Volume No. 10 Issue No.: 4 Page No.: 621-634 April-June 2016

 

UNDERSTANDING THE EFFECTS OF COPPER SULPHI - DE IN TRANSFORMER INSULATION BY DIFFERENT CHEMICAL AND ANALYTICAL TECHNIQUES

 

Ramachandra H.*1, Akshatha A.2 and Sundara J. R.2

1. Department of Chemistry, PET Research Foundation, PES College of Engineering, Mandya, Karnataka (INDIA)
2. R & D Management Division, Central Power Research Institute, Bangalore (INDIA)

 

Received on : January 16, 2016

 

ABSTRACT

 

A number of power transformer failures have occurred worldwide since 2004 due to the formation of semiconducting copper sulphide and its accumulation in paper layers. Detecting and analyzing the copper sulphide in the beginning of its formation in mineral oil is a tedious task due to many factors like its slow formation rate which makes it difficult to detection terms of usual electrical and dielectric measurements, its migration from paper to oil which makes it difficult to analyze accurately at any given instant of time. Hence, simultaneous use of different techniques has been made to understand the formation of copper sulphide in paper-oil insulation of transformers. Transformer oil samples containing different concentration of mercaptan sulphur ranging from10 to 20 ppm, dibenzyl disulphide of 50 to 300 ppm and 100 ppm of metal passivators, are exposed to thermal ageing at temperatures of 100 to 1500C for different durations in presence of paper covered copper conductors. It is practically impossible to detect and analyze individually all sulphur compounds present in the transformer oil. However, Dibenzyl disulphide (DBDS) in oil can be analyzed using gas chromatography equipped with mass spectrometry. Mercaptan sulphur or thiols present in the transformers or formed during thermal degradation of DBDS is analyzed by potentiometric titration. Analysis of total sulphur content of the oil sample is carried out using Wavelength Dispersive X-Ray Fluorescence (WDXRF). Dissolved copper in oil is analyzed by Atomic Absorption Spectroscopy (AAS).

 

Keywords : Dibenzyl disulphide, Mercaptan sulphur, Total sulphur, Contamination, Absorption

 

 

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