The effect of an underground to overhead transition point on the specification of sheath voltage limiters in underground networks

Sheath voltage limiter (SVL) specification is of vital importance for the protection of any underground cable system. This paper outlines the effects of an underground to overhead transition point on specifying the minimum requirements for SVLs on the underground system. The paper also details additional considerations for designers when specifying SVLs during the design phase of new installations. In particular this paper demonstrates the effect of overhead mutual impedance between the earth return path and the faulted phase and the effect of fault position on the transition point earth potential rise (EPR), and the corresponding effect this has on the SVLs in the underground section. Extensive modelling of the system has been undertaken in EMTP-RV and the results compared with field injection tests in order to illustrate the model´s accuracy and limitations.