ASME Conference Presenter Attendance Policy and Archival Proceedings

2014;():V002T00A001. doi:10.1115/POWER2014-NS2.

This online compilation of papers from the ASME 2014 Power Conference (POWER2014) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Simple and Combined Cycles

2014;():V002T08A001. doi:10.1115/POWER2014-32081.

An experimental investigation has been performed to study the film cooling performance of a smooth expansion exit at the leading edge of a gas turbine vane. A two-dimensional cascade has been employed to measure the cooling performance of the proposed expansion using the transient Thermochromatic Liquid Crystal technique. One row of cylindrical holes, located on the stagnation line, is investigated with two expansion levels, 2d and 4d, in addition to the standard hole. The air is injected at 90° and 60° inclination angle relative to the vane surface at four blowing ratios ranging from 1 to 2 at a 0.9 density ratio. The Mach number and the Reynolds number based on the cascade exit velocity and the axial chord are 0.23 and 1.4E5, respectively. The detailed local heat transfer coefficient over both the pressure side and the suction side are presented in addition to the lateral-averaged normalized heat transfer coefficient. The proposed expansion provides a lower heat transfer coefficient compared with the standard cylindrical hole over the investigated blowing ratios. Combining the heat transfer coefficient with the corresponding cooling effectiveness, previously presented, the smooth expansion shows a significant reduction in the heat load with more uniform distribution of the coolant over the leading edge region. The strong confrontation between the coolant jet and the mainstream, in case of 90° injection, yields a strong dispersion of the coolant with higher heat transfer coefficient and high thermal load over the vane surface.

Topics: Film cooling
Commentary by Dr. Valentin Fuster
2014;():V002T08A002. doi:10.1115/POWER2014-32125.

The objective of the paper is to present the through-flow design of a twin-shaft oxy-fuel turbine. The through-flow design is the subsequent step after the turbine mean-line design. The through-flow phase analyses the flow in both axial and radial directions, where the flow is computed from hub to tip and along streamlines. The parameterization of the through-flow is based on the mean-line results, so principal features such as blade angles at the mean-line into the through-flow phase should be retained. Parameters such as total inlet pressure and temperature, mass flow, rotation speed and turbine geometries are required for the through-flow modelling.

The through-flow study was performed using commercial software — AxCent(™) from Concepts NREC. The rotation speed of the twin-shaft power turbine was set to 7200 rpm, while the power turbine was set to 4800 rpm. The mean-line design determined that the twin-shaft turbine should be designed with two compressor turbine stages and three power turbine stages.

The through-flow objective was to study the variations in the thermodynamic parameters along the blade. The power turbine last-stage design was studied because of the importance of determining exit Mach number distribution of the rotor tip. The last stage was designed with damped forced condition. The term ‘damped’ is used because the opening from the tip to the hub is limited to a certain value rather than maintaining the full concept of forced vortex.

The study showed the parameter distribution of relative Mach number, total pressure and temperature, relative flow angle and tangential velocity. Through-flow results at 50% span and mean-line results showed reasonable agreement between static pressure, total pressure, reaction degree and total efficiency. Other parameters such as total temperature and relative Mach number showed some difference which can be attributed to working fluid in AxCent being pure CO2. The relative tip Mach number at rotor exit was 1.03, which is lower than the maximum typically allowed value of 1.2. The total pressure distribution was smooth from hub to tip which minimizes the spanwise gradient of total pressure and thus reduces the strength of secondary vortices. The reaction degree distribution was presented in the paper and no problems were revealed in the reaction degree at the hub. Rotor blades were designed to produce a smooth exit relative flow angle distribution. The relative flow angle varied by approximately 5° from hub to tip. The tangential velocity distribution was proportional to blade radius, which coincided with forced vortex design. Through-flow design showed that the mean-line design of a twin-shaft oxy-fuel turbine was suitable.

Commentary by Dr. Valentin Fuster
2014;():V002T08A003. doi:10.1115/POWER2014-32169.

In this work different concepts are investigated for combined heat and power production (CHP) from offshore gas turbines. Implementation of such technology could improve energy efficiency of offshore oil and gas production and lead to reduced fuel consumption and resulting CO2 emissions. Offshore electric power is in most cases generated by gas turbines operating in a simple cycle. However it would be desireable to increase energy efficiency by adding steam or CO2 bottoming cycles to produce power from the exhaust heat. However part of the heat from the gas turbine exhaust is normally used for onboard process heat for the oil/water separation process among others, this must be taken into consideration when estimating capacity for additional power production. Different CHP concepts will be evaluated at different operating conditions while running the turbines in both design and off-design mode The results show that it is possible to produce an additional 6–8 MW of electrical power from a 32 MW turbine (depending on the conditions) while using 15 MW of heat from the exhaust for on-board processing.

Commentary by Dr. Valentin Fuster
2014;():V002T08A004. doi:10.1115/POWER2014-32198.

Gas turbines play an important role in power generation, and it is therefore desired to operate gas turbines with high efficiency and power output. One of the most influential parameters on the performance of a gas turbine is the ambient condition. It is known that inlet cooling can improve the gas turbine performance, especially when the ambient temperature is high. This study examines the effect of inlet cooling with different operating parameters such as compressor inlet temperature, turbine inlet temperature, air fuel ratio, and pressure ratio. Furthermore, the coefficient of performance (COP) of the cooling system is considered a function of the ambient temperature. Aspen Plus software is used to simulate the system under a steady-flow condition. The results indicate that the cooling of the compressor inlet air can substantially improve the power output as well as the overall efficiency of system. More importantly, there exists an optimal temperature at which the inlet cooling should be operated to achieve the highest efficiency.

Topics: Cooling , Gas turbines
Commentary by Dr. Valentin Fuster
2014;():V002T08A005. doi:10.1115/POWER2014-32201.

One of the most efficient power plants in past decades is the gas turbine. Significant studies have been conducted on the effects of various design and operation parameters on gas turbine performance. However, it is still a challenge to find the optimal operating parameters for the best performance. One of the important parameters is the climate at which the gas turbine operates. The current study is on the performance of gas turbine with fog cooling, focusing on the effect of inlet air humidity and ambient temperature. The overall efficiency will be altered through inlet fog cooling and regenerative heating. Other components such as reheating are accompanied. The fog cooling is also compared to the chiller inlet cooling, in which the performance of coefficient (COP) varies with temperature difference. The analysis is conducted by using Aspen Plus software. The results indicate that a combination of fog cooling and regeneration as well as reheating can substantially improve the system thermal efficiency. Compared to the system with only fog cooling, the efficiency increases by 24.5 % when both regeneration and reheat systems are combined to the fogging cooled system.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2014;():V002T08A006. doi:10.1115/POWER2014-32246.

The Pressurized Fluidized Circulating Bed (PFCB) combined cycle was simulated. The simulations balance the energy between the elements of the unit, which consists of gas turbine cycle and steam turbine cycle. The PFCB is used as a combustor and steam generator at the same time. The simulations were carried out for PFCB combined cycle plant for two cases. In the first case, the simulations were performed for combined cycle with reheat in the steam turbine cycle. While in the second case, the simulations were carried out for the PFCB combined cycle with extra combustor and steam turbine cycle with reheat. For both cases, the effect of steam inlet pressure on the combined cycle efficiency was predicted. It was found that increasing of steam pressure results in increase in the combined cycle thermal efficiency. The effect of the inlet flue gases temperature on the gas turbine and on the combined cycle efficiencies was also predicted. The maximum PFCB combined cycle efficiency occurs at a compression ratio of 18, which is the case of utilizing an extra combustor. The simulations were carried out for only one fuel composition and for a compression ratio ranges between 1 to 40.

Commentary by Dr. Valentin Fuster

Advanced Energy Systems and Renewables (Wind, Solar and Geothermal)

2014;():V002T09A001. doi:10.1115/POWER2014-32005.

Solar energy is a renewable energy source that can generate electricity. When there is much solar radiation, there is not always a need for all the energy from the solar, and when the weather is cloudy there may be too little energy to meet demand. Thus, it is often wise to implement energy storage in systems with a large share of renewable energy. Latent heat storage is one of the most efficient ways of storing thermal energy. Sodium Sulfate Decahydrate (Glauber’s salt) has a larger energy storage density and a higher thermal conductivity. So the present work, built solar chimney power plant of 2m-radius of collector and a 4m chimney height integrated by phase change materials. Aim of designing and building solar chimney to estimate the effect of adding phase change materials as well as to examine the effect of inclination angle (16°, 8°). The results show that maximum temperature difference between collector exit and the ambient reached to 23.7°C for case (i) and for 17.7°C case (ii), the maximum air velocity reached 2.25 m/s that in case (ii) and reached 2.05 m/s in case (i).and maximum collector efficiency can be reached to 8.925% in case (ii).

Commentary by Dr. Valentin Fuster
2014;():V002T09A002. doi:10.1115/POWER2014-32017.

The present study explores the potential imbalance problem of the Aquifer Thermal Energy Storage (ATES) system at the Eindhoven University of Technology (TU/e) campus, Eindhoven. This ATES is one of the largest European aquifer thermal energy storage systems, and has a seasonal imbalance problem. Reasons for this issue may be the high cooling demand from laboratories, office buildings and the direct ATES cooling system. Annually, cooling towers use on average 250 MWh electricity for the removal of about 5 GWh of excess heat from the ATES to the surroundings. In addition, the TU/e uses a large amount of natural gas for heating purposes and especially for peak supplies.

Recovering the surplus heat of the ATES, a CO2 Trans-critical Heat Pump (HP) system to cover particularly peak demands and total heating demand is proposed, modeled and optimized. The model is validated using data from International Energy Agency. Based on simulation results, 708294 nm3 of natural gas are saved where two different scenarios were considered for the ATES efficiency, cost saving and green house gas reduction. In scenario I, the COP of the ATES increased up to 50% by which K€ 303.3 energy cost and 1288.5 ton CO2 are saved annually. On the other hand, it will be shown that the ATES COP in Scenario II will improve up to 20%. In addition, the proposed energy recovery system results in a 606 ton CO2 -reduction and K€152.7 energy cost saving for the university each year.

Commentary by Dr. Valentin Fuster
2014;():V002T09A003. doi:10.1115/POWER2014-32023.

A self-circulating solar thermosyphon (TS) was applied to hydropower generation for the first time. A TS consists of a solar thermal collector, condenser, buffer chamber, hydropower section, heat exchanger, and recuperator. In the present study, the power output level was 10−6 W for the solar irradiation input of 102 – 103 W. The coefficient is 10−9. Considering the Carnot’s coefficient, 0.13, for the heat source and sink of temperatures 70°C and 25°C, there is room for remarkable improvement in TS hydropower generation. Moreover, the solar thermosyphon hydropower generation may provide us with new ways of utilizing heat below a temperature of 100°C, which until now has been merely used for things such as hot water supply and floor heating.

Commentary by Dr. Valentin Fuster
2014;():V002T09A004. doi:10.1115/POWER2014-32035.

Isolated hybrid wind microgrids operate within three distinct modes, depending on the wind resources and the consumer grid demand: diesel-only (DO), wind-diesel (WD) and wind-only (WO). Few successful systems have been shown to consistently and smoothly transition between wind-diesel and wind-only modes. The University of Alaska – Fairbanks Alaska Center for Energy and Power (ACEP) has constructed a full scale test bed of such a system in order to evaluate technologies that facilitate this transition. The test bed is similar in design to the NREL Power Systems Integration Laboratory (PSIL) and sized to represent a typical off-grid community. The objective of the present work is to model the ACEP test bed in DO and WD modes using MATLAB™ SIMULINK© and then validate the model with actual full-scale laboratory measurements. As will be shown, the frequency responses are grouped into three classifications based on their behavior. The model is shown to be successful in describing the frequency response of relatively small (0.15 per unit) steps in load. Modifications to the excitation system model are discussed which could improve the accuracy for larger steps in load. The ACEP test bed and associated SIMULINK© model are to be used in future work to support investigating WO operation.

Topics: Microgrids , Wind
Commentary by Dr. Valentin Fuster
2014;():V002T09A005. doi:10.1115/POWER2014-32042.

In this work, the detailed model of a high temperature Solid Oxide Fuel Cell (SOFC) and Gas Turbine (GT) hybrid system was established by using MATLAB/Simulink platform, based on the equations of mass and energy balance and thermodynamic characteristics, with the consideration of various polarization losses and fuel cell heat loss. Influence of different biomass gases on the hybrid system performance was studied. Results show that the electrical efficiency could reach up to over 50% with four types of gasified biomass, higher than other hybrid power system using biomass gases. Biomass gases from different sources have different composition and calorific value, which significantly affect the hybrid system performance. The system output power and efficiency fueled with wood chip gas are higher than the system fueled with other three types of fuel. Restricted by compressor surge safety zone, the adjustable range of biomass gas fuel flow rate is small. The speed of the gas turbine has a significant impact on the hybrid system parameters such as output power and efficiency. When the rotational speed of the gas turbine is lower than the rated value, the hybrid system performance parameters change significantly, on the contrary, the hybrid system performance parameters change slightly.

Commentary by Dr. Valentin Fuster
2014;():V002T09A006. doi:10.1115/POWER2014-32049.

Pakistan has a hydro potential of approximately 42,000MW; however only 7,000MW is being utilized for electrical power production [1, 2]. Out of 42,000 MW, micro hydro potential is about 1,300MW [1, 2]. For typical site conditions (available flow rate and head) in Pakistan, Cross Flow Turbines (CFTs) are best suited for medium head 5–150m [3] for micro-hydro power production. The design of CFT generally includes details of; the diameter of the CFT runner, number of blades, radius of curvature and diameter ratio. This paper discusses the design of various CFTs for typical Pakistan site conditions in order to standardize the design of CFTs based on efficiency that is best suited for a given site conditions. The turbine efficiency as a function of specific speed will provide a guide for cross flow turbine selection based on standardized turbine for manufacturing purposes. Standardization of CFT design will not only facilitate manufacturing of CFT based on the available site conditions with high turbine efficiency but also result in reduced manufacturing cost.

Topics: Design , Turbines , Cross-flow
Commentary by Dr. Valentin Fuster
2014;():V002T09A007. doi:10.1115/POWER2014-32057.

Renewable energy continues to attract much interest due to the depletion of fossil fuels and unsettled political disputes. This study aims to evaluate the current status of energy generation on the campus of Eindhoven University of Technology (TU/e). Furthermore, it looks for ways for the TU/e to improve sustainability by finding and proposing alternative solutions. Therefore, a broad scope of various renewable energy sources (RES) has been investigated. From many aspects, the analysis of RES proves that biomass is the most appropriate source of renewable energy for the TU/e campus. Thus, the capability of harvestable biomass fuel in energy generation throughout a year has been investigated for this project, and it has been concluded that solid biomass waste from the campus can provide 1314 MWh heat load annually. In order to achieve as much energy from biomass as possible, a combined heat and power unit (CHP), in order to produce both heat and electricity for new student houses on the campus, has been modeled. Finally, the project results show that a small-scale CHP cycle is capable of producing 366 MWh electricity, as well as 772 MWh heat, annually.

Commentary by Dr. Valentin Fuster
2014;():V002T09A008. doi:10.1115/POWER2014-32058.

The implementation of renewable energy systems is often regarded by the consumer to be too costly and too complex to maintain and operate. For instance converting sunlight or wind energy to electricity along with the conditioning equipment required to put energy into the system can be cost prohibitive for a residential or commercial application. The proposed system implements multiple renewable energy components working in series. These components bypass those costly electrical energy conversions by converting the acquired energy into heat, which can be utilized to offset a portion of the energy consumed within the home or business. This system can be made completely transparent with little or no impact on the consumers’ lifestyle. Also, the proposed system, by only attempting to offset a portion of the current usage, will be simple and inexpensive to assemble and maintain with a short return on investment.

According to the U.S. Energy Information Administration an estimated 10 quadrillion Btu’s are consumed by 113.6 million houses in the United States, while 1.8 quadrillion Btu’s of the total energy is used for hot water heating [1]. It has been shown that approximately 20% of the energy costs associated with most residential and small commercial businesses stem from hot water heating. A patent-pending technology, called a viscous controller, attached at the base of a wind turbine, which operates in series with a traditional thermal solar collector to supplement the energy used in the hot water tank. This technology reduces the cost of the system and allows for the average homeowner and small business owner to offset their current energy usage, incorporate renewable energy sources, and offer a 4–5 year return on initial investment. More importantly, if this system is implemented in only a portion of the target market, it has the potential to completely offset the rising energy demands for the United States each year for the foreseeable future.

Topics: Heat , Hot water
Commentary by Dr. Valentin Fuster
2014;():V002T09A009. doi:10.1115/POWER2014-32069.

This paper presents the Computational Fluid Dynamics analysis of a Tesla bladeless turbine using compressed air as the working fluid. Multiple flow configurations are analyzed using both Laminar and the turbulent behaviors. The loading coefficient and the efficiency of turbines is evaluated for both the 2D and 3D cases. Multiples disc is a viable option but it is been observed they result in loss in performance for the laminar and turbulent simulations. In addition the inflection point of the laminar flow vanishes in the turbulent flow; the work presented is an initial step towards the realization of Tesla turbine.

Commentary by Dr. Valentin Fuster
2014;():V002T09A010. doi:10.1115/POWER2014-32088.

Renewable energy has become a promising solution to substitute fossil fuels in power generation. In particular, the use of solar energy is stretched to a wide range of applications, e.g. photovoltaic cells, solar water heaters, solar space heating, solar thermal plants. However, the combination of solar energy with the Rankine cycle is limited to few applications only. In this context, this study aims in investigating the practicality of employing solar heaters to operate a Rankine cycle for small scale power generation. The working fluid in this study is refrigerant R-134a. Sizing and calculations of the various components of the system are carried out based on a net output power of 1 kW. In comparison with available electricity sources in Lebanon, it was found that the proposed system is currently more expensive than public electricity. However, it can compete with private generators that currently fill the gap in electricity shortage. The main advantage herein lies in the friendly environmental load due to the absence of combustion gases.

Commentary by Dr. Valentin Fuster
2014;():V002T09A011. doi:10.1115/POWER2014-32115.

It is estimated that 30% of the over 1 billion cubic feet per day of natural gas produced in the Bakken shale field is lost to flaring. This flared gas, were it to be collected and used in DLE power generation gas turbine engines, represents approximately 1.2 GW of collective electric power. The main reason that much of this gas is flared is that the infrastructure in the Bakken lacks sufficient capacity or compression to combine and transport the gas streams. One of the reasons that this gas cannot be utilized on-site for power generation is that it contains significant amounts of natural gas liquids (NGLs) which make the gas unsuitable as a fuel for natural gas-fired gas turbine engines. A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed that converts liquid fuels into a substitute for natural gas. This LPP Gastm can then be used to fuel virtually any combustion device in place of natural gas, yielding emissions comparable to those of ordinary natural gas. The LPP technology has been successfully demonstrated in over 1,000 hours of clean power generation on a 30 kW Capstone C30 microturbine. To date, 15 different liquid fuels have been vaporized and burned in the test gas turbine engine. To simulate the vaporization of NGLs, liquids including propane, pentane, and naphtha, among other liquids, have been vaporized and blended with methane. Emissions from the burning of these vaporized liquid fuels in the test engine have been comparable to baseline emissions from ordinary natural gas of 3 ppm NOx and 30 ppm CO. Autoignition of the vaporized liquid fuels in the gas turbine is controlled by the fraction of inert diluent added in the vaporization process. The LPP technology is able to process an infinitely variable composition of NGL components in the fuel stream by continually adjusting the amount of dilution to maintain a heating value consistent with natural gas. Burning the flare gases containing NGLs from a well locally, in a power generation gas turbine, would provide electricity for drilling operations. A microgrid can distribute power locally to the camps and infrastructure supporting the drilling and processing operations. Using the flare gases on-site has the benefit of reducing or eliminating the need for diesel tankers to supply fuel for power generation systems and equipment associated with the drilling operations.

Topics: Microgrids , Emissions
Commentary by Dr. Valentin Fuster
2014;():V002T09A012. doi:10.1115/POWER2014-32143.

A small personal use wind turbine (PWT) is studied and tested for power, exergy and energy evaluation under different operating conditions. The wind turbine incorporates non-twisted blades of 1.5 m span and 0.27 m chord, using NACA 63418 airfoil. Using the earlier test results at pitch angles of 22°, 34° and 38° between the wind speeds of 4 m/s to 7 m/s, torque produced by each blade is determined. It is desired to calculate the torque as it is difficult to measure it for a small wind turbine. Using the governing equations and available computational fluid dynamics software, the total torque on each blade is determined. The resultant torque yielded the mechanical power output of the PWT. Using the available power, energy and exergy in the air flow, corresponding efficiencies are determined. To determine the changes in energy and exergy with respect to the wind speed, wind-chill factor expression is utilized. Results are collected for a wide range of wind speeds and pitch angles. Power, energy, exergy and their corresponding efficiency is evaluated to determine the optimal use pitch angle and ambient conditions. The pitch angles of 22° and 38o yielded high efficiencies although 22° produced the higher rotational speed as compared to 38°. The result suggests better performance for continuous wind speed conditions at low pitch angles — with respect to the rotating plane. For non-continuous wind conditions, higher pitch angles appeared beneficial.

Topics: Wind turbines
Commentary by Dr. Valentin Fuster
2014;():V002T09A013. doi:10.1115/POWER2014-32158.

Optimisation of Organic Rankine Cycles (ORCs) for binary cycle applications could play a major role in determining the competitiveness of low to moderate renewable sources. An important aspect of the optimisation is to maximise the turbine output power for a given resource. This requires careful attention to the turbine design notably through numerical simulations. Challenges in the numerical modelling of radial-inflow turbines using high-density working fluids still need to be addressed in order to improve the turbine design and better optimise ORCs. This paper presents preliminary 3D numerical simulations of a radial-inflow turbine working with high-density fluids in realistic geothermal ORCs. Following extensive investigation of the operating conditions and thermodynamic cycle analysis, the refrigerant R143a is chosen as the high-density working fluid. The 1D design of the candidate radial-inflow turbine is presented in details. Furthermore, commercially-available software Ansys-CFX is used to perform preliminary steady-state 3D CFD simulations of the candidate R143a radial-inflow turbine at the nominal operating condition. The real-gas properties are obtained using the Peng-Robinson equations of state. The thermodynamic ORC cycle is presented. The preliminary design created using dedicated radial-inflow turbine software Concepts-Rital is discussed and the 3D CFD results are presented and compared against the meanline analysis.

Commentary by Dr. Valentin Fuster
2014;():V002T09A014. doi:10.1115/POWER2014-32170.

Renewable energy resource is considered by many developed and developing countries as a promising and a cost effective candidate to provide energy. The operation of cooling systems in the United Arab Emirates (UAE) have some operating problems especially in summer such as severe grid dependent, excessive energy consumption, high emissions and high costs. So, more economically and environmentally friendly HVAC systems are desired to provide the required electricity demands for cooling loads while saving energy and having low emissions to the environment. In this paper, a parabolic trough solar collector is integrated with a triple effect absorption cooling system for sustainable development. A computer code is developed using Engineering Equation Solver (EES) software to obtain all required thermodynamic properties of water-lithium bromide (H2O/LiBr) solution and to optimize all operating parameters and carry out all detailed energy and exergy analyses for a 10 kW cooling capacity. In addition, the parabolic trough solar collector (PTSC) is also designed for the required cooling load and its overall dynamic behavior is also investigated. The solar irradiance available in the UAE on a monthly basis is used in the analysis of a PTSC-based HVAC cooling system. Energetic and exergetic efficiencies of the PTSC for every month are also evaluated under different operating conditions. The Overall monthly energy and exergy efficiencies of the integrated PTSC-based HVAC system for a constant mass flow rate of Therminol-66 and concentration ratio are calculated. The dynamic variation of the coefficient of performance of the integrated system with the solar irradiance and mass flow rate of the oil are also evaluated. Results show that both energetic and exergetic COPs are decreased with increasing the solar irradiance for a constant mass flow rate of oil and constant concentration ratio. It is found that increasing the mass flow rate of the oil from 0.1 to 0.5 kg/s results in decreasing the energetic COP from 2.15 to 1.98 and the exergetic COP from 2.05 to 1.93.

Commentary by Dr. Valentin Fuster
2014;():V002T09A015. doi:10.1115/POWER2014-32173.

Achieving higher emission reductions on one hand and employing lower cost concepts on the other hand are desirable in designing future power generator systems. Hence, interdisciplinary studies in a form of system concept modeling should be employed to conceptualize and construct economic and efficient low-carbon system concepts. The concept modeling starts with simple idealized models that preserve the key structural features of a system and adds complex features in the following stages to elucidate principles, relationships, and interfaces. For wind systems, the essential features for concept modeling are wind and load variations, and the main goal is to obtain the cost of electricity delivered by the system as a function of wind penetration (emission reduction); more complex features (storage, photovoltaic, transmission, etc.) are added in the following stages. In this work, an interdisciplinary concept modeling is provided to estimate the magnitude of cost versus performance using the wind/load data from Pennsylvania New Jersey Maryland Interconnection (PJM) LLC, and cost estimations published by the Energy Information Agency. The results show that system total cost increases modestly at low penetration, and it increases more rapidly when wind curtailment becomes significant. Eventually storage becomes cheaper than curtailment. The key question that should be answered in this modeling is the magnitude of electricity cost for high penetration, low emission systems.

Topics: Carbon , Tradeoffs
Commentary by Dr. Valentin Fuster
2014;():V002T09A016. doi:10.1115/POWER2014-32174.

Due to the increasing interest of producing power from renewable and non-conventional resources, organic Rankine cycles are finding their place in today’s thermal energy mix. The main influencers on the efficiency of an organic Rankine cycle are the working fluid and the expander. Therefore most of the research done up to date turns around the selection of the best performance working media and the optimization of the expansion unit design. However, few studies consider the interaction of the working fluids in the turbine design, and how this fact can affect the overall thermodynamic cycle analysis. In this work we aim at including the aerodynamic behavior of the working fluids and their effect on the turbine efficiency in the thermodynamic analysis of an organic Rankine cycle. To that end, we proposed a method for the estimation of the characteristics of an axial in-flow turbine in an organic Rankine cycle simulation model. The code developed for the characterization of the turbine behavior under the working fluid properties evaluated the irreversibilities associated to the aerodynamic losses in the turbine. The organic Rankine cycle was analyzed by using IPSEpro process simulator. A set of candidate working fluids composed of selected organofluorines and organochlorines was chosen for the analysis. The thermophysical properties of the fluids were estimated with the equations of state implemented in Refprop. Results on the energy and exergy overall performances of the cycle were analyzed for a case study with standard source and sink temperatures. For each fluid the number of stages and geometry of the turbine were optimized. It was observed that some working fluids that could initially be considered as advantageous from a thermodynamic point of view, had an unfavorable impact on the turbine efficiency, thus increasing the irreversibilities of the cycle. We concluded that if the influence of the working fluid on the turbine performance is underestimated, the real performance of the organic Rankine cycle could show unexpected deviations from the theoretical results.

Commentary by Dr. Valentin Fuster
2014;():V002T09A017. doi:10.1115/POWER2014-32175.

Ocean Thermal Energy Conversion (OTEC) is a form of renewable solar energy that has the capability to provide 24 hour base load, dispatchable power to electrical systems. This is a major advantage over solar PV and wind, which are intermittent and can have significant adverse effects on grid stability once penetration exceeds 10% of grid capacity. This paper describes OTEC technology, suitable areas for implementation, current levels of technology development, regulatory barriers, problems posed by intermittent power generation as well as how it is differentiated from intermittent renewable technologies and can enhance grid stability. The discussion of the OTEC technology will include the underlying thermodynamics, critical heat transfer requirements and efficiency issues associated with low temperature Rankine Cycle applications. The discussion of suitable areas for implementation will include required ocean temperatures, ocean topography, current fuel dependence and regulatory issues to be addressed. The discussion of problems posed by intermittent power generation on networks will include transient response of grids to sudden changes in production as well as ramp rate requirements as solar PV comes on and off line on a daily cycle. OTEC, as a base load generation source, will be discussed in terms of market factors and reserve requirements.

Commentary by Dr. Valentin Fuster
2014;():V002T09A018. doi:10.1115/POWER2014-32191.

A model centric approach for Monte Carlo simulation for evaluating the economic and reliability benefits of automated switches for storm restoration is presented. A very detailed circuit model with over 20,000 individual customers modeled is used in the simulation. The simulation uses non-constant equipment failure rates based upon actual utility measurements. As part of the Monte Carlo storm simulation, a reconfiguration for restoration algorithm is employed in determining the response to each outage. The reconfiguration for restoration algorithm can work with either manual or automated switches, or both. System reliability with and without automated switching devices is investigated. Cost benefits as well as reliability benefits are considered.

Topics: Smart grids , Storms
Commentary by Dr. Valentin Fuster
2014;():V002T09A019. doi:10.1115/POWER2014-32195.

In the last 20 years, emerging technologies such as fuel cells and microturbines have contributed to growth in the market for combined heat and power (CHP) in small-scale (5–5,000 kW) applications. Numerous studies utilizing performance assumptions have explored the theoretical potential for distributed CHP to save energy and reduce greenhouse gas (GHG) emissions, however actual performance may differ from expectations. Incentive programs in several states are beginning to yield information about actual (as opposed to potential) performance of small-scale CHP. This paper leverages over ten years of metered data from more than 500 different projects rebated by one such program: California’s Self Generation Incentive Program (SGIP). The population of projects includes established technologies (internal combustion engines, gas turbines) as well as emerging technologies. Performance measures examined include efficiencies, utilization, and GHG emissions impacts. A variety of Federal and State policies seek to increase the amount of small-scale distributed CHP in the coming years. It is imperative that knowledge about actual performance gleaned from metered data collected during the past decade be shared widely so that CHP’s potential to reduce energy consumption and GHG emissions is actually realized in the future.

Commentary by Dr. Valentin Fuster
2014;():V002T09A020. doi:10.1115/POWER2014-32200.

Photovoltaic utility-scale grid-connected power generation facilities have performance guarantee bases that often include a reference solar spectrum. EPC contractors are obligated to correct tested performance for solar spectrum, as is done for irradiance and cell temperature, to judge whether contractual performance guarantees have been satisfied. Air mass correlated with solar spectral irradiance offers a convenient way of accomplishing this. This paper offers an improvement in the versatility and accuracy of accounting for spectral effects in this manner. The effects on the spectral composition by atmospheric constituents, like aerosols and water vapor, are investigated. Spectral mismatch curves are derived that characterize the responses of the PV modules and the irradiance measurement device to both the estimated test and the reference solar spectra. Comparison of several supplier performance curves and spectral mismatch curves reveals significant discrepancies. An improvement in accuracy is proposed by the use of supplier spectral response data and estimated solar spectral profiles. Correcting for spectral effects has minimal impact at air mass values near the 1.5 reference value, but grows in significance with increasing air mass. Greater precision in accounting for solar spectral effects on PV plant performance is expected as this segment of the power generation industry matures. This paper proposes a methodology that addresses this expectation.

Commentary by Dr. Valentin Fuster
2014;():V002T09A021. doi:10.1115/POWER2014-32292.

It is well established that the power generated by a Horizontal-Axis Wind Turbine (HAWT) is a function of the number of blades B, the tip speed ratio λr (blade tip speed/wind free-stream velocity) and the lift to drag ratio (CL/CD) of the airfoil sections of the blade. The previous studies have shown that Blade Element Momentum (BEM) theory is capable of evaluating the steady-state performance of wind turbines, in particular it can provide a reasonably good estimate of generated power at a given wind speed. However in more realistic applications, wind turbine operating conditions change from time to time due to variations in wind velocity and the aerodynamic forces change to new steady-state values after the wake settles to a new equilibrium whenever changes in operating conditions occur. The goal of this paper is to modify the quasi-steady BEM theory by including a simple dynamic inflow model to capture the unsteady behavior of wind turbines on a larger time scale. The output power of the wind turbines is calculated using the improved BEM method incorporating the inflow model. The computations are performed for the original NREL Phase II and Phase III turbines and the Risoe turbine all employing the S809 airfoil section for the turbine blades. It is shown by a simple example that the improved BEM theory is capable of evaluating the wind turbine performance in practical situations where operating conditions often vary in time.

Commentary by Dr. Valentin Fuster
2014;():V002T09A022. doi:10.1115/POWER2014-32307.

The future distribution grid has complex analysis needs, which may not be met with the existing processes and tools. In addition there is a growing number of measured and grid model data sources becoming available. For these sources to be useful they must be accurate, and interpreted correctly. Data accuracy is a key barrier to the growth of the future distribution grid. A key goal for California, and the United States, is increasing the renewable penetration on the distribution grid. To increase this penetration measured and modeled representations of generation must be accurate and validated, giving distribution planners and operators confidence in their performance. This study will review the current state of these software and modeling barriers and opportunities for the future distribution grid.

Commentary by Dr. Valentin Fuster

Energy Water Nexus

2014;():V002T10A001. doi:10.1115/POWER2014-32020.

For the majority of cooling towers installed, of which there are greater than half a million installed in the U.S., tower design uses direct evaporative cooler technology where an ideally enthalpy-neutral process cools the process water stream to a temperature above the ambient wet bulb. This ambient wet bulb temperature is the limiting factor for the process cooling. As such the energy-water connection is clear, these cooling towers are direct consumers of treated water and their cooling performance is intimately tied to the process efficiency.

Topics: Cooling towers
Commentary by Dr. Valentin Fuster
2014;():V002T10A002. doi:10.1115/POWER2014-32051.

The reduction of water consumption and use is emerging as a top priority for all types of thermoelectric power plants. In the United States, thermoelectric power production accounts for approximately 41% of freshwater withdrawals [1] and 3% of overall fresh water consumption. [2] On the basis of responses to a 2011 Electric Power Research Institute (EPRI) Request for Information [3], the feasibility study [4,5,6,7] of a Thermosyphon Cooler Hybrid System (TCHS) [8], proposed by Johnson Controls, was funded under EPRI’s Technology Innovation (TI) Water-Conservation Program. The objective of this project was to further develop the TCHS design concept for larger scale power plant applications and then perform a thorough technical and economic feasibility evaluation of the TSC Hybrid System and compare it to a variety of other competitive heat rejection systems.

The Thermosyphon Cooler Hybrid System reduces power plant cooling tower evaporative water loss by pre-cooling the condenser loop water through a dry cooling process employing an energy efficient, naturally recirculating refrigerant loop. This paper details the results of a detailed feasibility study that was conducted to compare the cost and performance of the TCHS to a number of other potential wet, dry, and hybrid thermoelectric power plant heat rejection systems operating under varying degrees of water constraint. Installed system cost estimates were developed for the base all wet cooling tower systems, TCHS’s of varying sizes, air-cooled condenser (ACC) hybrid systems of varying sizes, and all dry ACC systems.

Optimized all wet cooling tower and all dry ACC system configurations were developed for five different climatic locations. A comprehensive power plant simulation program that evaluated the fuel and water requirements of the power plants equipped with the different heat rejection systems across the weather conditions associated with all 8,760 hours of a typical meteorological year was developed and then an extensive array of simulations were run each location. The summary data were organized in a separate interactive dynamic system comparison summary program to allow users to gain further insight into the relationships between the various heat rejection systems and the sensitivity of the results to changes in key input assumptions.

This paper details the data presented in the interactive dynamic system comparison summary program. This program displays the key metrics of the Annual Net Cost of Power Production, the Annual Net Power Plant Profit, the Annual Operating Profit, and the Internal Rate of Return as a function of the Percent Annual Water Savings Required for the various heat rejection systems at each of the five studied climatic locations studied. Key results and conclusions are presented.

Topics: Heat , Power stations , Water
Commentary by Dr. Valentin Fuster
2014;():V002T10A003. doi:10.1115/POWER2014-32075.

In regions that utilize thermal desalination as part of their water supply portfolio, the cogeneration of water and power in cogeneration desalination plants couples the supply sides of the electricity and water grids. For a fixed plant design, there is a limited range of ratios of generated electric power to produced water at any given time. Due to this coupling, electricity and water require co-optimization. In an environment in which electricity supply is determined by deregulated wholesale markets, this need for co-optimization suggests a need for integrated electricity and water markets. In this market, independent power producers, independent water producers and independent cogeneration plants would submit bids to satisfy demand over a time horizon to a clearing mechanism, indicating relevant physical constraints. The mechanism would then optimize supply of both electricity and water over the time horizon of interest. Recently, a simultaneous co-optimization method has been contributed for the economic dispatch of networks that include water, power and cogeneration facilities in such an integrated market. This paper builds upon this foundation with the introduction of the corresponding unit commitment problem.

Topics: Water
Commentary by Dr. Valentin Fuster
2014;():V002T10A004. doi:10.1115/POWER2014-32076.

The energy-water nexus is an area of increasing global concern and research. In several existing publications on the subject, the challenges of water use for power plant cooling and energy use for water supply are handled seperately. There is however also a need to consider the totality of interactions between the different elements of the engineered water and electricity systems, thus creating a system-of-systems model. A model of this form integrates water use for electricity supply and electricity use for water supply into a single framework, thus elucidating a wide range of interactions which can be influenced by policy and management decisions to achieve desired objectives. An engineering model capturing these interactions and based on first-pass models of the underlying physics of the various coupling and boundary points has been developed in previous work. In this work, the Jacobian of the resulting system of equations has been determined for a particular illustrative case. This Jacobian enables a sensitivity analysis of the inputs and outputs of this system-of-systems to changes in water and electricity demand to be carried out. As a concrete example, the Jacobian is used to examine the effect of a 10 % growth in both electricity and water demand on the set of system inputs and outputs.

Commentary by Dr. Valentin Fuster
2014;():V002T10A005. doi:10.1115/POWER2014-32103.

Combined cycle power plants fueled with natural gas have been increasingly preferred by regulatory agencies for new power generation projects, compared with traditional coal-fired plants. With growing concerns about water resource availability and the environmental impact of wet cooling systems, there has been an increasing trend for new combined cycle projects to incorporate dry cooling, often as a mandate for regulatory approval of the project. There appears to be little consideration given to the impact of less efficient dry cooling systems on unit efficiency, and particularly on increased fuel requirements and therefore carbon dioxide (CO2) emissions for a given power generating output. The trade-off between reduction of water use and increased fuel requirements with dry cooling should be included as part of the decision on the selection of cooling systems for new fossil plant construction.

Commentary by Dr. Valentin Fuster
2014;():V002T10A006. doi:10.1115/POWER2014-32178.

Water consumption is an important consideration when evaluating technologies for carbon capture and storage (CCS). It may in fact become a critical factor in certain regions where water is increasingly a source of conflict. For this reason, water consumption has the potential to become a challenging obstacle to adoption of CCS technologies. This analysis seeks to improve understanding of relative water costs of different CCS technology options. It also helps to identify areas where water use may in fact become a challenge and reveal opportunities for technological improvements that can help minimize these challenges.

A life cycle assessment approach was utilized to analyze both the water consumption from carbon capture and storage projects. While there have been previous analyses that have looked at the direct water consumption for some capture processes, there have been few studies that have taken a detailed look at water consumption throughout the complete life cycle of the of electricity production with CCS. This effort expands the system boundaries beyond those of previous analysis while evaluating a range of system configurations to facilitate technology comparison.

The range of system configurations considered in this analysis included both pre and post combustion capture systems and multiple sequestration scenarios. The system boundaries for the analysis include fuel production, fuel transport, combustion, capture, CO2 transport, and storage. Water consumption for conventional fossil fuel systems are also calculated for comparison purposes.

The results show that while all carbon capture technology pathways result in a net increase in water consumption relative to conventional coal generation, the choice of technology, especially capture technology, can play a significant role in minimizing the increase in water consumption. Integrated gasification combined cycle coal plants with carbon capture were found to be significantly more water efficient than either conventional power plants with post combustion capture or plants utilizing oxy-combustion processes. Also, while other stages of the life cycle do consume water, the volumes were small relative to the power plant operations and capture stages.

Commentary by Dr. Valentin Fuster
2014;():V002T10A007. doi:10.1115/POWER2014-32188.

Climate change has the potential to exacerbate water availability concerns for thermal power plant cooling, which is responsible for 41% of U.S. water withdrawals. This analysis describes an initial link between climate, water, and electricity systems using the National Renewable Energy Laboratory (NREL) Regional Energy Deployment System (ReEDS) electricity system capacity expansion model. Average surface water projections from Coupled Model Intercomparison Project 3 (CMIP3) data are applied to surface water rights available to new generating capacity in ReEDS, and electric sector growth is compared with and without climate-influenced water rights. The mean climate projection has only a small impact on national or regional capacity growth and water use because most regions have sufficient unappropriated or previously retired water rights to offset climate impacts. Climate impacts are notable in southwestern states, which experience reduced water rights purchases and a greater share of rights acquired from wastewater and other higher-cost water resources. The electric sector climate impacts demonstrated herein establish a methodology to be later exercised with more extreme climate scenarios and a more rigorous representation of legal and physical water availability.

Topics: Modeling , Climate , Water
Commentary by Dr. Valentin Fuster
2014;():V002T10A008. doi:10.1115/POWER2014-32190.

“Wastewater treatment plants are not waste disposal facilities but are water resource recovery facilities that produce clean water, recover nutrients (such as phosphorus and nitrogen), and have the potential to reduce the nation’s dependence on fossil fuels through the production and use of renewable energy and the implementation of energy conservation.” This quote from the 2011 WEF Renewable Energy Position Statement clearly calls attention to the role of wastewater management through Water Resource Recovery Facilities (WRRF) to address the needs of the Utility of the Future.

The water resources utility of the future will integrate these three major concepts of Nutrients, Energy and Water, and many cutting edge utilities are already implementing this management goal of resource recovery. This focus may initially have been internal to the water or wastewater utility, investigating sustainable energy management through energy conservation, increased renewable energy production (where feasible), and focus on overall energy management. The overall societal benefit of the resilience improvement through distributed generation is starting to be realized. The fact that a water resource recovery facility (wastewater plant) that generates its own energy can operate when the power is out is an asset during extreme events. In addition, this capacity can be coordinated with electric utilities to address peak loads and other system needs. Valuable energy products generated on-site at wastewater plants can also supply a portion of energy demand within their respective service areas.

On average, the energy content of wastewater (chemical, hydraulic and thermal) is five times greater than the energy required for treatment. The most common opportunity for on-site power generation is through biogas created through anaerobic digestion. However, technologies such as gasification, pyrolysis, and incineration may be used to generate electricity or fuel. District energy systems, facilities to generate renewable diesel or aviation fuel, hydrogen fuel cells, and in-line hydropower are all being installed today.

However, becoming net energy positive is not the only goal. Optimizing overall sustainability may actually require using more energy or producing less energy onsite. Treating water to higher standards is often more energy intensive. Similarly, using biogas as a transportation fuel reduces onsite power production and increased energy use is required to further process biosolids to maximize reuse potential and to recover nutrients and minerals (e.g., nitrogen, phosphorous, magnesium).

A number of utilities worldwide have already taken the leap and begun this transformation towards resource recovery. While it is not practical for all water resource recovery facilities to become energy positive or neutral, all can take steps towards increasing sustainability while also improving resilience in the energy sector.

Commentary by Dr. Valentin Fuster
2014;():V002T10A009. doi:10.1115/POWER2014-32232.

Water is a prime source to all living beings, but for humans it is even more because of its usage to extract power. The idea behind the water turbine is derived from the parental species of wind turbine. The operating fluid properties like density, specific weight of water draw out differences between the two turbine kinds. The objective of the present work is to experimentally investigate the performance of a two bladed Savonius water turbine with an aspect ratio of 1.21 at low water velocity conditions viz. 0.3 m/s, 0.65 m/s and 0.9 m/s. The variation of torque and power with the considered water velocities has been studied. Also a performance study has been conducted with the aid of Computational Fluid Dynamics (CFD) using Ansys 14.0. A detailed study on the flow characteristics has been done that elaborates the factors like torque variation at different angles of rotation of the turbine, revealing high torque generation at 270° position. Also the effect of tip speed ratio (TSR) on performance (Cp) has been studied and found that maximum Cp of 0.343 is obtained for water velocity of 0.65 m/s with a TSR of 0.643. The results obtained through CFD are in agreement with the experimental results.

Commentary by Dr. Valentin Fuster
2014;():V002T10A010. doi:10.1115/POWER2014-32278.

The United States Environmental Protection Agency (USEPA)’s announcement that it will revise the effluent limitation guidelines for steam electric power generating units could affect not only how power plants use water, but also how they discharge it. The revised guidelines may lower discharge limits for various contaminants in flue gas desulfurization (FGD) wastewater including mercury, selenium, arsenic, and nitrate/nitrite. Although the specific details of the guidelines are unknown at present, the power industry is evaluating various technologies that may address the new effluent limitation guidelines and promote water conservation. Moreover, the power industry is looking for avenues to increase water usage efficiency, reuse and recycle throughout its plant processes. Final rule approval is expected by the middle of 2014 and new regulations are expected to be implemented between 2017 and 2022 through 5-year NPDES permit cycles. discharge limits for various contaminants including arsenic, mercury, selenium, and nitrate/nitrite [1]. These pollutant limits may be below the levels achievable today with conventional treatment [2].

A growing interest exists in zero liquid discharge (ZLD) facilities and processes in power plant operations. Potentially stringent discharge limits along with water conservation and reuse efforts are two of the major drivers to achieve ZLD. Potential pollutant levels are so low that ZLD may be the best option, if not an outright requirement [1].

Thermal ZLD systems have been the subject of increased interest and discussion lately. They employ evaporating processes such as ponds, evaporators and crystallizers, or spray dryers to produce a reusable water stream and a solid residue (i.e. waste). Evaporators and crystallizers have been employed in the power industry for a number of years. However, typical A growing interest exists in zero liquid discharge (ZLD) facilities and processes in power plant operations. Potentially stringent discharge limits along with water conservation and reuse efforts are two of the major drivers to achieve ZLD. Potential pollutant levels are so low that ZLD may be the best option, if not an outright requirement. A key disadvantage of thermal ZLD is its high capital cost. One way to reduce this cost is to pre-treat the liquid stream using innovative membrane technologies and reverse osmosis (RO).

Commentary by Dr. Valentin Fuster

Thermal Hydraulics and CFD

2014;():V002T11A001. doi:10.1115/POWER2014-32038.

Thermal and hydrodynamic concepts are of a vital importance; therefore their assessments are unavoidable for the purpose of hydraulic systems. The present study implements the practical updated knowledge of the expertise for both of the hydraulic and thermal fields in an expert system model. This is implemented in order to improve the performance of hydraulic system by considering the thermal effect on the hydraulic system operation. Accordingly, a computer program (Hydraulic System Calculations), designated as (HSC) implements a Visual Basic language in the Microsoft Visual Studio 2010 software has been built. Regardless of the design requirements, the code is capable to deal with (18) possible connection types of the actuators, in series or parallel, arrangements. The suggested code provides the designer with a number of choices, different kind of connections, to resolve the problem of hydraulic oil overheating which may arise during the continuous operation of the hydraulic unit. As a result, the (HSC) is able to minimize the human errors, effort, time and cost of hydraulic machine design.

Commentary by Dr. Valentin Fuster
2014;():V002T11A002. doi:10.1115/POWER2014-32052.

This paper focuses on providing better view for the understanding of rotating stall phenomenon in centrifugal compressors by using numerical simulations and presents a study of the role of air injection method in delaying stall inception by using different injection parameters aiming at increasing the efficiency of this method. Results showed that the formation of stall begins at the impeller inlet due to early flow separation at low mass flow rates and due to the increase of the turbulence level and the absence of fluid orientation guidance at the vaneless region. The flow weakness causes back flow that results in the formation of the tip leakage flow which causes stall development with time. Results also showed that using air injection at specified locations at the vaneless shroud surface at injection angle of 20° and with injection mass flow rate of 1.5% of the inlet design mass flow rate, can delay the stall onset to happen at lower mass flow rate about 3.8 kg/s comparing with using injection with angle of 10° with different injection mass flow rates and also comparing with the case of no injection.

Topics: Compressors
Commentary by Dr. Valentin Fuster
2014;():V002T11A003. doi:10.1115/POWER2014-32053.

This study presents a numerical simulation of the formation of rotating stall and the initiation of surge in order to study the connection between stall and surge in centrifugal compressors. Also, the current paper introduces an optimization of the air injection method as a way to increase the surge margin. Results showed that during stall, the compressor is exposed to velocity and pressure fluctuations varying with time, and these fluctuations are increased suddenly and causing surge initiation. The major part which is responsible for the sudden increase in fluctuations is the vaneless region because it was found that the problem starts at the impeller exit near the shroud surface and then transfers to the impeller inlet. Results also showed that during surge, forces on the impeller blades increase to nearly double of its initial value and then decrease again. By using air injection at the vaneless region with different injection angles, it was found that injection with angle of 30° has a good effect on preventing surge and minimizing the pressure fluctuations comparing to other injection angles results. Results showed finally that the surge margin can be increased by using the injection with angle of 30° and with injection mass flow rate of 1% of the design inlet mass flow rate and this causes the surge limit to shift from 4 kg/s to 3.9 kg/s.

Commentary by Dr. Valentin Fuster
2014;():V002T11A004. doi:10.1115/POWER2014-32107.

In this work, we present the design and fabrication a high-pressure pool boiling facility to conduct pool boiling experiments on horizontal heated surfaces under elevated pressures, up to 20 bar. Previous research has shown that micro- and/or nano-structured surfaces and coated surfaces will increase heat transfer coefficients up to one order of magnitude at atmospheric pressure. However, most boiling applications are subjected to high pressure, especially in the power industry. Pressure inside a boiling water reactor in a nuclear power plant will reach as high as 75 atm (75.99 bar). In order to determine how heat transfer is enhanced at increased pressures, with deionized water and refrigerants, on modified surfaces, a special experimental setup needs to be designed and fabricated. Difficulties in making such an experimental setup come from stabilizing the system pressure, sealing the test setup and visualizing the boiling conditions in the vessel. Both advantages and disadvantages of this design will be discussed and possible methods for improvements will be proposed. Preliminary test results on a plane copper surface are also included. Future research will be focusing on boiling of water and refrigerants on micro-structured copper surfaces, graphene coated, and Teflon© coated surfaces under high pressure.

Commentary by Dr. Valentin Fuster
2014;():V002T11A005. doi:10.1115/POWER2014-32127.

Hydraulic systems are characterized by their ability to import large forces at high speeds and are used in many industrial motion systems, also, in applications where good dynamic performance is important. This research concentrates on static and dynamic performance of a linear hydraulic system under different operating conditions in case of connecting an Electro Hydraulic Servo Valve (EHSV) and a Proportional Directional Flow Control Valve (PDFCV). High technology is used for measuring and recording the experimental results which achieves accurate evaluations. Experiments have been conducted in case of no-load and under load 5560 N. Supply pressure has been changed from 10 up to 50 bar. Effect of pressure and load variation on hydraulic system performance has been studied. It is concluded that increasing the load decreases the bandwidth frequency, but increasing the supply pressure increases the bandwidth frequency. Comparing the time lag of the system considering connecting the (EHSV) with that in case of connecting (PDFCV), it’s observed that in the present investigation the time lag improves by about 86.4% in case of free-load and by about 95.3% in case of system loaded.

Commentary by Dr. Valentin Fuster
2014;():V002T11A006. doi:10.1115/POWER2014-32154.

A windcatcher is a structure placed on the roof of a building for providing natural ventilation for interior space working by wind power. It draws out the inside stale air to the outside and supplies the outside fresh air for the building’s interior space.

In this paper, the effect of different types of windcatcher’s inlet\outlet on the air flow, flow velocity and flowrate through a three-dimensional room fitted with a two-sided windcatcher is observed numerically, using a commercial computational fluid dynamics (CFD) software package. The standard RANS K-ε CFD method is used in the simulations. The flow pattern, flow velocity and flowrate of the inside ventilation flow is considered for the six different types of a two-sided windcatcher’s inlet\outlet.

It is found that the shape of the inlet\outlet of windcatcher strongly affects flow pattern, flow velocity and flowrate and the performance of square windcatcher is higher than the circular one specially in ventilating the living area (lower part) of a room.

Commentary by Dr. Valentin Fuster
2014;():V002T11A007. doi:10.1115/POWER2014-32261.

CFD (Computational Fluids Dynamics) simulations of HRSGs (Heat Recovery Steam Generators) can improve and optimize the performance of combined cycle power plants. For example CFD results can help to analyze the effect that different working conditions such as changes in power or fuel quality can have on the uniformity of the flow. A uniform flow is important because the tubes inside the HRSG are more susceptible to corrosion and rupture when the flow distribution is strongly nonuniform. An accurate modeling of the flow and heat transfer characteristics is paramount in order to obtain a realistic representation of the process. However, a big problem in CFD modeling of HRSGs, or any equipment with tube-and-shell heat exchangers, is the different length scales of the equipment, which vary from a few centimeters for the tubes diameter to tens of meters for the HRSG vertical height. The problem is that these different length scales would require a very large computational mesh and consequently a very expensive simulation. To overcome this problem, a common approach in CFD simulations of HRSG has been to model the tube banks following a porous media approach, where the tubes are represented by a volume with a porosity factor which gives the volume fraction of fluid within the porous region. Using this model a pressure drop and the total heat absorbed due to the presence of the solid tubes is calculated. However, due to the recent advances and relatively lower prices of computer equipment it is now possible in a relatively economical way to explicitly include the tube banks in the CFD models of HRSGs. In this study a CFD model of a HRSG is presented where the tube banks are included in the geometric model. Results using this model show the fluid flow and heat transfer between the numerous tubes. A further advantage, in contrast to the porous media model, is that the flow inside the tubes is also modeled which gives a more realistic representation of the phenomena inside the tubes.

Commentary by Dr. Valentin Fuster

Nuclear Plant Design, Licensing and Construction

2014;():V002T12A001. doi:10.1115/POWER2014-32014.

Using software automation technology can significantly improve the quality and productivity of nuclear power software development. Based on the ‘tree’ data structure, this paper proposed Breadth First Search (BFS) based nuclear power software source code framework automatic generation algorithm called CFAA (Code Framework Automation Algorithm). CFAA uses ‘tree’ data structure to represent architecture of nuclear power software, then utilizes BFS to traverse all tree nodes to generate software source code framework. CFAA enables programmers to focus more on nuclear power software architecture design and optimization, and then generate the skeleton source code automatically. CFAA has been applied to COSINE (Core and System Integrated Engine for design and analysis) software development. Practice proved that CFAA can improve the efficiency of building nuclear power software framework, while reducing the defect rate of nuclear power software development.

Commentary by Dr. Valentin Fuster
2014;():V002T12A002. doi:10.1115/POWER2014-32059.

Operating nuclear power plants typically have backup electrical power supplied by diesel generators. Although backup power systems are designed with redundant trains, each capable of supplying the power requirements for safe shutdown equipment, there is a common-mode seismic failure risk inherent in these customary backup power arrangements. In an earthquake, multiple equipment trains with similar, if not identical, components located side-by-side are exposed to inertial forces that are essentially identical. In addition, because of their similar subcomponent configurations, seismic fragilities are approximately equal. In that case, the probability of multiple backup power system failures during an earthquake is likely to be dependent on, and nearly the same as, the individual seismic failure probability of each equipment train.

Post-earthquake inspections at conventional multiple unit power stations over the last 40 years identified this common-mode seismic failure risk long before the tsunami-related common-mode failures of diesel generators at Fukushima Daiichi in March 2011. Experience data from post-earthquake inspections also indicate that failure probabilities of diverse sets of power generation equipment are independent and inherently less susceptible to common-mode failures.

This paper demonstrates that employing diverse backup power designs will deliver quantifiable improvements in electrical system availability following an earthquake. These improvements are illustrated from available literature of post-earthquake inspection reports, along with other firsthand observations. A case study of the seismic performance of similarly configured electrical power generation systems is compared to the performance of diverse sets of electrical power systems. Seismic probabilistic risk analyses for several system configurations are presented to show the benefit of improved post-earthquake availability that results from designing new backup power systems with greater diversity.

Commentary by Dr. Valentin Fuster

Performance Testing and Performance Test Codes

2014;():V002T13A001. doi:10.1115/POWER2014-32067.

In the field of Power Generation, Operators — Plant Owners, Utilities, IPPs … — have had to face severe constraints linked not only with price of electricity and cost of fuel, but also with more and more demanding environmental constraints. It appears that the next atmospheric emission coming under scrutiny is CO2. Some small scale laboratory size experiments and pilot scale tests demonstrating the ability to capture CO2 before it reaches the atmosphere have already been conducted, and some industrial scale demonstrators are already at the permitting stage and will soon reach construction.

In order to anticipate the needs of Performance Tests within this coming market, ASME decided to form a new committee in order to prepare and deliver ASME Performance Test Code – PTC 48 “Overall Plant Performance with Carbon Capture” test code. This new code may be seen as an evolution of ASME PTC 46 “Performance Test Code on Overall Plant Performance” 1996 (currently under revision), which goes beyond the sole verification of components to provide guidelines for testing a full Plant.

Capturing CO2 from fuel–fired power plants will have a significant impact on net capacity and net heat rate of the plant. Such plants will, in addition to the Power Block and Steam Generator, also include systems not commonly included in non-CO2 capture power plants. The addition of an ASU (Air Separation Unit, for oxy-combustion with CO2 capture) and/or CPU (CO2 Purification Unit, for oxy-combustion or post-combustion CO2 capture) has made necessary the preparation of a dedicated test code based upon same guiding principle than PTC 46, i.e. treating the plant globally as a “Black Box”. This approach allows correction of output and efficiency at the plant interfaces, but at the exclusion of internal parameters. It is anticipated that the code can inform development of regulations that define the rules and obligations of Operators.

Currently, the proposed PTC 48 aims at fossil fuel fired Steam-electric power plants using either post-combustion CO2 capture or oxy-combustion with CO2 capture technologies. Combined cycles and Integrated Gasification Combined Cycles — IGCCs — are not addressed.

Commentary by Dr. Valentin Fuster
2014;():V002T13A002. doi:10.1115/POWER2014-32098.

The Organic-Rankine-Cycle (ORC) offers a great potential for waste heat recovery and use of low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low temperature level, and it is, therefore, of major importance to design ORC components with high efficiencies and minimized losses. The use of organic fluids creates new challenges for turbine design, due to real-gas behavior and low speed of sound. The design and performance predictions for steam and gas turbines have been mainly based on measurements and numerical simulations of flow through two-dimensional cascades of blades. In case of ORC turbines and related fluids, such an approach requires the use of specially designed closed cascade wind tunnels. In this contribution, the specific loss mechanisms caused by the organic fluids are reviewed. The concept and design of an ORC cascade wind tunnel are presented. This closed wind tunnel can operate at higher pressure and temperature levels, and this allows for an investigation of typical organic fluids and their real-gas behavior. The choice of suitable test fluids is discussed based on the specific loss mechanisms in ORC turbine cascades. In future work, we are going to exploit large-eddy-simulation (LES) techniques for calculating flow separation and losses. For the validation of this approach and benchmarking different sub-grid models, experimental data of blade cascade tests are crucial. The testing facility is part of a large research project aiming at obtaining loss correlations for performance predictions of ORC turbines and processes, and it is supported by the German Ministry for Education and Research (BMBF).

Commentary by Dr. Valentin Fuster
2014;():V002T13A003. doi:10.1115/POWER2014-32116.

Discharge coefficients for three flow nozzles based on ASME PTC 6 are measured under many flow conditions at AIST, NMIJ and PTB. The uncertainty of the measurements is from 0.04% to 0.1% and the Reynolds number range is from 1.3×105 to 1.4×107. The discharge coefficients obtained by these experiments is not exactly consistent to one given by PTC 6 for all examined Reynolds number range. The discharge coefficient is influenced by the size of tap diameter even if at the lower Reynolds number region. Experimental results for the tap of 5 mm and 6 mm diameter do not satisfy the requirements based on the validation procedures and the criteria given by PTC 6. The limit of the size of tap diameter determined in PTC 6 is inconsistent with the validation check procedures of the calibration result. An enhanced methodology including the term of the tap diameter is recommended. Otherwise, it is recommended that the calibration test should be performed at as high Reynolds number as possible and the size of tap diameter is desirable to be as small as possible to obtain the discharge coefficient with high accuracy.

Commentary by Dr. Valentin Fuster
2014;():V002T13A004. doi:10.1115/POWER2014-32177.

An accurate correction methodology is essential when analyzing test data and trending performance. One of the most critical parameters for steam turbines, which can result in large corrections, is condenser back-pressure or exhaust pressure.

Many large fossil and all nuclear steam turbines are configured with either two or three low pressure condensing exhaust hoods. All exhaust hoods may not operate with the same condenser pressure. Factors affecting condenser pressures between hoods could include the cooling water arrangement, uneven fouling, tube plugging, air removal effectiveness, etc. The biggest impact is likely due to the cooling water arrangement. In a parallel arrangement, the condenser cooling water splits between the shells with each shell receiving an equal amount of flow at the same inlet temperature. In a series arrangement, all cooling water enters and exits the first shell before entering the next shell. In this arrangement the cooling water temperature entering the second shell is higher than the temperature entering the first shell resulting in the condensers operating at different exhaust pressures.

One common practice is to apply a single exhaust pressure correction factor based on the average exhaust pressure of all condenser shells. In cases where the differences in condenser pressure are small, this practice can provide accurate corrected turbine performance. As the difference in condenser pressures increases, the potential for introducing error in the corrected performance results also increases.

This paper will discuss the mechanism of why multi-pressure operation can result in correction errors if not modelled correctly and will also quantify the potential impact of these errors on the corrected performance results. In addition, guidance will be given on how exhaust pressure correction curves should be created and applied to most accurately model the performance of the turbine cycle when multi-pressure operation exists.

Commentary by Dr. Valentin Fuster
2014;():V002T13A005. doi:10.1115/POWER2014-32184.

Correction curves are of great importance in the performance evaluation of heavy duty gas turbines (HDGT). They provide the means by which to translate performance test results from test conditions to the rated conditions. The correction factors are usually calculated using the original equipment manufacturer (OEM) gas turbine thermal model (a.k.a. cycle deck), varying one parameter at a time throughout a given range of interest. For some parameters bi-variate effects are considered when the associated secondary performance effect of another variable is significant. Although this traditional approach has been widely accepted by the industry, has offered a simple and transparent means of correcting test results, and has provided a reasonably accurate correction methodology for gas turbines with conventional control systems, it neglects the associated interdependence of each correction parameter from the remaining parameters. Also, its inherently static nature is not well suited for today’s modern gas turbine control systems employing integral gas turbine aero-thermal models in the control system that continuously adapt the turbine’s operating parameters to the “as running” aero-thermal component performance characteristics.

Accordingly, the most accurate means by which to correct the measured performance from test conditions to the guarantee conditions is by use of Model-Based Performance Corrections, in agreement with the current PTC-22 and ISO 2314, although not commonly used or accepted within the industry.

The implementation of Model-based Corrections is presented for the Case Study of a GE 9FA gas turbine upgrade project, with an advanced model-based control system that accommodated a multitude of operating boundaries. Unique plant operating restrictions, coupled with its focus on partial load heat rate, presented a perfect scenario to employ Model-Based Performance Corrections.

Commentary by Dr. Valentin Fuster
2014;():V002T13A006. doi:10.1115/POWER2014-32187.

The accuracy of a thermal performance test is typically estimated by performing an uncertainty analysis calculation in accordance with ASME PTC 19.1 or equivalent. The resultant test uncertainty estimate is often used as a key factor in the commercial contract, in that many contracts allow a test tolerance and define the test tolerance to be equal to the test uncertainty. As such, the calculated test uncertainty needs to accurately reflect all of the technical factors that contribute to the uncertainty. The test uncertainty is a measure of the test quality, and, in many circumstances, the test setup must be designed such that the uncertainty remains lower than test code limits and/or commercial tolerances.

Traditional uncertainty calculations have included an estimate of the measurement uncertainties and the propagation of those uncertainties to the test result. In addition to addressing measurement uncertainties, ASME PTC 19.1 makes reference to other potential errors of method, such as “the assumptions or constants contained in the calculation routines” and “using an empirically derived correlation”. Experience suggests that these errors of method can in some circumstances dominate the overall test uncertainty. Previous studies (POWER2011-55123 and POWER2012-54609) introduced and quantified a number of operational factors and correction curve factors of this type.

To facilitate testing over a range of boundary conditions, the industry norm is for the equipment supplier to provide correction curves, typically created using thermodynamic models of the power plant to predict the response of the system to changes in boundary conditions. As noted in various PTC codes (PTC-22, PTC-46, and PTC-6) it is advisable to run the test at conditions as close to the rated conditions as possible to minimize the influence of the correction curves. Experience suggests that large deviations from rated conditions, and the associated influence of the correction curves, can result in decreased accuracy in the final corrected result. A discussion of these types of situations via case studies is discussed, as well as a means by which to reduce the uncertainty contributions from correction curves considerably.

Topics: Uncertainty
Commentary by Dr. Valentin Fuster
2014;():V002T13A007. doi:10.1115/POWER2014-32189.

A hybrid wet-dry cooling system can reduce water consumption at a power plant while minimizing the performance penalty of an air-cooled condenser (ACC). Automatic allocation of turbine exhaust steam among the wet and dry sections provides robust performance. However, the performance test for the unit must be carefully designed to prove the guarantees for water conservation and thermal performance with minimal uncertainty.

A hybrid wet-dry cooling system of the “parallel” type is modeled based on recently-constructed power plants. Effects of typical off-design test conditions are demonstrated. Techniques are recommended for designing an effective performance test for a hybrid wet-dry cooling system based on the use of existing Performance Test Codes (PTC).

Commentary by Dr. Valentin Fuster
2014;():V002T13A008. doi:10.1115/POWER2014-32205.

This paper examines the concepts and methods involved in the uncertainty analysis of a differential pressure flow measurement, including which variables have the greatest influence on the uncertainty, and how to effectively manage the influence of error sources on the measurement. An uncertainty analysis will provide the user with a good measure of actual and/or potential system performance and can be instrumental in identifying potential areas of improvement in system performance. The wide availability of instruments of all types and levels of performance presents a difficult decision to those who are responsible for project success and budgets. Optimizing the investment in instrumentation is possible when the required performance is known based an appropriate uncertainty analysis.

Commentary by Dr. Valentin Fuster
2014;():V002T13A009. doi:10.1115/POWER2014-32299.

PTC46 — currently under revision — is now a well known Code used worldwide in the field of overall Plant testing, and methodology proved effective in a majority of cases. However, there are occasional situations where strict and direct application of the codes does not work and unconventional solution needs to be found. Author shows how nevertheless the principles set in the code allow to select a solution so that Performance test may be conducted through two examples.

Topics: Testing
Commentary by Dr. Valentin Fuster

Student Paper Competition

2014;():V002T14A001. doi:10.1115/POWER2014-32092.

The present study addresses SYNGAS combustion in static chamber, using both experimental and numerical approaches, in order to derive the quenching distance and heat flux in laminar syngas–air flames. Three typical mixtures of H2, CO, CH4, CO2 and N2 are considered as representative of the syngas coming from wood gasification, and its laminar combustion will be performed in a static spherical vessel. A two dimensional CFD model is used and validated under experimental runs. The classical Woschni model based on the hypotheses of forced convection and the Rivère model based on kinetic theory of gases are included in the CFD approach. The paper considers two different approaches for chemical reactions: the use of eight reactions and the multizone model. Temperature and pressure analysis is also being carried out. The numerical results are in good agreement with experimental ones. This study could be very useful in predicting the physical conditions of the quenching distance where the measurement is not possible such as in engines and the possibility of using this model in internal combustion engines.

Topics: Combustion , Syngas
Commentary by Dr. Valentin Fuster
2014;():V002T14A002. doi:10.1115/POWER2014-32102.

The purpose of this research is to experimentally study how vertical mini-fins affect the overall heat transfer on a solid surface under external condensation conditions. Filmwise condensation is a major factor when designing steam condensers for thermoelectric power plants. These plants currently account for 40% of freshwater withdrawal and 3% of freshwater usage in the United States. Filmwise condensation averages five times lower heat transfer coefficients than those present in dropwise condensation. Due to the elevated nucleation rates in thermoelectric power plant condensers, filmwise condensation is the dominant condensation regime. The film thickness is directly proportional to the condenser’s overall thermal resistance on a surface under filmwise condensation. This research investigates the potential of mini-fins to mitigate the onset and effect of filmwise condensation, thus reducing thermal resistance and maximizing heat transfer. The overall heat transfer is determined by measuring the temperature gradient across aluminum test sections. The experimental setup was designed to control the cooling load, pressure, and steam quality in order to measure the temperature gradient under steady state conditions. By comparing the overall heat transfer of surfaces with different mini-fins, the optimal surface geometries can be found. Preliminary results show that mini-fins can improve the overall heat transfer ratios. Future work will introduce other mini-fin shapes, as well as focus on investigating the most efficient heat fluxes for each mini-fin.

Commentary by Dr. Valentin Fuster
2014;():V002T14A003. doi:10.1115/POWER2014-32121.

In this paper, a new method of generating power by “wind-induced vibration” (WIV). A lead zirconate titanate (PZT) beam which has a very high power density is installed on the bluff body which will have WIV with the bluff body has been explored. Both numerical computation and experimental work have been taken to measure the capacity of the power generating system. Two different shapes of bluff bodies have been tested. In numerical section, the lift and drag coefficient and the vortex shedding frequency have been computed to verify how the dimensionless parameter Vr affects the fluid field. An one-degree-freedom system has been added to describe the wind-induced vibration, and the vibrational frequency and amplitude of the vibration have been monitored. The fluid-structure interaction has been solved by a hybrid method of finite volume method (FVM) and finite element method (FEM). From numerical simulation, the conclusions can be given that as the non-dimensionalised mass m* is about 780, the vortex induced vibration (VIV) response of a single cylinder is quite different comparing with Govardhan&Williamson. Then a wind tunnel test has been taken to measure the voltage output of the PZT, and we have gotten a result quite close to the data of numerical method.

Commentary by Dr. Valentin Fuster
2014;():V002T14A004. doi:10.1115/POWER2014-32144.

Wind is always blowing somewhere. From this perspective, a logical hypothesis is that a base load generator might be created by using long distance transmission to connect distant wind farms. This paper tests that hypothesis by putting numbers to it. It is generally accepted that geographic diversity has a smoothing effect on wind fluctuations for cumulative production [1]. This paper addresses the question of whether or not geographic diversity provides system capacity as well. A scenario of interest is the interconnection of wind farms on the East Coast (PJM Interconnection) with wind farms in the Midwest (MISO, the Midcontinent Independent System Operator). Wind is characterized by the Cumulative Distribution Function (DF). Effective Load Carrying Capacity (ELCC) is a metric that defines system capacity, the load that a system can deliver at an acceptable level of reliability. This paper compares standalone wind on PJM with standalone wind on MISO and with standalone wind for interconnected PJM + MISO. A fourth comparison shows the theoretical limit, what could be achieved if wind from PJM and MISO were independent of each other. This analysis quantifies the capacity benefits of long distance transmission.

Commentary by Dr. Valentin Fuster
2014;():V002T14A005. doi:10.1115/POWER2014-32152.

Increasing penetration of intermittent renewable electricity into the grid, coupled with development of new communication and control strategies, is creating challenges and opportunities for demand response (DR) to balance the grid. This paper presents a model characterization of a controllable buildings Variable Air Volume HVAC (VAV HVAC) system capable of implementing control strategies that provide flexibility to the grid. A Model Predictive Controller (MPC) capable of reliably varying the modeled power by ±20%, or up to ±2 GW on a national scale, every five minutes without compromising occupants comfort was built. A climate analysis was performed in order to assess the availability of controllable resources in sixteen cities. It is found that this control strategy could be implemented up to 99% of the time in the hottest regions, but as low as 10% of the time in the coldest.

Commentary by Dr. Valentin Fuster
2014;():V002T14A006. doi:10.1115/POWER2014-32156.

The vortex-induced vibrations of a rhombus cylinder are investigated using two-dimensional unsteady Reynolds-Averaged Navier-Stokes simulations at high Reynolds numbers ranging from 10,000 to 120,000. The rhombus cylinder is constrained to oscillate in the transverse direction, which is perpendicular to the flow velocity direction. Three rhombus cylinders with different axis ratio (AR=0.5, 1.0, 1.5) are considered for comparison. The simulation results indicate that the vibration response and the wake modes are dependent on the axis ratio of the rhombus cylinder. The amplitude ratios are functions of the Reynolds numbers. And as the AR increases, higher peak amplitudes can be made over a significant wide band of Re. On the other hand, a narrow lock-in area is observed for AR=0.5 and AR=1.5 when 30,000<Re<50,000, but the frequency ratio of AR=1.0 monotonically increases at a nearly constant slope in the whole Re range. The vortex shedding mode is always 2S mode in the whole Re range for AR=0.5. However, the wake patterns become diverse with the increasing of Re for AR=1.0 and 1.5. In addition, the mechanical power output of each oscillating rhombus cylinder is calculated to evaluate the efficiency of energy transfer in this paper. The theoretical mechanical power P between water and a transversely oscillating cylinder is achieved. On the base of analysis and comparison, the rhombus cylinder with AR=1.0 is more suitable for harvesting energy from fluid.

Commentary by Dr. Valentin Fuster
2014;():V002T14A007. doi:10.1115/POWER2014-32172.

Analytical and experimental analyses of a variable electromotive-force generator (VEG) show the advantages of this modified generator in hybrid electric vehicle and wind turbine applications with enhancing the fuel efficiency and expanding the operational range, respectively. In this study, electromagnetic analysis of a modified two-pole DC generator with an adjustable overlap between the rotor and the stator is studied using 3-D finite element simulation in ANSYS. The generator stator is modeled with two opposite pole pieces whose arcs span between 15° to 90° in the counterclockwise direction and −15° to −90° in the clockwise direction. A semicircular cylinder whose arc spans between −90° and 90° is used to model the generator rotor. A tetrahedral mesh is used to provide a solution for changes in the electromotive force at different frequencies and overlap ratios. For a constant electromagnetic flux density and fixed number of coils, the changes in the electromotive force at different overlap ratios between the rotor and the stator are obtained in static conditions. There is a very good correlation between the results from simulation and those from analytical and experimental studies.

Commentary by Dr. Valentin Fuster
2014;():V002T14A008. doi:10.1115/POWER2014-32231.

Automatic fault location on the distribution system is a necessity for a resilient grid with fast service restoration after an outage. Motivated by the development of low cost synchronized voltage phasor measurement units (PMUs) for the distribution system, this paper describes how PMU data during a fault event can be used to accurately locate faults on the primary distribution system. Rather than requiring many specialized line sensors to enable fault location, the proposed approach leverages a PMU data stream that can be used for a variety of applications, making it easier to justify the investment in fault location. The accuracy of existing automatic fault location techniques are dependent either on dense deployments of line sensors or unrealistically accurate models of system loads. This paper demonstrates how synchronized voltage measurements enable sufficiently accurate fault location with relatively few instrumentation devices and relatively low fidelity system models. The IEEE 123 bus distribution feeder is examined as a test case, and the proposed algorithm is demonstrated to be robust to variations in total load and uncertainty in the response of loads to voltage sags during a sample set of varied fault conditions.

Commentary by Dr. Valentin Fuster

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