| 摘要 |
The present invention relates to a method for current compensation of a protection system for protecting a zone in a power system, which zone comprises a number of transmission lines connected to power sources and a number of transmission lines connected to a number of loads where the power sources and the loads are arranged outside the zone and a number of current transformers (CT) arranged to the transmission lines, wherein the method comprises the steps of continuously measuring all the incoming currents (I<SUB>in</SUB>) to the zone, continuously measuring all the outgoing currents (I<SUB>out</SUB>) from the zone, continuously calculating the differential current (I<SUB>d</SUB>) according to I<SUB>d</SUB>=I<SUB>in</SUB>-I<SUB>out</SUB>, continuously calculating q=I<SUB>out</SUB>/I<SUB>in</SUB>, continuously comparing q with set values and continuously comparing I<SUB>out </SUB>with a set value Set1. The invention is characterised by setting I<SUB>out</SUB>=I<SUB>in</SUB>=I<SUB>comp </SUB>at the instant when q changes and I<SUB>out </SUB>exceeds the value set1, which is an indication of the occurrence of a fault external to the protection zone due to saturation of the CT of the faulted outgoing transmission line, and using the value I<SUB>comp </SUB>in the protection system in order to prevent tripping of the protection system. The present invention also relates to a device and a computer program product for performing the method.
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