The VLF-45 very low frequency withstand voltage test device offers switchable output frequencies of 0.1 Hz, 0.05 Hz, and 0.02 Hz, with a rated voltage of 45 kV and load capacities of 1.1 μF (0.1 Hz), 2.2 μF (0.05 Hz), and 5.5 μF (0.02 Hz). The device is suitable for handover and preventive insulation withstand voltage tests of 35 kV and below cross-linked polyethylene (XLPE) insulated power cables, high-voltage generators, and large motors. The following explains selection and usage points from the perspective of engineering parameters.
During selection, the load capacity of the device must be calculated based on the capacitance of the test object. Taking 8.7/10 kV cables as an example, the capacitance per kilometer is approximately 0.2–0.4 μF, and the recommended single test length should not exceed 3 km (under 0.1 Hz conditions). If the test object capacitance exceeds the rated load at the corresponding frequency, switch to a lower frequency (0.05 Hz or 0.02 Hz) to increase load capacity. When purchasing, typical test object parameters should be provided to the supplier for matching verification.
Handover tests are based on GB 50150-2016, with a test voltage of 3U₀ and a duration of 60 minutes. For example, the test voltage for 8.7/10 kV cables is 26 kV, and for 26/35 kV cables it is 78 kV. Preventive tests are based on DL/T 596-2021, with a test voltage of 2.5U₀ for 15–60 minutes; North China Power Grid regulations require 2.1U₀ for 5 minutes; Jiangsu Electric Power Company regulations require 3U₀ for 20 minutes. Purchasing personnel should clarify the regulatory requirements of the region where the equipment will be used and confirm that the device's maximum voltage meets the highest test voltage.
After wiring is completed, perform a no-load voltage rise test first to confirm that voltage and current displays are normal. After the test, the test object must be fully grounded and discharged using a discharge rod, and wiring can only be removed after confirming there is no residual voltage. The device should have overcurrent, overvoltage protection, and grounding detection functions. During procurement, attention should be paid to whether the protection configuration meets on-site safety regulations.
The device is suitable for 35 kV and below XLPE cables, detection of insulation defects at the ends of high-voltage generators (more effective than power frequency), and insulation assessment during handover and major overhaul of large motors. Very low frequency withstand voltage tests are not applicable to 110 kV and above XLPE cables. Purchasing personnel should confirm the applicable scope based on the test object type and voltage level.
