KUNMING, Nov. 23 -- Southwest China's Yunnan Province has deployed unmanned aerial vehicles to replace humans in the arduous inspection of its 90,000-km power transmission lines, most of which are located in out-of-the-way mountains.

The mountainous border province has upgraded grids and extended power supplies to remote villages in the recent poverty reduction campaign, but it has suffered from a paucity of workers for power line inspection.

"To inspect 100 km of power lines (in Yunnan), it takes 20 days for human workers, but only four days for a drone," said Gerin Dingdru, a staff member of the Yunnan branch of China Southern Power Grid. He said the drones also spared workers from climbing transmission towers, reducing the risk of falls and electric shocks.

The drones are flown automatically, boasting an efficiency five to 10 times higher than flight missions requiring human operators, while the cost is more than halved, said Gerin Dingdru. This makes the practice particularly suitable for Yunnan's complex landscape and climate.

Since over 80 percent of Yunnan's power transmission lines are tucked away in high mountains and deep valleys, the power supplier company introduced drone inspections in 2014 but was plagued by a lack of competent operators. It has since 2017 worked on a route planning system and an automatic piloting system, which make automatic drone inspections possible.

The company said about 65 percent of power line inspections in Yunnan are now conducted by automatic drones.