CHAPTER XVIII.
POLE LINES FOR POWER TRANSMISSION.
Long transmission lines should follow the most direct routes between generating and sub-stations as far as practicable. The number of poles, cross-arms, and insulators increases directly with the length of line, and the weight of conductors with the square of that length, other factors remaining equal. Every material deviation from a straight line must therefore be paid for at a rather high rate.
Distribution lines necessarily follow the public streets in order to reach consumers, but the saving of the cost of a private right of way and ease of access are the main considerations which tend to keep transmission lines on streets and highways. Except in very rough or swampy country, the difficulty of access to a pole line on a private right of way is not a serious matter and should be given but little weight. The cost of a private right of way may be more important, and should be compared with the additional cost of the pole line and conductors if erected on the public highway. In this additional cost should be included any items for paving about the poles, extra pins, insulators, and guys made necessary by frequent turns in the highway, and the sums that may be required to secure the necessary franchises. There is also the possible contingency of future legislation as to the voltage that may be maintained on wires located over public streets. These considerations taken together give a strong tendency to the location of long transmission lines on private rights of way, especially where the amount of power involved is great and the voltage very high.
A transmission line 80.3 miles in length recently erected between Rochester and Pelham, N. H., by way of Portsmouth, where the generating station is located, to feed an electric railway system, operates at 13,200 volts and is mainly located on private rights of way. Deeds conveying the easements for this right of way provide that all trees or branches within one rod on either side of the line may be cut away. The transmission line between Niagara Falls and Buffalo, about twenty-three miles long and operating at 22,000 volts, is largely on a private way thirty feet wide.
Fig. 80.—Transmission Line of New Hampshire Traction Company over Hampton River Bridge, 4,623 Feet Long.