The voltage induced in the secondary coil is directly proportional to its number of turns.
The current induced in the secondary coil is inversely proportional to its number of turns.

Main parts of Power Transformer:

Different types of Losses:

Reason for Failures in Transformers:

a.Defective Manufacturing:

b.Failures due to Mechanical Damages:

c.Failure in Dielectric Circuits

d.Failures in Electric Circuits:

e.Failures in Magnetic Circuits:


a.Open circuit Test:

b.Short circuit Test:

c.Transformer Regulation Test:

d.Winding Resistance Test

This test is performed to find out the resistance of the winding By applying small DC voltage to the winding and measuring the Corresponding current . This is more feasible for HV winding.

e.Polarity Test:

This is required for identifying the primary and secondary phase polarities

f.Load Test:

Load test is requred to find out total loss that takes place when A transformer is loaded . In this test actual temperature rise ,voltage regulation and efficiency of the Transformer can be obtained

g.Ratio Test:

This test is performed to find out % of winding ( normally on primary side ) Included / Excluded from the circuit When a tap is changed This is one of the Important pre commissioning test

h.Insulation test of Transformer (Meggering)

i.BDV Tests on transformer oil

j.D G A Analysis of Transformer oil

Tips to reduce Failures in Distribution Transformer:

Transformer Maintainence

Cleaning of bushings and external surface of tank cooling pipes Monthly
Checking of oil levels in the conservator and gauge glass Monthly
Checking of silica gel in the breather and replacement is necessary Monthly
Checking of oil level in the oil seal of breather and top up if necessary Monthly
Checking of HG fuse and LT fuse and renew if necessary (correct gauge shall be maintained) Monthly
Checking breaker operation Monthly
Checking of vent pipe diaphragm Monthly
Checking of terminal loose connections is any and tightening the same Monthly
Checking for any oil leaks and rectification (including replacement of oil seals if required) Monthly
Taking tong tester reading during peak load hours and remedial action whenever load exceed 80% rated capacity Quarterly
Noting down neutral currents and load balancing in all the three phase Quarterly
Measurement of IR values Half Yearly
Testing of oil for BDV, acidity Half Yearly
Checking of lightening arrestors and replacement if required Half Yearly
Measurement of earth resistance checking of earthing system and rectification if required Half Yearly
Overhaul of Transformer Once in 5 years
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