Transient grounding performance of metal sheathed power cables

Power systems often use coated and/or uncoated metallic sheathed cables for medium and low voltage distribution. The metallic sheaths of such cables are connected to the grounding systems and may have significant grounding effects. In case of uncoated metallic sheathed cables they act as extended grounding electrodes while coated cables connect different grounding systems at transformer stations and customer premises. This usually improves the grounding conditions at the source transformer station but potentially dangerous voltages might be transferred to other locations. This paper analyses the lightning current distribution between the local grounding system, stoked by lightning, and connected cable metal sheaths. It is shown that after the first tens of microseconds local grounding system loses its function and cables take away nearly all lightning current.