Page 126 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 53 : To measure the insulation resistance of

Electrical machineries

Objectives

At the end of this exercise you shall be able to:
• check & identify the insulation resistance tester (Megger), its construction, scale & terminals
• practice the use of megger and testing of insulation resistance
• test the insulation resistance of Electrical machines- Motors, Generators, Transformers and cables
• prepare table of insulation resistance of different Electrical machineries.

Requirements

Tools/Equipments/Instruments
• Combination Plier 165mm, • Defective Motor, Generator,
insulated - 1 No. transformer Any rating - 1 No. each
• Screw Driver 150mm, insulated Materials/Components
stem - 1 No.
• Neon Tester 75mm, 500 V - 1 No. • PVC copper probes with
• Electrician knife Insulated - 1 No. crocodile clip 1.5 sq.mm - 1 Set
• Megger, dynamometer type 500 V - 1 No. • Test lamp 100 W, 230V - 1 No.
• Megger, electronic type 500 V - 1 No. • Cotton waste - as reqd.
2
• Multi meter Digital, 3 digit - 1 No. • Armored cable 25 mm, 4 core - 2 m.
1/2
• Electric Motor, Generator,
transformer Any rating - 1 No. each
Procedure

TASK 1: Check the construction of megger and its scale
1 Draw the diagram of megger and measurement of insulation resistance.
2 Check and identify the construction, scale & rating of dynamometer megger & Electronic megger.
3 Check the battery of Electronic megger for good condition.

4 Keep the different Electrical machineries on wooden table for testing insulation resistance.

TASK 2: Measure the insulation resistance Electrical machineries with megger
1 Test the megger for its working condition before conducting insulation resistance test.
2 Short the L & E terminals of megger and rotate the handle at 160 RPM, see the deflection of needle which
should move towards zero for good working condition of megger. If doesn’t megger is defective
3 Similarly, check the Electronic megger by pressing its Test button.
4 Connect the L & E terminals of megger between A coil & B coil of induction motor and test the Insulation
resistance. The IR value should be greater than 2 MΩ.
5 Similarly, check the insulation resistance between motor coils & body of motor, and IR value must be greater
than 2 MΩ

6 In similar way, check the insulation resistance of transformer, armored power cable and other Electrical
appliances.
7 Conduct the insulation resistance test in defective Electrical machines & equipments and note the IR value
8 Record the test values in data sheet

109

CITS : Power - Electrician & Wireman - Exercise 52