Complex sentence: Steam turbine powered line shafts were commonly used to drive paper machines for speed control reasons until economical methods for precision electric motor speed control became available in the 1980s; since then many have been replaced with sectional electric drives.
Split into simpler sentences: Steam turbine powered line shafts were commonly used to drive paper machines. Most paper machines used steam turbine-powered line shafts until the 1980s, since then many have been replaced with sectional electric drives.