Abstract:
Transformer differential protection normally use dual slope or multiple slope characteristics to provide
stability during through fault and load conditions. It also uses harmonic blocking criteria to provide
stability during various transformer inrush conditions. The advancement in the materials used in
transformers can cause a reduction in harmonics during a transformer inrush which can lead to reduced
2nd harmonic settings down to 10% or lower in some applications. This paper discusses the impact of a
reduced 2nd harmonic threshold on the differential protection and highlights the benefits of waveform
recognition algorithms such as the gap detection and the CT saturation techniques to unblock the
differential protection during internal faults in the presence of harmonics. It also highlights the benefits
of an adaptive transient bias technique to provide high stability during through fault scenarios and
includes results of extensive RTDS testing and some of field performance examples.
S. Makwana, G. Lloyd, J. Snazell, B. Liu, B. Smith, Presented at PAC World Global Conference 2021, Virtual Event, August 2021
KEYWORDS: Transformer differential protection, transient bias, CT saturation, waveform recognition
