电气英文论文

Page1 Generators and Motors
From reference 1
1. Direct-current generators impress on the line a direct or continuous emf, one that is always in the same direction. Commercial dc generators have commutators, which distinguish them from ac generators. The function of a commutator and the elementary ideas of generation of emf and commutation are discussed in Div. 1. Additional information about commutation as applied to dc motors, which in general is true for dc generators, is given below.
2. Excitation of generator fields. To generate an emf, conductors must cut a magnetic field which in commercial machines must be relatively strong. A permanent magnet can be used for producing such a field in a generator of small output, such as a telephone magneto or the magneto of an insulation tester, but in generators for light and power the field is produced by electromagnets, which may be excited by the machine itself or be separately excited from another
source.Self-excited machines may be of the series, shunt, or compound type, depending upon the manner of connecting the field winding to the armature. In the series type of machine,the field winding (the winding which produces the magnetic field) is connected in series with the armature winding. In the shunt type, the field winding is connected in parallel,shunt, with the armature winding. Compound machines have two field windings on each pole. One of these windings is connected in series with the armature winding, and the other is connected in parallel or shunt with the armature winding.
3. Armature winding of dc machines may be of the lap or the wave type. The difference in the two types is in the manner of connecting the armature coils to the commutator.A coil is the portion of the armature winding between successive connections to the commutator.In the lap type of winding (see Fig. 7.1) the two ends of a coil are connected to adjacent commutator segments. In the wave type of winding (see Fig. 7.2) the two ends of a coil are connected to commutator segments that are displaced from each other by approximately 360 electrical degrees.The type
of armature winding employed affects the voltage and current capacity of the machine but has no effect upon the power capacity. This is due to the fact that the number of parallel paths between armature terminals is affected by the type of winding. For a wavewound machine there are always two paths in parallel in the armature winding between armature terminals. For a lap-wound machine there are as many parallel paths in the armature winding as there are pairs of poles on the machine. For the same number and size of armature conductors, a machine when wave-connected would generate a voltage that would equal the voltage generated when lap-connected times the number of pairs of poles.But the current capacity would be decreased in the same proportion that the voltage was increased. The current capacity of a machine when wave-connected is therefore equal to the capacity when lap-connected divided by the number of pairs of poles.
4. The value of the voltage generated by a dc machine depends upon the armature winding, the speed, and the field current. For a given machine, therefore, the voltage generated can be controlled by adjusting either the speed or the field current. Since generators are usually operated at a constant speed, the voltage must be controlled by adjusting the field current.
5. Separately excited dc generators are used for electroplating and for other electrolytic work for which the polarity of a machine must not be reversed.
Self-excited machines may change their polarities. The essential diagrams are shown in Fig. 7.3. The fields can be excited from any dc constant-potential source, such as a storage battery, or from a rectifier connected to an ac supply.The field magnets can be wound for any voltage because they have no electric connection with the armature. With a constant field excitation, the voltage will drop slightly fromno load to full load because of armature drop and armature reaction.Separate excitation is advantageous when the voltage generated by the machine is not suitable for field excitation. This is true for especially low- or high-voltage machines.
6. Series-wound generators have their armature winding, field coils, and external circuit connected in series with each other so that the same current flows through all parts of the circuit (see Fig.
7.4). If a series generator is operated at no
load (external circuit open), there will be no current through the field coils, and the only magnetic flux present
in the machine will be that due to the residual magnetism which has been retained by the poles from previous operation. Therefore, the no-load voltage of a series generator will be only a few volts produced by cutting the residual flux. If the external circuit is closed and the current increased, the voltage will increase with the increase in current until the magnetic circuit becomes saturated. With any further increases of load the voltage will decrease. Series generators have been used sometimes in street-railway service. They have been connected in series with long trolley feeders supplying sections of the system distant from the supply point in order to boost the voltage. However, power rectifiers have replaced dc generators for most installations of this type.
Keywords: generator
From reference 2
Since triphased asynchronous generators are mainly used in conversion systems of a eolian energy into electric energy, their functional stability represent is
of great importance. As a first step, the factors that radically affect the functional stability of these generators have been established. Thus, it was decelat the powerful influence of the capacitor bank – that provides the necessary reactive power for the
magnetization of the ferromagnetic core – over the functional stability of the triphased asynchronous generator with short circuit rotor. The functional stability is greatly influenced by the charge character (type) as well. The experimental work emphasized – through the functional features – the way these parameters influence the stability area of the asynchronous generators. As far as triphased asynchronous generators with coiled rotor are concerned, the controllable blind power was analyzed the analogy being made with the situation of the necessary controllable generating capacity for of the triphased asynchronous generator with short circuit rotor.
Keywords : triphased asynchronous generator.
[1] D.M. Eggleston, F.S. Stoddard – Wind turbine engineering design, Van Nostrand Reinhold Company New York 1986;
[2] V. I lie, L. Almaşi, şa – Utilizarea energiei vântului, Ed. Tehnică, Bucureşti, 1984;
[3] Kovacs Pal –Analiza regimurilor tranzitorii ale maşinilor electrice, Ed. Tehnică, Bucureşti 1980 ;
[4] R.J. Harrington, F.M.M. Bassiouny – New Approach to Determinate the Critical Capacitance for Self - Excited Induction Generators, IEEE Trans. On Energy Conversion, vol. 13, no.3, sept. 1998, pp.244 - 250;
[5] Colliez, C., Tounzi, A., Piriou, F. – Vector Control of a Autonomous Induction Generator connected to a PWMRectifier. EPE `97, Trondheim, Norvegia, vol. 2, pp. 711-716;
[6] Alan, I., Lipo, A. T. – Control of a Polyphase Induction-Generator/ Induction- Motor Power Conversion System Completely Isolated from the Utility. IEEE Trans. On Ind. App., vol.30, no.3, may/june 1994, pp. 636-647
[7] Florin Iov – Stadiul actual în conversia energiei eoliene (Referat nr.1 – în cadrul pregătirii tezei de doctorat) martie 1998;
[8] Florin Iov –Studiul ansamblului turbină eoliană – generator asincron autoexcitat (Referat nr.2 – în cad rul pregătirii tezei de doctorat) iunie 1999;
Page2 Electrical Energy Transmission
From reference 1
Growing populations and industrializing countries create huge needs for electrical energy. Unfortunately, electricity is not always used in the same place that it is produced, meaning long-distance transmission lines and distribution systems are necessary. But transmitting electricity over distance and via networks involves energy loss.
So, with growing demand comes the need to minimize this loss to achieve two main goals: reduce resource consumption while delivering more power to users. Reducing consumption can be done in at least two ways: deliver electrical energy
more efficiently and change consumer habits.
Transmission and distribution of electrical energy require cables and power transformers, which create three types of energy loss:
the Joule effect, where energy is lost as heat in the conductor (a copper wire, for example);
magnetic losses, where energy dissipates into a magnetic field;
the dielectric effect, where energy is absorbed in the insulating material.
The Joule effect in transmission cables accounts for losses of about 2.5 % while the losses in transformers range between 1 % and 2 % (depending on the type and ratings of the transformer). So, saving just 1 % on the electrical energy produced by a power plant of 1 000 megawatts means transmitting 10 MW more to consumers, which is far from negligible: with the same energy we can supply 1 000 - 2 000 more homes.
Changing consumer habits involves awareness-raising programmers, often undertaken by governments or activist groups. Simple things, such as turning off lights in unoccupied rooms, or switching off the television at night (not just putting it into standby mode), or setting tasks such as laundry for non-peak hours are but a few examples among the myriad of possibilities.
On the energy production side, building more efficient transmission and distribution systems is another way to go about it. High efficiency transformers, superconducting transformers and high temperature superconductors are new technologies which promise much in terms of electrical energy efficiency and at the same time, new techniques are being studied. These include direct current and ultra high voltage transmission in both alternating current and direct current modes.
Keywords: electrical energy transmission
From reference 2
Disturbing loads like arc furnaces and thyristor rectifiers draw fluctuating and harmonic currents from the utility grid. These non sinusoidal currents cause a voltage drop across the finite internal grid impedance, and the voltage waveform in the vicinity becomes distorted. Hence, the normal operation of sensitive consumers
is jeopardized.
Active filters are a means to improve the power quality in distribution networks. In order to reduce the injection of non sinusoidal load currents shunt active filters are connnected in parallel to disturbing loads (Fig. 1). The active filter investigated in this project consists of a PWM controlled three-level VSI with a DC link capacitor.The VSI is connected to the point of common coupling via a transformer. The configuration is identical with an advanced static var compensator.
The purpose of the active filter is to compensate transient and harmonic components of the load current so that only fundamental frequency components remain in the grid current. Additionally, the active filter may provide the reactive power consumed by the load. The control principle for the active filter is rather straightforward: The load current ismeasured, the fundamental active component is removed from the measurement, and the result is used as the reference for the VSI output current.
In the low voltage grid, active filters may use inverters based on IGBTs with switching frequencies of 10 kHz or more. The harmonics produced by those inverters are easily suppressed with small passive filters. The VSI can be regarded nearly as an ideally controllable voltage source. Inmedium voltage applications with power ratings of several MVA, however, the switching frequency of today’s VSIs is limited to some hundred Hertz. Modern high power IGCTs can operate at around 1 kHz. Therefore, large passive filters are needed in order to remove the current ripple generated by the VSI. Furthermore, in fast control schemes the VSI no longer represents an ideal voltage source because the PWM modulator produces a considerable dead-time.In this project a fast dead-beat algorithm for PWM operated VSIs is developed [1].This algorithm improves the load current tracking performance and the stability of the active filter. Normally, for a harmonics free current measurement the VSI current
would be sampled synchronously with the tips of the triangular carriers. Here, the current acquisition is shifted in order to minimize the delays in the control loop. The harmonics now included in themeasurement can be calculated and subtracted from
the VSI current. Thus, an instantaneous current estimation free of harmonics is obtained.
Keywords: active filters
From reference 3
This report provides background information on electric power transmission and related policy issues. Proposals for changing federal transmission policy before the 111th Congress include S. 539, the Clean Renewable Energy and Economic Development Act, introduced on March 5, 2009; and the March 9, 2009, majority staff transmission siting draft of the Senate Energy and Natural Resources Committee. The policy issues identified and discussed in this report include: Federal Transmission Planning: several current proposals call for the federal government to sponsor and supervise large scale, on-going transmission planning programs. Issues for Congress to consider are the objectives of the planning process (e.g., a focus on supporting the development of renewable power or on a broader set of transmission goals), determining how much authority new interconnection-wide planning entities should be granted, the degree to which transmission planning needs to consider non-transmission solutions to power market needs, what resources the
executive agencies will need to oversee the planning process, and whether the benefits for projects included in the transmission plans (e.g., a federal permitting option) will motivate developers to add unnecessary features and costs to qualify proposals for the plan.
Permitting of Transmission Lines: a contentious issue is whether the federal government should assume from the states the primary role in permitting new transmission lines. Related issues include whether Congress should view management and expansion of the grid as primarily a state or national issue, whether national authority over grid reliability (which Congress established in the Energy Policy Act of 2005) can be effectively exercised without federal authority over permitting, if it is important to accelerate the construction of new transmission lines (which is one of the assumed benefits of federal permitting), and whether the
executive agencies are equipped to take on the task of permitting transmission lines.
Transmission Line Funding and Cost Allocation: the primary issues are whether the the federal government should help pay for new transmission lines, and if Congress should establish a national standard for allocating the costs of interstate transmission lines to ratepayers.
Transmission Modernization and the Smart Grid: issues include the need for Congressional oversight of existing federal smart grid research, development, demonstration, and grant programs; and oversight over whether the smart grid is actually proving to be a good investment for taxpayers and ratepayers.
Transmission System Reliability: it is not clear whether Congress and the executive branch have the information needed to evaluate the reliability of the transmission system. Congress may also want to review whether the power industry is striking the right balance between modernization and new construction as a means of enhancing transmission reliability, and whether the reliability standards being developed for the transmission system are appropriate for a rapidly changing power system.
Keywords: electric power transmission
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energy transmission system,” IEEE Trans. Ind. Electron., vol. 46, pp. 23–30, Feb. 1999.
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Page3 Requirements of an Electric Supply System
From reference1
Connections to external 330 kV power grids are provided using an open 330 kV switchyard. The plant is connected to the Lithuanian power grid using two transmission lines L-454 and L-453, 330 kV each, to the Belorussian power grid using three transmission lines L-450, L-452 and L-705, and to the Latvian power grid using one transmission line L-451.
Connections to external power grids at 110 kV are provided using the first section of the open 110 kV switchyard. The plant is connected to the Lithuanian power grid using one transmission line “Zarasai” 110 kV, and to the Latvian power grid using one transmission line L-632.
Connections between the open switchyards at 330 kV and 110 kV are established using two coupling autotransformers AT-1 and AT-2, types ATDCTN- 200000/330. Power of each autotransformer is equal to 200 MV×A. The autotransformers have a device for voltage regulation under load. The device type is RNOA-110/1000. 15 positions are provided to regulate voltage in a range (115 ± 6) kV.
The open 330 kV switchyard is designed using "4/3" principle (four circuit breakers per three connections) and consists of two sections. Circuit breakers are placed in two rows. The first section of the open switchyard 110 kV is designed using “Double system of buses with bypass” structure. The second section of open switchyard 110 kV is connected to the first section through two circuit breakers C101 and C102. The second section has the same design as the first one. The following
transmission lines are connected to the second section: L-Vidzy, L-Opsa, L-Statyba, LDuk Ötas. These transmission lines are intended for district power supplies, so they are not essential for electric power supply for the plant in-house operation.
Air circuit breakers of VNV-330/3150A type are used in the open 330 kV switchyard. Air circuit breakers of VVBK-110B-50/3150U1 type are used in open switchyard 110 kV. To supply power loads on voltage level 330 kV and 110 kV, aerial transmission lines are used. Electrical connections of external grids 110 and 330 kV are presented in Fig. 8.1.
Keywords: transmission lines
From reference 2
Abstract
This paper addresses sustainability criteria and the associated indicators allowing
operationalization of the sustainability concept in the context of electricity supply. The criteria and indicators cover economic, environmental and social aspects. Some selected results from environmental analysis, risk assessment and economic studies are shown. These studies are supported by the extensive databases developed in this work. The applications of multi-criteria analysis demonstrate the use of a framework that allows decision-makers to simultaneously address the often conflicting
socio-economic and ecological criteria. “EnergyGame”, the communication-oriented software recently developed by the Paul Scherrer Institute (PSI), provides the opportunity to integrate the central knowledge-based results with subjective value judgments. In this way a sensitivity map of technology choices can be constructed in an interactive manner. Accommodation of a range of perspectives expressed in the energy debate, including the concept of sustainable development, may lead to different internal rankings of the options but some patterns appear to be relatively robust.
Introduction
The public, opinion leaders and decision-makers ask for clear answers on issues concerning the energy sector and electricity generation in particular. Is it feasible to
phase out nuclear power in countries extensively relying on nuclear electricity supply and simultaneously reduce greenhouse gas emissions? What are the environmental and economic implications of enhanced uses of cogeneration systems, renewable sources and heat pumps? How do the various energy carriers compare with respect to accident risks? How would internalization of external costs affect the relative competitiveness of the various means of electricity production? What can we expect from the prospective technological advancements during the next two or three decades? Which systems or energy mixes come closest to the ideal of being cheap, environmentally clean, reliable and at the same time exhibit low accident risks?
How can we evaluate and rank the current and future energy supply options with respect to their performance on specific sustainability criteria?
The Swiss GaBE Project on “Comprehensive Assessment of Energy Systems” provides answers to many issues in the Swiss and international energy arena. A systematic, multidisciplinary, bottom-up methodology for the assessment of energy systems, has been established and implemented. It covers environmental analysis, risk assessment and economic studies, which are supported by the extensive databases developed in this work. One of the analysis products are aggregated indicators associated with the various sustainability criteria, thus allowing a practical operationalization of the sustainability concept. Apart from technical and economic aspects an integrated approach needs to consider also social preferences, which may be done in the framework of multi-criteria analysis.
Keywords: criteria indicators
From reference 3
Mobility of persons and goods is an essential component of the competitiveness of European industry and services as well as an essential citizen right. The goal of the EU's sustainable transport policy is to ensure that our transport systems meet society's economic, social and environmental needs.
The transport sector is responsible for about 30% of the total final energy consumption and for about 25% of the total CO2 emissions. In particular the
contribution of road transport is very high (around 80% and 70% respectively). These simple data shed light on the necessity to move towards a more sustainable transportation system, but also suggest that a technological/systemic revolution in the field will positively impact the overall world’s sustainable development.
From a technological point of view, a lower dependency from not renewable energy sources (i.e. fuel oil) of the road transport is the main anticipated change. In particular electric engines possibly represent the natural vehicle evolution in this direction. Indeed they have much higher energy efficiency (around three times that of internal combustion engines, ICE) and do not produce any kind of tailpipe emissions. How the electricity will be supplied to the vehicles is still unpredictable due to the too many existing uncertainties on the future development, but the electrification of the drive train will contribute to having alternative energy paths to reduce the nearly total dependency on crude oil. In particular, vehicle range and performances allowed by the different possibilities will play a key role on the debate.
At the moment a great attention is attracted by electric vehicles, both hybrid and not, that will allow users to recharge their vehicles directly at home. This kind of vehicle can represent a real future alternative to the ICE vehicles in particular for what concerns the daily commuting trips (whose range is quite low). It is therefore important to understand what might be the impact on the electric supply system capabilities of this recharging activity.
In this light the present study carries out an analysis of this impact for the Province of Milan (of particular relevant due the very high daily commuting trips) at a 2030 time horizon. Key issue of the analysis is the estimation of a potential market share evolution for the electric vehicles. The results obtained show that even with a very high future market penetration the impact of the vehicles on the annual energy consumption will be quite negligible. On the contrary they also show that without an appropriate regulation (e.g. the intelligent integration of electric vehicles into the existing power grid as decentralised and flexible energy storage), they could heavily impact on the daily electric power requirements.
Keywords: electric vehicles
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