What are the conditions for series resonance to occur? Wuhan UHV specializes in the production of series resonance, with a wide range of product selection and professional electrical testing. To find series resonance, choose Wuhan UHV.
In a series circuit composed of resistors, inductors, and capacitors, when the capacitance reactance XC=inductance reactance XL is equal, series resonance occurs, and the phase of the voltage U and current I in the circuit are the same. When a series resonance occurs in a circuit, the impedance of the circuit Z=√ R2+XC-XL2=R, the total impedance in the circuit is the smallest, and the current will reach its maximum value. This may generate high voltages on inductors and capacitors that are many times greater than the power supply voltage, hence series resonance is also known as voltage resonance.
Series resonance is divided into frequency modulation and induction modulation. It is generally composed of a variable frequency power supply, excitation transformer, reactor, and capacitive voltage divider. The capacitor and reactor of the test sample form a series resonant 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.
The series resonance withstand voltage test is a new method of high voltage testing that uses the inductance of a reactor and the capacitance of the test object to form an LC series circuit, adjusts the voltage frequency output of the variable frequency power supply, achieves series resonance, and obtains high voltage on the test object. It has been well received by experts and has been widely used at home and abroad.
Currently, we have developed many detection instruments using the principle of series resonance, including series resonance test devices, cable variable frequency series resonance test devices, substation variable frequency series resonance test devices, and resonant boost devices for CVT inspection.
According to the principle of resonance, we know that when the inductance value X1 of the current reactor L is equal to the capacitance value Xc in the circuit, the circuit reaches resonance state. At this time, only the circuit resistance R consumes active power in the circuit, while reactive power oscillates back and forth between the reactor and the capacitor of the test sample, thereby generating high voltage on the test sample.
The conditions for series resonance to occur:
X L =X C
Due to the high voltage generated by series resonance in L and C, it may cause damage to the breakdown of coils or capacitors. Therefore, in power engineering, series resonance should be avoided as much as possible, and series resonance testing devices will also be used to detect the power system.
Advantages of series resonance
1. The required power capacity is greatly reduced. The series series series resonance test device uses resonant reactors and the capacitance of the test object to generate resonance, thereby obtaining the required high voltage and high current. In the entire system, the power supply only needs to provide the active consumption part of the system. Therefore, the required power supply for the test is only 1/Q times the test capacity (Q is the quality factor).
2. The weight and volume of the equipment have been greatly reduced. In a series resonant power supply, not only is the bulky high-power voltage regulating device and ordinary high-power power frequency test transformer eliminated, but the resonant excitation power supply only requires 1/Q of the test capacity, greatly reducing the system weight and volume, usually 1/5-1/10 of ordinary test devices.
3. Improve the output voltage waveform. A resonant power supply is a resonant filtering circuit that can improve the waveform distortion of the output voltage, obtain a good sine wave, and effectively prevent the false breakdown of the test sample caused by harmonic peaks.
4. Prevent large short-circuit currents from burning the fault point. In the resonant state, when the weak point of the insulation of the test sample is broken down, the circuit immediately becomes detuned (capacitance changes, not meeting the resonance condition), and the circuit current rapidly decreases to 1/Q of the normal test current. However, when using parallel resonance or traditional test transformers for AC withstand voltage testing, the breakdown current immediately increases by tens of times. Compared with the two, the short-circuit current is hundreds of times different from the breakdown current. So, series resonance can effectively identify insulation weaknesses without the concern of large short-circuit currents burning the fault point.
5. There will be no overvoltage recovery. When the test sample experiences breakdown and flashover, due to the loss of resonance conditions, the high voltage immediately disappears, the arc is immediately extinguished, the protective circuit of the device is activated, and the output is cut off.