Flash-over testing of overhead insulators
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The document discusses various causes of insulator failure including cracking due to unequal contraction and expansion of materials from changing climatic conditions, defective insulation materials that are porous due to low manufacturing temperatures, improper glazing leaving the surface susceptible to flashover, and mechanical stresses exceeding tolerances. It also outlines various tests to evaluate insulators including power frequency dry and wet flashover tests, impulse voltage tests, temperature cycling, puncture voltage, porosity, and mechanical strength tests. Routine tests include proof load testing and corrosion resistance evaluations.
![1] Flashover Test
■ Power Frequency Dry
Flashover Test of Insulator
■ Power Frequency Wet
Flashover Test or Rain Test
of Insulator
■ Impulse Frequency Flash
over Voltage Test of Insulator](https://image.slidesharecdn.com/flashovertestingofoverheadinsulators-190717180647/85/Flash-over-testing-of-overhead-insulators-6-320.jpg)
![2] Performance Test of Insulator
■ Temperature Cycle Test of Insulator
■ Puncture Voltage Test of Insulator
■ Porosity Test of Insulator
■ Mechanical Strength Test of Insulator](https://image.slidesharecdn.com/flashovertestingofoverheadinsulators-190717180647/85/Flash-over-testing-of-overhead-insulators-11-320.jpg)
Flash-over testing of overhead insulators
- 1. By: S A G A R D REVA UNIVERSITY
- 3. Causes of Insulator Failure ■ Cracking of Insulator Consist of mainly 3 different materials: ■ Main Porcelain body, ■ steel fitting arrangement and ■ Cement Main Cause: Changing climatic conditions Output: Unequal Contraction & expansion of materials
- 4. ■ Defective Insulation Material ■ If defective anywhere, the insulator may have a high chance of being puncher from that place. ■ Porosity in The Insulation Materials ■ Main Cause: manufactured at low temperatures ■ Output: it will make it porous, and hence Insulation failure occurs.
- 5. ■ Improper Glazing on Insulator Surface ■ Cause: insulator is not properly glazed. ■ Output: Moisture along with deposited dust on the insulator surface, produces a conducting path. As a result the flash over distance of the insulator is reduced. Hence, the chance of failure of insulator due to flash over becomes more. ■ Mechanical Stresses on Insulator ■ If an insulator has any weak portion due to manufacturing defect, it may break from that weak portion when mechanical stress is applied on it by its conductor.
- 6. 1] Flashover Test ■ Power Frequency Dry Flashover Test of Insulator ■ Power Frequency Wet Flashover Test or Rain Test of Insulator ■ Impulse Frequency Flash over Voltage Test of Insulator
- 7. Power Frequency Dry Flashover Test of Insulator ■ First the insulator to be tested is mounted in a practically manner ■ The terminals of the variable power frequency voltage source is connected to both electrodes (end terminals) of the insulators ■ The power frequency voltage is increased gradually up to a specific value ■ The voltage is maintained for 1 minute
- 9. Power Frequency Wet Flashover Test or Rain Test of Insulator ■ First and second procedure remains the same ■ Artificial raining condition: Sprayed with water at an angle of 45 degrees Precipitation should not be more than 5.08 mm per minute Water resistance 9/10/11 kΩ per cm3 Normal atmospheric pressure and temperature The power frequency voltage is increased gradually up to a specific value The voltage is maintained for 1min or 30 sec as specified.
- 10. Impulse Frequency Flash over Voltage Test of Insulator ■ The insulator is kept in similar manner of previous test ■ Then several hundred thousands Hz very high impulse voltage generator is connected to the insulator ■ Spark over voltage is noted ■ This ratio should be approximately 1.4 for pin type insulator and 1.3 for suspension type insulators
- 11. 2] Performance Test of Insulator ■ Temperature Cycle Test of Insulator ■ Puncture Voltage Test of Insulator ■ Porosity Test of Insulator ■ Mechanical Strength Test of Insulator
- 12. Temperature Cycle Test of Insulator 1. The insulator is first heated in water at 70oC for one hour. 2. Then this insulator immediately cooled in water at 7oC for another one hour. 3. This cycle is repeated for three times. 4. After completion of these three temperature cycles, the insulator is dried and the glazing of insulator is thoroughly observed. After this test there should not be any damaged or deterioration in the glaze of the insulator surface.
- 13. Puncture Voltage Test of Insulator 1. The insulator is first suspended in an insulating oil. 2. Then voltage of 1.3 times of flash over voltage, is applied to the insulator. ■ A good insulator should not puncture under this condition. Mechanical Strength Test of Insulator • The insulator is applied by 2½ times the maximum working strength for about one minute. • The insulator must be capable of sustaining this much mechanical stress for one minute without any damage in it.
- 14. Porosity Test of Insulator 1. The insulator is first broken into pieces. 2. immersed in a 0.5 % alcohol solution of fuchsine dye under pressure of about 140.7 kg ⁄ cm2 for 24 hours. 3. After that the sample are removed and examine. ■ The presence of a slight porosity in the material is indicated by a deep penetration of the dye into it.
- 15. Routine Test of Insulator ■ Proof Load Test of Insulator ■ In proof load test of insulator, a load of 20% in excess of specified maximum working load is applied for about one minute to each of the insulator. ■ Corrosion Test of Insulator 1. In corrosion test of insulator, The insulator with its galvanized or steel fittings is suspended into a copper sulfate solution for one minute. 2. Then the insulator is removed from the solution and wiped, cleaned. 3. Again it is suspended into the copper sulfate solution for one minute. 4. The process is repeated for four times. ■ Then it should be examined and there should not be any disposition of metal on it.
- 16. THANK YOU ■ Web Ref: ■ Pinterest.com ■ Eguhv.com ■ Electrical4u.com ■ Youtube.com ■ natradioco.com ■ Electricalunits.com ■ Ceramicmachine.com