Page 113 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

6 Check the oil level in transformer tank, conservator, buccholz relay.

Observations- a Oil level must be above the transformer core
b If oil level is below the transformer core – top up the oil.
7 Check the primary & secondary bushings / terminals.
Observations- a Bushings / terminals must be well tight and clean without any damage / crack.
b If Bushings / terminals have damage /burnt – Replace the same.
8 Check the Breather of transformer.

Observations- a Breather must have good silica gel with blue colour and correct oil level.
b If silica gel colour is brown – replace the same.
c Top up the oil.
9 Check the oil tank, cooling pipes for any mechanical damages & leakage.

Observations- a Oil tank and cooling pipes must be mechanically strong with good painting.
b If found any mechanical defects - take appropriate action.
10 Test the transformer with 3 Ph. Variac and measure the output voltage and transformer ratio.
Observations- a. The output voltage must be as rating of transformer.
11 Prepare the trouble shooting table of transformer.

Safety precautions:
1 Use proper tools and meters for testing of transformer.
2 Make sure that earth connection is made while testing the transformer.
3 Never test the transformer with full input voltage.

Trouble shooting table of transformer

Sl.No Problem Cause Remedy

1 Transformer does not turn ON Absence of input supply Check the input supply & rectify
Supply fuse failure Check & replace the fuse
Primary winding open Rewinding to be done
2 No output voltage Secondary circuit fuse failure Check & replace the fuse
Low primary voltage Check the input supply voltage
Single phasing Inform to EB authorities to check
Secondary winding open Rewinding to be done
3 Low output voltage Single phasing of input supply Inform to EB authorities to check
Input supply fuse failure Check & replace the fuse
One of secondary winding is Rewinding to be done
open
4 Vibration/ Humming noise Core assembly is loose. Tighten the core assembly bolts.
Low supply frequency Inform to EB authorities to check
Improper foundation/ Install the transformer properly
installation.

5 Over heating of transformer Excessive loading Reduce the load
Internal short in windings Rewinding to be done
Grounding of windings / core Improve the insulation
Low oil level Top up the T/f oil

96

CITS : Power - Electrician & Wireman - Exercise 47