Abstract

GUILLEN, Daniel; TORRES-GARCIA, Vicente  and  OLIVARES-GALVAN, Juan Carlos. Blocking index to improve negative sequence differential protection of power transformers using ATP/EMTP. Ing. invest. y tecnol. [online]. 2021, vol.22, n.1.  Epub July 30, 2021. ISSN 2594-0732.  https://doi.org/10.22201/fi.25940732e.2021.22.1.001.

This work introduces a new blocking index to improve the transformer differential protection performance based on the negative sequence. To ensure the reliability of any electrical network, the protection schemes are a primary task. Particularly, power transformer because these are subject to transient events such as turn-to-turn faults, magnetizing inrush currents, and overexcitation. In consequence, the transformer protection must operate properly under non-fault transient phenomena. To analyses internal faults and transient events in transformers, a negative sequence differential protection is implemented using ATP/EMTP software. The proposed scheme employs a differential protection scheme (87Q), which is mainly based on the angular difference between negative sequences of the primary and secondary currents by using a Relay Operating Angle (ROA). This improved protection introduces a blocking index to avoid incorrect operations during transformer energization because it has been reported that ROA may present false operations under transient events. The new introduced index represents a distance between sequences during the transient period, which helps to discriminate internal fault from inrush currents. In this sense, the authors present an evaluation of the introduced blocking index to avoid incorrect operations, especially when this protection is working under unbalanced conditions, or in non-fault transient conditions, such as magnetizing inrush current. Based on the results, the proposal presents good performance and its effectiveness is proved under different fault scenarios.

Keywords : Inrush current; internal fault; negative sequence; differential protection; relay operating angle; power transformer.

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