. Determination of the ratio of transformation and of the phase relations in transformers . Ratio and Phase of Transformers. 23 CURRENT TRANSFORMERS. The currents in the primary and secondary of a series trans-former may be determined by a dynamometer in each circuit, ofthe type aheady described ° in this bulletin. They are astatic,wound on frames of mahogany, have field coils which are woundwith stranded wire (for the higher ranges), air damping, and thedeflections are read with telescope and circular scale. As shownin the article cited, after being calibrated on direct current theseinstrumen
. Determination of the ratio of transformation and of the phase relations in transformers . Ratio and Phase of Transformers. 23 CURRENT TRANSFORMERS. The currents in the primary and secondary of a series trans-former may be determined by a dynamometer in each circuit, ofthe type aheady described ° in this bulletin. They are astatic,wound on frames of mahogany, have field coils which are woundwith stranded wire (for the higher ranges), air damping, and thedeflections are read with telescope and circular scale. As shownin the article cited, after being calibrated on direct current theseinstruments are correct for alternating currents of a wide range offrequency and any wave form. The current flows through the field coils of the dynamometerand through a standard resistance in series. The moving coil isconnected through a noninductive resistance of suitable value tothe terminals of the standard resistance. The deflection of theinstrument is a measure of the power expended in the standardresistance, and consequently is determined by the square of Fig. 9. To determine the phase relation between the currents in pri-mary and secondary, the two moving coils may be disconnectedfrom the standard resistances and connected in series v/ith eachother. They are supplied with current exactly in quadrature withthe primary current, so that there is no deflection of the dyna-mometer whose field coils are in the primary circuit. If the currentin the secondary circuit is not exactly reversed in phase with ^ E. B. Rosa, this Bulletin, 8, p. 43; 1907. Reprint No. 48. 24 Bulletin of the Bureau of Standards. Woi. 6. No. i. respect to the primary there will be a deflection in the second dyna-mometer, and this serves to measure the phase difference. Fig. 9 is a diagram of connections suitable for making bothmeasurements by simply throwing two switches 5^ and S^. T rep-resents the transformer, D^ and D^ the dynamometers, R^ and R^the standard resistances, r^ and rg resistances in
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