Large Transformer and Shunt Reactor - Specification, Design & Testing Aspects - User’s Perspective

Large power transformers and shunt reactors are largest and costliest equipment in the transmission network. Transformers being a long delivery item, reliable performance of these equipment are very important to maintain the availability of power system.

The specification forms the basis on which the manufacturer designs, manufacturers and tests a transformer. With the growth in size of power system and complexities of modem system, the adequacy of transformer specification plays a major role on its reliability. A good specification must properly consider the effect of application, system operating conditions, environmental considerations, site details, service conditions, termination details etc. so that the transformer is designed for the conditions under which it has to operate. Thus the adequacy of specification of transformers particularly that of high voltage and larger rating assumes tremendous importance and an inadequate specification can lead to a deficient design and poor reliability.

The various parts of transformers viz. magnetic circuit, insulation system, termination, cooling equipments etc. are designed as per specification details. Say for example insulation system is designed on the basis of electric insulation levels called in the specification. The performance of insulation system is a function of dielectric stress and dielectric strength. The dielectric stresses are governed by the test levels specified in the specification by the customer and dielectric strength depends on the design, material selection, the quality of manufacture, careful handling and maintenance at site. Similarly the magnetic circuit is being designed based on continuous and short time power frequency over voltages and its suitability depends on the design, material selection, the quality of manufacture, careful handling etc.

This paper will briefly discuss the salient consideration required for development of technical specification of large power transformer and their influence in the overall performance and reliability of the transformer from utilities' point of view.