THE INFLUENCE OF SURFACE RESISTIVITY ON ELECTRICAL INSULATORS OF THE REACTOR

Operational Safety Dept., National Center for nuclear safety

The paper presents an important simplification by introducing the surface resistivity to

classify and estimate the deterioration breakdown process. The results show that the

breakdown voltage increases with increasing surface resistivity of the insulator.

Several test methods have been developed to examine the performance of insulators in

a reactor’s electrical system. Factors which affect or influence surface resistivity on

insulators breakdown have been analyzed. The obtained values depend on a number

of factors, including temperature, applied voltage, humidity, moisture content,

electrification time and frequencies. Comparing or interpreting data is difficult unless

the test is controlled and defined, especially when a specimen is drying out after being

subjected to moist or humid conditions. The surface temperature at the breakdown

location has been measured and a good correlation with the decomposition

temperature of the insulators has been found. For electrode separations of 1mm or

greater the breakdown voltage does not increase linearly with the length of the

insulator. The breakdown voltage over an insulator is raised when the edge of the

insulator close to either electrode is rounded. Insulation deteriorations against time

and temperature changes which are important have been introduced. The breakdown

mechanisms of insulation operating under wet and dry conditions have been

discussed.