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INTERPRETATION OF FRA RESPONSE IN THE FREQUENCY REGION DOMINATED BY WINDING STRUCTURE
[Thesis]. Manchester, UK: The University of Manchester; 2017.
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Abstract
Frequency Response Analysis (FRA) has been regarded as an effective technique to detect displacement and deformation of transformer windings. The success of this technique is determined by the interpretation of FRA features. Models of transformer for deriving FRA interpretation rules are improved in recent years to simulate different winding conditions of transformers. The “wide frequency†transformer winding models developed at the University of Manchester will be used in this project. The research aims to establish the relationship among the physical dimensions of the winding, the electrical parameters of the winding equivalent circuit and the corresponding FRA responses. The approach is to implement a large quantity of sensitivity studies to aid the interpretation of FRA response. The overall aim is to achieve a better interpretation of FRA through further refining the transformer simulation models, ultimately to aid better condition monitoring of transformers. In this research, one phase transformer windings have been modelled and FRA measurements simulated. The simulation converts the geometry of transformer windings to an equivalent circuit model which contains the series capacitance, ground capacitance, inter-winding capacitance, self-inductance and mutual inductance. In terms of simulation work, firstly, sensitivity studies about the electrical parameters and the winding geometry have been implemented; the sensitive parameters of winding geometry which dominate the value of L or C have been identified. Secondly, two basic types of winding deformations were simulated on different winding constructions; consequently the influences of electrical parameters were obtained, moreover, the influence of mutual couplings are identified, it is suggested that the FRA features of un-tested-winding can be reflected on the FRA response of the winding-under-test through mutual inductive coupling in this case whilst the mutual capacitive coupling has little influence on the FRA response. Finally, a reduced matrix model is developed by simplifying the detailed model, which can maintain the main features of the FRA responses (the resonances and anti-resonances) produced by the detailed model.