Analisis Hubung Singkat Inter Bus Transformer (IBT) 500 MVA Paralel Empat Unit di GITET Kediri

Abstract

GITET Kediri is an extra-high-voltage substation that operates 500 kV, 150 kV, and 20 kV systems in an integrated manner. As of 2015, this facility operated three 500/150 kV Inter-Bus Transformers (IBTs) with a capacity of 500 MVA per unit, and was later expanded with the addition of a fourth IBT in 2020[1]. The bay configuration on the 150 kV side has been in place since 2017 with no changes to the equipment to date. Based on the provisions of IEC 60076-1 regarding transformer parallel operation, the four IBTs are deemed to meet the requirements because the impedance differences among the units fall within the ±7.5% range, namely 3.3%, 13.16%, 14.452%, and 14.375%[2]. The comparison results between simulation and manual calculations show the following short-circuit current values: a three-phase fault produces 26.978 kA (simulation) and 26.548 kA (calculation); a single-phase-to-ground fault produces 29.659 kA and 30.097 kA; a phase-to-phase fault of 23,363 kA and 23,066 kA; and a two-phase-to-ground fault resulting in 28,374 kA and 28,924 kA for phase AB, and 28,788 kA and 28,996 kA for phase BC. The breaking capacity of the PMT at IBT 1, 2, 4, and the Kertosono, Jayakertas, Tulungagung 1&2, Banaran 1&2, Trafo 1, Kopel 1&2, and Section A&B bays is recorded at 40 kA, while IBT 3 and Trafo 2 have a capacity of 50 kA. This study concludes that parallel operation of the four IBTs is feasible, given that the impedance difference remains within standard limits, and all 150 kV PMTs are deemed operational because the fault current does not exceed the PMTs’ capacity.