Page 112 - CITS - Electrician - Trade Practical
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ELECTRICIAN - CITS



           EXERCISE 47 : To demonstrate testing & trouble shooting

                                     of transformer

           Objectives

           At the end of this exercise you shall be able to
           •  list the common faults & defects in transformer
           •  test & measure the continuity of windings of transformer
           •  test the short circuit & earn fault in transformer
           •  prepare the trouble shooting chart of transformer


           Requirements

           Tools/Equipments/Instruments                        •   Tong tester (1000V, 200 A)          - 1 No.
           •   Combination plier (165mm, insulated)  - 1 No.   •   3 ph. Transformer, oil cooled (Any rating) - 1 No.
           •   Screw Driver set (150mm. 5 blades)  - 1 Set.    •   3 ph. Auto transformer (0-460 V)    - 1 No.
           •   Neon tester (75mm, 500 V)        - 1 No.        Materials/Components
           •   Electrician knife (Insulated)    - 1 No.        •   PVC copper wire (1.5 sq.mm)    - 2 meter.
           •   Spanner set (As required)        - 1 No.        •   Test lamp (100 W, 230V)        - 1 No.
           •   Hammer (1 Kg)                    - 1 No.        •   Transformer oil (Any grade)    - as reqd.
           •   Rubber mallet (0.5 kg)           - 1 No.        •   Silica gel (Any grade)         - as reqd.
           •   Multi meter (Digital, 3  digit)   - 1 No.       •   Cotton waste                   - as reqd.
                                 1/2
           •   Megger (500 V)                   - 1 No.
           Procedure


           TASK 1 : Testing of transformer for faults/defects
           1  Check the rating & specification of transformer to be tested.
           2  Make the visual inspection of all parts of transformer for any mechanical damage.

           3  Check the continuity and resistance of primary & secondary windings with multi meter.
               Observations-  a  Both windings must show continuity and resistance value.
                                        b  If Multi meter does not show continuity – open circuit in windings.
                                        c  If Multi meter shows continuity with zero resistance – short circuit in windings.
           4  Check the insulation resistance between primary & secondary windings with megger.

                Observations-  a  Insulation resistance value must be above 5 MΩ  OR as per manufacturer guideline.
                                         b  If Meggar value is less than  5 MΩ  – Insulation resistance is poor.
                                         c  If Meggar value is zero  – Short circuit in the windings.
           5  Check the insulation resistance between transformer core and windings.
               Observations-  a  Insulation resistance value must be above 5 MΩ

                                        b  If Meggar value is less than  5 MΩ  – Insulation resistance is poor.
                                        c  If Meggar value is zero  – windings shorted with core of transformer.










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