Sheath current

A sheath current is an electric current that flows along the outer conductor (shield or sheath) of a cable. In coaxial cable and high-voltage cables, sheath currents can arise from differences in ground potential, electromagnetic coupling, or electrical faults. In cross-bonded high-voltage cables, the distribution of sheath currents along the sheath can indicate the health of the grounding system, with irregular distributions signaling possible faults.[1]

Shielding the coaxial cable acts as a Goubau line

Sheath currents may affect the performance of signal or power transmission and can induce electromagnetic interference in nearby circuits. In coaxial cables, differences in ground potential at the ends of the cable can create common-mode voltages superimposed on the useful signal, effectively acting as noise. Such currents are often associated with ground loops or improper grounding.[1]

Countermeasures against sheath currents

High-frequency signal lines may attenuate or prevent sheath currents using a sheath current filter which is applied to a coaxial cable in or near the device. In the simplest case, this is a ferrite bead, it includes the coaxial inner and outer conductor and acts as a common-mode choke. At the same time, a ferrite bead has a transformer effect, so that a useful signal is confirmed as differential-mode. To increase the inductance compared to the unwanted common mode signal component, the cable can also be repeatedly passed through or wound around the bead.

Sheath current filter for high-power lines

In addition, higher frequency signals are often used with a capacitive coupling filter. More information is available in the article sheath current filter.

With a balun, sheath currents can be avoided when a balanced line is connected to an unbalanced line. Without the use of baluns, sheath currents will occur on the unbalanced line. A use for this is the combination of a symmetric dipole antenna with a coaxial line.

USB cable with a ferrite bead as a sheath current filter

References

  1. ^ a b Li, Gen; Chen, Jie; Li, Hongze; Hu, Libin; Zhou, Wenjun; Zhou, Chengke (2023). "Detection of irregular sheath current distribution for diagnosis of faults in grounding systems of cross‑bonded cables". IEEE Access. 11: 68453–68461. doi:10.1109/access.2023.3292542.

Content Disclaimer

Informasi ini disarikan dari Wikipedia dan disajikan kembali untuk tujuan edukasi. Konten tersedia di bawah lisensi CC BY-SA 3.0. Kami tidak bertanggung jawab atas ketidakakuratan data yang bersumber dari kontribusi publik tersebut.

  1. The information displayed on this website is sourced in part or in whole from Wikipedia and has been adapted for the purpose of restating it. We strive to provide accurate and relevant information, however:
  2. There is no guarantee of absolute accuracy. Wikipedia is an open, collaborative project that can be edited by anyone, so information is subject to change.
  3. It is not intended to constitute professional advice. The content displayed is for informational and educational purposes only. For important decisions (e.g., medical, legal, or financial), please consult a professional.
  4. Content copyright. Wikipedia is licensed under the Creative Commons Attribution-ShareAlike License (CC BY-SA). This means that content may be reused with appropriate attribution and shared under a similar license.
  5. Responsible use. Any risk arising from the use of information from this website is entirely the responsibility of the user.