A Novel Flux-Based Protection Scheme for Power Transformers

Internal Turn-Turn faults (TTF) are the most common failures in power transformers, which could seriously reduce their life expectancy. Although common protection schemes such as current-based differential protection are able to detect some of the internal faults, some other minor ones (such as TTFs and short circuit near the neutral point) cannot be detected by such schemes. Likewise, these relays may have false trip due to energizing inrush currents, transformer over excitation, and occurrence of CT saturation at one side. In this paper, a novel Linkage Flux Based (LFB) scheme is proposed to detect TTF in power transformers, which uses some Search Coils (SC) located on the transformer legs to sense the related linkage flux. Any difference in induced voltage in the corresponding SCs (located on any leg) suggests passing unsymmetrical linkage fluxes through them (unlike the normal conditions), which stands for the occurrence of a fault inside the transformer. The proposed technique not only can be used to protect power transformers, but also can be employed to find the fault location during repair activities, as well.