Performance Analysis for the Innovative 400 kV Double-Circuit 'Y' Composite Tower Under Backflashover Conditions

Nowadays, the increasing demand for power transmission capacity, because of the transition towards renewable energy sources, results in the realization of new overhead line and underground cable connections. Especially for new overhead line projects, Transmission System Operators are facing challenges related to a) acquiring permissions for new Right-of-Ways and b) the visual impact due to the public opposition to new overhead lines. Therefore, the need for compact tower designs, which should also meet the environmental impact requirements, is significantly increased. Until now, such designs are based on steel and concrete. However, in the recent years, focus has also been given on composite-based transmission towers, which could provide a remarkable alternative solution for fulfilling the above-mentioned requirements. Towards this direction, BYSTRUP designed the innovative 2x400 kV ‘Y’ composite tower, under the ‘Power Pylons of the Future (PoPyFu)’ project in Denmark; this tower design is characterized by its significantly reduced footprint, i.e. 22.5 meters high. The latter is mainly because no insulator strings are used, by utilizing each composite cross-arm as an insulator. One important design parameter regards the performance of the composite tower against lightning related outages. The lightning performance considers outages due to a) shielding failure flashovers and b) backflashovers. In [1], the performance of the 400 kV double-circuit ‘Y’ pylon against shielding failures and the optimal position of the shield wires were studied and verified by means of small-scale experimental tests. In this paper, focus was given on studying the performance of the ‘Y’ pylon against backflashovers. As starting points, the backflashover analysis was performed based on the modified tower design and on a conceptual earthing design. The results of the study were used to draw basic conclusions and give recommendations for further investigations related to the tower design.