Integrated VLF‑Tan Delta Diagnostic Tester

The MOEORW-WHVA30 is a 0.1Hz Very Low Frequency AC hipot tester integrated with Tan Delta dielectric loss measurement and DC withstand voltage capabilities. Designed as a portable, all-in-one diagnostic instrument, it addresses the challenge of testing high-capacitance electrical equipment such as power cables, large generators, motors, and power capacitors, where conventional power-frequency AC testing would require excessively bulky and costly transformers.

By employing 0.1Hz ultra-low frequency technology, the HVA30 reduces the required test power capacity to approximately 1/500 of that at 50/60Hz, enabling a compact 19.5 kg form factor without compromising test equivalence to power-frequency AC. The unit integrates a 7-inch capacitive touchscreen, a built-in thermal printer, and an ARM7 microcontroller with high-speed ADC acquisition, delivering fully automated test sequences from ramp-up to measurement and protection.

The WHVA30 complies with the Chinese power industry standard DL/T849.4-2004 General Technical Conditions for Very Low Frequency High Voltage Generators and aligns with international practices recommended by the IEC for VLF testing.

1. Integrated Tan Delta and Insulation Diagnostics
The HVA30 measures dielectric loss angle tangent, Tan δ, to assess insulation aging. By analyzing the ratio of resistive leakage current to capacitive current under 0.1Hz excitation, the instrument provides quantitative indicators of insulation degradation. Test results are compared against established thresholds, including standard deviation, slope, and mean values, to determine insulation condition as normal, recommended for follow-up, or requiring immediate action.

2. Advanced Digital Control Architecture
Built around a high-performance ARM7 microcontroller with high-speed ADC acquisition circuitry, the HVA30 implements digital frequency conversion and closed-loop negative feedback control. This design eliminates capacitive rise effects and ensures stable, distortion-free sinusoidal output across the full load range.

3. Fully Automated Test Sequences
The instrument manages the complete test cycle: self-diagnostic check, voltage ramp-up, constant-amplitude output, automatic shutdown, and capacitive discharge. Operators simply set test parameters, including voltage, frequency, duration, and protection limits, and initiate the sequence via the touchscreen.

4. Multi-Mode Output Flexibility
Supports VLF AC sinewave, VLF AC squarewave, DC +/− polarity, and vacuum bottle testing modes. Frequency selection from 0.01 Hz to 0.1 Hz in 0.01 Hz increments allows optimization for different test standards and load conditions.

5. Comprehensive Protection System
Multi-tier protection includes over-voltage protection, high-voltage-side over-current protection, and low-voltage-side over-current protection, with trip response time ≤10 ms. The controller connects to the high-voltage generator via optical isolation, ensuring operator safety.

6. On-Site Data Management
Equipped with a 7-inch capacitive touchscreen displaying real-time voltage and current waveforms and test data. Built-in thermal printer produces test reports immediately. Internal memory stores up to 50 test reports and 40 test sequences; optional USB flash drive expands storage indefinitely. PC software, HVR Control Center, enables data export, analysis, and report generation.

7. Rugged, Portable Design
Integrated construction with carrying handle; weighs only 19.5 kg and measures 430×360×250 mm. Operates reliably in field environments from −5°C to 45°C.

Power Cable Testing
XLPE and PILC cables up to 35kV class

Commissioning tests: 60 minutes at 3U₀

Preventive maintenance: 15 minutes at 3U₀

Simultaneous Tan Delta measurement for insulation condition assessment

Generator and Motor Testing
Medium and large generators, synchronous motors

Stator winding insulation withstand voltage and dielectric loss diagnostics

Single-phase capacitance values per table in the manual

Power Capacitors
High-capacitance load testing at reduced power requirements

Dielectric loss measurement for aging assessment

Vacuum Bottle Testing
Dedicated output mode for vacuum interrupter integrity verification

VLF Generation
The WHVA30 employs digital frequency conversion technology to generate a 0.1Hz or variable frequency high-voltage sinusoidal waveform from standard AC mains input. By reducing the test frequency to 1/500 of power frequency, the reactive power demand of capacitive loads decreases proportionally, allowing a lightweight design that replaces massive series-resonant or power-frequency test transformers.

Tan Delta Measurement
For a cable under test, the insulation can be modeled as a parallel combination of insulation resistance, R, and capacitance, C. Under AC excitation:

• Resistive current, or leakage, is in phase with voltage and indicates insulation degradation.
• Capacitive current leads voltage by 90° and is proportional to cable length and type.

The loss angle δ is the angle whose tangent equals the ratio of resistive to capacitive current:

Tan δ = I_resistive / I_capacitive

A higher Tan δ value indicates greater insulation loss and accelerated aging. The HVA30 measures Tan δ at multiple voltage levels, 0.5U₀, 1.0U₀, and 1.5U₀, during the test sequence and compares results against standard criteria for pass or fail assessment.

The system incorporates arc-burning regulation and arc-extinguishing trip modes, allowing controlled fault conditioning or immediate trip upon arc detection, protecting both the equipment under test and the tester itself.

Monthly Power-On in Humid Climates
In regions with high humidity or during rainy seasons, if the instrument is stored for extended periods, it is recommended to power on the unit for approximately two hours each month to dissipate internal moisture and protect electronic components.

Storage Conditions
Store in a ventilated indoor environment at −20°C to +60°C, relative humidity below 85%, free from corrosive gases. Do not place directly against floors or walls.

Transportation
Use original packaging with foam padding. Protect from rain, dust, and mechanical impact during transport.

Fuse Replacement
The power inlet incorporates a fuse holder. If the screen does not illuminate upon power-on, check and replace the fuse with the specified rating.

Troubleshooting Guide