Using computer software to carry out various short-circuit operations is simpler, faster and less error. Because of the accuracy of manual calculation, the resistance of generator, transformer and transmission line and the excitation current of transformer are ignored in the equivalent circuit, so the load is estimated approximately. In the calculation of standard parameters, the difference between the rated voltage of each component and the average rated voltage of the corresponding voltage level is ignored, and it is considered that the transformer ratio is equal to the ratio of the average rated voltage of its corresponding side, that is, all components are only represented by reactance, which simplifies the circuit but also brings errors.