Transient Electric Currents from Plastic Insulators

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Abstract
Change of voltage across a solid insulator produces a transient electric current. Measurements of such currents from the polymers of methyl methacrylate, monochlorotrifluoroethylene, ethylene, styrene, and tetrafluoroethylene were made for times from 10 to 104 seconds after change in voltage at 25°C, 47°C, and several points below room temperature. The current produced by applying a constant voltage to an undisturbed specimen decays as the negative nth power of the time, where n is a constant between 0.7 and 1.1. The currents from polyethylene and polytetrafluoroethylene do not conform to the superposition principle, in contradistinction to what is usually reported for solid insulators. The currents at 100 seconds exhibit maxima at −32°C for polymethyl methacrylate and at −50°C for polymonochlorotrifluoroethylene. It is suggested that permanent electric dipoles play an important role in the currents from polymethyl methacrylate and polymonochlorotrifluoroethylene.