The pilot reported he had completed one line-pull in the helicopter and had gone back to the landing zone to refuel. After refueling, the pilot flew to the puller machine that was now at another structure. The rope was hooked up by the linemen as normal, but the hydraulic fluid had frozen on the puller machine and it was inoperative. The line was then unhooked by the linemen and the pilot was waved off. The pilot returned to the landing zone to wait for the puller machine to be repaired. After several minutes, the pilot heard the puller operator radio that the machine was operational, and he took off to head back to the structure. He received a second radio call that the machine was not ready, and the pilot turned and started back to the landing zone again. The pilot was concerned that the helicopter would need to be refueled again since pulls typically take about an hour. While flying parallel to the power lines and descending for landing at the fuel truck, he looked at the instrument panel timer to determine the fuel burned. As he looked back outside the helicopter, he saw the middle phase straw line and then felt the main rotor blades impact the straw line about 150 ft agl. The pilot reported the straw line is a 3/8-inch steel wire that is somewhat rusted and difficult to see in most lighting conditions. The pilot then landed near the fuel truck uneventfully. Three of the six main rotor blades were substantially damaged. The pilot reported there were no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation.