Transient EMF induced in LV cables due to wind turbine direct lightning strike

This paper presents a novel, easy to use, engineering method for determining the transient electromotive force (EMF) induced in low-voltage (LV) cables, connecting the wind turbine with a near-by transformer, in the event of direct lightning strike into the top of the wind turbine tower. Proposed method is based on the application of the travelling wave analysis onto the system consisted of wind turbine tower, earthing system of wind turbine, earthing system of near-by transformer station and LV cables connecting the wind turbine with associated transformer. Hence, this design gives rise to a complex, mutually connected, earthing system. Direct lightning strike to the wind turbine initiates a travelling wave process in the system consisted of lightning channel, wind turbine tower and earthing system of the wind turbine. Due to the transient nature of the observed phenomenon, current and voltage states at the earthing system as well as in the associated low-voltage cables are formed through the propagation and reflection of the accompanying travelling waves. Transient EMF induced in LV cables could endanger cable main insulation and insulation of the associated transformer LV winding. Developed theory is subsequently applied on the concrete wind turbine example.