Trouble Shooting Chart of 3 Phase Transformer

Sr. No

Trouble/ symptoms

Possibility of causes

Tests/ Remedies/ Rectification

1

Insulation resistance between core windings lowered down

Over heating. Moisture entry Lightening and switching surges.

Check transformer coil. Replace or filter the oil. Dry the
transformer. Check series reactors, lightening arrestors.

2

Humming Noise

Loose stamping and fittings.

Check and tighten the nut-bolts and stamping.

3

Rusting/ corroding of tank.

Oil might be having more acidity.

Take acidity test of oil. Use activated ammonia.

4

sagging

Used wrong grade oil. May be due to overheating.

Replace the present oil with appropriate grade oil. Remove the causes
as explained in Sr. No. 5

5

General over heating.

Overload faulty ventilation oil level might have gone down. Much more
sludge formation in oil. If transformers are connected in parallel and
sharing improper load.

Reduce the load. Check space margins on all sides of the transformer.
Check cooling system exhaust fans properly working or not. Make up the oil.
Filter the oil, take off the oil by drain valve, clean core and tank, and
refill the oil. Voltage ration and percentage impedances be checked. Check
tap changers.

6

Unequal heating on bank of Y-connected transformer with earthed
neutral.

Internal / External earth fault on one of the phase.

Locate the fault and repair the same.

7

Overheating ON or OFF Load.

Primary voltage may be more or frequency may be lower.

Check the voltage w.r.t. rated value and correct it. Check frequency
as per rated value and corrective majors May be taken.  

8

Low secondary voltage.

Wrong voltage selection.

Adjust the voltage with correct selection of tapping.

9

In case of 3-phase transformers unequal phase voltage.

May be due to internal /external earth fault.

Locate the faults and repair.

10

Locale heating.

Excessive eddy currents.

Check core clamping bolts, nuts fitting and remove the fault.