Complex sentence: There exists a 500 kV overhead powerline (with two circuits) crossing of the Yangtze River at Nanjing in China built in 1992 and which uses two 257 metre tall pylons built of reinforced concrete, which may be the tallest pylons built of concrete in the world.
Split into simpler sentences: There exists a 500 kV overhead powerline (with two circuits) crossing of the Yangtze River at Nanjing in China built in 1992. It uses two 257 metre tall pylons built of reinforced concrete, which may be the tallest pylons built of concrete in the world.