What is very low frequency testing?
VLF test frequency is typically 0.1 Hz, which is much lower than the power frequency of 50/60 Hz. A VLF tester applies high-voltage alternating current to a cable to verify whether the cable insulation can withstand the specified voltage. Because the frequency is very low, the capacitance and power required by the test equipment can be significantly reduced, making it particularly suitable for on-site testing of long-distance medium- and high-voltage cables.
1.What are the main applications of VLF?
- Withstand Test
Determines whether the cable insulation has serious defects.
- Insulation Diagnosis
When combined with tests such as Tan Delta (dielectric loss), it can assess the degree of cable insulation aging.
- Fault Prevention
Identifies potential insulation issues before cables are put into service or during routine maintenance, reducing the risk of breakdown during operation.
(Goldhome) VLF System Technology
When performing the aforementioned VLF standard tests, Goldhome's HMCOP series of ultra-low-frequency high-voltage generators have been specifically optimized to align with the core scientific principles:
1.High-fidelity pure sine wave (true 0.1 Hz AC electric field) alignment: The core of VLF testing lies in utilizing a pure AC electric field to prevent space charge accumulation.
Goldhome Technology: Traditional analog frequency modulation is prone to waveform distortion; Goldhome employs fully digital waveform synthesis technology, achieving an output waveform distortion of <0.5%. This not only perfectly simulates a power-frequency electric field but also serves as the "clean reference voltage" required for high-precision dielectric loss (Tan Delta) diagnostics.
2.Flexible Multi-Band Frequency Modulation (Overcoming High Capacitance Limits) Principle: The longer the cable, the greater its capacitance (C), and the more power required.
Huamei Technology: In addition to the standard 0.1 Hz, the equipment supports intelligent frequency modulation at 0.05 Hz and 0.02 Hz [gdhmdq.com]. When testing medium-voltage cables several kilometers long, the system automatically lowers the frequency, increasing the equipment's maximum load-driving capacity severalfold without adding to the size or weight of the on-site test instrument. This makes it ideal for long-cable applications such as wind farms and power collection networks.
3.Microsecond-Level Dual Closed-Loop Protection (Ensuring On-Site High-Voltage Safety) Principle Alignment: One of the core objectives of a withstand voltage test is to "induce on-site breakdown of defects."
Huamei Technology: When insulation breakdown occurs in a cable during testing, an extremely high-voltage counter-wave is generated instantaneously. Goldhome has designed an opto-isolated control system combined with a dual electronic/mechanical rapid-shutdown mechanism to instantly lock out the high-voltage output within microseconds (μs), ensuring the absolute safety of both operators and the VLF instrument.
