High-tension transmission lines

The relation between distance and voltage is well known. The past ten or a dozen years have witnessed a steady advance in the voltages in commercial use. Additions from the experimental and undeveloped regions of high voltage have been conquered and brought into the domain of commercial service. The line between that which is practicable, and that which is indefinite and uncertain, has continually advanced. Each increase in voltage introduces new problems, reveals new classes of phenomena and presents difficulties more complex. Problems in construction and design and installation of apparatus; problems in insulators and line construction; problems in switching, controlling and measuring current; problems in lightning and static protection have been presented and solved with each advance in voltage. It has not been so many years since 100 or 200 kW. to be transmitted 20 or 30 miles at 10,000 volts, was considered a somewhat remarkable undertaking. The progress in high ´tension transmission is indicated by the transformer statistics of one of the large manufacturing companies. Transformers for 10,000 volts and over have been built during the past twelve years. Units recently built have three times the output of the largest transformers of five years ago. The aggregate output has been over a million kilowatts. The average kilowatt output per month during the past year is equal tJ the total output during the first seven years. The output of the past two years has exceeded that of the preceding ten years.