Excerpt from Transactions of the American Society of Civil Engineers, Vol. 61: December, 1908

For 140° variation Of temperature, the change in tension per square inch is 26 810 lb. In the former, and 21450 lb. In the latter case. To avoid this variation in the tension of the contact wire, an automatic adjustment Of its length has been adopted on the line, blankenese-ohlsdorf, near Hamburg, Germany, recently opened for traffic.

If the contact wire is firmly held by rigid suspenders without hinges, the sliding bow which rises between succeeding suspenders bends the wire in a rather sharp curve as it approaches them. At the suspenders this curve is convex downward. To prevent the jumping of the sliding bow at these curves, it must be very light, and the wire must be under high tension. At a speed of 75 miles per hour the Sliding bow, with suspenders 10 ft. Apart, must make eleven complete up-and-down oscillations per second. With such rapid oscillations, even if they are Of very small amplitude, it is very difficult to prevent jumping and sparking; it is impossible, without springs between the bow and its heavy supporting frame, unless the bow itself is a Spring.

The bending strains in the wire at the suspenders are also Objectionable. To avoid large deflection of the contact wire by the pressure of the sliding how, its minimum tension in summer must be considerable. The tension in winter is then very large. To this must be added the bending strains arising from the deformations caused by wind pressure, changes of temperature, and the pressure Of the slid ing bow. At high speed the latter is very variable because the bow oscillates rapidly. The consequent bending strains in the contact wire are greatly reduced, in the blankenese-ohlsdorf line, by the use of a supplementary steel wire some distance above and parallel with the copper contact wire. The contact wire is hung by loops, 3 m. Apart, from this steel wire, and can rise at these loops, thus permitting the wave raised by the sliding bow to pass unhindered.

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