A NEW APPROACH TO FAST INRUSH CURRENT DISCRIMINATION BASED ON TRANSFORMER MAGNETIZING CHARACTERISTICS

This paper investigates the necessity of pro- tection devices that implement fast relaying algorithms for distribution systems to meet the demands for high reliabil- ity from the viewpoint of power quality. In designing high speed protection systems, the fast discrimination of magne- tizing inrush current is also indispensable to prevent the false tripping of relays. The conventional method of inrush cur- rent detection for transformer protection recognizes the ra- tio of the second harmonic component of the differential cur- rent. The authors propose a new approach to detecting the inrush current based on the transformer magnetizing char- acteristics. An inrush current occurs when the transformer core becomes saturated. The proposesd method estimates the transformer core saturation by the linear relation between the differential current and the integral of voltage. Experi- mental results obtained on a single-phase transformer and a three-phase transformer are presented.

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