Investigating the application of frequency response analysis for diagnosing tap changer on power transformer

Electrical distribution power transformers operate on transmission and distribution systems which require different voltage levels. A sufficiently constant level of grid potential is maintained by mechanically regulating the turn ratio in the transformer winding, which can be achieved through OLTC or DETC. Since the tap changer is the only moving component of the transformer, it is particularly vulnerable to degradation mechanism. Many diagnosis tools have been developed to evaluate the mechanical integrity of tap contacts since many years ago. However, studies related tap changer diagnosis using FRA is still lacking. This thesis adapts, frequency response analysis which is proven to be a powerful and globally popular diagnostic tool in detecting power transformer mechanical integrity. Since this method is comparative, thus interpretation of FRA signal is still challenge and required skilled personnel to identify the cause of Fault. Two common tap changer deformation mechanisms and four types of transformer based connection test types are established. A lumped transformer model has been developed to identify the underline causes of FRA response curve changes between faulty and normal conditions for better interpretation. This model mainly focusses on low and mid frequency regions due to fact, that major changes occurs at the above-mentioned regions. In addition to that, this new technique of OLTC diagnosis will be recommended for future detection of tap changers faults and diagnosis of winding degradations simultaneously since they are interconnected by using the same instrument