Transformer Fault Diagnosis Based On No-Load Current Analysis

Abstract

Transformer is most widely used electrical equipment in electrical network. It is required to operate transformer in reliable condition. Under normal operating condition transformer is a highly e cient machine. But there may be the possibilities of unsatisfactory performance of transformer. In order to operate transformer in healthy condition various protections are provided. When there is any abnormality in transformer, it can be diagnose based on various techniques. The most widely used technique is Dissolved Gas Analysis (DGA). The diagnosis of faults can also be done by analyzing the transformer no-load current. As no-load current of transformer contains harmonics, for faulty transformer the no-load current and its harmonic contents will be di erent. And hence for given fault we can calculate the amount of harmonics in no-load current. The amount of harmonic and magnitude of no-load current will indicate the type of fault in transformer. The harmonic extraction from no-load current has been done using Fast Fourier Transform. The signal contains information; the no-load current has the information regarding internal condition of transformer. In this report the e ect of three-phase transformer connection on its no-load line current is shown using MATLAB Simulink. This can also be veri ed by practical experiments. This information can be useful for further comparison of no-load current of any faulty transformer. The harmonic contents in no-load current and its magnitude is the good indicator for particular fault in transformer. The analyses of no-load current harmonics give clear indication of possible fault. From the knowledge of the no-load current magnitude and its %THDi transformer internal fault has been diagnose. The quality of core material and winding condition can be predicted from the no-load current analysis. The increase in %THDi of no-load current is related to core abnormalities and increase in %THDi and magnitude of no-load current is related to winding abnormalities. In this report it is proved from practical experiments that winding fault increases no-load current magnitude as well as %THDi, where as core fault increases only no-load current %THDi. The inter-turn fault in particular winding can also be diagnosed using no-load current analysis. The increase in magnitude of no-load current leads to the inter-turn fault in secondary winding and increase in magnitude and %THD of no-load current leads to the inter-turn fault in primary winding. The practical results lead to the same conclusion.