Underlying secrets of procuring power transformers

Underlying secrets of procuring power transformers
Ajay K Dhagat, Advisor, Prolec GE India, writes why the reliability of transformers is important for continuous power
Electrical systems design needs extra care, precaution and safety factor to achieve a reliable electrical distribution network. In transmission or distribution, nearly 50 per cent of investment cost goes toward power transformers.
A transformer is 99 per cent efficient, robust equipment which maintain the grid balance. In India, it is believed that a transformer performs well if there is no oil leakage or failure. However, this is a myth. Taking advantage of a non-compliant transformer, working normally without any failure, corrupt manufacturers supply underrated or high-loss transformers without the knowledge of the end users.
The cost of transformer varies depending on weight and grade of used core and copper. This encourages non-complaint manufacturers to use less material to gain cost benefits of 7-15 per cent. Import data from a major Indian port showed that more than one third of transformer core material imported in a year through that port was second quality. The Ministry of Steel recently has released an amendment, banning import of low-grade CRGO steel.
Another way of non-compliance is manipulation of losses during inspection by doctoring the measuring instruments. Many non-compliant manufacturers do not follow standards and make huge errors, sometimes intentionally. There can be a difference of 4 to 5 per cent with such practices which include using shunts in measurement circuit and manipulation of heat run test (HRT), current and potential transformers, and winding resistance measurement.
Unlike other power equipment, transformer efficiency is difficult to check at site. Following are the concerns that remain:

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