Online refurbishment of old transformers – selection focused on the percentage of relative water saturation in oil
This article focuses on refurbishment / reconditioning for extension of life-expectancy of old transformers of EHV (extra high voltage 66 kV and above) class.
byby K. K. Murty et al.
The useful life of AC and DC substations is defined by the Central Electricity Regulatory Commission, Government of India vide notification No. L-1/236/2018/ CERC, dated 7 March 2019, as only 25 years [1].
However, transmission utilities should endeavour to extend the life expectancy of the transformer to 35–40 years, adopting good practices of maintenance for the transformers, as they are the most expensive and vital equipment in a power utility.
The old power transformers were identified for online reconditioning, adopting the following criteria:
a. rendered continuous service for over 20 years,
b. percentage of relative water saturation r in the transformer oil: > 15 % [2], c. deterioration trend in IR and PI values.
Besides enhancing the life expectancy of old transformers, this process also resulted in many intangible benefits to the utility and the end-users, through the reduction in the outage, load curtailment, loss of revenue, cost of transformer replacement, leading to better consumer services and greater satisfaction. This includes as many as 205 of old EHV transformers of the total fleet of around 600 units. In addition, EHV Transformers were successfully refurbished for moisture over a period of five years in the Transmission Utility in the state of Madhya Pradesh in (India).
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