Packet-like Space Charge Behavior Research Articles

Numerical analysis of packetlike charge behavior in low-density polyethylene by a Gunn effectlike model

Under some conditions, charges may transport like an isolated packet in polyethylene. It has been demonstrated that many factors, such as applied field strength, temperature, and material itself, influence on formation and migration of space charge packet, which cause many difficulties in understanding the general mechanism of the phenomenon. In this paper, based on the analysis about the influences of charge injection, carriers’ migration, and the interaction between the free charge and trap in polyethylene on packetlike space charge behavior, a new physical model is established to give a physical description of packetlike charge behavior in low density polyethylene (LDPE). This model includes some interesting features: (1) it gives an exact calculation of charge changes in all positions of specimens; (2) the negative differential mobility mechanism of Gunn effect in semiconductor is introduced to explain the generating process of space charge packet; (3) field-induced charge detrapping model is utilized to simulate the diversity of packetlike charge packet behavior under different applied fields. By considering such a model, we simulate two kinds of positive packetlike charge behavior in LDPE from different research groups. The simulated results show well fitting with the experiment data.

Numerical simulation of charge packet behavior in low-density polyethylene based on Gunn effect-like model

Packet-like space charge behavior usually induces the electric field distortion and strongly affects the electrical performance of low-density polyethylene. In this paper, we analyze the influence of charge injection, carriers migration and interaction between the free charge and trap in polyethylene on packet-like space charge behavior and introduce the mechanism of Gunn effect to describe the generating process of space charge packet. Based on this, we simulated two kinds of packet-like space charge behaviors with different variation trends and in different applied fields reported by different research groups. The simulated space charge packet shows very good fitting with the experiment data in both packet amplitude and migration velocity. The simulation results also indicate that the injection conditions and trap level depth play an important role in the diversity of packet-like space charge behavior.

Numerical simulation of space charge packet behavior in low-density polyethylene under direct current voltage

Packet-like space charge behavior is a kind of special transport behavior of space charge in polyethylene. It has been demonstrated that many factors, such as the intensity of applied field, temperature and material have great influence on the formation and migration of space charge packets. This would cause much difficulty in understaning the general mechanism of the phenomenon. In this paper, on the basis of analysis of charge injection and migration, the interaction between the charge and charge trap and the influence of electric field on charge trap level, a model is proposed to simulate the packet-like space charge behavior. We suppose thar there exists a negative differential relationship for the charge velocity against the electric field when the electric ficld exceeds a threshold value. By considering the negative differential relationship, we simulated various kinds of packet-like charge behaviors and the results of numerical simulation show a good agreement with the experimental results issued by different research groups.

Packet-like space charges and conduction current in polyethylene cable insulation

Packet-like space-charge behavior in polyethylene for cable insulation was studied by utilizing the laser-induced pressure-pulse technique. Space charge observation under various conditions showed that the charge packet was formed in the specimen doped with antioxidant, especially when the specimen is oxidized. Periodic formation and transport of charge packets led to a small current oscillation. The charge packet seemed to be formed in the bulk, and the internal field of 1.2 to 1.4 MV/cm, in the region where the packet was formed was periodically enhanced from 2 to 2.5 MV/cm by space-charge accumulation. This suggests that the packet formation is caused by carrier generation under the highly enhanced field. The antioxidant deteriorated by oxidation was shown to be a possible origin of the carrier generation.