2025-2026 Mainstream Technical Features
According to the latest industry standards (such as IEEE 400.2-2024 and China DL/T 596-2025), modern very low frequency (VLF) high-voltage generators have the following advanced features:

Table
Feature Dimension | Detailed Description
Output Waveform | Sine wave or cosine square wave. Cosine square wave is widely adopted due to its high energy utilization efficiency and minimal damage to insulation. The waveform distortion rate is typically required to be < 3%.
Frequency Settings | Standard configuration is 0.1Hz (most commonly used), some models support 0.05Hz, 0.02Hz to accommodate larger capacitive loads.
Load Capacity | Measured by capacitance value, common specifications are 1.1μF @ 0.1Hz, high-end models can reach 2.2μF or even 5.5μF (at lower frequencies). It can cover 35kV cables several kilometers long.
Intelligent Control | Microcomputer fully automatic control: one-key boost, automatic voltage stabilization, timing, and automatic voltage reduction. It features V-A characteristic curve display, real-time monitoring of voltage/current waveforms.
Protection Functions | Overvoltage protection (<20ms action), overcurrent protection, zero-position start, high-voltage output short-circuit protection, and discharge protection.
Diagnostic Functions | Some high-end models integrate partial discharge (PD) monitoring modules (sensitivity up to 5pC) and insulation degradation trend analysis algorithms, not only for withstand voltage testing but also to assess insulation life.
Portability | Using high-frequency inverter technology and lightweight design, the main unit typically weighs between 15kg-30kg, with a built-in printer and optional battery power supply.
Data Management | Large capacity storage for historical test data, USB export, and automatic generation of test reports compliant with State Grid/China Southern Power Grid standards.

4. Typical Test Procedure
Wiring: Connect the ground wire (crucial), connect the high-voltage wire to the cable core, and short-circuit and ground the remaining phases.
Parameter Setting: Input the capacitance value of the test object (or choose automatic estimation), set the target voltage (e.g., 2.5U₀ or 3U₀), and the withstand voltage time (usually 15-60 minutes).
Automatic Boost: The instrument automatically boosts at a set rate (e.g., 1kV/s), monitoring leakage current and waveform in real-time during the process.
Withstand Voltage Timing: Timing starts automatically after reaching the target voltage. If breakdown occurs or leakage current exceeds the limit, the instrument immediately alarms and cuts off the output.
Automatic Discharge: After the test, the instrument controls the internal discharge resistor to automatically discharge the test object, ensuring personnel safety before disconnecting wires.

5. Selection and Usage Recommendations
Select based on cable length and voltage level: Calculate the total capacitance of the cable under test (