The IEC 61850 standard-based protection scheme for power transformers

Abstract

Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have a harmonic restraint element and trips the overcurrent relay during the inrush conditions. Therefore, to prevent the malfunction caused by the transformer magnetizing inrush current, a novel harmonic blocking method is developed, implemented and tested in the RSCAD simulation environment. The IEEE 14 bus transmission system is considered as a case study. The IEEE 14 bus system is modelled and simulated in the DIgSILENT and RSCAD simulation environments respectively. The developed harmonic blocking scheme is implemented in the Hardware-In-the-Loop (HIL) simulation environment using Real-Time Digital Simulator and numerical protection IEDs. The developed scheme uses the Harmonic Blocking element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit it from tripping during the transformer magnetizing inrush current conditions. The hardwired and GOOSE simulation results are analysed for the transformer differential protection and the backup overcurrent protection schemes for internal, external events and transformer magnetizing inrush current conditions. The simulation results proved that the IEC61850 standard-based protection scheme is faster than the hardwired. Therefore, the speed and reliability are improved using the IEC61850 standard-based GOOSE applications to the transformer digital protective relaying system.