In the series circuit of resistance and inductance, the phenomenon that the voltage applied to the circuit terminal is in phase with the total current is called series resonance. At this time, the resistance is the smallest and the current is the largest. It is likely that a high voltage many times larger than the power supply voltage will be generated on the inductance of the capacitor. Because series resonance will produce overvoltage and large current and damage electrical equipment, it must be avoided as much as possible in power engineering.
In general, the voltage across the circuit is different from that of an AC circuit consisting of a resistor R, an inductor L and a capacitor C. If the parameters or power frequency of the circuit elements (L or C) are adjusted, they can be in the same phase, and the whole circuit is purely resistive. This state of the circuit is called resonance.
The total impedance of the circuit reaches the extreme value or approaches the extreme value in the resonance state. According to different circuit connections, resonance can be divided into series resonance and parallel resonance. We should prevent the harm caused by resonance at ordinary times, but we should make full use of its characteristics in science and application technology. The series resonance configuration is flexible, reactors can be used in series and parallel, meeting the requirements of different test objects, realizing multi-purpose of one machine and high cost performance.