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Mechanism of Water Treeing

OBJECTIVES AND APPROACH. OBJECTIVESDETERMINE MECHANISM OF WATER TREEINGKnowledge of Mechanism Will Help:IDENTIFY MOST-EFFECTIVE DIAGNOSTIC METHOD(S) DEVELOP IMPROVED MATERIAL APPROACHUSE COMBINATION OF ELECTROCHEMICAL, MECHANICAL AND SPECTROSCOPIC TECHNIQUES TO CAUSE AND DETECT WATER TREEING

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Mechanism of Water Treeing

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    1. Mechanism of Water Treeing Tzipi Cohen-Hyams, Adam Tornheim and Thomas M. Devine

    2. OBJECTIVES AND APPROACH OBJECTIVES DETERMINE MECHANISM OF WATER TREEING Knowledge of Mechanism Will Help: IDENTIFY MOST-EFFECTIVE DIAGNOSTIC METHOD(S) DEVELOP IMPROVED MATERIAL APPROACH USE COMBINATION OF ELECTROCHEMICAL, MECHANICAL AND SPECTROSCOPIC TECHNIQUES TO CAUSE AND DETECT WATER TREEING Near-Term Objective: Compare/contrast Laboratory Water Trees with Water Trees of Field-Aged Cable

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    4. 4 Detection of Water Trees in Aged Cables Inspection of a 24 year-old, failed XLPE aged cable obtained from Walter.

    5. 5 Inspection of a 24 year-old, failed XLPE aged cable for the presence of Water Trees According to the procedure of A. C. Ashcraft and R. M. Eichhorn, „METHOD FOR VISUALIZATION OF WATER TREES BY STAINING”, IEEE Trans. Electr. Insul, Vol EI-13 No 3, June 1978. A four inch section of cable was stripped of its jacket and insulation shield. The cable was then cut into wafers approximately 80 mils in thickness and 40 mils. The wafers were polished up to 1200 grit, and were examined using an Optical microscope. Then the 40 mils wafers were placed in a 70?C Methylene Blue solution for 7-10 minutes. After staining, the cable wafers were rinsed in DI water to remove any excess dye solution. The cable wafers were then allowed to dry and then examined with a stereo-microscope (We used a 4.5X magnification stereoscope) and a conventional microscope. To date, optical microscopy of the cable using methylene blue dye has not revealed water trees. We used Raman spectroscopy for studying the effect of the dye on the Raman spectra. We also used conventional Raman spectroscopy to study the structural changes during electrical testing.

    6. 6 Detection of Water Trees in Aged Cables Inspection of a 24 year-old, failed XLPE aged cable obtained from Walter. On 12/3/07 we received a number of aged cables from San Diego.

    7. 7 Cables received from San Diego 220 mils High Molecular Weight PE from 1970; manufactured by Anaconda, underground direct buried. Cable failed. 220 mils High Molecular Weight PE from 1969; manufactured by Anaconda, underground direct buried. Unjacketed. Cable failed. Unknown manufacture 175 mils XLPE insulation from 1984; manufactured by Pirelli. Cable failed. 175 mils XLPE insulation, unknown year; manufactured by Pirelli. Cable failed. Burnt cable from blown fuses from 1981; manufactured by Pirelli (probably XLPE). Unjacketed 175 mils XLPE from 1979. A new TR-XLPE 175 mils cable.

    8. 8 Finding Water Trees METHYLENE BLUE STAINING TECHNIQUE from San Diego utility A four inch section of cable is stripped of its jacket and insulation shield. The cable is then cut into wafers approximately 20 mils in thickness. The wafers are then placed in a boiling Methylene Blue solution for 10-15 minutes. Staining time varies with the thickness of the cable wafers and the newness of the methylene blue solution. After staining, the cable wafers are rinsed in hot water to remove any excess dye solution. The cable wafers are then allowed to dry and then examined with a stereo-microscope. (30X magnification stereoscope with a 100 mil reticle ). The the top and bottom of the stained wafer cable are examined with an index of refraction oil or Silicon oil to cut down on the surface distortion (Scratches) from cutting the wafers and it allows you to look inside the wafer rather than looking at the surface. Methylene Blue Solution (250 ML Of Solution) 250 milliliters of distilled or dionized water. 8 milliliters of Ammonium Hydroxide Solution. One gram of Methylene Blue Powder.

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    10. 10 Insert needle electrode into polymer (cylindrical hole in (2)) Fill polymer sample with electrolyte (aqueous NaCl) Insert second electrode into electrolyte Apply high voltage between electrodes Raman spectroscopy Forming Water Trees in the Laboratory

    11. 11 Testing Apparatus: NST

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    13. 13 RAMAN SPECTROSCOPY

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