Online Conditioning Monitoring of Oil Immersed Power Transformers: Overview of Dissolved Gas Analysis

Online Conditioning Monitoring of Oil Immersed Power Transformers: Overview of Dissolved Gas Analysis

Yassmine Maioui and Tero Lappalainen

Abstract— Power transformers are considered as key components of the power system as they play an important role in delivering and transmitting power to the customer. The oil immersed power transformers are one the multiples type of conventional transformers widely used. Their failure can lead to enormous technical and economical losses. It is therefore important for the utilities as well as the power grid to maintain and monitor the transformer in an accurate and reliable way. In this paper, an overview of the on-line monitoring dissolved gas analysis is provided. It includes a definition of the concept, the main characteristics of the existing types of DGA online monitoring, as well as the various benefits provided by the solution according to the needs of the stakeholders. Finally, current challenges and future trends are discussed and

Index Terms—on-line condition monitoring, dissolved gas analysis, power transformer, oil immersed power transformers, key gases.

I. INTRODUCTION

Power transformers are considered as the key components of the power grid and the most expensive elements of the power system. Their reliability and efficiency influence the energy supply and availability of a specific area. However, power transformers a subject to thermal and electrical stresses through their life time increasing the risks of outages and failures. It was estimated that 5 out of 1000 power transformers will fail within a period of a year [1]. The failure of a power transformer can lead to enormous power system disturbances and thus loss of cost benefits.

It was reported that high voltage oil filled transformers were subject to failure representing 12,8% of the fire catastrophes within the power distribution sector. This underlines the importance of a reliable and continuous monitoring of the transformer [2]. The Dissolved Gas Analysis monitoring is considered to be the most important monitoring solution mainly used. However, due to various limitations discussed in this paper, utilities are reluctant in its adoption and prefer the use of offline monitoring despite the lack of reliability and accuracy provided. This paper discusses the main challenges and advantages of the DGA online monitoring seeking the promotion and the increase of the implementation of this technology.

II. PROBLEM STATEMENT

Power transformer outage causes substantial, immediate economic losses and further is to be expected in form of high repair costs or a lengthy delivery time for the replacement transformer. Oil immersed power transformer deliveries range roughly between 12 to 24 months depending on the transformer size,