Power transformer differential protection for three Eskom feeders

Abstract

Differential protection's purpose is to offer phase fault protection that is both quicker and more discriminative than that provided by basic overcurrent relays. Transformer differential protection is the primary protection against earth faults and phase-to-phase faults. CTs on the HV side are counterbalanced by CTs on the LV side. There are a variety of distinct connections, but there are a few key considerations that apply to every design. This sort of protection continually monitors and compares the current flowing between CTs (in this example, HV and MV CTs) inside a protected zone. The following are the primary requirements of this protection, Highest sensitivity, Load stability over the whole tap range, Stability in through-fault circumstances, Stability for magnetizing inrush with associated DC offset decay, when a zone fault is identified, simultaneously opens both HV and MV breakers.