Dynamic Behavior of Space Charge in Double-layer Insulation Structure under High External Electric Field

Compared with single-layer insulation, multilayer insulation structures have more forms and features, thus are widely used in the fields of oil-paper insulation, power cables and communication cables. However, there are fewer researches conducted on the space charge characteristics of multi-layer insulation structures, and the analysis of the interface space charge in those structures is not in-depth. This article takes the `skin-foam-skin' insulation structure of the frequency-shift pulse track signal cables as an example, which are commonly used in railway systems. We carried out room-temperature space charge measurement of the three parts of the `skin-foam-skin' insulation including LDPE, FPE, HDPE, and the double-layer structure of FPE/HDPE and FPE/LDPE separately, based on pulse electro-acoustic (PEA) method. Meanwhile, thermal property of PE samples was also tested. The result shows that a large amount of positive charge injection and accumulation occurred in the single-layer HDPE films. And due to the difference in the carrier mobility during the depolarization process, there was obvious positive charge accumulation near the interface of the FPE/LDPE double-layer structure. Besides, a small amount of negative charge is accumulated at the interface of the FPE/HDPE double-layer structure. This result not only provides a reference for the characterization and evaluation of the space charge characteristics of multi-layer insulation materials, but also provides basic data support for the subsequent selection and extraction of aging characteristics of multi-layer insulation.