. Electric railway journal . assengers when the car was completely loaded. Thecars in question had a capacity with all heaters in fulloperation, of 27,000 per hour, while, when the carwas carrying eighty passengers, the total heat givenoff by them was about 24,000 per hour. March 13, 1915] ELECTRIC RAILWAY JOURNAL 515 Chart for Use in Transforming MotorSpeed Curves for Different Voltages* BY F. CASTIGLIONI, NEW YORK It is often necessary to calculate the speeds at which■a railway motor will run at one voltage when a speed-current curve for some other voltage is available. Ifthe m
. Electric railway journal . assengers when the car was completely loaded. Thecars in question had a capacity with all heaters in fulloperation, of 27,000 per hour, while, when the carwas carrying eighty passengers, the total heat givenoff by them was about 24,000 per hour. March 13, 1915] ELECTRIC RAILWAY JOURNAL 515 Chart for Use in Transforming MotorSpeed Curves for Different Voltages* BY F. CASTIGLIONI, NEW YORK It is often necessary to calculate the speeds at which■a railway motor will run at one voltage when a speed-current curve for some other voltage is available. Ifthe motor resistance is known this can be done, for anyvalue of current, by means of the formula:s, _ Et — IrTt ~ E1 — Tr where s, is the speed, from the curve corresponding tothe voltage Ex and the current /, and s2 is the calculatedspeed corresponding to E., and /. This formula simplystates that the speed, for any value of current, is pro-portional to the counter-emf. This formula can be used in plotting a chart like that. 3O0 SffO S60 B*0 tSO BOO /BO /SO *9C /BO /OO BO 60 40 BO CHART FOR THE TRANSFORMATION OF THE SPEED CURVEOF RAILWAY MOTORS FOR DIFFERENT VOLTAGES shown, by means of which the transformation can bemade very quickly. The chart consists of two parts: (1) a set of straightlines plotted between hot motor resistance and Ir dropfor a large number of current values; (2) a set ofcurves plotted between Ir drop and the speed ratios2/sJ or ( — Ir) -h (E1 — Ir), for a variety of voltageranges liable to be encountered in every-day work. Asthere is a definite Ir drop corresponding to each valueof / and a definite speed ratio corresponding to each set■of values of E„ E2 and /, the speed ratio can be quicklycalculated from the charts as follows: Use of the Charts To determine the speed ratio for, say, a voltage changefrom 600 to 450 volts at a current value of 280 amp fora motor having a hot resistance of ohm, we beginat the point on the hot resistanc
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