Critical technical aspects during design, manufacturing and testing of India's first 1200 kV UHVAC transformer

Considering the power demand-supply equation of the next two decades in the Indian subcontinent, 1200 kV UHVAC system has emerged as one of the most viable options for bulk power transfer from power hubs to distant load centers. While higher transmission efficiency is the prime motive of UHVAC system, reliability in commercial operation remains the biggest challenge, more so, due to worldwide paucity of its experience. The UHVAC transformer is probably one of its most important links and needs a critical approach from all angles before putting into the field operation.

The paper aims at providing an insight into various technical aspects while developing India's first 1200 kV transformer for its National Test station. The paper elucidates dielectric considerations of a UHVAC Auto transformer, with regard to 1200 kV winding & lead exit assembly. Apart from dielectric considerations, UHVAC transformer has unique design features like significantly higher solid insulation content, higher axial and radial clearances of windings as compared to EHV transformer. These unique features greatly influence the short circuit behavior and cooling design of the transformer. The paper explains the specific considerations to take care of short circuit integrity and cooling adequacy of an UHV AC transformer.

The paper also throws light on special technological considerations like processing & other manufacturing aspects to take care of specific features. It also shares the test methodology adopted for generation and control of high voltage parameters for a 333 MVA, 1200 kV transformer.