Principle of Ultra-Low Frequency Insulation Withstand Voltage Test
The ultra-low frequency insulation withstand voltage test is actually an alternative method to the power frequency withstand voltage test. As we know, when conducting power frequency withstand voltage tests on large generators, cables, and other test objects, due to their large capacitance in the insulation layer, a test transformer or resonant transformer with large capacity is required. Such huge equipment is not only bulky and expensive but also very inconvenient to use. To solve this problem, the power sector has adopted a method of reducing the test frequency, thereby reducing the capacity of the test power supply. Years of theory and practice at home and abroad have proven that using a 0.1Hz ultra-low frequency withstand voltage test instead of the power frequency withstand voltage test not only provides equivalent effectiveness but also greatly reduces the size and weight of the equipment. Theoretically, the capacity is about one five-hundredth of that at power frequency. The test procedure is greatly simplified, offering more advantages compared to the power frequency test. This is why developed countries commonly adopt this method. Our country's power department has commissioned the Wuhan High Voltage Research Institute to draft the industry standard "Test Method for Ultra-Low Frequency (0.1Hz) Withstand Voltage of Cross-linked Polyethylene Insulated Power Cables at 35KV and Below". Our country is promoting this method, and this instrument is developed according to this need. It can be widely used for AC withstand voltage tests on cables, large high-voltage rotating motors, and power capacitors.
Product Introduction
This product combines modern digital frequency conversion advanced technology, adopts microcomputer control, and the voltage boosting, voltage reduction, measurement, and protection are fully automated, with manual intervention possible during the automatic voltage boosting process. Due to full electronization, it is small in size and light in weight, with a large-screen LCD display that is clear and intuitive, and can display output waveforms and print test reports via a printer. The design specifications fully comply with the industry standard DL/T849.4-2004 "General Technical Conditions for Special Testing Instruments for Power Equipment, Part 4: General Technical Conditions for Ultra-Low Frequency High Voltage Generators", making it very convenient to use. Currently, both domestic and international methods use mechanical methods for modulation and demodulation to generate ultra-low frequency signals, resulting in non-standard sine waveforms, large measurement errors, spark discharge in the high-voltage part, bulky equipment, and the need for high-power high-voltage resistors for discharge shaping in the second and fourth quadrants of the sine wave, leading to high overall power consumption. This product can overcome these shortcomings. In addition, it has the following special features that need to be highlighted:
★ Current, voltage, and waveform data are all directly sampled from the high-voltage side, ensuring data authenticity and accuracy.
★ Overvoltage protection: When the output exceeds the set voltage limit, the instrument will shut down for protection, with an action time of less than 20 milliseconds.
★ Overcurrent protection: Designed with dual protection for high and low voltage sides. The high-voltage side can be shut down for protection according to the set value; the low-voltage side will shut down for protection when the current exceeds the rated current, with action times both less than 20 milliseconds.
★ The high-voltage output protection resistor is designed inside the voltage booster, so no external protection resistor is needed.
★ Due to the adoption of a high-low voltage closed-loop negative feedback control circuit, the output has no capacitive rise effect.
Note: The above information and technical parameters are compiled and released by Yangzhou Darui Electric Co., Ltd.
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