VLF + TD + PD Multi-Function System: One 0.1Hz Hipot Tester That Replaces Three

If you've ever had to drag a separate VLF Hipot, tan delta bridge, and partial discharge detector out to a substation, you already know why theVLF + TD + PD multi-function system has caught on with utility crews and cable diagnostic labs. It rolls all three jobs into one portable instrument.

A 30–80 kV Tester in One Box

Output is rated from 30 kV up to 80 kV, with an automatic frequency sweep from 0.1 Hz down to 0.01 Hz, so even long XLPE feeders with several microfarads of capacitance can be energized off a standard 230 V / 50 Hz (or 120 V / 60 Hz) wall outlet.

Under the hood it runs on digital frequency conversion technology, with the whole voltage boost, buck, measurement, and protection cycle handled by a microcontroller. Units rated 60 kV and below use a fully integrated solid-state stack — no oil tanks, no heavy ferromagnetic core — keeping the chassis light enough for one technician to move. Above 60 kV, an in-line step-up transformer is added, but the control electronics stay the same.

Why Field Engineers Like It

• Closed-loop HV sampling. Current and voltage are picked off the high-voltage side directly, so you don't get the capacitive rise effect that plagues open-loop VLF designs.
• Smart auto-protection. No fiddling with OV/OC setpoints. The MCU calculates trip values from sample capacitance and target test voltage, then shuts down on overvoltage, overcurrent, low-impedance faults, or flashover.
• Numbers you can trust. Voltage and current accuracy hit ±3%, waveform distortion stays under 3%, and peak symmetry error is also ≤3% — fully consistent with IEEE 400.2 VLF withstand requirements for XLPE, EPR, and PILC cables.
• Touchscreen UI. A large color HMI shows the sinusoidal output waveform live, so you can confirm the cable is being stressed cleanly.

Tan Delta and Partial Discharge — Optional, But Worth It

The 1.1.5 revision adds DC hipot, tan delta, and partial discharge channels. That means you can measure dielectric loss, insulation resistance, capacitance, and PD activity during the same withstand test — a real time-saver compared to running three diagnostics back-to-back.

Built for Outdoor Substations

It works from −10 °C to +40 °C up to 85% RH, includes a 150 kV-rated HV output cable, and refuses to energize until the ground stake is verified. For utilities, wind farms, and industrial plants responsible for MV cable maintenance, this VLF + TD + PD multi-function system replaces a rack of legacy instruments with one box that's easier to ship, easier to run, and easier to trust.

Need  testing technical support or equipment consultation? Our engineering team is ready to provide professional advice.