Design considerations for selection of High temperature low sag conductor for overhead lines

Indian Power System has made rapid strides in the past two decades and poised for phenomenal growth in coming years to make pace with the economic resurgence in the country. However, high population density, growth of habitation & infrastructure and increasing environmental concerns have thrown challenges for the planners and developers of power systems to deal with the right-of-way (ROW) constraints and to maximize the power output per ROW. Power Grid Corporation of India Ltd. (POWERGRID) in its endeavor for sustainable development of transmission network in the country has taken various initiatives involving new technologies/innovative solutions in this regard. High Temperature Low Sag Conductors (HTLS) offer an option of increasing the power transfer capacity of thermally challenged overhead transmission lines and are capable of being operated continuously at temperatures in the range of 150ºC-210ºC while exhibiting lower sag vis-à-vis conventional conductors. Because of higher temperature operation, these conductors can carry higher power (upto 2–2.5 times equivalent size conventional conductors) at nearly equivalent sag. Various types of HTLS conductors are being used by transmission utilities in different countries viz. INVAR, GAP, ACSS, ACCC, ACCR etc. Such conductors have been globally used for uprating of existing transmission lines thereby eliminating the need of constructing additional transmission lines along the same corridor and preserving the scarce ROW. POWERGRID has introduced the HTLS conductors in the country and adopted the same for re-conductoring of existing lines as well as for some of the new 400 kV lines by adopting twin HTLS conductors in place of quadruple/triple bundle conventional conductors, resulting in optimization of resources, efforts & cost.

Design and selection of appropriate HTLS conductor is an important exercise for both reconductoring and new line construction applications involving various design considerations depending upon case to case. The paper briefly highlights different type of HTLS conductors and covers important design considerations for selection of HTLS conductor for different applications. Salient features & parameters of HTLS conductors used by POWERGRID for different transmission line projects are also presented in the paper.