The series resonance test device is divided into frequency modulation type and inductance modulation type, generally consisting of a variable frequency power supply, excitation transformer, reactor, and capacitive voltage divider. The capacitor of the test object and the reactor form a series resonance connection. The voltage divider is connected in parallel to the test sample to measure the resonant voltage on the test sample and provide an overvoltage protection signal.
In a series circuit composed of resistors, inductors, and capacitors, when the capacitive reactance XC is equal to the inductive reactance XL, i.e. XC=XL, the phase of the voltage U and current I in the circuit are the same, and the circuit exhibits resistance. This phenomenon is called series resonance; When a series resonance occurs in a circuit, the impedance of the circuit Z=√ R ^ 2+(XC-XL) ^ 2=R, the total impedance in the circuit is minimized, and the current will reach its maximum value.
If the resonant frequency is equal to the power supply frequency, the voltage on both the inductor and capacitor can exceed the power supply voltage by many times, just like swinging on a swing. As long as it conforms to its pitch, it can swing higher and higher without using a lot of force, thus boosting the voltage. In theory, the impedance of the capacitor and inductor cancels out, leaving only the DC resistor, so the current can be large. Resistors are energy consuming components, capacitors and inductors are energy storage components, and the power supply is the energy supply component; If the energy added during a cycle is greater than the energy consumed by the resistor, the system energy increases (the voltage across the inductor and capacitor increases), the circuit current increases, and the energy consumption of the resistor increases, thus achieving balance. Wire and cable testing uses series boosting to obtain high voltage.