Abstract
Space charge migration characteristics play an important role in the evaluation of polymer insulation performance. However, an accurate description of charge carrier mobility in several typical insulating polymers such as polyethylene, polypropylene is currently not available. Recently, with the observation of a series of negative charge packet movements associated with the negative differential resistance characteristic of charge mobility in LDPE films, the extraction of charge mobility from the apparent charge packet movement has been attempted using appropriate methods. Based on the previous report of the successful derivation of charge mobility from experimental results using numerical methods, the present research improves the derivation accuracy and describes the details of the charge mobility derivation procedure. Back simulation results under several typical polarizing fields using the derived charge mobility are exhibited. The results indicate that both the NDR theory and the simulation models for the polyethylene materials are reasonable. A significant migration velocity difference between the charge carrier and the charge packet is observed. Back simulations of the charge packet under several typical polarizing fields using the obtained E-v curve show good agreement with the experimental results. The charge packet shapes during the migrations were also found to vary with the polarizing field.
Highlights
Since it was recognized that space charge has a non-negligible effect on the insulation performance of polymer materials[1,2,3,4], many researchers have explored space charge effects, obtaining many insights[5,6,7]
Several recent studies have indicated that charge mobility in insulating materials such as PE and PP has a non-linear dependence on the local electric field[13,14,15,16], making the estimation of charge mobility in these materials more complicated
The approach for the generation of charge carriers in the material is similar to the electron beam irradiation method in the TOF technique[17], building on the observation of the charge displacement current in the previous methods, our method is based on a more direct observation of the phenomena by using a space charge distribution measurement technique known as the laser-induced pressure pulse (LIPP) method[18]
Summary
The description of a rough charge mobility retrieval procedure can be found in[22]. The core concept is to generate an E − v curve describing the relationship between the charge carrier velocity v and the local electric field E. An initial curve that approximately describes the E − v characteristics is determined from measurements at given applied electric fields For this purpose, a large amount of charges is injected inside the samples by electron beam irradiation. Only the charges in the packet subjected to the local electric field near the modified key point are affected by the change of the velocity. When all key points have been adjusted, the order of the key points is randomized, and the entire procedure is repeated two or three times. This is done to reduce the influence of the artefacts in the calculation on the results.
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