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What is a transformer?

Transformer is a static device used to transfer electrical energy from one circuit to other circuit.

What are the Characteristics of transformer?

   Normally operates at high efficiency. This implies the total loss of transformer should be low. (Please see www.bee.com for losses specified by Government of India for losses in respect of star rating transformers. Please see www.cea.gov.in and www.ecbc.com for losses for energy efficient transformers)

   It should withstand short circuit and switching impulses. This implies that the impedance should match that specified in IS 2026 without negative tolerance. Further the clearances between core and Low voltage winding, Low Voltage winding and High Voltage winding etc shall match with that specified in IS 2026.

  The core should not get saturated when an increase in voltage/frequency by not more than 10% is encountered. This implies that the operating flux density shall be between 1.3 tesla to 1.6 tesla.

   The Temperature rise in windings over ambient temperature should not exceed 50 degree and the oil should not exceed 40 degree. This implies that the current density of the conductor should be between 2 A/mm2 to 3.6A/mm2.

What are the steps to be taken by customer to ensure that he is buying the correct transformer?

   The customer should insist for the Test Certificate and delivery challans for the main materials viz Core,Copper/ Aluminum, Oil, Tape Changer, M.S Tank bought by the manufacturer.

  The customer should carry out at least two stage inspectionsviz one at the time of core & coil assembly and at the time of tanking and carrying out final testing.

   The customer should insist on measuring the voltage, current at transformer end only and not at the testing bench end.

  The customer should insist on a declaration from the manufacturer declaring that the rating of transformer has not been de rated and if it is found de rated at a later date then the manufacturer will replace the transformer free of cost.

   The customer should insist on a declaration from the manufacturer declaring the values of flux density of core, current density of conductors and clearances as per actual construction and in case if the values declared are found to be wrong at a later date the manufacturer should replace the transformer free of cost.

How do I select a suitable supplier for a transformer?

   Please carry out inspection of manufacturer’s factory premises and verify their Designing Capability, manufacturing Capability and Testing Capability.

  Please ascertain the current failure rate for the transformers supplied by the manufacturer.

   Please compare the Total Owning Cost, QAP and transparency.

   Please compare the delivery commitment.

   Please compare their after sale service and guarantee/warranty period.