A city power supply bureau conducted an acceptance test on a newly laid 15km 10kV XLPE cable.

Urban distribution network renovation: A city power supply bureau conducted an acceptance test on a newly laid 15km 10kV XLPE cable. Using a 60kV/0.1Hz VLF device, the test was carried out in 5 segments, each taking only 20 minutes. In one segment, the tanδ value abnormally increased at 0.8 times the test voltage. After diagnosis, moisture was found in the intermediate joint, preventing an explosion after commissioning. Power plant auxiliary power cables: In a narrow cable mezzanine, traditional series resonant equipment could not enter. A portable VLF generator was used to easily complete the withstand voltage test on a 35kV main feeder cable. 5. Operation precautions Wiring specifications: Non-tested phases must be reliably grounded to prevent induced high voltage from harming personnel or affecting test results. Full discharge: After the test, the cable still holds charge. A dedicated discharge rod must be used for full discharge (first through a resistor, then directly to ground), for no less than 5 minutes. Environmental factors: Dirt or moisture on the terminal surface can affect results. Clean and install shielding rings before testing. Standard execution: Strictly set the test voltage (usually 2.5U0 or 2.0U0) and time (usually 15-60 minutes) according to GB/T 3048.8 or DL/T relevant standards. Summary and recommendations Essential equipment: If you are responsible for the operation and maintenance of 10kV or 35kV XLPE cables, the very low frequency high voltage generator is a must-have device. It has completely replaced the DC high voltage generator in this field. Configuration strategy: Basic version: Only for withstand voltage pass testing, choose basic models from mainstream domestic brands (such as UHV, Moen) with high cost performance. Advanced version: If you need to evaluate cable life and troubleshoot hidden faults, be sure to choose a high-end model with dielectric loss diagnosis (Tan Delta) function. Pitfall avoidance guide: Do not buy old equipment that can only output "cosine square wave" and cannot switch to "sine wave", to avoid not meeting the latest acceptance standards. Do you need specific model recommendations for a specific voltage level (such as "35kV submarine cable" or "10kV distribution network"), or do you want to understand the specific criteria for dielectric loss diagnosis? The very low frequency high voltage generator (0.1Hz High Voltage Generator, abbreviated as VLF) is a specialized device for AC withstand voltage testing of medium and high voltage cables (especially cross-linked polyethylene XLPE cables). It solves the problems that traditional DC withstand voltage damages XLPE cables and that power frequency (50Hz) series resonant equipment is too bulky to carry. It is currently the recommended first choice for 10kV-35kV cable acceptance and preventive tests worldwide (including Chinese national standard GB/T 3048.8, IEC 60502-4). Combined with the latest technical standards and market applications from 2025-2026, here is an in-depth analysis: 1. Core function and working principle Why "very low frequency"? Disadvantages of DC withstand voltage: For XLPE cables, DC withstand voltage will generate "space charge" in the insulation layer. If not fully dissipated after the test, it may cause electric field distortion and breakdown at the moment of commissioning. Therefore, national standards have prohibited the use of DC withstand voltage for XLPE cables. Limitations of power frequency withstand voltage: Although 50Hz AC withstand voltage is the most realistic, it requires huge series resonant reactors (weighing several tons), which is not suitable for field operations in narrow spaces such as urban distribution networks, tunnels, and shafts. Advantages of 0.1Hz: Equivalence: 0.1Hz sine wave has excellent equivalence with 50Hz in detecting insulation defects (especially when combined with "cosine square wave" or "sine wave" modes). Portability: According to the capacitive load power formula