By sion932 
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The power frequency series resonant device is mainly used for AC withstand voltage testing of high-voltage cross-linked cables, transformers, generators, GIS and SF6 switches, and other high-voltage power equipment such as busbars, bushings, and transformers. A device that uses tuned inductors and load capacitors to generate power frequency series resonance and obtain power frequency test voltage. Series resonance testing equipment is widely used in industries such as power, metallurgy, petroleum, and chemical engineering, and is suitable for the handover and preventive testing of high-capacity, high-voltage capacitive specimens.
There are two types of power frequency resonance: series resonance and parallel resonance. These two methods have similar compensation effects based on the power supply capacity. After achieving full compensation, the input capacity can be reduced to less than 1/Q of the test output capacity.
Series resonance
L – inductance of adjustable reactor CX – capacitance of test object
R – Equivalent series resistance calculated based on the active loss of the adjustable reactor, the dielectric loss of the tested object, and the comprehensive loss of the circuit.
Adjust the inductance of the adjustable reactor in the series circuit so that its inductance XL at power frequency f is equal to the capacitance XCX of the load capacitor. At this point, complete resonance is achieved, and the inductance of the reactance is the inductance L at the resonance point. When the circuit is fully resonant
The load capacitance CX is basically constant. When L is adjusted to reach full resonance L0, IX is adjusted. When the required UC value is reached, the withstand voltage test begins.
Under complete series resonance, the power supply only provides UJ to establish IX, and the excitation power PJ=UJIX with COS Φ=1 overcomes the equivalent comprehensive active loss IX2R in the circuit, exciting and maintaining stable resonance. Series resonance is a resonance caused by voltage compensation or low voltage excitation.
Main characteristics of series resonant withstand voltage circuit
Due to full compensation of resonant reactive power, the power of the power supply and equipment is only less than 1/10 of the required capacity of the tested object (1/Q>10); The device has a small volume, light weight, large output capacity, and requires a small power supply capacity. It is inexpensive, easy to operate, and safe to use;
Series resonance is actually a current filtering circuit, which makes the current passing through the test sample basically the fundamental current, and the waveform distortion rate (THD) of the output voltage is extremely small, which is superior to all types of existing AC withstand voltage equipment;
The short-circuit current after flashover or breakdown of the test sample is only 1/10 or less of the pre short-circuit test current (1/Q), which can effectively prevent the expansion of damage to the fault point after breakdown;
Immediately after flashover, the arc will be automatically extinguished, and the process of establishing the resonant state voltage after extinguishing the arc is relatively long (in seconds), which is a steady-state establishment process without considering voltage overshoot or the danger of restoring overvoltage in microsecond level and millisecond level transient processes.
Prioritize tuning operation
In order to ensure the safety and smooth progress of the experiment, during the series resonance withstand voltage test, it is necessary to first adjust L to reach the full resonance L0 at a given low initial excitation voltage UJ0 (usually a few hundred volts), and slowly increase the voltage within a small range of detuning degree ST until UC reaches the predetermined withstand voltage value.