Ein Verfahren zur Bestimmung der Erdschlussentfernung

A method for determining the earth fault distance in high impedance grounded networks is presented here. With the transient processes having decayed in case of an earth fault, the grid tunes into a steady state error condition in which it can be operated initially. Starting out from the stationary earth fault condition a line model of a unilaterally powered feeder with one load based on a PI-element is developed using a for-wire-representation. The circuit analysis is performed using complex AC calculation and Kirchhoff’s laws. The examinations are based on a network with isolated neutral point. The resulting system of equations is non-linear in its basic form. However, it can be lead back to an elementary solvable cubic equation in the unknown fault distance parameter. Another solution is offered by the Newton-Raphson method. The non-linear system of equations can be transformed into a linear equation system by transferring the phase-to-earth capacitances placed at the load to the front of the feeder. Here two kinds of solutions are possible: „a direct solution with an unbalanced load“ or „a least squares solution using a symmetrical load“. MATLAB implementations of these four algorithms form the basis of further analyses. All metrological investigations were carried out at the grid and power plant model of the Kaiserslautern University. Here, various error scenarios were established concerning fault distance, -resistance and the size of the remaining healthy network. A total of 480 single measurements were recorded and analysed with the algorithms. In order to test the earth fault detection capability of the algorithms also measurements on error-free feeders were carried out. In addition to fundamental frequency considerations, the evaluation of all data sets using the 5th and the 7th harmonics is a central topic. The focus is on the usability of these higher harmonics for earth fault distance calculation and -detection with the algorithms mentioned above. Of particular importance is the question of to what extent the algorithms originally designed for the use in a network with isolated neutral point are also suitable for earth fault distance calculation using the higher harmonics in a resonant grounded network. Finally, the presented method is extended to feeders consisting of inhomogeneous conductor material, since this constellation is of practical importance. Inhaltsverzeichnis Seite 7