Ultra-low frequency high voltage generator test instrument——utilizing 0.1Hz ultra-low frequency power supply



The Ultra-Low Frequency (VLF) High Voltage Generator is a specialized device used in power systems for insulation withstand voltage testing of large capacitive equipment (such as long cables and large generators).

Simply put, it is a test instrument that "achieves great results with small means"——by utilizing a 0.1Hz ultra-low frequency power supply, it reduces the required power capacity for testing to 1/500 of that at power frequency (50Hz), thereby replacing bulky power frequency test transformers with lightweight equipment.

Combining the latest industry standards (2024-2026) and technological developments, I have compiled the core principles, purchasing guide, and pitfall avoidance suggestions for this equipment:

1. Core Principle: Why can it "achieve great results with small means"?

Its core logic is based on the physics formula 

Power frequency (50Hz): When conducting withstand voltage tests on long cables, the capacitive reactance is very small, requiring enormous current and capacity, making the equipment extremely heavy.

Ultra-low frequency (0.1Hz): By reducing the frequency by 500 times, the capacitive reactance increases by 500 times, and the required test current and power supply capacity are theoretically only 1/500 of that at power frequency.

Working process:

Input: Connect to ordinary 220V or 380V mains power.

Frequency conversion: Through rectification and inverter circuits (IGBT/MOSFET), convert power frequency electricity into 0.1Hz (or 0.05Hz/0.02Hz) low-voltage AC.

Voltage boosting: Increase the voltage to 30kV~90kV through a step-up transformer.

Output: Output a standard sine wave (or cosine square wave) high voltage to test the specimen.

2. Main Application Scenarios

Power cables: Especially cross-linked polyethylene (XLPE) cables rated 35kV and below. This is the most important application because DC withstand voltage can damage XLPE cable insulation, while power frequency AC withstand voltage equipment is too heavy; ultra-low frequency is the best alternative.

Large generators/motors: Insulation withstand voltage testing of stator windings.

Power capacitors, bushings, and other capacitive equipment.

3. 2026 Purchasing and Pitfall Avoidance Guide

Currently, there are many products on the market. Based on the latest industry feedback and standard updates, please pay attention to the following points when purchasing:

⚠️ Standard Version Update (Important)

Old standard: DL/T 849.4-2004 (abolished).

New standard: DL/T 849.4-2024 "General Technical Conditions for Special Test Instruments for Power Equipment - Part 4: Ultra-Low Frequency High Voltage Generator", officially implemented on June 25, 2025.

Recommendation: When purchasing, ensure that the equipment complies with the 2024 version of the new standard, which represents the latest measurement accuracy and safety requirements.