Page 113 - CITS - Electrician - Trade Practical
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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







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                                    CITS : Power - Electrician & Wireman - Exercise 47
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