电气自动化专业外文文献及翻译---短路电流-电气类(编辑修改稿)

电气自动化专业外文文献及翻译---短路电流-电气类(编辑修改稿)内容摘要：

e can now reach the following conclusions:  The short circuit current always has a decaying DC aperiodic ponent in addition to the stationary AC periodic ponent.  The magnitude of the short circuit current depends on the operating angle of the current. It reaches a maximum at c = 90 (purely inductive load). This case serves as the basis for further calculations.  .The short circuit current is always inductive. Methods of short circuit calculation The equivalent voltage source will be introduced here as the only effective voltage of the generators or work inputs for the calculation of short circuit currents. The internal voltages of generators or work inputs are short circuited, and at the position of the short circuit (fault position) the value ( is used as the only effective voltage (Figure ).  The voltage factor c [5] considers (Table ):  The different voltage values, depending on time and position  The step changes of the transformer switch  That the loads and capacitances in the calculation of the equivalent voltage source can be neglected  The subtransient behavior of generators and motors  This method assumes the following conditions:  The passive loads and conductor capacitances can be neglected  The step setting of the transformers do not have to be considered  The excitation of the generators do not have to be considered  The time and position dependence of the previous load (loading state) of the work does not have to be considered Fig. : Network circuit with equivalent voltage source a) threephase work, b) equivalent circuit in positive sequence system Superposition method The superposition method is an exact method for the calculation of the short circuit currents. The method consists of three steps. The voltage ratios and the loading condition of the work must be known before the occurrence of the short circuit. In the first step the currents, voltages and the internal voltages for steadystate operation before onset of the short circuit are calculated (Figure ). The calculation considers the impedances, power supply feeders and node loads of the active elements. In the second step the voltage applied to the fault location before the occurrence of the short circuit and the current distribution at the fault location are determined with a negative sign (Figure ). This voltage source is the only voltage source in the work. The internal voltages are shortcircuited. In the third step both conditions are superimposed. We then obtain zero voltage at the fault location. The superposition of the currents also leads to the value zero. The disadvantage of this method is that the steadystate condition must be specified. The data for the work (effective and reactive power, node voltages and the step settings of the transformers) are often difficult to determine. The question also arises, which oper。