By hvhipot 
HV Hipot Electric Co., Ltd. specializes in producing series resonance (also known as power frequency withstand voltage test device). Next, we will share with you the principle and quality factor of series resonance.
The principle of series resonance:
Resonance is a special phenomenon that occurs in a circuit composed of R, L, and C components under certain conditions. Firstly, let’s analyze the conditions under which resonance occurs in a series circuit of R, L, and C, as well as the characteristics of the circuit during resonance. R. The complex impedance of a series circuit of L and C under the action of a sine voltage U is Z=R+j ω L − 1 ω C=R+jXL − XC=R+jX, where reactance X=XL – Xc is a function of angular frequency ω, and X varies with ω. When ω changes from zero to ∞, X changes from – ∞ to+∞. When ω<ω 0 X＜0， The circuit is capacitive; When ω>ω 0, X＞0， The circuit is inductive; When ω=ω 0, X (ω 0)=ω 0L − 1 ω 0C=0, and the circuit impedance Z (ω 0)=R is pure resistance. Voltage and current are in phase, and we call the working state of the circuit at this time resonance. Due to this resonance occurring in a series circuit of R, L, and C, it is also known as series resonance. Equation 1 is the condition for resonance to occur in a series circuit. From this equation, the resonant angular frequency ω 0 can be obtained as follows: ω 0=1LC. The resonant frequency is f0=12 π LC. It can be seen that the resonant frequency of a series circuit is determined by the circuit’s own parameters L and C. It is independent of external conditions and is therefore also known as the natural frequency of the circuit. When the power frequency is constant, the circuit parameters L or C can be adjusted to make the natural frequency of the circuit consistent with the power frequency and resonate; When the circuit parameters are constant, resonance can occur by changing the power frequency to match the natural frequency of the circuit.
Quality factor of series resonance:
When a series circuit resonates, its reactance X (ω 0)=0, so the complex impedance Z ω 0=R of the circuit appears as a pure resistance, and the impedance is at its minimum value. During resonance, although the reactance X=XL – Xc=0, both the inductive and capacitive reactance are not zero, but they are equal. We refer to the inductive or capacitive impedance during resonance as the characteristic impedance of a series resonant circuit, denoted as ρ, that is, ρ=ω 0L=1 ω 0C=1LC ∙ L=LC ρ. The unit of measurement is ohms, which is determined by the circuit parameters L and C and is independent of frequency. In engineering, the ratio of characteristic impedance to 9 is commonly referred to as the quality factor of a series circuit, represented by Q, that is, Q=ρ R=ω 0LR=1 ω 0CR=1LLC quality factor,also known as resonance coefficient, sometimes abbreviated as Q value.