There is always an opposite component. For example, when calculating wires for long-distance power lines, not only the active resistance, but also the capacitive, is taken into account. And considering the inductive resistance, it must be remembered that both the conductors and the power source make their adjustments to the calculations.

Determining the total resistance of the circuit segment, it is necessary to combine the active and reactive components. Moreover, it is impossible to obtain a direct sum by an ordinary mathematical action, therefore, we use a geometric (vector) method of addition. Perform the construction of a rectangular triangle, the two legs of which are active and inductive resistance, and the hypotenuse is complete. The length of the segments corresponds to the actual values.

Consider the inductive resistance in an AC circuit. Imagine a simple circuit consisting of a power source (EMF, E), a resistor (active component, R) and a coil (inductance, L). Since the inductive resistance arises from the self-induction emf (E si) in the turns of the coil, it is obvious that it increases with increasing inductance of the circuit and an increase in the current flowing along the contour.

The Ohm's law for such a chain looks like:

E + E cu = I * R.

Having determined the current derivative with time (I pr), it is possible to calculate the self-induction:

E cu = -L * I pr.

The "-" sign in the equation indicates that the action of E si is directed against changing the current value. The Lenz rule states that for any current change, there is an EMF of self-induction. And since such changes in alternating current circuits are natural (and constantly occur), then E s forms a significant counteraction or, which is also true, resistance. In the case of a DC power supply, this dependence is not fulfilled and when attempting to connect a coil (inductance), a classical fault would occur in such a circuit.

To overcome E si, the power source must create such a potential difference at the spool terminals that it is sufficient to at least compensate for the resistance E s. This implies:

U cat = -E si.

In other words, the voltage on the inductance is numerically equal to the electromotive force of self-induction.

Since with increasing current in the circuit the magnetic field increases , which in turn generates a vortex field that causes the countercurrent to increase in the inductance, then we can say that there is a phase shift between the voltage and the current. Hence follows one feature: since the EMF of self-inductance hinders any change in the current, when it increases (the first quarter of the period on the sinusoid), a counter-current field is generated, but on the contrary (the second quarter), the induced current is co-directed with the main current. That is, if theoretically to admit the existence of an ideal power source without internal resistance and inductance without an active component, then the oscillations of the energy "source-coil" could occur indefinitely.