Wuhan UHV specializes in producing series resonance (also known as series resonance test device). Next, we will share with you the application of series resonance in power cables in power systems.
As is well known, power cables are high-capacity electrical equipment in the power system. Before being laid and put into operation, power cables need to undergo voltage withstand tests to ensure their integrity. However, traditional voltage withstand equipment has a small capacity and cannot meet the requirements of long-distance cable voltage withstand tests. At this time, it is necessary to utilize resonance, which has both advantages and disadvantages in the power system.
We know that when the circuit frequency, inductance, and capacitance satisfy the resonance condition, the circuit resonates, and the voltage on the test sample is Q times the output voltage of the excitation transformer high voltage end. Q is the system quality factor, which is the voltage resonance multiple, generally ranging from tens to hundreds or more. First, adjust the output frequency of the variable frequency power supply to induce series resonance in the circuit, and then adjust the output voltage of the variable frequency power supply under the condition of circuit resonance to achieve the test value of the sample voltage. Due to the resonance of the circuit, a smaller output voltage of the variable frequency power supply can generate a higher test voltage on the test sample CX.
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 to 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.
