Practical Significance
Many a times it is essential to measure insulation resistance of cable before installation as well as whenever power breakdown in a shop or section of industry occurs. The value of insulation resistance measured decides the condition of cable. It is essential to know the procedure & interpretation of value of insulation resistance.
Practical Outcome
1. Use the Megger to measure insulation resistance of cables.
Relevant Affective domain related Outcome(s)
i. Practice good housekeeping with safety measures.
ii. Demonstrate working as a leader/a team member.
iii. Maintain tools and equipment.
iv. Follow ethical practices.
Minimum Theoretical Background
Insulation resistance quality of an electrical system degrades with time, environment condition i.e. temperature, humidity, moisture and dust particles. It also get impacted negatively due to the presence of electrical and mechanical stress, so it becomes very necessary to check the IR (Insulation resistance) of equipment at a constant regular interval to avoid any major electrical shock.
Megger is an instrument designed, to measure extremely high value of resistance.
Megger measures the extremely high value of resistance, hence called megaohmmeter. It is also used for measurement of insulation resistance, hence called insulation tester.
Practical set-up / Circuit diagram / Work Situation
Connection Diagram:
Resources Required
Precautions to be followed
1. The megger should not be used on live system.
2. The handle of the megger should be rotated in clockwise direction.
3. Don’t touch the terminals of megger while conducting a test; otherwise it will give an electric shock.
4. Rotate the handle of megger at its rated speed.
5. Keep the megger in horizontal position while operation.
Procedure
1. Connect the L terminal of megger to conductor under test as shown in Fig. 2.
2. Connect the E terminal of megger to other conductors connected together and to sheath.
3. Rotate the handle of megger at its rated speed.
4. Observe the reading.
5. Note down the reading in observation table.
6. Repeat the steps for other conductors.