Dispersing the clouds: Gain clear insight into your bushings using advanced diagnostic methods

Abstract Bushing diagnosis can include various methods, from a simple visual inspection or a conventional power/dissipation factor measurement, to the latest high-tech broadband dielectric frequency...

byMartin ANGLHUBER, Juan VELÁSQUEZ


Abstract

Bushing diagnosis can include various methods, from a simple visual inspection or a conventional power/dissipation factor measurement, to the latest high-tech broadband dielectric frequency response measurements. This article explains the different bushing insulation types and shows which problems can occur in bushings and which diagnostic methods can be used to detect them. Each measurement has its advantages and disadvantages and some are more suitable for onsite measurements, others for quality control of new bushings. Case studies show the effectiveness of advanced dielectric measurement principles in detecting moisture and aging problems.

Keywords: bushing, dissipation factor, moisture, aging, power transformer

1. Introduction

Bushings are a vital part of power transformers and other assets as they act as insulators and transmit electrical power in or out of a power transformer. No active action or mechanical movement is required, and maintenance measures like the changing of worn parts are also not needed. Compared to the rest of the power transformer they are quite low-priced. All of these facts could lead to the conclusion that condition diagnosis of bushings is not economical as they can just be replaced when any failure occurs.

However, such a conclusion would be very short-sighted. About 41% of all bushing failures on high-voltage power transformers lead to a fire or explosion of the transformer – this corresponds to a complete loss of the transformer [1]. Also, about 37% of all fires or explosions of power transformers are caused by bushing failures [1]. This shows how important it is to prevent bushing failures, not just in order to avoid unplanned outages but also to avoid the loss of assets in dramatic circumstances.

This paper shows which problems can lead to the failure of bushings and how diagnostic methods can be used to detect those problems at an early stage.

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