Product introduction
VLF Hipot Instruments, often referred to as high voltage VLF generators, are specialized high-voltage test equipment used for insulation diagnostics and withstand voltage testing of medium and high-voltage electrical assets, primarily cables, but also generators, transformers, switchgear, and more.
Their defining characteristic is: An output frequency significantly lower than power frequency (50Hz or 60Hz), typically between 0.01 Hz and 1 Hz, with 0.1 Hz being the most common and standardized test frequency.
Product Parameters
Technical parameter
| Power supply | AC220V±5%, 50/60Hz. If using a generator, it must be a digital inverter generator with 220V output and power >8kW. Ordinary generators or UPS power supplies are prohibited. |
| Output Voltage | 30kV, 40kV, 50kV, 60kV, 70kV, 80kV, 80kV, 90kV |
| Output frequency | 0.1Hz, 0.05Hz, 0.02Hz,0.01Hz |
| Load Capacity | 0.1Hz-0.5μF, 0.05Hz-1.0μF,0.02Hz-2.5μF,0.01Hz-5μF |
| Measurement accuracy | 3% |
| Voltage positive,negative peak error | ≤3% |
| Voltage waveform distortion | ≤5% |
| Operating Environment | Temperature: -10℃~+40℃ |
| Humidity | ≤85%RH |
Comparison of mechanical and electronic performance of 0.1Hz voltage test equipment
| 0.1Hz Voltage resistant device type | High pressure control system | High voltage waveform | Energy saving | noise | Mechanical life | Electrical life |
| Mechanical type | High voltage mechanical switch toggles polarity | Square wave | No energy saving: the excess energy is consumed with high-power resistance | high | short | short |
| Electronic type | High voltage electronic switches switch polarity | Sinusoidal wave | Energy conservation: Excess power is fed back into the grid | slight | There is no | long |
Core Principle & Purpose Of VLF Hipot instruments
1. Replacing Power Frequency Withstand Testing: Performing 50/60 Hz AC withstand tests on long cables or high-capacity equipment (like large generators) requires massive, heavy, and expensive test transformers and power supplies (requiring MVA-level capacity). High voltage VLF technology solves this problem.
2. Electrical Equivalence: Theory and practice demonstrate that the electrical stress (electric field strength) applied to insulation materials under 0.1 Hz high voltage VLF is equivalent to that under 50/60 Hz power frequency. This means VLF hipot instruments effectively detect the same insulation defects (like voids, cracks, impurities, water trees) as power frequency withstand tests.
3. Equipment Miniaturization: Due to the extremely low frequency (0.1 Hz is 1/500th of power frequency), the required reactive power is drastically reduced. This allows VLF hipot instruments to be much smaller, lighter, and less costly than power frequency test sets (typically 1/10th or less) for the same output voltage level, greatly improving portability and making them ideal for field use.
4. Detecting Water Treeing Degradation: For extruded insulation cables like XLPE, 0.1 Hz VLF cable testing is considered more effective than traditional DC hipot testing at revealing "water treeing" degradation and is less damaging to the insulation.
Main application areas of VLF Hipot Instruments
1. Power cable
Specific scenario: Handover and preventive testing of cross-linked polyethylene (XLPE) cables
Technical advantage: It can effectively detect insulation defects such as water branches and is the mainstream testing method for cables of 35kV and below.
2. Rotating motor
Specific scenario: Factory and maintenance testing of large generators and motors
Technical advantage: It replaces power frequency withstand voltage and significantly reduces the demand for large power equipment.
3. Other capacitive devices
Specific scenarios: power capacitors, bushings for high-voltage composite equipment (GIS), etc
Technical advantage: Solve the problem of large capacitance and inability to carry conventional power frequency testing equipment into the field.
Frequently Asked Questions
What equipment is VLF Hipot Instruments mainly used for testing?
The UHV VLF Hipot Instrument is designed for insulation withstand voltage testing of high-capacitance electrical equipment, including:
Medium and high voltage XLPE power cables
Cable joints and terminations
Generator stator windings
Large motor windings
Substation cable systems
It is widely used for field preventive testing and commissioning tests.
Why is VLF used instead of power-frequency withstand testing for cables?
For high-capacitance equipment (especially long cables), power-frequency testing requires a very large power source, which is difficult to implement on site.
VLF (Very Low Frequency, 0.1 Hz) offers:
Compact and lightweight test setup
Low power capacity requirement
Easier field operation
Minimal impact on the power grid
Ideal for long cable systems
What is the output voltage range of VLF Hipot Instruments?
UHV provides multiple voltage levels:
30 kV
40 kV
50 kV
60 kV
80 kV
Higher voltage available on request
The configuration is selected based on cable rated voltage and relevant standards.
What output waveforms are available?
UHV VLF systems support several waveform options:
Sine wave
Square wave
Cosine-rectangular wave
Different waveforms are used depending on test standards and application requirements.
What is the standard test frequency?
Typical frequencies include:
0.1 Hz (most commonly used)
0.05 Hz (high-capacitance cables)
0.02 Hz (ultra-high capacitance loads)
The system can automatically optimize frequency based on the load.
Does the system support automatic testing?
Yes.
The UHV VLF Hipot Instruments support full automatic operation, including:
One-key test start
Automatic voltage ramp-up
Automatic timing
Automatic voltage holding
Automatic ramp-down
Automatic data storage
What safety protection functions are included?
The system integrates multiple protection features:
Over-voltage protection
Over-current protection
Flashover protection
Breakdown protection
Grounding protection
Zero-start interlock
Emergency stop function
All designed to ensure safe and stable operation.
How is test pass/fail determined?
Evaluation is generally based on:
Whether breakdown occurs
Whether leakage current is abnormal
Whether voltage remains stable
Whether the required test duration is completed
The system automatically records the full test process for analysis.
Does it support diagnostic testing?
Some advanced UHV models support extended functions such as:
Dissipation factor (Tan Delta) testing interface
Partial discharge (PD) testing interface
Cable insulation condition assessment
Used for condition evaluation, not only pass/fail testing.
Is VLF Hipot Instruments suitable for field use?
Yes, it is designed for field applications:
Compact and easy to transport
Suitable for substation environments
Operable by one or two people
Fast deployment
We are a leading professional manufacturer of VLF Hipot instruments in China, with over 22 years of experience in R&D, production, and quality control.
We don't just sell instruments – we provide complete pre-sales consultation, customization options (voltage, frequency, cable length), on-site training.
Looking for a reliable VLF Hipot instruments supplier? Contact us to get VLF Hipot Instruments price.
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