Luai M. Alhems

A Microstructural Study of the Damage Sustained by Copper Shield Used in an Underground Medium-Voltage Cable

We show that a 3-mm-thick copper tape acting as metallic shield in an underground medium-voltage cable has been prematurely damaged by overheating. Detailed microstructural characterization has shown that the damage is characterized by: (a) formation of CuO on the copper surface as well as localized melting and perforation, (b) distortion and cracking of the outer protection jacket of polyvinyl chloride allowing the copper tape to come into contact with high sulfate-containing soil leading to deposition of CuSO4 on the copper surface, and (c) breakdown of the underlying layer of insulation shield. Most evidence suggests that overheating has been related to high return fault current exceeding the current-carrying capability of the copper tape used in the application. It is concluded that such a problem may be combated by using grounded objects with higher resistance to minimize the effect of return fault current and/or using copper shields with better current-carrying capability.

Study of limit concentrations of DBDS and sulfur mercaptan in power transformers

The study presents the results of experimental investigation of finding out the limit concentrations of DBDS and sulfur mercaptan for safe and prolonged operation of power transformers in the local environmental conditions of Saudi Arabia. For experimental investigation of limit concentrations of DBDS and sulfur mercaptan, new oil free of sulfur compounds was acquired. Four specimens of this were spiked with 2.2, 3.9, 5.4 and 10.2 ppm of DBDS and another four with free sulfur mercaptan RSH concentrations of 0.00, 0.52, 1.07, 2.13, and 7.10 ppm. The covered conductor deposition (CCD) tests were performed in accordance with IEC 62535 method on all the specimens. The experimental results indicated that the concentration of DBDS should always be <;5 ppm and sulfur mercaptan <;1 ppm in the new oils before putting in to the service.

Correlation Between the State of Atomic Order in Selected (Ni–Mo–Cr)-Based Alloys and Their Corrosion Resistance

AbstractA study has been conducted to determine the effect of the state of atomic order in Hastelloy alloys C-276, C-4, and C-22 on their corrosion properties. It is shown that alloy C-22 outperforms alloys C-276 and C-44 in terms of resistance to aqueous oxidizing and reducing media in the annealed condition with face-centered cubic structure containing short-range order. This behavior could be related to the optimized combination of Cr and Mo in alloy C-22 with the smaller addition of W. However, the three alloys are found to be resistant to stress-corrosion cracking despite the combination of short-range order and relatively low stacking fault energy. Long-range ordering to a Pt2Mo-type superlattice with body-centered tetragonal structure is found to enhance the resistance to aqueous corrosion with alloy C-22 still outperforming alloys C-276 and C-4. However, the three alloys become highly susceptible to stress-corrosion cracking. The results are correlated with the ordered microstructure and its effect on the deformation behavior.

Microstructural and Strength Investigation of Geopolymer Concrete with Natural Pozzolan and Micro Silica

In pursuit of finding sustainable building material, geopolymer concrete is developed utilizing aluminosilicate materials such as fly ash. Silica and alumina are the main precursors of alkali activation. The amount of silica and alumina in the source materials plays a significant role in the strength and microstructural development of such a concrete. If the source materials are supplemented by the addition of these precursors, the properties can be enhanced. Therefore, the reported study investigates the effect of incorporating micro silica at 5%, 7%, and 10% by weight, as partial replacement to natural pozzolan on the strength and microstructural properties of geopolymer concrete. Compressive strength was determined on the specimens cured in the oven maintained at 60 °C as well as at room conditions. Scanning electron microscopy (SEM) was utilized to determine the morphology of the developed alkali-activated paste (AAP). The results indicated that the natural pozzolan could be utilized, without any silica fume addition, to develop geopolymer concrete with reasonable strength that could be used for construction purposes if cured at elevated temperature. Further, concrete developed by replacing natural pozzolan with silica fume exhibited improved strength and microstructural characteristics. Seven percent micro silica replacement showed better compressive strength results and denser microstructure compared to the ones prepared with other replacement levels. The results of this study provided important information to synthesize natural pozzolan-based sustainable building material with enhanced properties.

Experimental investigation of temperature effect on corrosive sulfur formation in transformers

This paper presents experimental findings of the effect of temperature on corrosive sulfur formation in transformers. To conduct the experimental study, new transformer oil was randomly selected and heated at 40, 60, 80, 120, and 150 °C temperature for 72 hours each along with copper strips wrapped with insulation paper and immersed in oil in accordance with IEC-62535 standard test covered conductor deposition (CCD). The oil, copper strips, and the insulation paper samples were evaluated using gas chromatography-sulfur chemiluminescence detector (GC-SCD), X-ray fluorescence spectroscopy (XRF), inductively coupled plasma optical emission spectrometry (ICP), and scanning electron microscopy (SEM) tests after 72 hours exposure at each temperature. The values so obtained, were analyzed and effect of temperature on various parameters was studied individually and as well as collectively. It was found that temperature plays an important role on corrosive sulfur formation process inside the transformers and hence the temperature of the oil should be kept within the allowed operating ranges for avoiding unforeseen failures.

Digital energy meter testing under adverse field conditions

Accuracy tests were performed on whole-current and transformer-operated electronic energy meters under conditions that reflected the actual adverse metering site conditions. Analysis of the test data reveals the deleterious effect of high ambient temperatures on the measurement accuracy and precision of electronic meter indications. Based on the study results, measures are recommended to address concerns about the reliability/accuracy of energy measurement in uncontrolled, adverse conditions.

Maximum acceptable concentrations of dbds, sulphur mercaptan and optimal concentration of passivators for safe and prolonged operation of power transformers

The study presents the results of experimental investigation of finding out the maximum acceptable concentrations of DBDS, sulfur mercaptan, and optimal concentration of passivator for safe and prolonged operation of power transformers in the local environmental conditions of Saudi Arabia. For experimental investigation of optimal concentrations of DBDS and sulfur mercaptan, new oil free of sulfur compounds was acquired. Four specimens of this were spiked with different concentrations of DBDS and another four with free sulfur mercaptan RSH concentrations. The covered conductor deposition (CCD) tests were performed in accordance with IEC 62535 method on all the specimens. Next, to study the effect of passivator concentrations and temperatures on corrosive sulfur formation, 10 specimens from new oil were spiked with different concentrations of BTA and Irgamet 39. Copper strips were immersed in these specimens and the vials containing the oil and the copper strips were subjected to different temperature from 50 to 150°C for 24 hours in the oven. The experimental results indicated that the concentration of DBDS should always be <;4 ppm and sulfur mercaptan <; 1 ppm in the new oils before putting in to the service. Based on the effectiveness of the passivators, BTA was found to be effective with 50 ppm concentration at 150°C compared to Irgamet 39 which was effective only with 150 ppm concentration.

Quantifying the value of pumped storage hydro (PSH) in the Saudi electric grid

The potential increase of the connected capacity of renewable energy sources in Saudi Arabia will open the doors for more investment in energy storage especially pumped storage hydro (PSH). New PSH, particularly in areas with increased wind and solar capacity, would significantly improve system reliability while reducing the need to construct new fossil-fueled generation. PSH is proving to be an established technology for renewable power because it can absorb excess generation and release it during peak demand times. PSH can also provide many ancillary services to the power system that should be added to the benefits of PSH projects, such as increased flexibility, primary frequency response, following reserves, and fast-acting regulation reserves. PSH is typically not adequately represented during the optimization of the commitment and dispatch formulations in which reduces their perceived benefits. The paper discusses how to quantify PSH benefits to the power system operators so that the PSH projects would be more economically viable to the Kingdom and more appealing for private investment. Potential market changes that can help PSH in todays restructured markets are presented and discussed in this paper.

Economic analysis of retrofitting existing gas turbine power plants with cogeneration facility

Cogeneration refers to the generation of combined heat and power (CHP), which is more efficient than a central power plant generating only electricity. The proportion of power generation using CHP is growing world-wide due to efficiency improvements and environmental benefits. Exhaust heat from GT power plants can be fed to boilers for producing steam. Steam is used for reservoir flooding, petrochemical industries, food processing etc. Operational gas turbine power generation plants can be retrofitted to co-generation power plant to produce steam in addition to electrical power. A computational preliminary economic feasibility study of retrofitting a given existing gas turbine power generation plant into a co-generation power plant is presented in this paper. A 80 MW GE-6111FA frame has been selected for the present study. The work includes the effect of relative humidity (RH), ambient air temperature, etc., on economics of the power plant. GTPRO/PEACE software has been used for carrying out the analysis. The RH and temperature have been varied from 30 to 45 % and from 80 to 100° F, respectively. For a decrease of inlet air temperature by 10 °F, net plant output and efficiency have been found to increase by 4.3 and 1.4 %, respectively for GT only situation. However, for GT with cogeneration scenario, for a decrease of inlet air temperature by 10 °F, net plant efficiency has been found to be increased from 33.3 % (GT only) to 63.4 % (cogeneration). For situations with and without cogeneration, break even fuel price has been found to vary from 2.6 to 3.0 USD/MMBTU respectively and break even electricity price have been found to vary from 0.018 to 0.022 USD/kWh respectively. For the simulation conducted, emission has been found to be 344352 ton/year.