Abstract
The effect of humidity on insulation resistance of some commercial fibrous insulating materials was investigated. To avoid experimental errors due to inconstancy of other conditions, the influence of temperature, applied voltage and etc. was also studied.
It is shown in this paper that, after the voltage is applied to the sample, the charging effect occurs and the temtperature rises and the distribution of absorbed moisture changes, owing to the leakage current through the material: therefore, the resistance at a given condition should be computed by obtaining the leakage current at the initial instant the e.m.f. is applied to the material. And it is stated that, generally the humidity has very profound influence on the insulation resistance of fibrous materials, and the relation between insulation resistance and relative humidity which is varied in a cyclic manner, represents a hysteresis loop due to the hygroscopic hysteresis property of the fibrous material, hence the resistance at a certain humidity should be exressed with the record of previous change of humidity; for the practical purpose, however, it is convenient to express the insulation resistance at a specified humidity with the average value of resistancelcorresponding to that humidity, obtained from the hysteresis curve of resistance against humidity. And it is recommended to express the relation between such average resistance and humidity by an empirical formula log10R=a-bh/1-ch2, where R is the average resisrance for relative humidity h, and a is a constant depending on the insulation resistance of the material itself at zero humidity, while b and c are constants expressing the effect of humidity on the resistance. For eleven materials, these constants are obtained by experimental results; and it is shown that they are very nearly equal for materials of vegitable origins, but they differ considerably for the other materials of animal and mineral origins or treated material. Finally it is stated that the effect of humidity on the insulation resistance of such materials may be determined by measuring average resistances corresponding to three different humidities and computing constants in the above formula.
