Determination of the constants of instrument transformers . eck not requiring the use of a dynamometer was furnishedby the method mentioned above, of using a vibration galva-nometer as detector, and placing variable inductances in the twoparts of high resistance. This requires a simultaneous balance ofresistance and inductance. It is fully as sensitive as the dyna-mometer method. The values of ratio given by the two methodsagreed precisely, but the phase angles showed a discrepancy ofabout ^ While this difference is too small to have any prac-tical significance, it appeared as a constant di
Determination of the constants of instrument transformers . eck not requiring the use of a dynamometer was furnishedby the method mentioned above, of using a vibration galva-nometer as detector, and placing variable inductances in the twoparts of high resistance. This requires a simultaneous balance ofresistance and inductance. It is fully as sensitive as the dyna-mometer method. The values of ratio given by the two methodsagreed precisely, but the phase angles showed a discrepancy ofabout ^ While this difference is too small to have any prac-tical significance, it appeared as a constant difference, and wasthought to be due to a charging current into the galvanometer. In Figs. 5 to 9 are shown load curves of typical potential trans-formers, designed especially for use with measuring instruments,from different makers. The full-line curves are for noninductiveload, while the isolated points shown in some instances are for thehighly inductive load of the potential coil of a watthour meter, 288 Bulletin of the Bureau of Standards. [, No 10 15 20 25 30 WATTS LOAD 35 40 45 50 1 Fig. 5.—Potential transformer M^. Isolated points Pand R are phase angle and ratio plotted involt-amperes for inductive load, 20 per cent power factor.
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