In the period 2003-2011, lightning over-voltages accounted for about 47% of the total number of distribution transformer failures observed in the service area ofAES Sul, a power company that operates in the state of R...In the period 2003-2011, lightning over-voltages accounted for about 47% of the total number of distribution transformer failures observed in the service area ofAES Sul, a power company that operates in the state of Rio Grande doSul, in South Brazil. This paper presents the results of an investigation on the influence of the distance between transformer and MV arresters on the surges at the transformer windings caused by direct strikes to the MV network. The analysis, performed through simulations using the Alternative Transients Program, shows that in general higher voltages are produced by subsequent strokes. Although in relation to the primary side the surges transferred to the secondary are much less affected by the distance between transformers and primary arresters, such distance should always be kept as short as possible in order to reduce the probability of occurrence of transformer failures due to over-voltages at the MV bushings.展开更多
This paper presents an analysis of 64 lightning‐induced voltage waveforms recorded in an experimental system implemented in the campus of the University of São Paulo,Brazil.The voltages were measured on a 10 m h...This paper presents an analysis of 64 lightning‐induced voltage waveforms recorded in an experimental system implemented in the campus of the University of São Paulo,Brazil.The voltages were measured on a 10 m high,2.7 km long un‐energized overhead line consisting of two conductors installed on 6 m crossarms.One of the conductors had surge arresters,while the other one was left unprotected.Strictly speaking,all the recorded voltages on the unprotected conductor were bipolar,but in many cases only one semi‐cycle could be considered important for practical purposes.Different criteria are discussed for the determination of the waveshape parameters,which may differ signifi-cantly from those of the standard lightning impulse voltage(1.2/50μs).Based on the proposed criterion for classifying the induced voltages,unipolar waveforms accounted for 67%of the total and,except for one case,all of them had positive polarity.The median values of the front time and time‐to‐half‐value were,respectively,5.2μs and 15.8μs.Bipolar waveforms were 33%of the total and in approximately 62%of the cases the first semi‐cycle was of positive polarity.In 91%of the cases the voltage peak occurred either in the first or the second semi‐cycle.展开更多
文摘In the period 2003-2011, lightning over-voltages accounted for about 47% of the total number of distribution transformer failures observed in the service area ofAES Sul, a power company that operates in the state of Rio Grande doSul, in South Brazil. This paper presents the results of an investigation on the influence of the distance between transformer and MV arresters on the surges at the transformer windings caused by direct strikes to the MV network. The analysis, performed through simulations using the Alternative Transients Program, shows that in general higher voltages are produced by subsequent strokes. Although in relation to the primary side the surges transferred to the secondary are much less affected by the distance between transformers and primary arresters, such distance should always be kept as short as possible in order to reduce the probability of occurrence of transformer failures due to over-voltages at the MV bushings.
文摘This paper presents an analysis of 64 lightning‐induced voltage waveforms recorded in an experimental system implemented in the campus of the University of São Paulo,Brazil.The voltages were measured on a 10 m high,2.7 km long un‐energized overhead line consisting of two conductors installed on 6 m crossarms.One of the conductors had surge arresters,while the other one was left unprotected.Strictly speaking,all the recorded voltages on the unprotected conductor were bipolar,but in many cases only one semi‐cycle could be considered important for practical purposes.Different criteria are discussed for the determination of the waveshape parameters,which may differ signifi-cantly from those of the standard lightning impulse voltage(1.2/50μs).Based on the proposed criterion for classifying the induced voltages,unipolar waveforms accounted for 67%of the total and,except for one case,all of them had positive polarity.The median values of the front time and time‐to‐half‐value were,respectively,5.2μs and 15.8μs.Bipolar waveforms were 33%of the total and in approximately 62%of the cases the first semi‐cycle was of positive polarity.In 91%of the cases the voltage peak occurred either in the first or the second semi‐cycle.
