Function Of Transformer Oil h1u70

Transformer oils are subject to electrical and mechanical stresses while a transformer is in operation. In addition there is contamination caused by chemical interactions with windings and other solid insulation, catalyzed by high operating temperature. The original chemical properties of transformer oil change gradually, rendering it ineffective for its intended purpose after many years. Oil in large transformers and electrical apparatus is periodically tested for its electrical and chemical properties, to make sure it is suitable for further use. Sometimes oil condition can be improved by filtration and treatment. Tests can be divided into: 1. 2. 3. 4.

Dissolved gas analysis Furan analysis PCB analysis General electrical & physical tests:  Color & Appearance 

Breakdown Voltage

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Water Content

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Acidity (Neutralization Value)

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Dielectric Dissipation Factor

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Resistivity

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Sediments & Sludge

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Flash Point

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Pour Point

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Density

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Kinematic Viscosity

The details of conducting these tests are available in standards released by IEC, ASTM, IS, BS, and testing can be done by any of the methods. The Furan and DGA tests are specifically not for determining the quality of transformer oil, but for determining any abnormalities in the internal windings of the transformer or the paper insulation of the transformer, which cannot be otherwise detected without a complete overhaul of the transformer. Suggested intervals for these test are: 

General and physical tests - bi-yearly

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Dissolved gas analysis - yearly

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Furan testing - once every 2 years, subject to the transformer being in operation for min 5 years.

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Main article: Transformer oil testing Some transformer oil tests can be carried out in the field, using portable test apparatus. Other tests, such as dissolved gas, normally require a sample to be sent to a laboratory. Electronic on-line dissolved gas detectors can be connected to important or distressed transformers to continually monitor gas generation trends. To determine the insulating property of the dielectric oil, an oil sample is taken from the device under test, and its breakdown voltage is measured on-site according to the following test sequence:    

In the vessel, two standard-compliant test electrodes with a typical clearance of 2.5 mm are surrounded by the insulating oil. During the test, a test voltage is applied to the electrodes. The test voltage is continuously increased up to the breakdown voltage with a constant slew rate of e.g. 2 kV/s. Breakdown occurs in an electric arc, leading to a collapse of the test voltage. Immediately after ignition of the arc, the test voltage is switched off automatically.

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Ultra fast switch off is crucial, as the energy that is brought into the oil and is burning it during the breakdown, must be limited to keep the additional pollution by carbonisation as low as possible. The root mean square value of the test voltage is measured at the very instant of the breakdown and is reported as the breakdown voltage. After the test is completed, the insulating oil is stirred automatically and the test sequence is performed repeatedly. The resulting breakdown voltage is calculated as mean value of the individual measurements.