Symmetrical components based advanced scheme for detection of incipient inter-turn fault in transformer

Phase current based transformer differential protection is commonly used for detection of inter-turn fault. Initial pick-up and commonly used dual slope characteristics provides security against spill current due to on-load tap changer (OLTC) operation and CT saturation because of through fault. However, this limits ability to detect presence of inter-turn fault at an incipient stage. This paper presents a novel approach based on use of negative sequence components for incipient inter-turn fault detection. This technique offers higher sensitivity as compared with conventional phase based protection scheme. A comparison with conventional scheme with commonly used settings is presented for unbalanced load, over-voltage and under-voltage conditions. Experimental results indicate that the proposed scheme is able to detect fault involving 3% turns and fault current of 1 p.u.