ABSTRACT

Distribution Transformers (DTs) and supply cables /conductors are major and most critical assets for an electrical disctribution company. Reliable and efficiency operation of distribution transformer is one of the key performance index (KPI) for the DISCOM. In India, transformer failure rate for the state distribution companies is reported officially in the range of 12-15% whereas at the same time for a private DISCOM, transformer failure rate is well below 1%.

By design a transformer is the most efficient and long lasting electrical machine. Efficency of power transformer could be as high as 99.75% whereas for distribution transformer, design efficiency could be in the range of 98.5% to 99.5%. A transformer is designed to have a life of 20 to 25 years. However, undesirable operating conditions reduces operating life of transformer to 5-6 years and efficiency could drop to 95% or even less.

A transformer will work satisfactorily when it is feeding to the loads for which it is designed for and balanced loads. However in actual practice, transformers with a K factor of 1 is feeding increasingly non linear and un balanced loads. These factors cause increased operating temperature of transformer, reduced efficiency and reduced life of transformer. In cases of extreme third harmonic pollution the neutral points are often the victim resulting in burn out and failure.

This case study depicts how a distribution company addressed above issues thus improving life, reliability and efficiency of the transformer.

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