Transfer function method to diagnose axial displacement and radial deformation of transformer windings

Abstract:Researchers have used various methods to determine the parameters of transformer-equivalent circuits in transient studies. But most of these previous algorithms had difficulty finding the equivalent circuit parameters in a bigger model. This paper presents a new method to extract the inductance matrix of a detailed model for an air core winding for transient studies using frequency-response measurement data. This matrix can be determined with acceptable accuracy by using the proposed method. The biggest advantage of the proposed method is a reduction in the search space, and thus, speedier problemsolving. Simulations showed that the use of the proposed method leads to better behavioural quality of a transformer winding. The simulation results of the previous and proposed methods were compared with the help of a 20/0.4 kV, 1600 kVA transformer. This comparison showed the accuracy and superiority of the proposed method.

Abstract:With the increasing age of the primary equipment of the electrical grids there exists also an increasing need to know its internal condition. For this purpose, off-and online diagnostic methods and systems for power transformers have been developed in recent years. Online monitoring is used continuously during operation and offers possibilities to record the relevant stresses which can affect the lifetime. The evaluation of these data offers the possibility of detecting oncoming faults early. In comparison to this, offline methods require disconnecting the transformer from the electrical grid and are used during planned inspections or when the transformer is already failure suspicious. This contribution presents the status and current trends of different diagnostic techniques of power transformers. It provides significant tutorial elements, backed up by case studies, results and some analysis. The broadness and improvements of the presented diagnostic techniques show that the power transformer is not anymore a black box that does not allow a view into its internal condition. Reliable and accurate condition assessment is possible leading to more efficient maintenance strategies.

ResumenEste artículo presenta la implementación de un modelo para el análisis del comportamiento en frecuencia de los parámetros de un transformador eléctrico. El modelo se obtiene a partir de la curva de la prueba de Respuesta en Frecuencia del transformador (FRA). Esta prueba consiste básicamente en obtener una característica del transformador y comparar el resultado con una referencia del mismo, tomada anteriormente y considerada como normal. Las diferencias pueden indicar algún tipo de daño en el transformador. Se hace la descripción del modelo, de la manera como se realizó su implementación, del procedimiento para obtener sus parámetros y de su aplicación en el análisis de variaciones en las curvas obtenidas en los ensayos de FRA. Este modelo es una herramienta que puede emplearse como ayuda para identificar problemas de tipo mecánico en el transformador. Palabras clave: transformador, parámetros del transformador, respuesta en frecuencia, FRA Implementation of an Electric Transformer Model for its Frequency Response Analysis AbstractThis article presents the implementation of a model for the analysis of the frequency behavior of a transformer. The model is obtained from the Frequency Response Test (FRA). This test consists basically of obtaining the characteristics of the transformer and comparing the results with those of a reference transformer, which are previously known and considered as normal-The differences indicate that the transformer has certain damage. The article describes the model, its implementation, the procedure to obtain its parameters and its application in the analysis of the curve variations obtained by the FRA tests. This model represents a good tool that can be used as support to identify some type of mechanical problem in the transformer.