The detection of ionic impurities in insulation

Ionic impurities in insulation not only affect its insulating properties but can result in undesirable electrochemical action and premature failure under electric stress. Impurities may ionize in traces of water the insulation, but it is also known that electrochemical effects can occur in the absence of moisture; in such cases the impurities ionize in the insulation itself. A sensitive test for ionizable organic impurities a material is the measurement of the electrical conductivity of an extract of the material in a suitable pure organic solvent. Details of recommended test are given. Solvent extraction tests are suitable for testing materials before they are assembled into equipment. Ionic impurities in a liquid-impregnated solid dielectric, such as in oil-impregnated-paper capacitors or cables, can be detected without harm to the assembly by studying the loss-angle/voltage characteristic. This technique may be used for studying changes in ion concentration during service.