Fault localization using SFRA – Part I
Detection of winding inter-turn faults – Part I
This article deals with inter-turn fault detection in the transformer winding, inter-turn fault which occurs due to insulation degradation between one or more sequential turns of the winding. If the fault is not detected at the earliest stage, it propagates to the nearby turns of the winding during certain period of time and it causes irreversible damage to the winding. Therefore, it is necessary to detect inter-turn fault to save the transformer from catastrophic failure.
Power transformers are critical components of the energy transmission and distribution process in electric power system. In view of increasing demand for reliable and high-quality energy supply, electrical utilities are more interested in avoiding transformer failures. Transformers are in service under different environmental, electrical, and mechanical conditions and may be subjected to enormous hazards during the course of operation. Any fault in transformers will cause the interruption of the power supply.
Inter-turn fault in the windings is one of the internal faults within the transformer. A short circuit of a few turns of the transformer winding will give rise to a heavy fault current in the short-circuited turns, but changes in the transformer terminal current will be very small, due to the high ratio of transformation between the whole winding and the short-circuited turns.
Once the inter-turn faults occur, a large circulating fault current is induced in the shorted turns, leading to localized thermal overloading in the defective region of the winding. Over certain period of time, the generated heat in the defective region will cause the fault to increase in size, and will involve another phase or ground conductor.
In the present study, transformer winding is modelled using ANSYS software (using finite element method and analysis through electrostatics and magnetostatics solvers) based on physical dimension data of the winding; parameters such as capacitance and inductance are extracted by performing electric and magnetic field analysis and capacitance and inductance parameters are used for circuit modelling of transformer winding for inter-turn fault detection study. Proposed methodology will be useful for design engineers to detect inter-turn faults by predicting the fault factor characteristics with the help of electrical equivalent circuit model of transformer winding using only the physical dimension data of the transformer.