VLF (Very Low Frequency) Testers are suitable for testing power cables transformers switchgear rotating machinery and other electrical apparatus. 1. Data of current voltage wave form can be directly sampled at high voltage side so the data is real and accurate. 2. Overvoltage protection: If the output exceeds the set limit of voltage the instrument will shut-down to protect itself the actuation time is less than 20ms. 3. Overcurrent protection: It is high-low voltage dual protection in the design the accurate shut-down protection can be made according to the set value at high voltage side; If the current on low voltage side exceeds the rated current the instrument will take shut-down protection the actuation time are both less than 20ms. 4. A high voltage output protective resistor is provided in the voltage boost body in the design and this eliminates the need of additional protect