The Application of Correlation Technique in Detecting Internal and External Faults in Three-Phase Transformer and Saturation of Current Transformer

A new technique based on correlation coefficients analysis of current waveforms is used to detect an internal fault that occurs in a three-phase transformer as well as to distinguish it from external faults. The technique depends on the changes in current waveforms that occur during the faults. Autocorrelation has been added to cross-correlation in one scheme for better fault discrimination and to increase speed in detecting the fault within a very short time. The proposed algorithm is so fast that it is able to detect faults within less than 3 ms. The technique also overcomes the problem of the current transformer's saturation, which is considered one of the biggest problems in protection methods especially in differential protection. The new algorithm was tested practically and the results were processed using the LabVIEW and MATLAB programmes. The practical test results show that the internal faults, particularly an interturn fault type with only two turns, are shorted and can be detected and correctly identified from the external fault.