How resonance occurs and analysis of its series resonance principle



Series resonance AC withstand voltage test occupies a crucial position in generator insulation testing. Today, let's systematically learn about how resonance occurs and its principle analysis. A resonant circuit is an AC circuit with resistance R, inductance L, and capacitance C; generally, the phase of voltage and current in the circuit is different. If we adjust the parameters of circuit components (L or C) or the frequency of the power source, the entire circuit exhibits pure resistance. When the circuit reaches this state, it is called resonance. The purpose of studying the resonance phenomenon is to understand this objective phenomenon, fully utilize the characteristics of resonance in science and technology, and simultaneously prevent the harm it may cause. According to different circuit connections, it can be divided into series resonance and parallel resonance. In the case of series resonance, the inductor voltage and capacitor voltage are equivalent, that is, the inductor and capacitor absorb different amounts of equivalent reactive power, making the reactive power absorbed by the circuit zero. The electric field energy and magnetic field energy are constantly changing, and the total electromagnetic field energy of the entire circuit remains unchanged; the energy from the excitation power circuit is converted into resistance heating. To maintain oscillation, the excitation must continuously provide energy to compensate for the heat consumption of the resistance. Compared with the total electromagnetic field energy in the circuit, the less energy each oscillating circuit consumes, the better the quality of the circuit. First, when the C series circuit resonates, we need to analyze the characteristics of the circuit, as shown in Figure 1: The complex impedance of the C series circuit is as follows. Under the action of sinusoidal voltage, the complex impedance of the circuit is as follows. In the formula, the reactance x=xl, xc is a function of angular frequency w, and the change of x with w is shown in Figure 2. When w changes from 0 as shown in Figure 2, x changes from - to + as shown in W. When w 0, when x is capacitive, when w 0, when x is inductive, when w=w0, when impedance z(w0)=r is pure resistance, voltage and infinity. The current is in phase, and we call this the working state of circuit resonance. Since this resonance occurs in the RLC series circuit, we can also call it series resonance, series resonant circuit, etc. It can be seen that the resonant frequency of the series circuit is determined by its own parameters L and C, which is independent of external conditions. When the power supply is fixed, L and C can be adjusted to make the natural frequency of the circuit resonate with the power frequency. Frequency conversion series resonance mainly refers to the voltage and current of the studied series circuit reaching the same phase, that is, the inductive reactance and capacitive reactance of the inductor and capacitor in the circuit are equal in value and time, making the studied circuit exhibit pure resistive characteristics. Under a given terminal voltage, the maximum current will appear in the studied circuit. The circuit consumes the maximum active power. (1) Resonance definition: In a circuit, when the energy of two components is released by one reactance module in the circuit, and the other reactance module must absorb the same energy, the energy of the two components is equal, that is, there will be energy pulsation between the two reactance components. The conditions for series resonant circuit are as follows: when q=qi2, xl=i2, xc or xl=xc, the resonance condition of the r-l-c series circuit is obtained. (4) Whether it is series or parallel resonance, the complete energy exchange between L and C is achieved when resonance occurs. That is, the released magnetic energy is completely converted into electric field energy and stored in the capacitor, and the capacitor discharges at another moment, and then is converted into magnetic energy stored in the inductor. (5) In a series resonant circuit, since the series L and C flow the same current, the energy exchange is carried out through the change of voltage polarity; in a parallel circuit, the two ends of L and C are the same voltage, so the energy conversion is the opposite current phase of the two components. (6) Inductance and capacitance are still two components in resonance, otherwise energy cannot be exchanged; but from the perspective of equivalent impedance, they become one component: zero resistance or infinite resistance. Return to Sohu, see more