Shield Transfer Impedance: What are the exact EMC performance parameters and screening effectiveness metrics for (N)TSCGECEWÖU 12/20kV individually screened medium-voltage flexible cables in industrial and VFD applications?
The shield transfer impedance (STI) for (N)TSCGECEWÖU 12/20kV cables with individual concentric copper screens is approximately 0.005–0.012 Ω/m at 50/60 Hz power frequency, representing the electrical impedance that coupling currents encounter as they attempt to penetrate the copper screen and reach the main conductor. At higher frequencies relevant to VFD variable switching (around 10 kHz), the STI increases slightly to approximately 0.008–0.015 Ω/m due to skin-effect limitations in the copper conductors. At even higher frequencies extending into the megahertz range (1–10 MHz) where harmonic emissions and EMI are most problematic, the STI rises further to approximately 0.02–0.08 Ω/m depending on the copper screen material properties and frequency-dependent conductor resistance. The shielding effectiveness, measured as the attenuation in decibels (dB) of external electromagnetic fields trying to couple energy into the cable conductors, is typically 60–80 dB at 100 kHz and remains above 40 dB even at 1 MHz, demonstrating excellent EMI rejection across the industrial frequency range. These metrics establish that individual concentric copper screens provide substantially superior EMC performance compared to traditional overall braided screens, particularly in reducing conducted emissions in VFD-driven machinery where rapid voltage switching and harmonic currents create severe electromagnetic stress on nearby control cables and sensitive electronic systems.