The sequential fault analysis feature enables the calculation and analyse of particular fault situations. Multiple sequential faults (in the form of fault impedances) can be applied to nodes, cables, overhead lines and elements. This makes it possible to analyse multiple or "cross country" faults. All currents and voltages in the network are calculated for each sequence. Next to simulating a fault, also the opening of a switch can be performed during the fault analysis.
In Vision, sequential fault analyses are performed using the compensation method. In contrast to IEC 60909, the network is represented actively and loads, overhead line capacities and shunts are included in the network.
The following illustration shows a simple Vision network consisting of three nodes. Node K1 is connected to the source and node K3 contains a load, a generator and a motor. There is a symmetrical fault with a fault impedance of Rf + jXf on node K2.
Vision network with a fault on node K1
For sequential fault analysis, Vision replaces the network illustrated above with the one illustrated below.
Network modelling for sequential fault analysis
The source, generator and motor are replaced by a Norton equivalent, assuming a "pre-fault" voltage determined by the loadflow. R and X are determined for the components, using the method indicated in the component description.
The symmetrical fault has been attached to node K2 in the form of an impedance of Rf + jXf.
When a sequential fault analysis is performed, the subtransient short-circuit current Ik" at each identified fault location is calculated. All voltages, branch currents and element currents are calculated as well. Currents and voltages can be displayed in complex form or as absolute values per phase (a, b, c) or per system (zero sequence, normal, inverse).
The voltages are represented as phase voltages.
See also: