As shown if RL4 closes then the input goes to the 160V tap and the output comes from the 240V. if the mains voltage rises, RL1 changes over and the input is applied to the 190V tap. if the mains rises more RL3 changes over and the input goes to the 215V tap.
RL4 is a safety relay, it should only be closed when all the other relays have finished switching. If you switched the unit on without it, the incoming mains, which should be 230V would be applied to the 160V tap so the output voltage would be 240/160 X 230 ~345 V until RL1 switched over.
Frank