Distribution Transformers

Transformers are among the most efficient machines ever designed by mankind, and are usually built of copper or aluminum. As copper has conductivity almost twice that of aluminum, it is often preferred in transformer construction. The largest power transformers have efficiencies at full load of 99.75%. Distribution copper-based transformers are smaller, less efficient and more lightly loaded. Transformers in urban distribution (typically 250-1,000kVa) may lose 1-2% of energy transformed as heat. For smaller transformers in rural areas (50-100kVa), efficiency in operation can be as low as 95% Most of the distribution transformers installed by the State Electricity Boards use high levels of energy which results in huge losses.

A large number of Distribution Transformers used in India, particularly in smaller ratings such as 25KVA, 63KVA, 100KVA (11KV/415V, 3 phase) use conventional materials and methods of manufacture, resulting in very high losses. The failure rate of these transformers is very high, around 16% (in Govt. SEBs), which is not favorably comparable to international norms of 1 to 2%. Further the life of these conventional transformers is very low (6-8 years). The higher failure rate also adds to the already high Transmission & Distribution (T&D) losses in the power distribution network of SEBs.

  • Inherent low loss material

  • Special skills not needed during jointing and termination (significant percentage of transformer failure can be attributed to defective joints and termination)

  • Copper scores over Aluminium in several respects such as conductivity, resistance, thermal conductivity, better withstanding capability during short circuit, etc.

  • Easy availability and competitive pricing favours “Copper” usage.

Copper is needed for maintaining and growing life, be this for humans, animals or plants. In humans, it is key to the foetus during pregnancy, to healthy brain function throughout life, and to the repair of wounds and injuries. The human body does not manufacture copper, so it needs to be obtained from food and water. Copper deficiency—which means consuming too little dietary copper—can lead to a range of serious diseases ranging from blood and blood vessel irregularities to abnormal bone formations and hypopigmentation of the skin.

  • Reduces technical losses, thereby saving power procurement costs

  • Allows for further improvement in energy efficiency of transformers as mandated by BEE in PAT-2 cycle

  • Improves transformer reliability, thereby reducing downtime

  • Increases kVA capacity of the transformer

  • Creates an opportunity for the DT OEM or repairer to become a stakeholder in network O&M

When purchasing transformers it is important to compare the cost of the losses over the entire lifetime of the various types considered. DNV GL’s Transformer Loss Calculation Tool enables you to choose the economically most efficient transformer based on lifetime parameters such as capitalized cost, CO2 emissions, payback time and internal rate of return. In a clear summary table and intuitive graphs the tool provides you with additional information about the no-load and load loss evaluation (A and B factors), in case these are not known in advance. It calculates transformer losses when there are harmonics in the loading.

A pilot study was also undertaken We have undertaken pilot study on a 100 kVA & 200kVA DT at a public and private DISCOM respectively implementing the Active Repair solution.


DT Active Repair (English)


Active repair of DT [Distribution Transformer]


Economic impact of DT failure in India