. Electric railway journal . connection was made be-tween these grounds and the track rails. In addition to these arresters on the poles, aluminumcell arresters are installed in the substation on thepositive busbars and on each feeder. No trouble what-ever has been experienced from lightning, although anunusually large number of severe thunder storms oc-curred during the past summer. Sag, Tension and Temperature Calculations to determine the strength required ofthe messenger and contact wires, and the sags andtensions at different temperatures, were made in thefollowing way: As the catenary is
. Electric railway journal . connection was made be-tween these grounds and the track rails. In addition to these arresters on the poles, aluminumcell arresters are installed in the substation on thepositive busbars and on each feeder. No trouble what-ever has been experienced from lightning, although anunusually large number of severe thunder storms oc-curred during the past summer. Sag, Tension and Temperature Calculations to determine the strength required ofthe messenger and contact wires, and the sags andtensions at different temperatures, were made in thefollowing way: As the catenary is very flat, the error in the use ofthe equation of a parabola rather than the true cate-nary, is well within the limits of error made in theerection of the line. T = s = L + TsMA IT E (1) .(2).(3) T = tension in pounds w = weight per foot in pounds L = length of span in feet y = sag in feet s = length of wire in feet E = elongation in feet, due to stress onlyM = modulus of elasticityA = area of cross-section in square inches. CANADIAN NORTHERN OVERHEAD CONSTRUCTION-SUPPORT IN MONTREAL TUNNEL -MESSENGER To determine the sags and corresponding tensionsat certain temperatures under different conditions ofloading, it is necessary first to assume as a workingbasis the sag desired at normal temperature, usually70 deg. Fahr. As an example of how the calculationswere carried out we will take the y2-in. steel messengerand figure the sags and stresses for different loads. Normal temperature i 70 deg. Fahr. Sag at normal temperature 20 in. Span length 150 ft. Weight per foot, messenger, contact wire and hangers lb. Assumed ice load, per foot lb. Assumed wind load, per square foot 9 1b. Area cross-section of messenger sq. in. Modulus of elasticity of messenger 26 X 10 From equation 1 in the preceding column, the tensionunder normal conditions is: wV _ X 1502 T = 2100 lb. 8 X 1-67 The length of the messenger at normal temperature andunder normal load is found from equati
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