负载运行的变压器及直流电机导论

资料简介：

　　The Transformer on load﹠Introduction to DC MachinesThe Transformer on load
　　It has been shown that a primary input voltage can be transformed to any desired open-circuit 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 ampere-turns 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 ampere-turns nearly cancel the whole of the secondary ampere-turns. This being so, the mutual flux suffers only a slight modification and requires practically the same net ampere-turns as on no load. The total primary ampere-turns are increased by an amount necessary to neutralize the same amount of secondary ampere-turns. In the vector equation,; alternatively, . At full load, the current is only about 5% of the full-load 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, .
　　负载运行的变压器及直流电机导论
　　负载运行的变压器
　　通过选择合适的匝数比，一次侧输入电压可任意转换成所希望的二次侧开路电压。可用于产生负载电流，该电流的幅值和功率因数将由而次侧电路的阻抗决定。现在，我们要讨论一种滞后功率因数。二次侧电流及其总安匝将影响磁通，有一种对铁芯产生去磁、减小和的趋向。因为一次侧漏阻抗压降如此之小，所以的微小变化都将导致一次侧电流增加很大，从增大至一个新值。增加的一次侧电流和磁势近似平衡了全部二次侧磁势。这样的话，互感磁通只经历很小的变化，并且实际上只需要与空载时相同的净磁势。一次侧总磁势增加了，它是平衡同量的二次侧磁势所必需的。在向量方程中，，上式也可变换成。满载时，电流只约占满载电流的5%，因而近似等于。记住，近似等于的输入容量也就近似等于输出容量。