Particle Effect on Transformer Oil

Particle Effect on Transformer Oil : Technical Note

Sanjay Miglani, Director, mk teknology1 Pvt. Ltd., New Delhi

M: 09810550075 Email: [email protected]

Transformer oil is one of the most essential components for conventional oil immersed

transformers as it acts both as electrical insulation and thermal coolant. The dielectric strength of

the oil and more specifically the level of oil contamination determine the dielectric safety margin

of the transformer insulation system.

AC breakdown voltage tests are usually used for quality check of mineral oils during transformer

operation. It can be seen that particle effects on ac oil breakdown voltages.

The oil samples Can be filtered through a 0.2µm membrane filter unit for 3 cycles. It was found

that after 3 cycles, the oil is clean enough and the particle number in oil samples could not

decrease further even more filter cycles were given. The particle number in oil samples can be

decided using PAMAS S40 or SBSS liquid particle counting system systems supplied by mk

teknology1 Pvt. Ltd., New Delhi, which can detect particles with diameter from 1µm to 100µm.

The particle counting results can be obtained such as shown in following table:

The ‘clean’ oil is defined as per CIGRE (INTERNATIONAL COUNCIL

ON LARGE ELECTRIC SYSTEMS) the particle content with a diameter larger than 5µm is

down to 300 per 100ml in a oil sample. As can been seen from the filtering results, the particle

numbers in ‘processed’ oil samples were almost reaching the number given in the definition of

‘clean’ oil.

Subsequently oil can be prepared for AC withstand voltage tests and multiple tests can be

conducted as per the ASTM D1816 test stan

From the results, it can be noticed that the dielectric strengths of ‘processed’ oils is increased

significantly comparing to those of ‘as

and highest breakdown voltages. The higher dielectric stre

fewer particles suspended in the oil.

the particles with different sizes, the more possibilities for different sized particles to be in the

path between the two electrodes to initiate streamers, the less predictable the breakdown voltage

may be. This results in the deviation between the measured breakdown voltage and the fitting

value at low probabilities. Therefore with fewer particles, it is more difficult

breakdown in the ‘processed’ oils and consequently, the breakdown voltages are higher and more

consistent.

oil can be prepared for AC withstand voltage tests and multiple tests can be

conducted as per the ASTM D1816 test standard.


significantly comparing to those of ‘as-received’ oil, in terms of mean breakdown voltage, lowest

and highest breakdown voltages. The higher dielectric strength for ‘processed’ oils is caused by

fewer particles suspended in the oil. Which means less weak links. For ‘as-received’ oil, the more


two electrodes to initiate streamers, the less predictable the breakdown voltage


value at low probabilities. Therefore with fewer particles, it is more difficult


oil can be prepared for AC withstand voltage tests and multiple tests can be


received’ oil, in terms of mean breakdown voltage, lowest

ngth for ‘processed’ oils is caused by

received’ oil, the more


two electrodes to initiate streamers, the less predictable the breakdown voltage


value at low probabilities. Therefore with fewer particles, it is more difficult to initiate


Particle Effect on Transformer Oil

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