It is is very important to check the Dielectric Strength of transformer oil because it is a sine-qua-non to ensure the reliability of operations of power transformers.
Besides various tests, examining the dielectric strength test of transformer oil is one of the main test which helps to determine and ensure the insulating properties of oil under extreme voltage. Dielectric strength has to be higher than the threshold value. Nevertheless, this strength can be reduced by contaminants such as water, sediment, various acids and conducting particles. The causes and reasons behind these particles and contaminants may vary. The weakening of strength does leakage of current between HT and LT winding. In some instances, it can result in the spark or short circuit. One main sign of the purity of the oil is its cleanliness and dryness, but it still does not confirm the absence of pollutants.
Let us decompose the words in the phrase above:
- Dielectric word refers to a bi-dimensional or two-dimensional test mechanism having two electrodes on its either sides to complete an electrical circuit. The spheres in the electrodes have an average size of 2.5mm each.
- An oil breakdown meter refers to a testing mechanism or device used for the testing of a sample of any oil by a test cell having electrodes. Electrical components like transformers, capacitors, switches, etc. are used to help assess the condition of the oil. After testing the oil and its’ breakdown spot, it can be approximately opined whether the oil has aged due to increased watery content, sludge or excessive oxidizing or checked if oil is in its’ original state and exhibits its’ properties quite fairly.
The most widely used kind of oil breakdown meter is the Insulating Oil Tester which is designed for the easy, and accurate determination of the dielectric strength of insulating oils poured in electric apparatuses like transformers, etc. mentioned above. They are ideal for on-site testing and laboratory use. The most usual on-site testing is a check, on, of course, oil’s electrical strength which should be carried out in accordance with the requirements of BS 5874.
Standards for the eligible oil breakdown metres
There are various kinds of oil testers and they come in various models. Models capable of measuring the dielectric breakdown voltage have to be up to 100 kV to determine the electrical strength of the oil. Also, there are various standards for the electrical devices used to measure the strength of the oil being tested. Some standards are ASTM D877, ASTM D1816, and many more.
Amperis’ Loss tangent meter in dielectric oil TAND220A
The measuring instrument type TAND220A complies with the new IEC 61620 standard and is based on "low amplitude, low frequency, alternate square wave method" and does precise and accurate measurement of volume conductivity and relative permittivity. The measurement of volume conductivity in the range of 0.01 pS/m to 20'000 pS/m allows the use of the instrument for examination of highly-resistive liquids even at ambient temperature.
The Amperis’ Loss tangent meter in dielectric oil TAND220A works with low voltage and low current levels and represents no danger at all for its operators.
A paradigm of application of TAND220A is the quality assessment of mineral oil used in high voltage apparatus such as power and instrument transformers, capacitors, etc. some investigations have also proved the fact that the conductivity of oil is influenced by impurities and ionic components, introduced or produced in it. Therefore, the oil conductivity exhibits the quality of oil in a reliable manner.
Furthermore, it has also been seen that the moisture in oil has no major influence on its conductivity.
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