مهندسی برق قدرت

[peter-se]

سلام دوستان من 1متن 5صفحه ای انگلیسی با معنی فارسیش در رابطه با رشته برق فورا لازم دارم ممنون میشم کمکم کنید

[amirabbas_sz]

دوستان بارها خواهش کردیم که از درخواست مقاله آماده بهمراه ترجمه خودداری کنید چون خلاف ماهیت و هدف بخش دانشجویی هست. هر چی دلتون میخواد مقاله انگلیسی با موضوع مشخص درخواست بدید. سپاسگزارم

[peter-se]

خوب پس لطف کنید 1مقاله ی 3 صفحه ای انگلیسی در رابطه با رشته ی برق برام پیدا کنید .باز هم ممنون

[amirabbas_sz]

Central Solar Power for the Southwest
By Cara Libby, EPRI

As utilities in the United States seek to develop renewable energy projects, one promising option is central station solar power (CSSP). CSSP includes solar thermal technologies, such as central receiver and parabolic trough, as well several photovoltaic (PV) technologies. Solar thermal is of particular interest due to the emerging ability to integrate thermal storage into the plant design, thus improving operating flexibility and enabling the plant to operate during more hours of the day.

Click here to enlarge image

Testing a parabolic trough in New Mexico. Photo courtesy Sandia National Laboratory.
Over the next five years, close to six gigawatts of concentrating solar power capacity are planned worldwide, including several new large-scale plants in the U.S. Southwest. This trend is expected to continue as energy companies broaden their generation mix and prepare to meet state renewable portfolio standards.

The Electric Power Research Institute (EPRI) recently completed a feasibility study for the development of a 50 to 500 megawatt (MW) CSSP plant in New Mexico by mid-2011. The study was backed by six utilities, including Public Service Company of New Mexico, El Paso Electric, San Diego Gas & Electric, Southern California Edison, Tri-State Generation & Transmission Association and Xcel Energy.
The study included a comprehensive evaluation of potential plant sites, solar technologies, plant designs, economics and financial incentives, and regulatory and environmental issues. A key requirement was that the plant be installed and operational by mid-2011. As a result, only sites with access to firm transmission were considered for further study and technologies were evaluated based on demonstrated commercial readiness. The levelized cost of electricity was used as the basis for quantitatively comparing different technology and design options.
Based on a technical and environmental analysis of potential plant sites, two locations met the plant siting requirements and were selected for further consideration. Within the study’s framework, parabolic trough technology was identified as the most mature and economical technology for this application.
The results of this feasibility study provide key information for understanding the parameters involved for future deployments of solar technology in the American Southwest and other parts of the world.

Site Assessment

The study initially identified six siting regions encompassing most of central, western and southwestern New Mexico. An initial project team review of water availability and transmission resources within these regions eliminated four areas from further consideration and left two areas to be studied in more depth.
Specific sites within the two preferred siting regions were determined using U.S. Geological Survey 7.5-minute quadrangle maps. Siting specialists examined the maps and located eight potential greenfield sites. All of these sites were field-observed to verify features and collect property information. Four sites were eliminated based on results of the field reconnaissance activities’ this left four candidate sites to be studied in more detail.
A scoring system was developed specifically for this siting study to evaluate and rank the candidate sites. The criteria included direct normal irradiance/capacity factor, access to the transmission grid, natural gas located in the vicinity, potential for water availability, constructability considerations, area available for expansion, and other factors.
Ultimately two sites were selected for further consideration. One site is in central New Mexico inside the Albuquerque-Santa Fe load center. The other is in southwestern New Mexico where the solar resource is best.
A request for information (RFI) process was used to collect information on the current status of the solar industry. The following solar thermal technologies were evaluated:
Central receiver. These plants use a field array of large mirrors, called “heliostats,” that track the sun and focus its light onto a central receiver mounted on top of a tower. Commercial operation is currently being demonstrated at the 10 MW PS-10 plant in Spain.
Compact linear Fresnel reflector. This technology consists of rows of solar collectors that reflect solar radiation onto a tower-mounted linear receiver, consisting of a series of steel tubes surrounded by a reflective surface. CLFR is still early in development and has never generated standalone electricity.
Dish/engine. This system uses a parabolic reflector to focus sunlight onto a receiver located at the focal point of the dish. The sunlight heats a working fluid, which transfers the heat to a small engine used to generate electricity. Dish/engine technology has been demonstrated at small scale, but there are currently no operating commercial plants.
Parabolic trough. These plants use a field of linear parabolic collectors to redirect and concentrate sunlight onto a tube receiver. Solar parabolic trough is a commercially proven technology, with plant sizes up to 80 MW successfully operating in the United States.
Four PV technologies were also evaluated: fixed, flat-plate with crystalline silicon; fixed, flat-plate with thin-film; one-axis tracking, flat-plate with crystalline silicon; and two-axis tracking, concentrating PV.
PV technologies rely on materials that produce electric currents when exposed to light, utilizing semiconductors such as silicon. Flat-plate crystalline silicon is the most mature PV technology available today. Thin film is a less mature development that is capturing a growing share of PV markets. Although its performance trails crystalline silicon, it is easier to manufacture and has lower capital costs. Concentrating PV (CPV) systems use concentrating optics or lenses that gather sunlight and concentrate its intensity onto small PV cells, minimizing the amount of PV material needed. CPV systems can provide higher conversion efficiencies than conventional flat-plate systems. They have, however, been slow to gain a commercial foothold until just recently in central station installations. PV panels can be fixed mounted or mounted on single- or dual-axis drives. Although over 10 GW of PV is deployed worldwide, the largest PV plants are just over 20 MW.
Based on three criteria—commercial status, current levels of deployment and ability to ramp up manufacturing for a 2011 project—three technologies were selected for further evaluation: central receiver, parabolic trough and PV. The cost and performance of the selected technologies were then analyzed in more detail to compare the levelized cost of electricity (LCOE) for several technology and design options.
The solar thermal electric plant design cases that were assessed included plant capacity, thermal energy storage capacity, natural gas hybridization, and cooling designs. Sensitivities around natural gas cost and annual radiation were also investigated. Due to the simplistic and modular nature of PV, only a 50 MW plant size was evaluated.
The LCOE was calculated to compare technology and plant design options using a common set of assumptions and ultimately determine which technologies and plant designs would be most economical for a CSSP plant in New Mexico during the time frame being considered.
The study showed that securing financial incentives will be essential for any solar plant. This study identified the types of incentives that will have the greatest impact on the LCOE. Stacking all the existing financial incentives resulted in LCOE reductions of 30 percent or more.

Technology Selection

Parabolic trough technology was selected for this project based on the combination of large-scale, commercial operating experience, low cost of energy relative to other solar technology options and operating flexibility through thermal storage or hybridization.
Thermal storage and natural gas hybridization both had the effect of lowering the LCOE compared to the base case design. Adding thermal storage to the trough plant design was shown to improve the plant’s capacity factor and slightly lower the cost of energy. Similarly, hybridized solar thermal plant designs supplemented with natural gas firing also produce lower-cost electricity than the base case. Although wet cooling lowers the LCOE by about 2 percent on average, dry cooling is preferred due to water availability issues in New Mexico.
Central receiver technology was not selected due to the limited experience with large-scale, molten salt central receiver plants, the scale-up risk and the high cost to finance the first large plants.
The project team concluded that system effects, such as grid stability, and integration costs need to be better understood before a 50 MW or larger PV project can be prudently developed. The LCOE for each of the four PV technologies was determined to be significantly higher than parabolic trough and central receiver technologies.
An assessment was conducted to determine the major environmental and regulatory issues associated with project development at each of the two candidate sites. A 15-month regulatory plan was developed to guide the permit application process. Overall, the assessment found that most project impacts will be acceptably minor or approved with mitigation measures.
Parabolic trough was recommended for this specific project based on the technical and economic feasibility of developing a 50 to 500 MW plant in the mid-2011 timeframe. Two viable siting areas were investigated and will be considered for development. The results of this project will be beneficial to any energy company or project developer considering a central solar plant project. The cost data for a range of technology options and design configurations can be used in planning and siting solar plants in other locations.
Author: Cara Libby is a Project Manager in EPRI’s Generation Sector. She works in the Office of Innovation with a focus on emerging renewable energy technologies. Before joining EPRI in 2006, Ms. Libby worked as a Project Leader in the Energy Systems Laboratory at GE Global Research Center. Ms. Libby is a mechanical engineer with a B.S. degree from Johns Hopkins University and an M.S. degree from Stanford University. A free public summary report is available on EPRI’s website at www.epri.com/seig.
Power Engineering July, 2008

[amirabbas_sz]

Properly Monitor Your Scrubber Chemistry
By Brad Buecker, Contributing Editor

Within the last several years the flue gas desulfurization (FGD) market has mushroomed and many utilities have purchased and are erecting wet FGD systems. Critical to proper operation of these systems will be accurate liquids and solids monitoring of the process streams. This article examines many of the most important analyses for which new scrubber personnel must prepare and equip laboratories.

Corrosion Prevention

Chlorine in coal converts to hydrogen chloride (HCl) during combustion. HCl, of course, is an acid and it reacts with limestone to produce calcium and magnesium chloride (CaCl2 and MgCl2). Both are very soluble salts. Chloride concentrations may reach several thousand mg/L in scrubber quenchers. High alloy metals to resist chlorides are expensive, so often materials are selected to handle the calculated maximum chloride concentration, but no more. So, if the process is allowed to operate at a higher chloride concentration, severe corrosion can result.





More than one technique is available to monitor chlorides. Most sophisticated is ion chromatography (IC), which can also analyze many other anions from FGD or other process streams. For those with limited budgets, chloride monitoring by ion specific electrode is an alternative. This technique operates similarly to other ion specific methods, in which the electrode senses the ion of particular importance. Yet another possibility is titration analysis, such as the method offered by the Hach Co. Very simple in nature, it gives good results for the chloride concentrations typically encountered in wet scrubbers.

Scrubber Slurry Alkalinity

Limestone (CaCO3) or hydrated lime [Ca(OH)2] are the principal reagents in wet scrubbers. Consider the simplified reaction outlined below, which illustrates the initial reaction of limestone with the acidic solution produced by sulfur dioxide absorption (SO2 + H2O ⇔ 2H++ + SO3-2) into the scrubber slurry sprays.

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Extremely important is constant measurement of the alkalinity in the scrubber module or modules, as too much alkalinity will waste reagent while lean alkalinity will impair SO2 removal. The technique universally employed in wet scrubbers is pH monitoring. These measurements must be continuous, with control of reagent feed rates based upon the readings. For the lab staff, grab-sample pH analyses are very important to make sure that the in-line probes/monitors are accurate.

Scrubber Slurry Density

Most systems utilize slurry sprays to contact the flue gas. As sulfur dioxide is absorbed and water evaporates, the slurry density increases. The slurry circulating pumps can only handle so much mass before electrical requirements are exceeded. Like pH, scrubbers are equipped with continuous density monitors, typically utilizing radioactive detectors. Again, the lab staff needs to monitor density on a grab sample basis to ensure the accuracy of the continuous instruments. A common method is use of a pycnometer, where the vessel is first filled with water and weighed, and then is rinsed and filled with slurry sample and weighed. The specific gravity ratio of the slurry vs. water is then compared to a chart or table, which gives the slurry density.

Solids Analyses

Equation 1 outlined the primary scrubbing reaction. Of course, as sulfur dioxide is removed from the flue gas, it becomes a solid material that must be handled and removed from the scrubber. In the absence of any other reactants, calcium and sulfite ions will precipitate as a hemihydrate, where water is actually included in the crystal lattice of the scrubber byproduct.

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However, oxygen in the flue gas greatly influences chemistry. Aqueous bisulfite and sulfite ions react with oxygen to produce sulfate ions (SO4-2).

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Approximately the first 15 mole percent of sulfate ions co-precipitates with sulfite to form calcium sulfite-sulfate hemihydrate [(CaSO3·CaSO4) ·½H2O]. Any sulfate above the 15 percent mole ratio precipitates with calcium as gypsum.

Click here to enlarge image


Control of solids chemistry offers interesting challenges and is extremely critical to operation. Experience has shown that operation in either a completely oxidized state (no calcium sulfite-sulfate hemihydrate in the scrubbing slurry) or a completely un-oxidized state (no gypsum in the slurry) minimizes scaling in the scrubber. Scale buildups can be extremely problematic, as deposit formation on scrubber internals and subsequent gas flow restrictions may cause unit de-rates and even forced outages if gas flow is severely restricted.
A typical deciding factor on the choice of oxidized or non-oxidized byproduct involves the handling characteristics and commercial value of the solid. Calcium sulfite and calcium sulfite-sulfate hemihydrates are soft materials that tend to retain water. They have little value as a chemical commodity. For this reason, many scrubbers are equipped with forced-air oxidation systems to introduce additional oxygen to the scrubber slurry. A properly designed oxidation system will convert all of the liquid sulfite ions to sulfate ions. Sulfate of course precipitates with calcium as gypsum, which forms a cake-like material when subjected to vacuum filtration. In many cases, 85 to 90 percent of the free moisture in gypsum can be extracted by this relatively simple mechanical process. Low moisture is a common requirement of wallboard manufacturers. Removal of free moisture also reduces the chloride concentration of the byproduct, which is a critical aspect for wallboard production.
The technique that has proven itself very well for scrubber solids analysis is thermogravimetry. A thermogravimetric analyzer (TGA) is a quantitative not a qualitative instrument, so the operator needs to have a good idea of the primary constituents in the sample before analysis. If the sample compounds decompose at distinct and separate temperatures, it becomes easy to calculate the concentration of the original materials. Wet-limestone scrubber byproducts lend themselves well to this technique. The following equations illustrate the decomposition chemistry of wet-limestone FGD solids. The typical decomposition temperature ranges are also shown.

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Figure 1 illustrates a TGA analysis of a pre-dried scrubber solids sample containing all three of the major constituents. For the moment we will ignore the decomposition shown at 600 C. This will be addressed shortly.

Click here to enlarge image

The calculations to determine original constituent concentrations are straightforward. The molecular weight of gypsum is 172 and that of the water forced out is 36, so the initial gypsum content is determined by multiplying the weight loss (5.772 percent) times a factor of 172 ÷ 36 (4.78). For calcium sulfite-sulfate hemihydrate, the factor is 131.9 ÷ 9 (14.6), where the mole ratio of calcium sulfite to calcium sulfate is assumed to be 85:15. For the calcium carbonate decomposition, the factor is 100.1 ÷ 44 (2.27). Thus, for the analysis shown in Figure 1, the gypsum content is 27.6 percent, the calcium sulfite-sulfate hemihydrate content is 12.0 percent and the calcium carbonate content is 22.3 percent.

This sample comes from a wet-limestone scrubber that serves the dual purpose of removing SO2 and flyash from the gas stream. The analytical procedure includes an isothermal step at 600 C, where the furnace atmosphere is temporarily switched from nitrogen to air. This allows any unburned carbon to combust, which otherwise would decompose during the final weight loss step. The effect is clearly illustrated by the vertical slope at 600 C in Figure 1. Following the isothermal step, the initial heating rate resumes and the furnace ramps up to 1000 C. The calcium carbonate decomposition then proceeds unmasked.

Click here to enlarge image

Another valuable aspect of this technique is to determine the efficiency of the scrubbing process, commonly described as reagent utilization. Figure 2 shows an analysis of the byproduct from another FGD system with forced oxidation. As can be seen, the vast majority of the byproduct, nearly 96 percent, consists of gypsum, with just under 2 percent un-reacted calcium carbonate in the byproduct. This represents very good limestone utilization. Depending upon the size of the steam generator, and, of course, the back-end scrubber, each percentage increase in unused limestone can cost the utility thousands of dollars per year.

Author: Brad Buecker is a contributing editor for Power Engineering. He recently joined Nalco Co. as an Industry Technical Consultant having previously served as an Air Quality Control Specialist and Plant Chemist for Kansas City Power & Light Co. He has previous experience as a chemical cleaning services engineer, a water and wastewater system supervisor and a consulting chemist for Burns & McDonnell Engineers. He also served as a results engineer, flue gas desulfurization (FGD) engineer and analytical chemist for City Water, Light & Power, Springfield, Ill. Buecker has written more than 70 articles and columns on steam generation, water treatment and FGD chemistry, and he is the author of three books on steam generation topics published by PennWell Publishing, Tulsa, Okla. Buecker has an AA in pre-engineering from Springfield College in Illinois and a BS in chemistry from Iowa State University. He is a member of ACS, AIChE, ASME, and NACE.
Power Engineering July, 2008

[kkm7]

دانلود نرم افزار ETAP و فایل های مرتبط

جهت دانلود نرم افزار ETAP و فایل های مرتبط به لینک زیر مراجعه کنید :

دانلود :

http://www.megaupload.com/?d=YVW7YZ04

for help
راهنما :

http://www.etap.com/tutorials.htm

[kkm7]

PLC Ladder Simulator

یکی از دغدغه های کسانی که تازه شروع به برنامه نویسی PLC نموده اند اطمینان از عملکرد صحیح برنامه شان قبل از انتقال آن به PLC است و چون معمولاً برنامه نویسان جوان و تازه کار از زبان Ladder برای شروع کار استفاده می کنند این نرم افزار می تونه کمک بسیار خوبی برای پیشرفت آنها در کار خود باشد. امیدوارم این نرم افزار را دانلود کنید و از آن لذت ببرید.

پسورد فایل http://eeesoftware.******.com می باشد.

دانلود

توجه : به جای ستاره ها b l o g f a بدون فاصله ها و البته به احتمال زیاد پسورد بدون http:// هست

[h-taher]

با سلام خدمت شما
با سلام .
دوستان اگه راجع به طرز کار مترو قرار دهید .هر چه کاملتر و علمی تر باشه ممنون میشوم
در مورد برقهاي فشار قوي كه در ايستگاه هست
چه موتورهايي استفاده مي شود ؟؟
و برق موتور (مترو)چگونه وصل مي شود ؟؟

[h-taher]

با سلام خدمت مديديت محترم
من چند تا نرم افزار در رابطه برق مي خواستم كه بيشتر در مورد مهندسي برق قدرت باشه

نرم افزار نقشه كشي سيم هاي برق ساختمان
نرم افزار محاسبه كابل و راه اندازي موتورها
نرم افزار طراحي شبكه انتقال و وارد كردن اطلاعات
و نرم افزار هاي ديگه كه بدرد برق قدرت هست
اگر ممكنه نرم افزارهايي كه بهتر و كاملتر هستند را معرفي كنيد
اگر جايي هست كه مي تونم تهيه كنم بگيد در غير اينصورت لينك دانلودش را بگيد
اگر مطلب مفيدي در مورد كار يا توضيح در مورد نرم افزار ها داريد بگيد
با تشكر از شما

[h-taher]

اگر ممكنه در مورد تعمير نگهداري موتورها مقاله ايي ارائه دهيد
چگونگي انجام تعميرات
طرقه سيم كشي استاتور و نمره سيم لاكي قطبها و فهميدن عيب موتورها