Corona-resistant Polyimide Films Research Articles

Insulation improvement of an all-solid pulse forming line with film dielectric

A pulse forming line (PFL) cascaded in the radial direction by multistage rolled strip line units is put forward. With this method, the dielectric thickness of the rolled strip line unit is decreased. So, the reliability of the PFL under a high voltage will increase. At the same time, the difficulty for rolling the PFL will decrease. The factors affecting the pulse lifetime of the rolled PFL are analyzed by theory and simulation, and two improvement methods are put forward. First, the electric field enhance at the edges of the electrodes of the rolled PFL is so large that corona discharge occurs at these positions. The improvement method is to use the combination dielectric layer combined by corona-resistant polyimide (PI) films and polypropylene (PP) films as the dielectric of the rolled strip line unit. With this method, the normal electric field of the electrode edges is decreased. Besides, the corona resistance of the dielectric layer is much improved because the PI film has a good performance under corona discharge. Second, the positions where the output foils are located are the insulation weakness of the PFL because these positions are discontinuous. The improvement method is to increase the insulation thickness of these positions. A rolled PFL is cascaded by 3 stages of rolled strip lines, which has a charging voltage of 90 kV. According to the lifetime test, the pulse lifetime of the rolled PFL reaches 300 000 pulses, which is 100 times larger than the pulse lifetime of a rolled PFL without the improvement method.

Study on charge transport mechanism and space charge characteristics of polyimide films

As a core component of AC drive electric locomotive, performance of inverter-fed motor directly influences the stability and reliability of locomotive running. However, insulation early failures occur frequently. Presently, polyimide film, as a special type of engineering plastic film, widely applied in turn to turn insulation and turn to ground insulation of inverter-fed motors is a kind of basic insulating material. This paper investigates charge transport mechanism and space charge characteristics of polyimide films based on measuring and comparing space charge accumulation threshold field between corona-resistant and common polyimide films and analyzing the effect of temperature on space charge distribution. The results reveal that space charge accumulation threshold field of corona-resistant polyimide film is higher than that of common polyimide film; the adding of nano-particles effectively increases dielectric properties of corona-resistant film. Additionally, raising temperature promotes the electrode injecting charge and increases the charge energy and conductivity which gradually enhances space charge number and extends trapping position into the bulk, closely related to polyimide film insulation aging and breakdown which is an important characteristic.

Conduction Current Characteristics and Carrier Mobility ofBoth Original and Corona-Resistant Polyimide Films

The electric conduction current characteristics of both Dupontoriginal and corona-resistant polyimide films (100 HN and 100 CR) beforeand after corona-aging eight hours under electric field of 10 kV/mm and20 kV/mm were measured. The results show that the conduction current of100 CR is about one order of magnitude larger than that of 100 HN. Basedon the space charge aging theory, the electric degradation thresholdobtained from the space charge limit current plot is 40 kV/mm for 100 CRand 35 kV/mm for 100 HN, and decreases with the increasing corona-agedfield. By measuring the depolarization current of the two films at170°C, it is observed that the decay of depolarizationcurrent of 100 CR is faster than that of 100 HN. Based on thedepolarization current curve, the apparent carrier mobility and trapdepth of 1.2×10−13 m2/Vs to 3×10−14 m2/Vsand 1.052 eV to 1.105 eV for 100 CR, 1.12×10−13 m2/Vsto 8×10−14 m2/Vs and 1.054 eV to 1.069 eV for 100 HNwere, respectively, calculated during depolarizing.