Condition Assessment of Power Transformers Based on Health Index Value

Patryk Bohatyrewicz,Janusz Płowucha,Jan Subocz

doi:10.3390/app9224877

Abstract

In electric power systems, health index algorithms are mostly used for evaluation of the transformer population. In this method, some assessment criteria are insensitive when it comes to judging the technical state of the edges of the age spectrum. This paper presents a new health index calculation method that aims to improve the overall effectiveness of the assessment. The proposed algorithm is based on regularly conducted oil diagnostics and easily available maintenance data to enable estimation and updating of the device’s health status in short intervals from an operational point of view. This method is compared to another health index algorithm built from the same parameters, but with different weights and an alternative result assessment philosophy. The two health index calculation methods are tested on a population of 96 power transformers and then compared to results obtained with an expert system, which is based on much more advanced diagnostic tests to determine the technical condition of the unit. The results of the experiment show that proper selection of weighting factors of the transformer’s technical condition parameters during health index calculation may help in simplifying its assessment while maintaining satisfactory accuracy in comparison to a highly advanced expert method.

Highlights

IntroductionUnplanned long-term shutdown of units is a significant expense for transmission network operators
The operation of transformers is crucial in the context of power system management
The decisive factor is exploitation time rather than the technical state of the transformer. This leads to a situation in which most units that have been in operation for over 40 years are marked as bad or risky in terms of their future

Summary

Introduction

Unplanned long-term shutdown of units is a significant expense for transmission network operators For this reason, the demand for ensuring low failure frequency of transformers is natural. Several methods can be used, which have been explained in a detailed study [2] and in the American Transformer Diagnostics Guide [3] These techniques can be performed as periodic maintenance or advanced diagnostic procedures or can be implemented in the form of online monitoring systems. Most common techniques, such as oil diagnostics, insulation resistance tests, turns ratio measurements, and inspection of accessories, are performed relatively often and in the state of normal trouble-free operation, with the general technical condition of the transformer being determined on their basis. In the case of transformers with developing defects or aged units, some advanced methods are used to assess their technical condition, such as frequency domain spectroscopy (FDS)

Results

Discussion

Conclusion