N. T. Sudar’

We present the results of an experimental study of the pulse electrical strength of polyethylene terephthalate and polypropylene films when they are subjected to a single electric pulse. It has been found that the breakdown of these films is possible both at the front and at the plateau of the pulse, and the probability of breakdown at the front increases with pulse amplitude. We recorded a jump in the durability of the films at the transition from breakdown at the front to breakdown at the pulse plateau.It is shown that the processes that prepare the film electrical breakdown develop faster at the pulsefront than at the plateau. We discuss a possible physical mechanism to explain this effect.

—The impedance spectra of composite nonwoven materials based on nano- and microfibers of polyvinylidene fluoride copolymer with trifluoroethylene modified with polypyrrole with various degrees of doping are studied in the frequency range 1 × 10³–1.5 × 10⁷ Hz. It is found that an increase in the degree of doping of the polypyrrole coating of nanofibers leads to a decrease in the imaginary and real components of the electrical impedance. Regardless of their size, the shape of the hodographs is close to the arc of a circle based on the axis of the real component, which allows considering the studied material as a nanocomposite polymer electrolyte, the dielectric characteristics of which can be reversibly changed.

The impedance spectra of composite nonwoven materials based on nano- and microfibers of polyvinylidene fluoride-trifluoroethylene copolymer modified by polypyrrole with different doping degree were studied in the frequency range 1000 Hz-5 MHz. It was found that an increase in the doping degree of polypyrrole coating of nanofibers leads to a decrease in the imaginary and real components of the electrical impedance. Regardless of their magnitude, the shape of the hodographs is close to circular arc resting on the ReZ axis, which allows us to consider the studied material as a nanocomposite polymer electrolyte whose dielectric characteristics can be reversibly changed.

The dielectric properties of polycrystalline fullerite films with a thickness of ~300 nm included in p-Si/C₆₀/InGa structures under dc electric fields with a strength up to 3.3 × 10⁷ V/m have been investigated in the frequency range of 30–10⁶ Hz. It is established that, at negative polarity of an InGa electrode (when electron injection from the metal to fullerite is facilitated), an anomalous increase in the sample capacitance is observed at frequencies below 1000 Hz (the capacitance at a low frequency is higher than that at a high frequency by a factor of more than 10³). An explanation for this effect is proposed.

During electrical breakdown of a thin film of polypropylene, radiation of a radio pulse was detected. The pulse duration is about 400 ns. The spectrum of the radio pulse consists of three main frequencies. The relationship between the breakdown channel resistance and the observed spectrum is substantiated

An explanation of the difference in the electrical properties of polymers in the DC and AC electric fields is proposed. Energy release during recombination of electrons and holes injected into a polymer dielectric is considered as a factor accelerating the processes of electric aging of these dielectrics in an AC field. It is shown that nonradiative relaxation of electron excited states causes breaks of bonds in macromolecules and formation of free radicals. Due to the lower ionization energy of free radicals (compared to the original molecules), the rate of charge accumulation in the polymer dielectric increases, which leads to a decrease in its durability in an AC field compared to the durability of polymers in a DC field.

A technique for measuring the rate of change in the breakdown-channel resistance and estimating the true amplitude and duration of the breakdown current was developed. This technique is based...

An explanation is proposed for the difference in the electrical strength properties of polymers in DC and AC fields. Energy release during recombination of electrons and holes injected into a polymer dielectric is considered as a factor accelerating the process of electrical aging of these dielectrics in AC field. It is shown that the nonradiative relaxation of electronic excited states, which causes bond breaks in macromolecules and the formation of free radicals, leads to the formation of deep electron traps in a polymer dielectric, as a result of which the ionization of macromolecules in the electric field is accelerated due to electron transitions into these traps. In solid-state plasma, a shielding effect occurs, leading to a decrease in the ionization potential of molecules. As a result, the ionization rate of macromolecules increases, i.e. the rate of formation of charge carriers, which leads to a decrease in the electrical life time of the polymer dielectric in AC field compared with the life time of polymers in DC field.

We have studied the effect of the leading edge steepness of a high-voltage pulse front on the dielectric strength of 3-μm-thick polyethylene terephthalate film. It is found that its breakdown electric field strength increases logarithmically from 550 to 700 MV/m upon an increase in the voltage growth rate (pulse front steepness) from 2 to 70 GV/s. It is shown that the experimental data can be described using the concept of the ionization mechanism of polymer breakdown, which is not associated with the evolution of impact ionization in polymers, and accounting for the decrease in the overvoltage coefficient in a polymer dielectric upon an increase in the pulse front steepness.

We have studied the effect of the leading edge steepness of a high-voltage pulse front on the dielectric strength of 3-μm-thick polyethylene terephthalate film. It is found that its breakdown...