Detection of Power Transformer Winding Deformation Using Improved FRA Based on Binary Morphology and Extreme Point Variation

Frequency response analysis (FRA) has recently been developed as a widely accepted tool for power transformer winding mechanical deformation diagnosis, and has proven to be effective and powerful in many cases. However, there still exist problems regarding the application of FRA. FRA is a comparative method in which the measured FRA signature should be compared with its fingerprint. Small differences of FRA signatures in certain frequency bands might be produced by external disturbance, which hinders fault diagnosis. Additionally, the existing correlation coefficient indicator recommended by power industry standards cannot reflect key information of signatures, namely the extreme points. This paper proposes an improved FRA based on binary morphology and extreme point variation. Binary morphology is first introduced to extract the certain frequency bands of signatures with significant difference. A composite indicator of extreme point variation is adopted to realize the diagnosis of fault level. A ternary diagram is constructed by the area proportions of the binary image to identify winding faults, which has a potential to realize cluster analysis of fault types.

I. Introduction

The power transformer is one of the most valuable and expensive pieces of equipment in a power substation; it is of significance to ensure its stable, reliable, and safe operation [1]. Core failure, overvoltage, aging of insulation, insulation failure, and winding deformation are the key factors affecting the occurrence of a transformer fault, even resulting in the outage of the transformer and power network. The statistics obtained by CIGRE working groups have revealed that the winding deformation fault causes one third of all transformer failures. Winding deformation is typically induced by winding electromagnetic force, where the force is the outcome of an external short-circuit (SC) current and internal magnetic field [2]–[4]. Besides, earthquake, careless transportation, aging of insulation material, and explosion of combustible gas in the transformer oil could also be reasons for giving rise to winding mechanical faults [5] –[7]. The ability of the transformer to guard against SC current will decrease considerably after the occurrence of a minor winding deformation fault; winding mechanical deformation faults and interturn SC faults are easily produced and develop simultaneously. Minor winding faults eventually develop into catastrophic failure if no steps are taken, which will result in the outage of the transformer and decrease the economic benefits. Thus, timely detection and diagnoses of winding deformation fault are required.