Calculations > IEC 61363

First, nodes (or a node) have to be selected in order to start IEC 61363 calculation. After that the calculation can be started from the menu Calculate | IEC 61363.

Options

The following calculation options can be set in Options:

•Calculation times in periods of nominal frequency or in milliseconds. These are the moments in time, for which the short-circuit current is to be calculated.

•Three initialization options: initialization using nominal data (U0=Unom, I0=Inom), initialization by the loadflow calculation (U0=Uloadflow, I0=Iloadflow) and the calculation from no-load conditions (U0=Unom, I0=0). The choice of initialization option has influence on the internal e.m.f.’s of machines and on the resulting short-circuit currents. In case of initialization using loadflow calculation attention must be paid to the convergence of the loadflow in island mode (for more details see Island mode).

•Use Ikd parameter of synchronous machines: if this option is used, the steady-state short-circuit current is adjusted in such a way that it becomes equal to the data entered on tab Dynamic | IEC 61363 for respective machine. If Ikd of a synchronous machine is set to zero, then Ikd for this machine is calculated automatically.

•force Ikd of synchronous machines to at least 3xInom: in case this option is set, the steady-state short-circuit current is forced to be at least 3 times the nominal current for each synchronous machine. This is valid for the case of short-circuit at the generator terminals. With increase of (electrical) distance to the short-circuit point the short-circuit current decreases. The forcing of the steady-state short-circuit current (that represents the forcing of the field voltage/current of a synchronous generator) takes place only if the steady-state short-circuit current is smaller than 3 times Inom.

•display warnings: warnings, for instance, for the forcing of steady-state short-circuit current of synchronous machines can be switched on and off. Error messages are always displayed.

Algorithm

The algorithm of the calculation is as follows. First, the short-circuit currents for all synchronous and asynchronous machines are calculated (at times set in Vision Options). These short-circuit currents are equal to the currents during short-circuits at machines terminals. Further, equivalents of the machines that are connected to the same node are found according to Sections 7.3 and 7.4 of the standard. If there are only asynchronous motors connected to a node, then parameters of equivalent asynchronous motor are determined (Section 7.3). If there are synchronous machines present (or a combination of synchronous and asynchronous machines), then parameters of equivalent synchronous generator are computed (Section 7.4). Decrease of the short-circuit current with (electrical) distance is modelled by adjustment of the time constants and impedances of equivalent machines. Resistances and reactances of passive branches (that are connected to machines in series) are used for this adjustment. The manner, in which it is done, is described in Section 8.2 of the standard. Vision applies equivalencing of machines and passive branches step by step until the network becomes fully equivalenced. In the end situation there remains only one synchronous generator, which is connected to the short-circuited node. Currents of this fictive generator are equal to the total short-circuit currents during short-circuit at the selected node.