Role of copper in continuously transposed conductors
This article explores the critical importance of the proper selection of copper, one of the key raw materials used in the making of continuously transposed conductors for extra high voltage power transformer windings. Windings are one of the most vulnerable components of a power transformer in terms of withstanding various types of electrical disturbances that lead to transformer failure. They have to satisfy complex transformer requirements, but also fit into the economics reasonably well in order to be competitive. Therefore, the expectations about the transformer health and longevity will largely depend on the right choice of its active components and the materials used in their production.
Keywords: continuously transposed conductors, CTC, copper, transformer windings
It has always been a challenge for a power transformer designer to have a winding solution that not only satisfies complex transformer requirements, but also fits into the economics reasonably well in order to be competitive. With the growing market in the power sector, the demand for higher reliability index has also increased several folds. One such example is the imposition of additional five-year warranty for transformers by the Power Grid Corporation of India (PGCIL) in case any defects, as specified in their contract, are observed within the warranty period of the transformer in service.
During its life cycle, a transformer undergoes short circuit faults, comprehensive axial and radial forces, a loss of insulation life due to degradation of oil/paper, overloading, lightning and switching transients – all of which may lead to premature failure of a transformer in service.
A sharp increase in premature failures of extra high voltage (EHV) power transformers and reactors has forced the energy supplying authorities to run a deeper analysis of the risks involved in such failures and a loss of huge revenue due to the resulting outage. Figure 1 presents an analysis of the main causes of power transformer failures recorded between 1997 and 2001, while a similar analysis for a 20-year period between 1991 and 2010 is plotted in Figure 2.
Figure 1. Causes of power transformer failures (1997-2001)
Figure 2. Causes of power transformer failures (1991-2010)