Page 112 - CITS - Electrician - Trade Practical

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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