Retrofitting of 245 kV OIP bushing with longer oil-end
This article focuses on an original case history of replacement of a leaky 245 kV OIP bushing of a 220/132/33 kV, 160 MVA, transformer on site at the 220 kV Jabalpur substation, in Madhya Pradesh state in India with an available 245 kV OIP bushing having longer L-2. To retrofit the same turret adopter, an extension piece was fabricated, with an innovative idea of utilizing locally available materials and in-house resources in minimum downtime on site, without relocating or dismantling the transformer, thus giving the Transmission and Distribution Utilities tangible advantages such as large savings of revenue by way of dismantling transportation of the transformer to the OEM’s works for its repairs; repair charges, post-repair transportation to the site followed by erection and commissioning of the transformer on the site etc. and also avoiding dissatisfaction amongst all categories of consumers at large.
Keywords: turret, OIP bushing, draw lead
Maintaining large inventory of major components of transformers for a large fleet of transformers in any transmission utility is a very costly and uneconomical affair. With this in mind, the Bureau of Indian Standards, New Delhi, had issued an Indian Standard IS:12676:1989 titled “Oil Impregnated Paper Insulated Condenser Bushings-Dimensions and Requirements” for the most sensitive and essential component of the transformer, the OIP-Bushings. However, some of the manufacturers do not follow the aforesaid IS and design their transformers at their own convenience and constraints putting the end users/customers into trouble whenever EHV bushings fail or need replacement.
One such incidence took place in June 2016 at the 220 kV Jabalpur substation in India, where the need for replacement of a 245 kV bushing of a 160 MVA, 220/132 kV transformer made by GEC (year of manufacture – 1993) arose. The available 245 kV OIP bushing in the stores of M.P. power transmission utility was with longer length of L-2 (oil end length from flange to bottom) and to install the same was not possible as it would have fouled with the core coil assembly clamping frame (end frame) of the transformer. The OEM of the transformer was contacted and the extension piece of turret or a longer turret was requested but they were not able to provide the requested item. The only option left was to accept this challenge. The proverb “necessity is the mother of invention” made us ponder and innovate an idea of fabrication of the extension cylindrical piece to extend the height of the original turret locally with available in-house resources.