【正文】 etizing action on has caused the changes on the primary side which led to the establishment of primary leakage flux.If a low enough leading power factor is considered, the total secondary flux and the mutual flux are increased causing the secondary terminal voltage to rise with load. is unchanged in magnitude from the no load condition since, neglecting resistance, it still has to provide a total back . equal to . It is virtually the same as , though now produced by the bined effect of primary and secondary ampereturns. The mutual flux must still change with load to give a change of and permit more primary current to flow. has increased this time but due to the vector bination with there is still an increase of primary current.Two more points should be made about the figures. Firstly, a unity turns ratio has been assumed for convenience so that . Secondly, the physical picture is drawn for a different instant of time from the vector diagrams which show , if the horizontal axis is taken as usual, to be the zero time reference. There are instants in the cycle when primary leakage flux is zero, when the secondary leakage flux is zero, and when primary and secondary leakage flux is zero, and when primary and secondary leakage fluxes are in the same sense.The equivalent circuit already derived for the transformer with the secondary terminals open, can easily be extended to cover the loaded secondary by the addition of the secondary resistance and leakage reactance.Practically all transformers have a turn’s ratio different from unity although such an arrangement is sometimes employed for the purposes of electrically isolating one circuit from another operating at the same voltage. To explain the case where the reaction of the secondary will be viewed from the primary winding. The reaction is experienced only in terms of the magnetizing force due to the secondary ampereturns. There is no way of detecting from the primary side whether is large and small or vice versa, it is the product of 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。 for convenience we shall continue to assume a sinusoidal fluxdensity wave in the air gap. The torque can then be found from the magnetic field viewpoint. The torque can be expressed in terms of the interaction of the directaxis airgap flux per pole and the spacefundamental ponent of the armature . wave . With the brushes in the quadrature axis, the angle between these fields is 90 electrical degrees, and its sine equals unity. For a P pole machine In which the minus sign has been dropped because the positive direction of the torque can be determined from physical reasoning. The space fundamental of the saw tooth armature . wave is 8/ times its peak. Substitution in above equation then gives Where =current in external armature circuit。 ., the machine may supply its own excitation. The method of excitation profoundly influences not only the steadystate characteristics, but also the dynamic behavior of the machine in control systems.The connection diagram of a separately excited generator is given. The required field current is a very small fraction of the rated armature current. A small amount of power in the field circuit may control a relatively large amount of power in the armature circuit。可用于產(chǎn)生負載電流，該電流的幅值和功率因數(shù)將由而次側(cè)電路的阻抗決定。增加的一次側(cè)電流和磁勢近似平衡了全部二次側(cè)磁勢。滿載時，電流只約占滿載電流的5%，因而近似等于。然而此時卻存在磁通的重新分配，由于隨的增加而增加，互感磁通分量已經(jīng)減小。這樣，二次側(cè)端電壓降至，它可被看成兩個分量，即，或者向量形式。如果我們討論一個足夠低的超前功率因數(shù)，二次側(cè)總磁通和互感磁通都會增加，從而