The Study Of Lightning Protection Performance For 500kV Parallel-Four-Circuit-Transmission-Lines

With power demand being continuously increased in our country, multi-circuittransmission line on the same tower is more widespread used. More electric power can betransmitted on multi-circuit transmission line, so it takes up a more important place in powersystem. The tower of multi-circuit transmission line, which is higher than the tower ofsingle-circuit transmission line, is more easily struck by lightning. Therefore, the problem oflightning protection is more serious and the study of lightning protection is even moreimportant. Recently, 220 kV four-circuit transmission line on the same tower and the voltagelevel which bellows it have been used widely in our country, whose performance of lightningprotection is recognized in operation. But 500 kV four-circuit transmission line on the sametower is developed in the preliminary stage, a great deal of problems exist and detailedcalculation and analysis is lacked for both performance of lightning protection andinfluencing factor. Therefore, it is essential to research this field.Lightning tipping on extra-high transmission line is mainly caused by shielding failureand back flashover. The calculation of them in regulations are only suited for single-circuittransmission line on low tower. For 500 kV four-circuit transmission line on the same tower,the calculation method in the regulations is not suited any more and the real lightningwithstand level of transmission line can not be calculated. Therefore, new model and methodmust be taken to calculate the performance of lightning protection for 500 kV four-circuittransmission line on the same tower.For 500kV four-circuit transmission line, two kinds of tower model are taken for examplebased on actual line. And calculation model of lightning protection suited for 500 kVfour-circuit transmission line is constructed, which can precisely reflect the process oflightning current transmitting on the tower. Based on ATP/EMTP, two kinds of model indifferent situation are analysed and calculated, and the performances of lightning protectionare found out. To ensure the accuracy of the calculation for shielding failure, the shieldingcontribution of shielding lines to phase conductor is considered, as well as the contributionbetween each line and the ground to phase conductors. In calculation of brake strikingperformance, multi-surge impedance model is used to describe the multi-circuit lines tower. Itis calculated particularly that the critical current required for back flashover of thismulti-circuit lines under different resistance values and phase conductors sequence. In orderto analyze improved solution for lightning protection of lines and provide guidance for designof projects, many means like changing types of tower head , changing phase conductors sequence, changing tower shielding lines bracket, changing shielding angle, increasingtriggering lightning rods are taken.