Power quality monitoringdeviceSeries resonance, as the name suggests, refers to the phenomenon where the terminal voltage and total current of a circuit are in phase in a series circuit of resistors, inductors, and capacitors. This phenomenon is called series resonance. The characteristic of series resonance refers to the circuit being purely resistive, with terminal voltage and total current in phase. At this time, the impedance is small, the current is high, and high voltage may be generated on the inductance and capacitance that is many times higher than the power supply voltage. Therefore, series resonance is also known as voltage resonance.

In power engineering, series resonance can cause overvoltage and large current, which can damage electrical equipment. Therefore, it is necessary to avoid series resonance. In a circuit where an inductance coil is connected in parallel with a capacitor, the phenomenon of the terminal voltage of the parallel circuit being in phase with the total current of the circuit is called parallel resonance. The total impedance of a parallel resonant circuit is large, so the total current of the circuit decreases. However, for each branch, its current may be much higher than the total current, so current resonance is also known as current resonance.

Parallel resonance does not generate resonance overvoltage that endangers the equipment, but each branch will generate overcurrent.The total impedance of a series resonant circuit during resonance is small and exhibits pure resistance, with a value equal to R. During resonance, the current in the series resonant circuit is large and in phase with the voltage. Its value is XL=XC at resonance, where XL or XC is the characteristic impedance of the circuit, denoted by the letter ρ Represented as the voltage at both ends of the inductor and capacitor being equal during resonance.

The direction is opposite, and Q is the quality factor of the series resonant circuit, which is an important parameter to measure the characteristics of the resonant circuit. The ratio of the characteristic impedance of a series resonant circuit to the resistance in the circuit is usually referred to as the quality factor of the circuit, denoted by the letter Q.