Abstract
Outages of overhead power lines due to lightningstrokes are one of the main causes of shortages of electricsupplies and economic losses of power utilities. Pole-topmetal oxide arresters can protect distribution lines againstinduced over-voltages, but they can be destroyed in case ofdirect lightning stroke. Long Flashover Arresters (LFAs)have been developed and used successfully for this purposeand have no possibility of being destroyed because thecurrent flows externally along its surface. Since fieldexperience with 10 kV LFAs has been very successful, it wasdecided to work on developing 13.8 kV LFAs, consideringthat it is the predominant voltage level of overheaddistribution lines in Brazil and other countries. Theperformance of LFA for quenching and dielectric tests hasbeen investigated through laboratory tests under conditionsthat typically represent electrical energy distributionsystems. Details about these tests and their results arepresented in this paper. Information about their design andapplications are also shortly presented.
1 INTRODUCTION
Outages of overhead power lines due to lightning strokesare one of the main causes of shortages of electricsupplies and economic losses of power utilities. Widelyseparated pole-top metal oxide arresters can protect adistribution line against induced overvoltages. The mainproblem of using pole-top metal-oxide arresters is thatthey can be destroyed at direct lightning stroke to anoverhead line [1].In many countries, covered conductors are used fordistribution overhead lines. Such conductors have manybenefits comparing with bared conductors but there is aproblem of conductors burn down by power arc follow,which occurs after application of lightning overvoltageand flashover of insulator. Arcing horns or similardevices, which are used in some countries for protectionof covered conductors against conductors burn down, donot protect overhead lines from lightning outages.In Russia, for lightning overvoltage and conductor-burnprotection of 10 kV overhead lines, Long FlashoverArresters (LFAs) have been used for more than threeyears [2, 3]. The operating principle is based on extensionof the impulse flashover channel on the arrester surfacethrough the creeping discharge effect. Owing to a longflashover length, the power arc gets extinguished. Themain advantage of LFA is that current passes outside theapparatus, flowing along arrester surface. Therefore, thearrester cannot be destroyed by excessive current, even atdirect lightning stroke. LFA’s construction is rathersimple and reliable.There are several types of LFA under development. LFAof Loop type (LFA-L) is intended for protection ofoverhead lines against induced overvoltages. Principle ofoperation and its design are detailed in [1]. LFA-Ls arerecommended to be installed one arrester per pole withphase interlacing [4]. LFA of Module type (LFA-M) canprotect overhead lines against induced overvoltages anddirect lightning strokes as well. In latter case it should beinstalled in parallel to each insulator at a pole [3].Experimental exploitation of LFAs started in 1999 andduring last three years more than 80 thousands arresterswere installed in various utilities. Since field experiencewith 10 kV LFAs in Russia is very successful, it wasdecided to work on developing 13.8 kV LFAs,considering that it is the predominant voltage level ofoverhead distribution lines in Brazil and other countries.Lightning has been reported as being the main source ofoutages on distribution networks, corresponding to 30 to60 % of these system outage indexes. This is particularlyconfirmed in Brazil, which has a very high incidence oflightning strokes due to its ground dimension and intertropicallocation. For example, considering two Brazilianutility companies installed in a region with ground flashdensity in the range of 4 to 8 flashes/(km2.year), lightningwas associated with approximately 35% and 43% of thetotal number of outages monitored during 1998 to 2002.


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