Ultra-Low Frequency High Voltage Generator (Very Low Frequency High Voltage Generator, abbreviated as VLF or 0.1Hz withstand voltage test device) is key equipment in power systems for AC withstand voltage tests on large-capacity test objects such as high-voltage cables (especially cross-linked polyethylene XLPE cables) and generator stator windings. It perfectly solves two major pain points: traditional power frequency (50Hz) test equipment is bulky and too heavy to move on-site, and DC withstand voltage tests are prone to generating "space charge" in XLPE cables, leading to insulation damage. Combining the technical standards and application status of 2026, here is an in-depth analysis of this device: 1. Core principle and necessity Why is ultra-low frequency (0.1Hz) needed? Capacitive current is greatly reduced: the cable is equivalent to a large capacitor. According to the formula