Prasad A. Venikar

A Novel Offline to Online Approach to Detect Transformer Interturn Fault

This paper presents an approach based on the use of transformer no-load and light load current harmonic analysis to detect the presence of an interturn fault at the incipient stage. The presence of fault is detected by performing a trend analysis of specific harmonic components and primary current magnitude. Transformer testing methods suffer from a common drawback of offline nature and require an expert opinion for accurate condition assessment. This paper presents a method that transforms no-load current harmonic analysis, which is a special test for transformer testing, into an online method at light load conditions. Thus, the necessity of complete shutdown and dependency on expert opinion is eliminated since it only requires one reference signature per phase. The proposed approach is verified for different vector groups of the three-phase core-type transformer and three independent units connected in star-star and for a fault on the low-voltage or high-voltage winding of the transformer. The presented experimentation shows that the proposed approach can detect the presence of a fault at an incipient stage involving less than 2% of turns and fault current up to 1 p.u. A case study is presented that validates the method for the transformer of a higher power rating.

Search coil based transformer inter-turn fault detection

Detection of transformer inter-turn fault at early stage is essential for increasing life of transformer and avoiding economical impacts. This paper presents a novel approach to detect transformer inter-turn fault by search coil induced voltage analysis. A healthy winding is associated with symmetrical leakage flux pattern. With initiation of inter-turn fault it does not remain symmetrical and creates distorted leakage flux pattern. This distorted leakage flux linking with search coil induces voltage based on degree of symmetry of leakage flux. Analysis of this induced voltage can detect presence of fault and also predict its severity.

Negative sequence based relay operate area approach to detect transformer inter-turn fault

This article presents a new approach for transformer inter-turn fault detection. Conventional differential scheme is provided with bias to prevent mal-operationin case of over-excitation, CT saturation, magnetising inrush, etc. However, this prevents conventional scheme from detecting inter-turn fault at incipient stage where less turns are involved in the fault. Proposed scheme overcomes this drawback by introducing Relay Operate Area (ROA) approach. The proposed two stage approach initially detects presence of fault and later confirms the presence for observation based on predefined loading conditions. Experimental results on laboratory transformer are presented which confirms the proposed approach.

Condition assessment of transformer by park's vector and symmetrical components to detect inter turn fault

Power transformer is a strategically important component of power system due to its location and size. Sudden failure of power transformer has both technical and economical impacts. Studies indicate that inter turn fault is one of the major cause of transformer failure. Detection of presence of such fault at an early stage is important to avoid further damage. Objective of this paper is to analyse the characteristics of current during inter turn fault using Parks vector and symmetrical components approach. Comparative assessment of Parks vectors and symmetrical components is also discussed. Use of percentage deviation of vectors from healthy condition is proposed for identification of existence of such fault.

Transformer incipient inter-turn fault detection based on no-load current harmonic analysis

This paper presents use of no-load current harmonic analysis to detect presence of inter-turn fault at incipient stage. At steady state, third and fifth harmonic components are predominant in transformer no-load current. Inception of fault results in decrease in THD and increase in increase in primary current. Based on reduction of total harmonic distortion (THD) of each phase and simultaneous increase in primary current, it is possible do detect presence of inter-turn fault. Wavelet analysis is also performed to validate the results. Proposed method offers higher sensitivity and accuracy as it can detect fault at incipient stage involving less than 2% turns and fault current up-to 1 p.u.

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.