【正文】 current and turns which causes the reaction. Consequently, a secondary winding can be replaced by any number of different equivalent windings and load circuits which will give rise to an identical reaction on the primary .It is clearly convenient to change the secondary winding to an equivalent winding having the same number of turns as the primary. With changes to , since the are proportional to turns, which is the same as .For current, since the reaction ampere turns must be unchanged must be equal to .. .For impedance, since any secondary voltage bees , and secondary current bees , then any secondary impedance, including load impedance, must bee . Consequently, and .If the primary turns are taken as reference turns, the process is called referring to the primary side.There are a few checks which can be made to see if the procedure outlined is valid.For example, the copper loss in the referred secondary winding must be the same as in the original secondary otherwise the primary would have to supply a different loss power. Must be equal to . does in fact reduce to .Similarly the stored magnetic energy in the leakage field which is proportional to will be found to check as . The referred secondary .The argument is sound, though at first it may have seemed suspect. In fact, if the actual secondary winding was removed physically from the core and replaced by the equivalent winding and load circuit designed to give the parameters ,and , measurements from the primary terminals would be unable to detect any difference in secondary ampereturns, demand or copper loss, under normal power frequency operation.There is no point in choosing any basis other than equal turns on primary and referred secondary, but it is sometimes convenient to refer the primary to the secondary winding. In this case, if all the subscript 1’s are interchanged for the subscript 2’s, the necessary referring constants are easily found。The Transformer on load﹠Introduction to DC MachinesThe Transformer on loadIt has been shown that a primary input voltage can be transformed to any desired opencircuit secondary voltage by a suitable choice of turn’s ratio. is available for circulating a load current impedance. For the moment, a lagging power factor will be considered. The secondary current and the resulting ampereturns will change the flux, tending to demagnetize the core, reduce and with it . Because the primary leakage impedance drop is so low, a small alteration to will cause an appreciable increase of primary current from to a new value of equal to . The extra primary current and ampereturns nearly cancel the whole of the secondary ampereturns. This being so, the mutual flux suffers only a slight modification and requires practically the same net ampereturns as on no load. The total primary ampereturns are increased by an amount necessary to neutralize the same amount of secondary ampereturns. In the vector equation,。 alternatively, . At full load, the current is only about 5% of the fullload current and so is nearly equal to. Because in mind that , the input kVA which is approximately is also approximately equal to the output kVA, .The physical current has increased, and with in the primary leakage flux to which it is proportional. The total flux linking the primary, is shown unchanged because the total back ., （）is still equal and opposite to . However, there has been a redistribution of flux and the mutual ponent has fallen due to the increase of with . Although the change is small, the secondary demand could not be met without a mutual flux and . alteration to permit primary current to change. The net flux linking the secondary winding has been further reduced by the establishment of secondary leakage flux due to , and this opposes . Although and are indicated separately, they bine to one resultant in the core which will be downwards at the instant shown. Thus the secondary terminal voltage is reduced to which can be considered in two ponents, . or vectorially . As for the primary, is responsible for a substantially constant secondary leakage inductance . It will be noticed that the primary leakage flux is responsible for part of the change in the secondary terminal voltage due to its effects on the mutual flux. The two leakage fluxes are closely related。 . ,。 capacitance effects must be taken into account whenever the rate of change of voltage would give rise to appreciable capacitance currents,. They are important at high voltages and at frequencies much beyond 100 cycles/sec. A further point is not the only possible equivalent circuit even for power frequencies .An alternative , treating the transformer as a threeor fourterminal network, gives rise to a representation which is just as accurate and has some advantages for the circuit engineer who treats all devices as circuit elements with certain transfer properties. The circuit on this basis would have a turns ratio having a phase shift as well as a magnitude change, and the impedances would not be the same as those of the windings. The circuit would not explain the phenomena within the device like the effects of saturation, so for an understanding of internal behavior.There are two ways of looking at the equivalent circuit:(a) viewed from the primary as a sink but the referred load impedance connected across ,or(b) Viewed from the secondary as a source of constant voltage