Sheath Voltage Limiter

Sheat Voltage Limiter (SVL)

In high-voltage underground power transmission systems, Sheath Voltage Limiters (SVLs) are widely used to control sheath voltages and to protect the system against overvoltage. SVLs are passive protective devices, typically consisting of zinc oxide (ZnO)–based varistors, designed to limit the potential differences between the cable sheath and earth, particularly during transient conditions and lightning impulses.

Under normal operating conditions, these devices exhibit high impedance, allowing only negligible leakage current to flow and remaining electrically passive within the system. When the sheath voltage exceeds a defined threshold, the SVL transitions to a low-impedance state and safely discharges the excess energy to ground. In this way, both the cable sheath and the connected equipment are effectively protected against sudden voltage surges.

SVLs are not continuously operating components; rather, they are non-linear, self-restoring devices that become active only during momentary overvoltage events and return to their insulating state once normal conditions are restored.

EMELEC SVL – SL (Station Low) – Class 2

This series is manufactured in our own production facilities, with all manufacturing and quality control processes carried out in accordance with our company’s standards.

For EMELEC SVL – SL products, type tests performed by CESI LAB (KEMA Laboratories) including:

* Operating duty test.

* Short-circuit test.

* Heat dissipation test.

* Insulation withstand test.

* Power-frequency voltage versus time test.

* Residual voltage test.

* Test to verify long-term stability under continuous operating voltage.

* Test to verify repetitive charge transfer rating (Qrs).