With the widespread deployment of cross-linked polyethylene power cables in transmission and distribution networks, the detection and maintenance of cable insulation status has become a key link in ensuring the safe operation of the power grid. Among numerous voltage withstand test methods, the 0.1Hz very-low frequency (VLF) voltage withstand test technology has become the preferred testing solution for cross-linked cables recognized by the industry and written into relevant regulations due to its significant advantages such as effective detection of insulation defects, small equipment size, and large capacity.
The VLF high voltage generator has thus become a high-frequency equipment used by the cable maintenance team. However, facing various specifications of VLF high voltage generators such as 30kV, 40kV, 50kV, 60kV, 70kV, 80kV, 90kV, etc. in the market, how to scientifically select based on cable voltage levels has become a core issue of concern for many power operation and maintenance personnel and equipment purchasers. Wuhan UHV Power Technology Co., Ltd. (hereinafter referred to as "Wuhan UHV") is rooted in the Wuhan Optics Valley high-voltage testing equipment industry circle, and combines years of on-site application data and fault diagnosis experience to provide professional VLF high-voltage generator selection guidelines for users.
Matching the rated voltage of the cable is the top priority in selection
The first and most crucial step in selection is to determine the rated voltage level of the tested cable. The voltage for VLF withstand voltage test is usually set to 2 to 3 times the cable phase voltage (U ₀) according to relevant regulations. Different voltage levels of cables correspond to different peak voltage requirements for VLF tester output: 5kV and 8kV level cables can choose VLF testers with 30kV peak voltage; The handover test for 15kV grade cables requires a peak voltage of approximately 31kV; Cables of 25kV and above require higher specification equipment.
The Wuhan UHV VLF high voltage generator provides multiple rated voltage outputs such as 30kV, 40kV, 50kV, 60kV, 70kV, 80kV, 90kV, etc., which can fully cover the testing needs of cables with voltage levels from 10kV and below to 35kV and above. It is worth noting that the new generation of products has achieved a single booster output of 90kV, upgrading from the old version of cascade output to single output, with simpler and more reliable wiring.
The carrying capacity determines the coverage of the test
Voltage level is not the only consideration for selection. The load capacity of VLF tester is equally crucial - it determines how long cables the tester can drive for effective testing. The power cable itself is a large capacitive load, and the equivalent capacitance of long-distance cables can reach several microfarads or even higher. If the large capacitance driving capability of the instrument is insufficient, it will result in severe distortion of the output waveform or the inability to boost to the target value at all.
The Wuhan UHV VLF high-voltage generator effectively solves this problem through multi frequency output design. The product supports four frequency levels: 0.1Hz, 0.05Hz, 0.02Hz, and 0.01Hz, with different frequencies corresponding to different load capacities. For example, the VLF-30/1.1 model has a load capacity of 1.1 µ F at a frequency of 0.1Hz, up to 2.2 µ F at 0.05Hz, 5.5 µ F at 0.02Hz, and 11 µ F at 0.01Hz. Users can flexibly choose the appropriate frequency range based on the actual length and capacitance of the tested cable. By optimizing the insulation process and software algorithms, the overall load capacity of the upgraded instrument has been increased by 25%.
Pure output waveform and safety protection are indispensable
In addition to voltage and capacity, output waveform quality is also an important consideration for selection. The waveform quality of a standard sine wave output VLF high-voltage generator is directly related to the accurate application of the test voltage peak and the reliability of breakdown determination. The VLF high voltage generator of Wuhan UHV is based on high-frequency switching power supply technology combined with step-up transformer topology, outputting a 0.1Hz sine wave voltage with clear technical specifications for waveform distortion rate and frequency stability. The measurement accuracy is 3%, the positive and negative peak voltage errors do not exceed 3%, and the waveform distortion does not exceed 5%. Compared to some technical solutions that use high-voltage capacitor charging and discharging to generate approximate sine waves, pure sine wave output can more realistically simulate the voltage stress that cables bear under working conditions, and the experimental conclusions are more convincing.
Security performance cannot be ignored either. The withstand voltage test belongs to high-voltage operation, and a sound protection mechanism is the bottom line requirement for equipment selection. The instruments of Wuhan UHV are equipped with multiple protection mechanisms, including output short-circuit protection, overvoltage protection, discharge protection, etc. It is particularly crucial that the instrument has a rapid discharge function with an automatic discharge circuit in the event of an end of the experiment or abnormal power outage, which can safely release the residual high-voltage energy on the tested cable in a very short period of time. The controller is connected to the low voltage generator through photoelectric control, ensuring safe and reliable use.
Intelligent upgrade enhances on-site operational efficiency
The demand for data and traceability in modern power testing is increasing day by day. The new generation intelligent VLF high voltage generator of Wuhan UHV adopts a 7-inch touch screen and imported high-speed AD acquisition circuit. The new high brightness full-color capacitive touch screen greatly enhances the user's operating experience under strong outdoor light. The human-computer interaction interface has been redesigned, with color schemes and layouts that are more in line with user operating habits. Added USB export function, allowing users to export historical data through a USB flash drive and view the data using upper computer software to generate standard Word format test reports. The product supports 60Hz power supply and adapts to the power frequency requirements of different countries and regions.
Wuhan UHV Power Technology Co., Ltd. is located in Wuhan, China Optics Valley, with thousands of square meters of standardized production facilities. The high-voltage experimental hall is equipped with a complete set of testing and calibration equipment, and all products undergo strict load aging and precision calibration processes before leaving the factory. For more selection information or customized configuration solutions, please visit the Wuhan UHV English official website( https://www.uhvtest.com/ )Or call for consultation.