IEC 60628:1985 pdf free download.Gassing of insulating liquids under electrical stress and ionization.
IEC 60628:1985 describes two procedures each using different apparatus to measure the tendency of insulating liquids to evolve or absorb gas when subjected, in cells having specific geometries, to electrical stress of sufficient intensity to cause an electric discharge through a gas phase in which a gas-oil interface is located. The methods described in this standard are suitable for purchase specifications, general selection of insulating liquids, product development and quality assurance.
2. General notes on the methods
2.1 These methods indicate whether insulating liquids are gas absorbing or gas evolving under the test conditions. The gassing behaviour of any one insulating liquid is primarily a function of its chemistry but changes in certain test parameters can modify the results significantly.
2.2 These methods can operate under a variety of gas phase, temperature and voltage stress conditions. In order to establish uniform criteria of measurement, specific test conditions are specified which experience has shown to be most informative of the general performance expected from the liquid dielectric in electrical equipment should ionization occur.
At present, however, though it is generally agreed that gas absorbency of the impregnant has a positive effect in minimizing ionization problems in impregnated insulation systems used at high electrical stress, correlation of gassing-cell test results with equipment performance is limited. Engineering judgement is necessary in interpreting the test results in relation to any intended application.
2.3 Both methods, have been originally designed for the range of gassing rates characteristic of mineral insulating liquids. The use of these methods with other liquids may require some adaptations in the dimensions of the test cell.
3. Outline of method
This method determines the gassing tendency of an insulating liquid under a hydrogen
atmosphere and expresses the results in terms of gassing rate over a relatively short test period.
After being dried and saturated with hydrogen gas, the insulating liquid and the hydrogen pocket above the liquid are subjected in the specified cell to a radial electrical stress under the following experimental conditions:
— voltage: 10 kV;
— frequency: 50 Hz or 60 Hz;
— temperature: 80°C;
test duration: 120 mm at 50 Hz or 100 mm at 60 Hz.
The rate of evolution or absorption of gas resulting from reactions at the gas-oil interface, is calculated as volume per unit of time from changes in pressure with time.
IEC 60628:1985 download
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