Benefits of truesinus® Digital Technology for VLF Testing

Truesinus® is a voltage generation technology invented and patented by BAUR for the VLF high voltage cable test equipment. This is a unique system based upon digital technology to produce truly sinusoidal voltage shapes. In a previous blog post (The Basics of VLF Testing) we described what very low frequency (VLF) testing was. Now we would like to go more into the technology within the compact high voltage testers to allow for accurate VLF testing and diagnostics.

Truesinus® is an ideal waveform for cable testing and diagnostics because it mimics the power frequency waveform a cable sees under operating conditions and, since the voltage output is sinusoidal, the voltage is given in RMS values.

IEC 60060-3 “High-voltage test techniques – Part 3: Definitions and requirements for on-site testing” is an international standard that defines the characteristics and requirements for testing with different voltage shapes. Under Section 9.3.1 Voltage wave shape, it reads:


Sinusoidal VLF voltage waveshape shall approximate a sinusoid with both half-cycles closely alike. The result of a high-voltage test is thought to be unaffected by small deviations from a sinusoid if the ratio of the peak to r.m.s. values is within √2 ± 5%.

NOTE If the ratio of peak to r.m.s. values is not within √2 ± 5%, it should be verified that positive and negative peaks do not differ by more than 2%.

In other words, the VLF voltage shape is not allowed to be highly distorted so as to not affect reproducibility and the testing results. The truesinus® technology produces a sinewave with less than 0.5% distortion. The below image comparing the truesinus® voltage wave shape to a competitor’s VLF voltage shape clearly shows the amount of distortion that could affect testing results.


Due to its digital generation, the truesinus® wave shape is independent of the load tested. This becomes particularly important when conducting VLF tan delta testing. No distortion is required so that the most accurate tan delta values can be measured. The deviations (delta) between the ideal 90° phase shift of voltage and current are extremely small, and when distortion of the sine wave is present, false values can be given. The below image will show that if a voltage or current wave is distorted even close or above 5%, the tan delta results can be very erratic and highly misleading. As a result, the load-independent truesinus® voltage generation allows for the most accurate tan delta results to be measured on the market.


Overview of the advantages:


  • Provides a precise basis for significant and reproducible cable tests or condition evaluation with tan delta or partial discharge measurements
  • Fully symmetrical waveform, meaning no long-term space charges can be created in XLPE cables
  • Independent of the load during testing – no distortion of the waveform
  • Allows non-destructive VLF testing and condition evaluation of high voltage cables in compliance with VDE, IEC, and IEEE 400 standards
  • Simultaneous measurements, such as monitored withstand tests (MWT) or Full MWT can be conducted
  • Sinusoidal waveform mimics power frequency


See our high voltage VLF testers          


See our VLF tan delta testers

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