Dezentrale und zentrale Fehlerortung in Mittelspannungsnetzen

摘要

Die Fehlerortung ist eine Automatisierungsfunktion, die für Verteilungsnetze, vor allem Mittelspannungsnetze, derzeit sehr eingehend diskutiert wird. Die Fehlerortung basiert auf den Impedanzmeßwerten, die digitale Distanzschutzgeräte im Fehlerfall ermitteln. Zusätzlich können zur eindeutigen Eingrenzung des Fehlerortes Signale von Kurzschlußanzeigern sowie Auslösemeldungen analoger Schutzgeräte und UMZ-Schutzgeräte herangezogen werden. Die Meldungen und Meßwerte können entweder dezentral in den Unterstationen oder zentral in der Netzleitstelle ausgewertet werden. Beide Konzepte wurden realisiert und über mehrere Jahre im praktischen Betrieb erprobt.%Fault localization is an automation function which is the subject of detailed discussion for distribution grids, especially for MV grids. The term is understood to mean very precise automatic detection, as immediately as possible after a fault has occurred, of the location of short circuits and shorts to ground. Fault locations are specified in line lengths relative to the affected stations. Fault localization is based on impedance values from digital protective relays. In radial networks signals from short circuit indicators can be used in addition to at least delimit the area containing the fault to a stretch between two installations. The measuring values and signals can either be processed and displayed remotely in the sub-stations or they can be processed centrally in a grid control centre. Decentralized or remote fault localization is a sub-system of station control technology in sub-stations on MV grids. To implement a fault localization system, protective relays are required which transmit via interfaces phase-related excitation signals, activation signals, measuring values for the fault impedance and, where appropriate, relative times to the station unit. The station unit of each substation holds a model of the downstream grid which must be updated from the control centre. The impedance measuring values from digital distance protection devices can also be transmitted to the control room computer where they are evaluated on a central basis. This means not only that measuring values from several protective devices can be linked together but also that messages from short circuit indicators and tripping commands from analogue distance protection devices and UMZ protection devices can be employed. In many cases, it is only this additional information which allows the fault localization without ambiguity. Central fault localization - in contrast to fault localization in the protective devices - can also be performed across branching points and also in grids operated in a mesh fashion. Since the electrical parameters of the grid are stored in the fault locator computer, conversion of impedance values into distances is also possible for changing types of conductors down a line, e.g. transition points from overhead wires to buried cables. Both concepts have been in practical operation in power distribution companies for three years now and show satisfactory results. The deviations between actual locations and those calculated by the fault locator were usually less than 500 meters. Deviations are caused by impedance measuring errors and were to be expected in this scale due to the fault tolerances in protective devices and instrument transformers.