Chuanhui Cheng

Bio: Chuanhui Cheng is an academic researcher from Xi'an Jiaotong University. The author has contributed to research in topics: Space charge. The author has an hindex of 1, co-authored 1 publications receiving 32 citations.

Interface charges between insulating materials

Abstract: Multi-layer insulations are commonly used in HVDC applications, giving rise to physical and chemical interfaces in the insulation systems. Space charges at the interface between insulators play crucial roles on the electric field distribution of such insulation systems. The issue arises in the design of high voltage direct current (HVDC) insulations. How to understand the behaviors, mechanisms and effects of interface charges on the electric field distribution? In the past two decades, this specific topic has attracted much interest. Much experimental evidence has shown that interface charges may not follow the classic Maxwell-Wagner-Sillar (MWS) theory. In this paper, the measurement techniques and the phenomena of space charge behaviors at the interfaces between different insulating materials are summarized. It is indicated that surface states should be included in the numerical simulation of the charge and field distributions.

Trap Distribution and Dielectric Breakdown of Isotactic Polypropylene/Propylene Based Elastomer With Improved Flexibility for DC Cable Insulation

Abstract: In this paper, we report on electrical and mechanical properties of isotactic polypropylene (PP) blended with polyolefin elastomer (POE) and propylene-based elastomer (PBE). Carrier trap distribution of the samples was estimated by isothermal surface potential decay measurement, while dc breakdown strength was measured through a pair of semicircle electrodes. Elongation at break and tensile strength were obtained to examine the variation in mechanical property of PP caused by the addition of elastomers. Furthermore, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) have been employed to assist the understanding of morphology of the blends, thermal properties, and mechanical properties. Obtained results have indicated that with the increase of the elastomer content from 0 to 30 wt%, the trap depth appeared to be shallower and the dc breakdown strength tended to be reduced for both PP/PBE and PP/POE samples. Compared with PP/POE blend, PP/PBE blend had deeper trap depth, which should be responsible for its higher dc breakdown strength. In addition, PP/PBE blend has presented a better performance in elongation at break and tensile strength measurement. With the growth of the elastomer content, the crystallinity of the blends appeared to decrease, whereas the melting and the crystallization temperatures did not change remarkably. The SEM inspections and DMA results revealed better compatibility between PP and PBE compared with that between PP and POE, which should be the reason for the better electrical and mechanical properties of PP/PBE blend. The blend of PBE with low content could result in remarkably improved flexibility of PP with acceptable electrical strength for dc cable insulation.

Compatibility dependent space charge accumulation behavior of polypropylene/elastomer blend for HVDC cable insulation

Abstract: Polypropylene (PP)/elastomer blend is a promising candidate for high voltage direct current (HVDC) cable insulation. Space charge accumulation in HVDC cable is an important factor for safe and stable operation of HVDC transmission system. In this paper, propylene based elastomer (PBE) and ethylene-octene copolymer elastomer (EOC) were added into PP to prepare the blend sample. Space charge accumulation behavior was estimated by the pulsed electro-acoustic (PEA) method, and the influence of compatibility between the PP and the elastomer on the charge accumulation behavior was investigated. Polarized optical microscope (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) measurements were performed to assist the understanding of the compatibility dependent space charge accumulation behavior. The obtained results showed that the amount of space charge in the PP/PBE blend was lower than that in the PP/EOC blend. As compared with the PP/EOC blend, higher crystallinity with integrated crystal morphology and β-crystal form were observed in the PP/PBE blend for better compatibility between PP and PBE. It is suggested that deeper trap centers are formed in the PP/PBE blend than in the PP/EOC blend due to the compatibility, by which the charge injection is restricted.

Study and Characterization of the Dielectric Behavior of Low Linear Density Polyethylene Composites Mixed with Ground Tire Rubber Particles

Abstract: The waste rubber vulcanizate, on account of its stable, cross-linked and three-dimensional structural arrangement, is difficult to biodegrade. Thus, the ever-increasing bulk of worn-out tires is a serious environmental issue and its safe disposal is still a challenging task reported widely by the scientific community. The rubber materials, once they end their useful life, may present difficulties to be reused or recycled. At present, only one tire recycling method is used, which involves grinding and separating steel and fibers from vulcanized rubber, and then using rubber for industrial applications, such as flooring, insulation, footwear. In this paper, a new compound material is presented from a base of reused tire powder (Ground Tire Rubber: GTR) as a mixer and linear low-density polyethylene (LLDPE) as a matrix. The reused tire powder, resulting from grinding industrial processes, is separated by sieving into just one category of particle size (<200 μm) and mixed with the LLDPE in different amounts (0%, 5%, 10%, 20%, 40%, 50% and 70% GTR). Due to the good electrical properties of the LLDPE, this study’s focus is settled on the electrical behavior of the obtained composites. The test of the dielectric behavior is carried out by means of DEA test (Dynamic Electric Analysis), undertaken at a range of temperatures varying from 30 to 120 °C, and with a range of frequencies from 1 to 102, to 3·106 Hz, from which permittivity, conductivity, dielectric constant and electric modulus have been obtained. From these experimental results and their analysis, it can be drawn that the additions of different quantities of GTR to LLDPE could be used as industrial applications, such as universal electrical cable joint, filler for electrical applications or cable tray systems and cable ladder system.

Space charge dynamics in double-layered insulation cable under polarity reversal voltage

Abstract: To investigate space charge behavior in double-layered cable insulation, a one-dimensional axisymmetric model for bipolar charge transport is built in this work. Effects of temperature gradient and electric field gradient in the radial direction are considered. The transient distribution of space charge and electric field under polarity reversal voltage is simulated with the developed model, and then the influence of interface position is analyzed to guide the design of double-layered insulation. The results indicate that space charge and electric field distributions are affected by temperature gradient and voltage polarity. Under polarity reversal voltage, the electric field is intensified by the residual space charge generated before polarity reversal, which causes the severe electric field distortion. In addition, the comprehensive electric field distortion factor is the least when the interface is located at the middle of the insulation layer, which is more beneficial to the stable operation of cable.