What is the resonance of currents

When studying the basics of electrical engineering, one of the stages inevitably considers the resonance of currents and voltages. These phenomena are inherent in alternating current circuits and can be both undesirable, requiring their consideration in the modeling of power and switching circuits, and useful.

For example, resonance in an alternating current circuit is very often used in radio engineering: a tuned oscillatory circuit based on the resonance of voltages makes it possible to amplify a low-power radio signal several times, because due to the transformations "capacitance-inductance", the active value of the voltage grows.

This oscillatory circuit is the basis for understanding how resonance of currents and (or) voltages occurs. It is a closed electrical circuit consisting of a capacitor connected in parallel (capacitance C) and a coil (inductance L). In them, due to the process of "transferring" energy from the electric field of the capacitance to the magnetic field of inductance, self-damped (due to the presence of the active component R) oscillations of a certain frequency exist.

At the resonant mode of operation of the electrical circuit, the resistance to the passage of current is represented only by the active component of R. There are resonance currents and resonance voltages. Let's consider their features.

The current resonance arises in a circuit with a capacitor and a coil connected in parallel, the nominal values of which are selected in such a way that the current flowing through C and L is equal to. As a result, the current value in the "CL" circuit is higher than in the common circuit.

The principle of operation is as follows: when the power is supplied, the capacitor accumulates charge (up to the rated voltage of the source). After that, it is enough to turn off the source and close the circuit to the circuit, so that the discharge process begins on the coil. The current passing through it generates a magnetic field and creates an EMF of self-induction, directed counter to the current. Its maximum value will be reached when the capacitor is completely discharged. Accordingly, this means that all the energy stored in the tank is converted into a magnetic field of inductance. However, due to the self-induction of the coil, the motion of the charged particles does not cease.

Since there is no countercurrent from the capacitor (it is discharged), it begins to recharge, but with a different polarity. As a result, the entire coil field is converted into a capacitor charge and the process is repeated. Due to the presence of the internal active component R, the oscillation fading is gradually occurring. Thus, the resonance of the currents is realized.

Resonance resonance occurs when the resistor R, coil L and capacitor C are connected in series. An important feature is the fact that the voltage of the power supply is lower than that of the capacitor and coil (on each element individually), however, the current equality is preserved. And the voltage and current coincide in phase. The main condition for the emergence and maintenance of this process is the equality of inductive and capacitive resistances. On this basis, the impedance is equal to the active resistance.

To determine the effective values of the voltages on the coil and the capacitor, Ohm's law is applied. In the case of a coil, it is equal to the product of the current by the inductive resistance (U1 = IX1). Accordingly, for the capacitor, the current must be multiplied by the capacitive resistance (U2 = IX2). Since the current is consecutively connected to the elements, and for the resonance X1 = X2, the voltages for the inductance and capacitance are equal. Hence, by increasing the reactive components, it is possible to achieve a significant increase in the voltages U1 and U2 while maintaining the unchanged EMF value of the power supply itself. The main field of application is radio engineering.