analysis of reducing back flashover faults with surge arresters on 69/138 kV double circuit transmission lines due to direct lightning strikes on the shield wires'
a b s t r a c tThis paper proposes a modelling and simulation process for assessing the energy absorption capability of metal oxide varistor (MOV) surge arresters used for lightning protection of wind turbines electrical systems situated in wind farms, when exposed to multiple lightning strokes. A section of an existing wind farm, suitable for lightning transient overvoltage analysis is implemented in the Electromagnetic transients programme-Alternative transients programme (EMTP-ATP) environment and modelled as a test system for analysing the energy absorbed by the medium voltage surge arresters when multiple lightning strokes are terminated on one of the blade of the wind turbines. Two well-established sets of multiple lightning current parameters are employed in the EMTP-ATP simulations; the natural downward negative multiple lightning strokes recommended by CIGRE TB 549 (2013) and the downward positive multiple lightning strokes recommended by IEC 61400-24-2010 for lightning protection level one (LPL1). The results show that the subsequent stroke causes the surge arresters to absorbed less than ten percent additional energy compared to that of the first stroke. This comparative analysis could be found beneficial when designing lightning overvoltage protection system and for selecting the most cost effective and optimal energy absorption capabilities of the surge arresters for the intended wind farms.
a b s t r a c tThe significance of the median natural lightning currents on the energy handling capabilities of surge arresters employed in wind farms is investigated. The Electromagnetic Transient Program Alternative Transient Program (EMTP-ATP) was used to simulate direct lightning strikes to the blade of an existing wind turbine in order to determine the current discharged through the surge arresters and hence the energy absorbed by the surge arresters located at different wind turbines. The values of the energy handling capabilities of surge arresters are generally published in manufacturers' datasheets. Yet, the impact of the subsequent lightning strokes is usually ignored. Also, the published energy handling capabilities are based solely on standard waveforms. This contribution uses two sets of natural lightning current parameters measured on instrumented towers at Mount San Salvatore and Morro do Cachimbo, to simulate lightning strikes to the wind turbine blade. The results show that the influence of the subsequent strokes can be significant for the current discharged through the surge arresters and the subsequent energy absorbed, especially at the stricken turbine.
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