Abstract

In transmission and distribution networks throughout the world and in Vietnam nowadays, power transformers that are operating in the networks often are in black-box condition, i.e. there is no internal information available in terms of geometrical structure and material parameters. Geometrical structure of power transformers includes mainly winding structure and additional parts such as a static end ring or a would-in shield coil, if any whereas main materials in power transformers consists of conductive, insulating and magnetic materials… This makes difficulties in faults diagnosis that is based on the approach of physical modeling in general and the so-called electrical equivalentcircuit based modeling in particular since the physical approach requires internal information of power transformers for calculating electrical parameters. In case the electrical equivalent-circuit approach is used, the diagnosis is then conducted based on the change of values of electrical parameters in the circuit before and after an alarm or a suspicious fault that happens when power transformers are in operation. Relevant international investigations conducted recently have mainly focused on test objects as power transformers in grey- or white-box condition, i.e. during manufacturing phase, since they have available geometrical structure and material properties. To show a possibility that blackbox power transformers could be investigated in a physical manner, this article introduces a new method in determining electrical parameters and geometrical structure applied on a black-box power transformer. The research is based on the Frequency Response Analysis technique and has developed recent relevant investigations of the authors. This enables investigations of the value change of electrical equivalent parameters of this transformer on its simulated frequency responses for the purpose of physical fault diagnosis of power transformers later on.