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Design, Construction, and Operation of Distribution Systems, MV Networks
Published in James Northcote-Green, Robert Wilson, Control and Automation of Electrical Power Distribution Systems, 2017
James Northcote-Green, Robert Wilson
Each and every item of an electrical plant will have defined maximum current that it can safely carry. For example, a particular design of 185 mm2 33 kV single-core cable with XLPE insulation, when laid in trefoil, bonded, and earthed at each end, can safely carry 560 amps when laid in air, 450 amps when laid in the ground (under specified conditions) and 400 amps when laid in ducts. If load higher than the ratings is applied, then the associated rise in temperature will degrade the cable insulation and may reduce its useful service life. Because network load varies on both a daily basis and an annual basis, many utilities apply an acceptable overload factor to their cables, for example, 10% continuous and 20% for three hours. The rationale behind an overload factor is that, for much of the life of the cable, it will operate significantly below its rated current, so for a short period, maybe during an abnormal system condition lasting for a few days, it is acceptable to take the small risk of longer term overload damage.
Phytostimulation of lowland soil contaminated with imidazolinone herbicides
Published in International Journal of Phytoremediation, 2020
Kelen Müller Souto, Rodrigo Josemar Seminotti Jacques, Renato Zanella, Sergio Luiz de Oliveira Machado, Andrisa Balbinot, Luis Antonio de Avila
In the rhizospheric soil of winter crops (Table 2), it was observed an increase on CO2 emission of in the rhizospheric soil of vetch and the combination of white clover + birdsfoot trefoil, regardless of the dose and the herbicide tested. Growing these legumes in succession to irrigated rice is remarkably important, because in addition to promoting soil decontamination, it contributes to the improvement of the physical, chemical and biological properties of the soil, as it was previously mentioned. Special attention should be paid to clover and birds foot trefoil combination, as these species are better adapted to the conditions of poorly drained soils. The ryegrass culture differed from the non-rhizospheric soil treatment for most of the herbicides concentration tested, indicating its potential for phytostimulation, but with a reduced effect compared with the winter legumes evaluated.
Measuring mental workload: ocular astigmatism aberration as a novel objective index
Published in Ergonomics, 2018
Raimundo Jiménez, David Cárdenas, Rosario González-Anera, José R. Jiménez, Jesús Vera
The number of aberrations per order increases as the order of the Zernike polynomials increases, and wavefront aberrations can be further classified based on their Zernike order as lower (n ≤ 2) or higher order aberrations (n ≥ 3). Both influence the visual performance of an individual but lower order aberrations, since are related to refractive error, can be easily alleviated by prescribing compensatory spectacles, contact lenses, or refractive surgery (Martin et al. 2011). However, higher order aberrations (HOA, n ≥ 3) cannot be easily corrected with these procedures and an adaptive optics system, phase plates, customised contact lenses, and customised refractive surgery are needed (Porter et al. 2006). Third order aberrations include trefoil and coma. Fourth order includes quatrefoil, secondary astigmatism and spherical aberration. Trefoil, coma, quatrefoil and secondary astigmatism are classified as a form of irregular astigmatism which results in an irregular or distorted wavefront (Dai 2008). Spherical aberration is influenced by pupil diameter and ocular accommodation and become to be important during dim lighting conditions, causing visual halos and night vision disturbances (Applegate et al. 2007). The fifth, sixth, seventh and eighth order aberrations are usually very small in magnitude and therefore negligible (Philip et al. 2012). However, wavefront aberrations represented with Zernike polynomials and their coefficients can be difficult to understand, and root mean square (RMS) is typically used as a global metric for optical quality (Pepose and Applegate 2005). RMS represents the deviation of the wavefront from a plane wavefront represented as a single digit (in microns [μm]) and it can be determined individually for lower or higher order aberrations or it can be calculated for the entire wavefront (Dai 2008). The higher the RMS wavefront error, the larger the wavefront aberration and the worse the optical quality. The development of wavefront sensor allows the rapid, accurate, repeatable and objective measurements of ocular aberrations, and RMS can be calculated using the information given by the aberrometer once a measurement has been taken (Rozema, Van Dyck, and Marie-José 2006). In addition, besides total ocular aberration, corneal and internal aberrations can also be obtained separately with good precision (Holzer, Goebels, and Auffarth 2006).