Assessment of Rogowski Coils for Measurement of Full Discharges in Power Transformers

Rudolf Ribeiro Riehl,José Renato Castro Pompéia Fraga,Guilherme Beraldi Lucas,Victor Puccia,André Luiz Andreoli,Bruno Albuquerque De Castro

doi:10.3390/ecsa-8-11309

Rudolf Ribeiro Riehl, José Renato Castro Pompéia Fraga + Show 4 more

Open Access

https://doi.org/10.3390/ecsa-8-11309

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Publication Date: Nov 1, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: Universidade Estadual Paulista (Unesp)

Abstract

Science and industry have sought to develop systems aiming to avoid total failures in power transformers since these machines can be working under overloads, moisture, mechanical and thermal stresses, among others. These non-conformities can promote the degradation of the insulation system and lead the transformer to total failure. In the incipient stages of these faults, it is common to detect Full Discharges (FDs), which are short circuits between degraded coils. Therefore, several techniques were developed to perform FD diagnosis using UHF, acoustics, and current sensors. In this scenario, this article presents a mathematical model for Rogowski coils and compares two different types of cores: Ferrite and Teflon. For this purpose, FDs were induced in an oil-filled transformer. The sensitivity and frequency response of the Rogowski coils were compared. This analysis was achieved using the Power Spectrum Density (PSD) and the energy of the acquired signals. Additionally, the Short-Time Fourier Transform (STFT) was applied to detect repetitive discharges. The results indicated that the Ferrite core increases the sensitivity by 50 times in the frequency band between 0 and 1 MHz. However, the Teflon core showed higher sensitivity between 5 and 10 MHz.

Highlights

The incidence of discharges in power transformers can be indicative of the deterioration of the machine insulation system
Partial discharges (PDs) and full discharges (FDs) are characterized as electric non-conformities that emit UV radiation, current pulses, and acoustic and electromagnetic waves, causing a progressive deterioration of the insulation components
Full discharge detection is crucial for power transformer maintenance plans

Summary

Introduction

The incidence of discharges in power transformers can be indicative of the deterioration of the machine insulation system These non-conformities can lead the transformer to total failure. According to Murugan and Ramasamy (2019), the failures of a transformer’s windings are commonly caused by short circuits due to internal overheating, conductor tilting, conductor bending, clamping system failure, axial instability, and deformations by careless transformer transportation [4]. All these mechanical stresses can impair the wire insulation and lead the transformer to FDs

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Discussion

Conclusion