Starting currents of transformers : with special reference to transformers with silicon steel cores . tive direction, corresponding to point i in Fig. 3. The galvano-meter was then connected. Opening the circuit, the resulting deflectioncorresponded to a change of flux 1-2, reversing the current produceda change 2-3; opening it produced a change 3-4; again reversing it pro-duced a change 4-1, completing the loop. Fig. 5 shows the hysteresis loop and magnetization curves for thetransformer used for the oscillograms. It was obtained by the methodexplained above. As an example, is given the galva
Starting currents of transformers : with special reference to transformers with silicon steel cores . tive direction, corresponding to point i in Fig. 3. The galvano-meter was then connected. Opening the circuit, the resulting deflectioncorresponded to a change of flux 1-2, reversing the current produceda change 2-3; opening it produced a change 3-4; again reversing it pro-duced a change 4-1, completing the loop. Fig. 5 shows the hysteresis loop and magnetization curves for thetransformer used for the oscillograms. It was obtained by the methodexplained above. As an example, is given the galvanometer deflec-tions for amp. Table 2 Current Change Deflection = A X K 1-2 9-5 59-5 2-3 2 3-4 9-5 59-5 4-i 2 = Resid. Mag. 29-75 — 9-5= The saturation curve was carried up to 119 amp. It is seen thatat this point the curve has become a straight line, which means that theiron has become saturated, and the increase in flux is taking placeonly in the non-magnetic space between the iron and coil. Conse-quently, the curve can be extended O 90 /80° 270 760° -450° S40 630 Fig. 6. Rush of Current on Closing the Primary Circuit of Transformer closed at o° point of e. m. f. wave. Residual magnetism = + 20 X K. YENSEN STARTING CURRENTS OF TRANSFORMERS 15 9. Calculations.—The data needed for the calculations of themagnetizing current are as follows :1. Normal hysteresis loop; 2 Magnetization curve up to straight line relation; 3. Total effective voltage impressed upon the transformer circuit; 4. Total resistance of circuit; 5. Total inductance of circuit. Sine wave e. m. f. is assumed in these calculations. Equation (8),gives the relation: .(8) AS = -BmaxA(cos0)-|^/vtA0 assuming the circuit to have negligible inductance outside the trans-former.
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