IEC 60628 Measurement of gassing of insulating liquids under electrical stress and ionization
Section 1. General
1 Scope
This standard 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.
WARNING! Attention is called to national regulations associated with the use of high voltage, hydrogen and solvents.
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.
