Electrical and Mechanical Properties of new Recyclable Power Cable Insulation Materials based upon Polyethylene Blends

Chemically crosslinked polyethylene (XLPE) has been used as electrical insulation for power cables since the 1970s due to its favourable combination of electrical and mechanical properties. However, as the electrical engineering community has become increasingly aware of the life cycle environmental impacts, XLPE has come under scrutiny for its lack of recyclability and the high process energies used in its manufacture. Although technologies are being developed to facilitate the re-use of XLPE at the end of its initial service life, the use of this material is inferior to fully recyclable and low process energy alternatives. In this investigation, we concentrated on the use of binary blends of linear and branched polyethylene (LPE / BPE) as potential replacement materials for XLPE, since such systems have the potential to combine comparable mechanical properties and enhanced breakdown strength with good recyclability. We compare the thin film AC ramp breakdown behaviour of blends as a function of temperature up to 97 oC. These consist of the same BPE in virgin and crosslinked states and in a blend with 20wt% LPE. These data are augmented with dynamic mechanical analysis. In concert, these data indicate that with appropriate morphological control the blended thermoplastic material exhibits superior properties to XLPE under conventional operating conditions and may even be suitable for higher temperature operation than XLPE. The paper will discuss the importance of polymer blending and blend physical properties in the context of the process requirements and the implications for cable manufacture and on cable electrical and environmental performance in comparison with XLPE

The effect of material processing on the dielectric properties of polystyrene boron nitride nanocomposites

Extensive experimental work in the area of polymer nanocomposites has been done over the past two decades to explore their potential. In this study, a range of related polymer nanocomposite materials was prepared using a solvent blending method, using dichloromethane (DCM), toluene (TOL) and chlorobenzene (CB) to dissolve the polymer, atactic polystyrene (a-PS), and disperse the filler, hexagonal boron nitride (hBN). Where TOL and CB were used, heat was used in material processing, whereas the material was processed at room temperature with DCM. The largest increase in breakdown strength is observed in the materials processed with TOL and CB. The hBN appears to be well dispersed in these systems and more agglomerated in the DCM system as shown from SEM

Electrical breakdown strength of boron nitride polyethylene nanocomposites

There is a growing demand for the design of high-performance insulators for high voltage applications. It was proposed that the addition of nanofillers to a polymer could potentially enhance the electrical properties of insulators when compared to the conventional unfilled or microfilled polymers [1]. These materials have captured the interest of many researchers worldwide since then, as present dielectric materials could benefit from improvements in properties such as dielectric strength, dielectric loss, electrical and thermal conductivity, and permittivity that nanodielectrics offer. However, many of the underlying principles remain uncertain, such as the polymer/nanofiller interface, and researchers are still exploring solutions to common challenges faced by nanodielectrics such as nanoparticle agglomeration [2].The work presented in this paper is based on a hexagonal boron nitride nanocomposite in a polyethylene blend host polymer. A polyethylene blend composed of 80% low density polyethylene (LDPE) and 20% high density polyethylene (HDPE) is chosen as the polymer matrix since it has a higher electrical breakdown strength than pure LDPE. Hexagonal boron nitride was chosen as a nanofiller because of its attractive properties for high voltage applications such as high dielectric strength, high thermal conductivity, and mechanical robustness [3]. A solution blending method is used to mix the nanoparticles in the polymer as better quality materials and nanoparticle dispersion are achieved.This paper will investigate the AC electrical breakdown behaviour of the prepared polymer nanocomposite materials. The electrical breakdown strength of the unfilled polymer will be compared to the untreated hexagonal boron nitride filled polymer at different loading levels. The addition of this nanofiller is expected to alter the dielectric strength due to changes in the material’s structure. The chemical structure of hexagonal boron nitride is illustrated in Figure 1, where there is an equal number boron and nitrogen atoms firmly bound together. The breakdown results will then be analysed using a two-parameter Weibull distributio

The effects of surface hydroxyl groups in polyethylene-silica nanocomposites

Logically, the surface chemistry of filler particles must be a key factor that governs how they interact with a polymer matrix, determining for example, how strongly the particles are bound into the matrix and how easy or difficult it is to achieve a homogenous dispersion of filler particles. This second point is surely one of the most basic challenges when producing a nanocomposite (poor dispersion is frequently stated as the cause of undesirable results). Many attempts have been made to modify the surface chemistry of filler particles through surface functionalization. Typically, this is achieved by chemically attaching polymer chains to the surface of the filler particles. In this paper we try a more direct approach; the surface chemistry of silica nanoparticles is modified by processing them at high temperature. This procedure removes hydroxyl groups from the surface of the filler particles, leaving siloxane groups which are stable at room temperature. Polyethylene composites were produced using both “as delivered” and high temperature processed nanosilica. After heat treatment the particles become hydrophobic which reduces the propensity for water uptake in the resulting nanocomposite and significantly modifies the dielectric response of the material

Review of high voltage direct current cables

Increased renewable energy integration and international power trades have led to the construction and development of new HVDC transmission systems. HVDC cables, in particular, play an important role in undersea power transmission and offshore renewable energy integration having lower losses and higher reliability. In this paper, the current commercial feasibility of HVDC cables and the development of different types of HVDC cables and accessories are reviewed. The non-uniform electric field distribution caused by the applied voltage, temperature dependent conductivity, and space charge accumulation is briefly discussed. Current research in HVDC cable for higher operation voltage level and larger power capacity is also reviewed with specific focus on the methodologies of space charge suppression for XLPE extruded cable

Thermoplastic cable insulation comprising a blend of isotactic polypropylene and a propylene-ethylene copolymer

There is much interest in the development of replacement materials for crosslinked polyethylene (XLPE) that are both recyclable (i.e. thermoplastic) and capable of high temperature operation. Thermally, polypropylene is the ideal choice, although its stiffness and low electrical breakdown strength make for a challenging materials design problem. We report here on the compositional optimization of a propylene homopolymer/propylene-ethylene copolymer blend in terms of its dynamic mechanical properties and thin film electrical breakdown strength. The extrusion of a trial mini-cable using the optimized blend is also discussed, which is shown to exhibit a significantly improved electrical performance, as gauged by its DC breakdown strength, than an XLPE-insulated reference

Enhancing drought tolerance and Striga hermonthica resistance in maize using newly derived inbred lines from the wild maize relative, Zea diploperennis

Open Access Journal; Published online: 18 Jan 2021Recurrent drought and Striga hermonthica (Del.) Benth parasitism constrains maize production in sub-Saharan Africa (SSA). Transfer of resistance genes from wild relatives can improve resistance to drought and Striga in tropical maize. The objectives of this study were to (i) determine the combining ability of 12 extra-early yellow maize inbreds derived from Zea diploperennis and tropical maize germplasm; (ii) classify the inbreds into heterotic groups using heterotic grouping based on the general combining ability (GCA) of multiple traits (HGCAMT) method; (iii) examine hybrid performance under contrasting environments; and (iv) examine the stability of hybrid combinations involving the inbreds. Sixty-six diallel crosses involving the inbreds plus four checks were evaluated for two years under drought, Striga-infested and rainfed environments in Nigeria. Significant differences (p < 0.05) were observed for the effects of genotype, environment, genotype × environment, GCA and specific combining ability (SCA) on grain yield and other measured traits. Inbred lines such as TZdEEI 7 × TZEEI 63 derived from Z. diploperennis and tropical germplasm exceeded the checks by a range of 28 to 41%. Across environments, the hybrid TZdEEI 1 × TZdEEI 7, which was derived from Z. diploperennis, was the highest-yielding with a grain yield of 4302 kg ha−1. The results revealed the predominance of GCA over SCA effects for most measured traits, suggesting that additive gene action governed the inheritance of Striga resistance and drought tolerance related traits in the inbreds. The 12 inbreds were classified into three heterotic groups, while TZEEI 79 and TZdEEI 7 were identified as inbred testers and TZdEEI 7 × TZEEI 12 as a single-cross tester across environments. Hybrid TZdEEI 9 × TZEEI 79 was the highest-yielding and most stable. Other promising hybrids were TZdEEI 7 × TZEEI 79, TZdEEI 1 × TZdEEI 7 and TZdEEI 12 × TZEEI 95. These hybrids should be extensively tested on-farm for potential commercialization in SSA. Overall, our results highlighted the importance of harnessing beneficial alleles from wild relatives of maize for improvement of resistance to Striga and tolerance to drought in adapted maize germplasm

Dust Devil Tracks

Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earth’s surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between ∼1 m and ∼1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of ≥500 μm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550–850 nm on Mars and around 0.5 % in the wavelength range from 300–1100 nm on Earth. The removal of an equivalent layer thickness around 1 μm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand-sized material that is eroded from the outer vortex area of a dust devil is redeposited in annular patterns in the central vortex region. This type of DDT can also be found in on Mars in orbital image data, and although in situ studies are lacking, terrestrial analog studies, laboratory work, and numerical modeling suggest they have the same formation mechanism as those on Earth. Finally, bright DDTs are characterized by their continuous track pattern and high albedo compared to their undisturbed surroundings. They are found on both planets, but to date they have only been analyzed in situ on Earth. Here, the destruction of aggregates of dust, silt and sand by dust devils leads to smooth surfaces in contrast to the undisturbed rough surfaces surrounding the track. The resulting change in photometric properties occurs because the smoother surfaces have a higher reflectance compared to the surrounding rough surface, leading to bright DDTs. On Mars, the destruction of surficial dust-aggregates may also lead to bright DDTs. However, higher reflective surfaces may be produced by other formation mechanisms, such as dust compaction by passing dust devils, as this may also cause changes in photometric properties. On Mars, DDTs in general are found at all elevations and on a global scale, except on the permanent polar caps. DDT maximum areal densities occur during spring and summer in both hemispheres produced by an increase in dust devil activity caused by maximum insolation. Regionally, dust devil densities vary spatially likely controlled by changes in dust cover thicknesses and substrate materials. This variability makes it difficult to infer dust devil activity from DDT frequencies. Furthermore, only a fraction of dust devils leave tracks. However, DDTs can be used as proxies for dust devil lifetimes and wind directions and speeds, and they can also be used to predict lander or rover solar panel clearing events. Overall, the high DDT frequency in many areas on Mars leads to drastic albedo changes that affect large-scale weather patterns

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe