Damped Oscillatory Waves (DOWs) are disturbances taking place in environments like power stations and can potentially affect equipment installed in the vicinity of disturbance sources. They can propagate along cables and affect equipment from circuits situated nearby, or generate magnetic fields. Testing principles, methods and levels for immunity against damped oscillatory waves propagated along cables are provided in IEC 61000-4-18, whereas testing for immunity against damped oscillatory magnetic fields is provided in IEC 61000-4-10.
The phenomena described in IEC 61000-4-18 refers to repetitive damped oscillatory waves that occur in power distribution stations or similar environments. Air-insulated power stations generate slow damped oscillatory waves (with frequencies 100 kHz and 1 MHz, and a typical source impedance of 200 Ω) and gas-insulated power stations generate fast damped oscillatory waves (with frequencies 10 MHz and 30 MHz and a source impedance of 50 Ω). A damped oscillatory wave is presented in the figure below.
Despite the fact that the phenomenon described in IEC 61000-4-12 is also a damped oscillation, this is actually a ring wave and is not to be confused with DOW described in the IEC 61000-4-18. Firstly, the ring wave is not a repetitive waveform, and not specific to power stations. Ring wave is a phenomenon specific to normal power grids and their environments, just like burst (IEC 61000-4-4) and surge (IEC 61000-4-5). This is also reflected by the characteristic impedance of a ring wave disturbance source, i.e. 12 Ω and 30 Ω.
How to conduct damped oscillatory wave testing?
EMC PARTNER’s solution for conducted immunity tests against damped oscillatory waves is based on the modular generator DOW-CG1. The cost-effective solution allows flexible configuration of any test system according to specific needs.
The Slow DOW module of DOW-CG1 generator offers a yet unmatched test level of 5 kV at direct output, allowing custom tests for development purposes. Furthermore, the 5 kV capability guarantee reaching the test levels from IEC 61000-4-10 at both 100 kHz and 1 MHz.
The slow DOW disturbances can be coupled onto power lines with the three-phase internal CDN rated up to 3 x 690 V / 3 x 32 A AC and 500 V / 32 A DC. An automatic overcurrent protection is already built-in the generator. For applying slow DOW disturbances on control, communication or auxiliary lines, two CDNs are available: CDN-DOW-DATA-LF can be used for up to 8 unsymmetrical lines and CDN-DOW-DATA-HF18 can be used for up to 8 high speed (1 Gbps) symmetrical lines according to figures 13 and 14 from IEC 61000-4-18. A test setup for high-speed Ethernet lines is presented in the diagram below. Hence, Gigabit Ethernet lines can be now easily tested.
As a particularity, IEEE/ANSI C37.90.1 allows application of slow damped oscillatory waves on communication lines with a capacitive coupling clamp (IEC 61000-4-18 does not recommend this practice for slow DOW). This can be performed with the DOW-CG1 generator and CN-EFT1000 capacitive coupling clamp.
For fast damped oscillatory wave tests, the DOW-CG1 must be equipped with a fast DOW module. The internal three-phase CDN can be used for power lines (same capabilities as above). The application of fast DOW on communication and control lines can be performed with the help of CN-EFT1000 capacitive coupling clamp.
Finally, DOW-CG1 can be optionally equipped with an insulation test module up to 8 kV, in order to meet additional requirements from the product standard IEC 60255-27. This module allows the application of 1.2/50 μs voltage impulses with precise energy (0.5 joule) at specified levels.
The flexibility of DOW-CG1 solution, its comprehensive range of accessories and outstanding features turn it into a strategic asset for any testing laboratory.