抄録
Generally, the fluctuation of arc resistance of electrical insulating materials is remarkably large even if the tests are carried out under the same condition with the same testing aparatus. In this paper, the cause of the fluctuation of arc resistance was discussed from the results of arc resistance tests on a large number of specimens.
The experimental method was nearly same as the ASTM D495-71 and various plastics was used as the test materials. For each material, 80-100 tests were carried out. The main results obtained are as follows:
(1) The frequency curve of arc resistance generally has plus skewness and can be represented approximately by a logarithmic normal distribution. Furthermore, this distribution curve agrees well with the result of calculation obtained by considering a stochastic process. Thus, it is considered that the phenomenon of arc deterioration is a statistical one.
(2) The loading with fillers, the temperature rise of circumference and the increase of test voltage equally decrease the fluctuation of arc resistance.
(3) No significant difference is observed on the fluctuation of arc resistance between the test with rod electrode and that with rectangular plate electrode in ASTM method.
(4) It is convenient to elucidate the fluctuation of arc resistance when the probability of arc deterioration p is introduced. This value of p can be obtained from the slope of log r-t curves, r being the non-deterioration probability. Moreover, p is small at the beginning but reaches nearly constant after a while.
(5) The non-deterioration probability can estimated when the log r-t curve is availabe. Even if the recurrent speed of discharge is different in each test as in the ASTM method, the non-deterioration probability r can be derived by using a number of the log r-t curves corresponding to each of the test steps.
