Insulating Oil Testing Practical

Insulating Oil Testing Practical
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1 Answer

Answer :

Practical Significance

Oil in the transformer is revealed to mechanical and electrical stress after some years. And also absorbs moisture, dirt, and dust from environment. Due to prolong service of transformer, oil tends to deteriorate. Therefore, regular testing of transformer oil is essential to avoid breakdown and to extend the service of transformer.


Competency and Practical Skills

This practical is expected to develop the following skills for the industry identified competency: ‘Plan wiring/cabling activities using relevant materials following safe practices’

i.Test insulating oil.

ii.Find dielectric test of insulating oil.


Practical Outcome

1. Dielectric strength test of one insulating oil sample.

2. Dielectric strength test of two different insulating oil samples of varied usages.


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

Insulating oil is used in transformers, oil immersed switch gear, circuit breakers, oil filled capacitors, tap changers, and fuses as insulating/cooling/dielectric/arc quenching medium. The important properties of insulating oil are Low viscosity, Low pour point, High flash point, excellent chemical stability and high dielectric strength. High dielectric strength ensures good insulation of electrical conductors and prevention of arcing between electrodes under the voltage stresses encountered in normal insulating oil service.


Low dielectric strength may result in many causes, the most common of which is foreign particles or fibers and water in combination. Individually their effect may be relatively small, but together a contamination of only a few parts in a million can cause considerable lowering of the breakdown voltage of the oil. High acidity, sludge and free water should not be tolerated, but will not necessarily reduce the dielectric strength below acceptable or specified levels.

Dielectric strength of oil is measured in kV/mm using oil testing kit shown in Fig. 1, whose circuit diagram is shown in Fig. 2. Indian standard IS. 6792: 1972 covers a method for determination of electric strength of insulating oils.


Practical set-up / Circuit diagram / Work Situation

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Resources Required

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Precautions to be followed

1. Read the instruction manual before using kit.

2. Follow instruction given by manufacturer.

3. Don’t use a dusty or fibrous cloth for cleaning the test cell as it may have loose dust or fibres.

4. Pour test oil into the test cell slowly to avoid formation air bubbles.

5. The test should be carried out in a dry place free from dust.


Procedure

1. Fill the test cell with sample of oil to be tested. The quantity will be as recommended by the manufacturer.

2. Stir the oil properly if bubbles are present in oil.

3. Put the test cell inside the testing unit.

4. Switch “ON” the kit.

5. Raise the voltage uniformly till the breakdown of oil occurs .

6. Record that voltage of breakdown.

7. Repeat the above procedure for three to six times (with fresh sample every time).

8. Repeat the above procedure for various oil samples.

9. The testing shall be done as per as per IS. 6792: 1972

10. Switch off the test kit.

11. Calculate the average value.

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