Showing papers on "Electricity generation published in 1996"

Analysis of a micro-electric generator for microsystems

Abstract: Supplying power to remote microsystems that have no physical connection to the outside world is difficult, and using batteries is not always appropriate. A solution is offered by the device proposed in this paper, which generates electricity from mechanical energy when embedded in a vibrating medium. This microgenerator has dimensions of around 5 mm × 5 mm × 1 mm. Analysis predicts that the power produced is proportional to the cube of the frequency of vibration, and that to maximize power generation the mass deflection should be as large as possible. Power generation of 1 μW at 70 Hz and 0.1 mW at 330 Hz are predicted for a typical device, assuming a deflection of 50 μm.

Analysis of the Transformation of Mechanical Impact Energy to Electric Energy Using Piezoelectric Vibrator

Abstract: We propose a new mechanism of electric power generation in which mechanical impact energy is transformed to electric energy by a piezoelectric transducer. To clarify the relationship between the input mechanical impact energy and the output electric energy in this method, we measured the electric output of a piezoelectric vibrator stimulated by an impact with a steel ball. An electrical equivalent model of the phenomenon is proposed to analyze the transformation efficiency as functions of the electromechanical coupling coefficient, the mechanical loss and the dielectric loss of the vibrator.

Biomass combustion for power generation

Abstract: An overview is given of the state of the art of biomass combustion power generation technologies with a capacity of more than 10 MWe. Biomass combustion technologies have been compared on a qualitative basis and a selection of individual biomass combustion power plants has been compared on a quantitative basis. Collected data were modified for comparison of the various power plants in the quantitative analysis. The qualitative analysis focused on the following technologies: pile, grate, suspension and fluidised-bed combustion. Fluidised-bed systems are found to have relatively high efficiencies and are also flexible with regard to fuel properties. Both fluidised-bed systems and vibrating grates are successful in limiting thermal NOx formation. Some recently built plants and some planned concepts are compared quantitatively on the basis of efficiency, investment costs and emissions. All electric efficiencies are close to or above 30% (at lower heating value). Of the plants fired solely by biomass, vibrating grates and circulating fluidised beds turn out to have the highest efficiency at the moment. Co-firing of 4.5% biomass in a pulverised coal boiler has an efficiency of about 37% (LHV). Expected efficiencies for large-scale (100 to 250 MWe) promising concepts are in the 39–44% (LHV) range. Investment costs range from 1200 to 2900 (1992)US$/kWe. High costs are often caused by additional features such as the firing of difficult fuels or combined heat and power production. None of the existing technologies is found to be superior with respect to all the criteria selected.

Efficiency of three wind energy generator systems

Abstract: This paper presents a method to calculate the average efficiency from the turbine shaft to the grid in wind energy converters. The average efficiency of three 500 kW systems are compared. The systems are: a conventional grid-connected four-pole induction generator equipped with a gear, a variable-speed synchronous generator equipped with a gear and a frequency converter, and a directly driven variable-speed generator equipped with a frequency converter. In this paper it is shown that a variable-speed generator system can be almost as efficient as one for constant speed, although it has much higher losses at rated load. The increased turbine efficiency that variable speed leads to has not been included in this paper. It is also found that a directly driven generator can be more efficient than a conventional four-pole generator equipped with a gear.

Power control system for a fuel cell powered vehicle

Abstract: A control system interrelatedly controls the electric power output and oxidant supply in a fuel cell electric power generation system. The power generation system comprises at least one fuel cell stack, and a plurality of electrical loads powered by the fuel cell stack, including an electric traction motor for propelling the vehicle, and a compressor for delivering oxidant gas to the fuel cell stack. The electric power output of the at least one fuel cell stack is dependent on the compressor speed. The control system comprises a summing device for determining the total instantaneous power demand of the electrical loads based on a plurality of sensed power demand signals, and a processor for generating a feed-forward output signal for adjusting the compressor speed to a value predicted to give fuel cell power output sufficient to satisfy the instantaneous power demand.

A permanent-magnet generator for wind power applications

Abstract: In order to achieve the gearless construction of a wind energy conversion system (WECS), a low-speed (i.e. multipole) generator is required. This paper examines an axial-field permanent-magnet synchronous wind power generator, mainly from the magnetic viewpoint. Both mechanical and electromagnetic designs are described as well as some primary test results concerning model generators having nominal power of 5 and 10 kW.

Power exploration for data dominated video applications

Abstract: In this paper we present our power exploration methodology for data dominated video applications. This formalized methodology is based on the observation that for this type of application the power consumption is dominated by the memory architecture. Hence, the first exploration stage should be to come up with an optimized memory organisation. Other important observations are that the power consumption of the address generators is of the same magnitude as that of the data-paths and that the address generators are better optimized using specialized techniques.

Development of transient stability control system (TSC system) based on on-line stability calculation

Abstract: This paper describes a new transient stability control system named the TSC system developed for application to the trunk power system of Chubu Electric Power Co. (CEPCO). The TSC system prevents wide-area power system blackout by shedding optimal generators when a serious fault occurs. This system has the following features: (1) the TSC system performs detailed stability calculations based on online information telemetered from the actual network, and it periodically evaluates the stability of the power system against contingencies with a high degree of accuracy. The system selects the optimum generators to be shed; (2) if a contingency actually occurs, the generators to be shed that were determined in advance are shed about 150 ms after fault occurrence to maintain the stability of the power system; and (3) the system can be applied to any power system configuration of CEPCO, such as a loop network, radial network, etc. The TSC system will be put into regular service in June 1995. It will be the world's first real-time stability control system that performs detailed transient stability calculations on a large power system online.

Optimization and control of autonomous renewable energy systems

Abstract: Recently, there has been a growing interest in harnessing renewable energy resources particularly for electricity generation. One of the main concerns in the design of an electric power system that utilizes renewable energy sources, is the accurate selection of system components that can economically satisfy the load demand. This depends on the load that ought to be met, the capacity of renewable resources, the available space for wind machines and solar panels, and the capital and running costs of system components. Once size optimization is achieved, the autonomous system must be controlled in order to correctly match load requirements with instantaneous variation of input energy. In this paper, a new formulation for optimizing the design of an autonomous wind-solar-diesel-battery energy system is developed. This formulation employs linear programming techniques to minimize the average production cost of electricity while meeting the load requirements in a realiable manner. The computer program developed reads the necessary input data, formulates the optimization problem by computing the coefficients of the objective function and the constraints and provides the optimum wind, solar, diesel, and battery ratings. In order to study the effect of parameters predefined by the designer on the optimum design, several sensitivity analysis studies are performed, and the effects of the expected energy not served, the load level, the maximum available wind area, the maximum available solar area, and the diesel engines' lifetime are investigated. A controller that monitors the operation of the autonomous system is designed. The operation of this controller is based on three major policies; in the first, batteries operate before diesel engines and hence the storage system acts as a fuel saver, while in the second diesel engines are operated first so that the unmet energy is lower but the fuel cost is high. According to the third policy, the supply is made through diesel engines only. This is done for the purpose of making a performance comparison between the isolated diesel system and the hybrid renewable energy system. The proposed optimization and control techniques are tested on Lebanese data. Although three different control policies have been adopted in this work, the software is able to accommodate other policies.

Models of power plants that generate minimum entropy while operating at maximum power

Abstract: Chambadal, Novikov, Curzon and Ahlborn have shown that the efficiency of an irreversible heat engine at maximum power output is 1−(T L /T H )1/2. This article describes several heat engine models in which the same efficiency formula can be derived by minimizing the rate of entropy generation. Included in the entropy generation is the usually overlooked contribution made by the components that provide a freely varying heat input to the power cycle.

Application of an optimisation method for determining the reactive margin from voltage collapse in reactive power planning

Abstract: Power system reactive power planning requires the computation of the reactive power margin from the point of voltage collapse in the steady-state in order to quantify the adequacy of the level of installed reactive power plant. This reactive margin is the difference between the maximum reactive load distributed across selected power system nodes and the reactive load at the planned system operating point. The margin can be estimated by applying an optimisation method using the total reactive load as the objective, with the load flow equations as equality constraints, whilst including system limits such as generator reactive capability limits as inequality constraints. This paper describes a full AC formulation of the optimisation problem. It is solved using an interior point implementation of the Newton method developed for the optimal power flow. This avoids potential difficulties in identifying the binding inequality constraints.

Methods and apparatus for low NOx emissions during the production of electricity from waste treatment systems

Abstract: Methods and apparatus for high efficiency generation of electricity and low oxides of nitrogen (NOx) emissions are provided. The electricity is generated from combustion of hydrogen-rich gases produced in waste conversion units using ultra lean fuel to air ratios in the range of 0.4-0.7 relative to stoichiometric operation in internal combustion engine-generators or ultra lean operation in gas turbines to ensure minimal production of pollutants such as NOx. The ultra lean operation also increases the efficiency of the internal combustion engine. High compression ratios (r=12 to 15) can also be employed to further increase the efficiency of the internal combustion engine. Supplemental fuel, such as natural gas or diesel oil, may be added directly to the internal combustion engine-generator or gas turbine for combustion with the hydrogen-rich gases produced in waste conversion unit. In addition, supplemental fuel may be reformed into a hydrogen-rich gas in a plasma fuel converter and then introduced into the internal combustion engine-generator or a gas turbine for combustion along with supplemental fuel and the hydrogen-rich gases produced in waste conversion unit. The preferred embodiment of the waste conversion unit is a fully integrated tunable arc plasma-joule heated melter with a common molten pool and power supply circuits which can be operated simultaneously without detrimental interaction with one another. In this embodiment, the joule heated melter is capable of maintaining the material in a molten state with sufficient electrical conductivity to allow rapid restart of a transferred arc plasma.

Comments on active power flow and energy accounts in electrical systems with nonsinusoidal waveforms and asymmetry

Abstract: Pricing of electric energy is based on the value of the integral of the load active power P measured by energy meters. At such a pricing, the electric power utilities waste some revenue for the energy delivered to current harmonic generating customers and/or customers causing current asymmetry. This is because the load generated current harmonics and unbalanced currents cause an increase in the active power loss in the distribution system. At the same time, the customers that do not generate harmonics but are supplied with distorted and/or asymmetrical voltage are billed not only for the useful energy but also for the energy which may cause only harmful effects on their equipment. It is shown in the paper that these two disadvantages of the tariff in single-phase systems could be eliminated if the energy account based on the value of the integral of the active power of only fundamental harmonic, P/sub I/, rather than on the integral of the whole active power P was used. These disadvantages could be eliminated in three-phase systems if the energy account is based on the integral of the active power of the positive sequence component of the fundamental harmonic.

Completely automated nuclear reactors for long-term operation

Abstract: The authors discuss new types of nuclear fission reactors optimized for the generation of high-temperature heat for exceedingly safe, economic, and long-duration electricity production in large, long-lived central power stations. These reactors are quite different in design, implementation and operation from conventional light-water-cooled and -moderated reactors (LWRs) currently in widespread use, which were scaled-up from submarine nuclear propulsion reactors. They feature an inexpensive initial fuel loading which lasts the entire 30-year design life of the power-plant. The reactor contains a core comprised of a nuclear ignitor and a nuclear burn-wave propagating region comprised of natural thorium or uranium, a pressure shell for coolant transport purposes, and automatic emergency heat-dumping means to obviate concerns regarding loss-of-coolant accidents during the plant`s operational and post-operational life. These reactors are proposed to be situated in suitable environments at {approximately}100 meter depths underground, and their operation is completely automatic, with no moving parts and no human access during or after its operational lifetime, in order to avoid both error and misuse. The power plant`s heat engine and electrical generator subsystems are located above-ground.

Power management and distribution system for a more-electric aircraft (MADMEL)-program status

Abstract: A complete, and somewhat revolutionary, system design approach is needed to exploit the benefits that a more-electric aircraft can provide. Traditional-mounted auxiliary drives, and bleed air extraction will disappear, to be replaced with integral engine starter/generators and electrically driven actuators and pumps. A five-phase Power Management and Distribution System for a More-Electric Aircraft (MADMEL) program was awarded by the Air Force to Northrop/Grumman Military Aircraft Division in September 1991. The objective of the program is to design, develop, and demonstrate an advanced electrical power generation and distribution system for a More-Electric Aircraft (MEA). The MEA emphasizes the use of electrical power in place of hydraulics, pneumatic, and mechanical power to optimize the performance and life cycle cost of the aircraft. This paper presents an overview of the MADMEL program and a top-level summary of the program results, development and test of major components to date. In Phase I and Phase II studies, the electrical load requirements were established and the electrical power system architecture was defined for both near-term (NT-year 1996) and far-term (FT-year 2003) MEA application. The detailed design and specification for the Electrical Power System (EPS), its interface with the Vehicle Management System, and the test set-up were developed under Phase III. Phase IV, fabrication and testing of the subsystem level hardware, has been completed. The overall system level integration and testing will be performed in Phase V starting October 1997.

Power generation system utilizing turbine and fuel cell

Abstract: A system for generating electricity comprises a fuel cell, a heating stage, and an integral, power generator. The power generator comprises a compressor, an electricity generator and a turbine. Hot exhaust gas from the fuel cell is used for driving the turbine, which in turn drives the generator and the compressor. Both the fuel cell and the generator produce electricity. The compressor is used for compressing air for use in the fuel cell. A portion of the waste heat from the turbine drive gas is used for preheating the air utilized in the fuel cell.

Biomass-Gasifier/Aeroderivative Gas Turbine Combined Cycles: Part B—Performance Calculations and Economic Assessment

Abstract: Gas turbines fueled by integrated biomass gasifiers are a promising option for base-load electricity generation from a renewable resource. Aeroderivative turbines, which are characterized by high efficiencies in small units, are of special interest because transportation costs for biomass constrain conversion facilities to relatively modest scales. Part A of this two-part paper reviewed commercial development activities and major technological issues associated with biomass integrated-gasifier/gas turbine (BIG/GT) combined cycle power generation. Based on the computational model also described in Part A, this paper (Part B) presents results of detailed design-point performance calculations for several BIG/GT combined cycle configurations. Emphasis is given to systems now being proposed for commercial installation in the 25-30 MW e power output range. Three different gasifier designs are considered: air-blown, pressurized fluidized-bed gasification; air-blown, near-atmospheric pressure fluidized-bed gasification; and near-atmospheric pressure, indirectly heated fluidized-bed gasification. Advanced combined cycle configurations (including with intercooling) with outputs from 22 to 75 MW are also explored. An economic assessment is also presented, based on preliminary capital cost estimates for BIG/GT combined cycles and expected biomass costs in several regions of the world.

A stove-top generator for cold areas

Abstract: This paper discusses the development and test of a prototype thermoelectric generator which is designed to use the heat of existing wood fired stoves that are typically used in the area for home heating. This generator is being developed by the Royal Institute of Technology, in Sweden, to provide small amounts of power to homes in the remote northern areas of the country which are beyond the electric grid. The paper discusses some of the aspects of the generator design, as well as the early results obtained and some of the lessons learned from the first home test site in Skerfa, Sweden, which is located near the Arctic Circle. The bismuth-telluride thermoelectric modules used in the generator are also discussed.

Biomass-gasifier/aeroderivative gas turbine combined cycles - Part A : Technologies and performance modeling

Abstract: Gas turbines fueled by integrated biomass gasifiers are a promising option for base-load electricity generation from a renewable resource. Aeroderivative turbines, which are characterized by high efficiencies at smaller scales, are of special interest because transportation costs for biomass constrain biomass conversion facilities to relatively modest scales. Commercial development activities and major technological issues associated with biomass integrated-gasifier/gas turbine (BIG/GT) combined cycle power generation are reviewed in Part A of this two-part paper. Also, the computational model and the assumptions used to predict the overall performance of alternative BIG/GT cycles are outlined. The model evaluates appropriate value of key parameters (turbomachinery efficiencies, gas turbine cooling flows. steam production in the heat recovery steam generator, etc.) and then carries out energy, mass, and chemical species balances for each plant component, with iterations to insure wholeplant consistency. Part B of the paper presents detailed comparisons of the predicted performance of systems now being proposed for commercial installation in the 25-30 MW e power output range, as well as predictions for advanced combined cycle configurations (including with intercooling) with outputs from 22 to 75 MW e . Finally, an economic assessment is presented, based on preliminary capital cost estimates for BIG/GT combined cycles.

Power generation plant and control apparatus therefor

Abstract: The object of the invention is to provide an electric power plant and a control apparatus therefor which can obtain an emergency power supply reliably through use of the turbine starter. Another generator different from the main generator coupled to the rotor shaft of the turbine is provided to the input side of the starter via a motor, and a control apparatus is provided for electrically connecting the starter and the generators responsive to a bus voltage from the in-house power supply unit which supplies electricity to a plurality of auxiliary equipment operating in the electric power plant. Thereby, an emergency power supply can be obtained reliably by the simple configuration of the invention without installing emergency power generation facilities such as a diesel engine, gas turbine or the like. In addition, an LCI device which has been utilized only at the time of turbine start up can be utilized advantageously also at the time of emergency when the in-house power supply is lost.

Air Bottoming Cycle: Use of Gas Turbine Waste Heat for Power Generation

Abstract: This paper presents a thermodynamic analysis of the Air Bottoming Cycle (ABC) as well as the results of a feasibility study for using the Air Bottoming Cycle for gas turbine waste heat recovery/power generation on oil/gas platforms in the North Sea. The basis for the feasibility study was to utilize the exhaust gas heat from an LM2500PE gas turbine. Installation of the ABC on both a new and an existing platform have been considered. A design reference case is presented, and the recommended ABC is a two-shaft engine with two compressor intercoolers. The compression pressure ratio was found optimal at 8:1. The combined gas turbine and ABC shaft efficiency was calculated to 46.6 percent. The LM2500PE gas turbine contributes with 36.1 percent while the ABC adds 10.5 percent points to the gas turbine efficiency. The ABC shaft power output is 6.6 MW when utilizing the waste heat of an LM2500PE gas turbine. A preliminary thermal and hydraulic design of the ABC main components (compressor, turbine, intercoolers, and recuperator) was carried out. The recuperator is the largest and heaviest component (45 tons). A weight and cost breakdown of the ABC is presented. The total weight of the ABC package was calculated to 154 metric tons, and the ABC package cost to 9.4 million US$. An economical examination for three different cases was carried out. The results show that the ABC alternative (LM2500PE + ABC) is economical, with a rather good margin, compared to the other alternatives. The conclusion is that the Air Bottoming Cycle is an economical alternative for power generation on both new platforms and on existing platforms with demand for more power.

Black-start and restoration of a part of the Italian HV network: modelling and simulation of a field test

Abstract: ENEL (Italian Electricity Board) planned a set of operator guidelines for the restoration of parts of their national grid starting from selected hydroelectric power plants and progressively reaching thermal power generating units. In order to improve hydrothermal power system restoration reliability, ENEL periodically executes field tests taking advantage of the maintenance outages of the thermal groups. The paper concerns the modelling and simulation of an experimental test performed on the Italian W network near the French border. The study makes use of a stability code provided with user defined model facilities, enabling an accurate description of loads and regulation equipment during the restoration process.