The AC withstand voltage tests of various large power transformers, power cables, steam turbines, hydro generators and other capacitive equipment must be carried out strictly according to the test procedures on a regular basis; Under power frequency conditions, due to the large capacitance of the test piece or high testing voltage requirements, the power supply capacity of the test device is also high. Traditional power frequency withstand voltage devices are bulky, heavy in weight, difficult to perform on site, difficult to assemble, and have poor flexibility. A better method is to conduct a voltage withstand test using series resonance.
The complete set of frequency conversion series resonance test device is a series resonance test device that uses tuned inductance and load capacitance to generate series resonance and obtain test voltage. The complete set of frequency conversion series resonance test device is composed of isolation transformer, frequency modulation and voltage regulation power supply, excitation transformer, reactor, capacitor voltage divider, etc; The voltage divider is connected in parallel to the test item, and the resonant voltage on the test item is measured using a frequency conversion series resonance test device to obtain an overvoltage protection signal; The frequency modulation power output is coupled to a series resonance circuit through an excitation transformer, providing excitation power for series resonance.
When the frequency conversion series resonance test is set to withstand voltage test, frequency modulation is performed at the initial voltage based on the calculated frequency. Firstly, check the grounding. The complete set of frequency conversion series resonance test equipment must be well grounded. The grounding point of the testing equipment and the grounding point of the generator core should be grounded simultaneously. In addition, the temperature measuring components and generator rotor also need to be grounded for protection. However, when starting the frequency modulation experiment, the results were not ideal, and the frequency did not meet the power frequency requirements. After the power outage, the external wiring was correct, suspecting the influence of the placement position of the two reactors. The induced reactance value was changed, the distance and position of the reactors were readjusted, the power frequency 50 Hz resonance point was found, the voltage was increased, and the withstand voltage value was maintained for one minute, The power frequency withstand voltage test passed smoothly. Through this experiment, we have accumulated valuable experience in the withstand voltage test of large high-voltage motors.
In practical applications, it has been found that when the voltage rises close to the test voltage, the speed of voltage rise is too fast, and the voltage fluctuation is large, even leading to voltage protection. Therefore, it is necessary to restart the test, which is detrimental to the safety of the equipment. However, if the voltage protection value is set too high, the complete set of frequency conversion series resonance test equipment cannot effectively protect the tested equipment from voltage.
There are several methods to improve the stability of the complete set of frequency conversion series resonance test equipment:
1. Select deviation from resonance frequency for testing
We know that in order to reduce the capacity of the test transformer, the Q value should be as large as possible, but when the Q value is large and deviates from the resonance frequency, the speed is relatively slow. Therefore, we can choose to deviate from the resonant frequency to boost the voltage and reduce the speed of voltage rise when the capacity of the complete set of frequency conversion series resonance test equipment allows.
2. Adjusting the quality factor of the circuit
From Q=Uc/U=1/ ω CR shows that in order to reduce the q value, it is necessary to increase the circuit resistance. In this way, the output capacity of the excitation transformer must also be increased in order to reach the test voltage. Therefore, when applying this method to the complete set of frequency conversion series resonance test equipment, it must be carried out under the conditions of allowable capacity.
3. Requirements for grounding resistance
The grounding wire should be reliably connected to the grounding body, and the grounding resistance should be less than 4 Ω
The KSTVF-A series variable frequency series resonance testing complete device is suitable for AC withstand voltage testing of transformers, circuit breakers, switches, GIS systems, cables, bushings, insulators, and other equipment. Equipped with multiple protection functions such as high-voltage overvoltage protection, low-voltage overcurrent protection, as well as detuning protection, zero position, flashover protection, emergency shutdown, undervoltage protection, etc. It can meet the requirements of high voltage and low current equipment testing conditions, as well as low voltage and high current equipment testing conditions, and has a wide range of application.
Kvtester Electronics Technology Co.,Ltd. is a high-tech enterprise specializing in power testing, testing, research and development, production, and sales of testing equipment. It has been engaged in the electrical testing industry for many years, and its products are of high quality. We welcome customers to come and purchase.
