Ultra-low frequency voltage generator uses mechanical methods for modulation and demodulation both internally and externally to generate ultra-low frequency signals, resulting in non-standard sine waveforms, large measurement errors, spark discharge in the voltage section, bulky equipment, and the need for high-power voltage resistors to shape the waveform in the second and fourth quadrants of the sine wave, leading to high overall power consumption. Years of theory and practice at home and abroad have proven that using 0.1Hz ultra-low frequency withstand voltage tests instead of power frequency withstand voltage tests not only provides equivalent effectiveness but also significantly reduces equipment size and weight. Theoretically, the capacity is about one five-hundredth of that of power frequency, and the operation is simpler, offering more advantages compared to power frequency tests. This is why developed countries generally adopt this method.
To resolve this contradiction, the test frequency is reduced, thereby lowering the capacity of the test power supply. Years of theory and practice at home and abroad have proven that 0.1Hz ultra-low frequency withstand voltage tests replacing power frequency withstand voltage tests not only provide equivalent effectiveness but also significantly reduce equipment size and weight, with capacity about one five-hundredth of that of power frequency, greatly simplifying the test procedure, and offering more advantages compared to power frequency tests. This is why developed countries generally adopt this method. Our Ministry of Electric Power has commissioned the Wuhan High Voltage Research Institute to draft the industry standard "Test Method for Ultra-Low Frequency (0.1Hz) Withstand Voltage of 35KV and Below Cross-linked Polyethylene Insulated Power Cables," and we are promoting this method. This instrument is developed according to our national needs and can be widely used in AC withstand voltage tests for cables, large rotating electrical machines, and power capacitors.
The ultra-low frequency voltage generator adopts microcomputer control, with fully automated voltage boosting, step-down, measurement, and protection, and allows manual intervention during the automatic boosting process. Due to its fully electronic design, the instrument is small in size, light in weight, features a large LCD display that is clear and intuitive, can display output waveforms, and prints test reports via a printer.
Functional design features of the ultra-low frequency voltage generator:
1. Current, voltage, and waveform data are directly sampled from the high-voltage side, ensuring data authenticity and accuracy;
2. Overvoltage protection: When the output exceeds the set voltage limit, the instrument will shut down for protection, with an action time of less than 20ms;
3. Overcurrent protection: Designed with dual low-voltage protection, and the high-voltage side can be precisely protected according to the set value;
4. Accurate shutdown protection; when the current on the low-voltage side exceeds the rated current, shutdown protection will be activated, with action times all less than 20ms;
5. The high-voltage output protection resistor is designed inside the voltage booster, so no external protection resistor is needed;
6. Due to the adoption of a low-voltage closed-loop negative feedback control circuit, the output has no capacitive rise effect.
