Abstract: Shenzhen substation is ultra-scale extending the NO.3 connecting transformer. 500 kV XLPE cable and GIB incoming feeder schemers of the NO.3 connecting transformer were analysed through techno-economic comparison in this paper. Compering to XLPE cable, GIB is more technically mature, superior performance and reliable. On the other side of life cycle cost (LCC), GIB schemer is economically feasible. The NO.3 connecting transformer incoming feeder finally adopt GIB schemer with length of 750 meters, its aerial installation path contains roof, wall, road and narrow area. Engineering experiences are summarized from three aspects of technical parameters, schemer design and foundation constructing. These experiences could be used for reference in other substation extending, where the tension space is too difficult to arrange and GIB is adopted.