电气专业英语论文

关于电气工程专业英语的作文Diving into the realm of electrical engineering is like exploring a vast, intricate web of innovation and technology that powers our modern world. This field, with its heart set on the pulse of progress, is not just about circuits and currents; it's a language of its own, with English at its core, bridging the gap between theory and application.Electrical engineering is a discipline that has evolved dramatically over the decades, and its language has kept pace, incorporating a rich lexicon of terms that describeeverything from the most fundamental components to the most cutting-edge technologies. For students and professionals alike, mastering the English terminology is crucial for understanding the principles that underpin electrical systems, from the microchip to the power grid.In this dynamic field, the ability to communicate effectively in English is paramount. Whether it's discussing the intricacies of a power electronics converter or thedesign of a high-voltage transmission line, precision in language is as important as precision in engineering. English serves as the universal medium for scholarly articles, technical specifications, and international conferences,where the latest research and developments are shared.Moreover, the language of electrical engineering is not static; it evolves with the field. New terms emerge astechnologies advance, such as "smart grid," "renewable energy," and "Internet of Things (IoT)," each reflecting the ongoing expansion of the discipline. Keeping up with these developments requires a commitment to continuous learning and an openness to embracing new concepts and terminologies.The study of electrical engineering English also extends beyond the technical. It encompasses the ability to interpret and create diagrams, to understand and apply mathematical models, and to engage in critical thinking about the implications of new technologies on society and the environment.In essence, the mastery of electrical engineering English is not just about the words; it's about the ideas they represent and the solutions they enable. It's about theability to connect with a global community of engineers, to contribute to a field that is constantly pushing the boundaries of what is possible, and to be part of a conversation that shapes the future of our world.。

有关电气专业的英语作文I have always been fascinated by electricity and how it powers the world around us. The ability to manipulate and control the flow of electrons is truly amazing.When I first started studying electrical engineering, I was overwhelmed by the amount of knowledge and information I needed to absorb. However, as I delved deeper into the subject, I found myself becoming more and more passionate about it.One of the most exciting things about electrical engineering is the endless possibilities it offers. From designing circuits to working on power systems, there is always something new and challenging to explore.I love the hands-on aspect of electrical engineering. There is something incredibly satisfying about building and testing circuits, and seeing the results of your work come to life.The field of electrical engineering is constantly evolving, and it is crucial to stay updated with the latest technologies and advancements. This constant learning and adaptation keep the profession exciting and dynamic.The problem-solving aspect of electrical engineering is what drew me to the field in the first place. I enjoy the challenge of identifying and solving complex electrical issues, and the sense of accomplishment that comes with finding a solution.The impact of electrical engineering on the world is undeniable. From powering homes and businesses to driving technological innovations, electrical engineers play a crucial role in shaping the modern world.In conclusion, electrical engineering is a diverse and dynamic field that offers endless opportunities for learning and growth. I am excited to continue my journey in this field and see where it takes me.。

电气专业的英语作文In the heart of technological advancement lies the field of electrical engineering, a discipline that has been pivotal in shaping our modern society. This essay will explore the importance of electrical engineering, its applications, andits impact on various sectors.First and foremost, electrical engineering is the backbone of modern communication systems. The development of wireless technologies, such as Wi-Fi and cellular networks, has been made possible through the expertise of electrical engineers. These technologies have revolutionized the way we communicate, allowing for instant messaging, video calls, and the seamless sharing of information across the globe.Moreover, the field has played a crucial role in the advancement of renewable energy sources. Solar panels, wind turbines, and other forms of green energy rely heavily on electrical engineering to convert, distribute, and manage the energy they produce. This has led to a significant reductionin our reliance on fossil fuels, contributing to a cleanerand more sustainable future.In the medical sector, electrical engineering has also made a profound impact. Medical imaging technologies, such as MRIand CT scans, rely on complex electrical systems to function. These systems are essential for diagnosing and treating awide range of medical conditions, thereby improving patientoutcomes and saving lives.Furthermore, the automotive industry has been transformed by the integration of electrical engineering. Electric vehicles (EVs) are becoming increasingly popular due to their environmental benefits and efficiency. The design and production of EVs require a deep understanding of electrical systems, batteries, and power management, all of which are at the core of electrical engineering.Lastly, the field of electrical engineering is integral to the development of smart cities. Smart grids, intelligent transportation systems, and automated infrastructure are all dependent on sophisticated electrical systems. These systems are designed to optimize energy use, reduce waste, and improve the overall quality of life for city dwellers.In conclusion, electrical engineering is a multifaceted discipline that has a profound impact on various aspects of modern society. From communication to renewable energy, medical technology to transportation, and smart city development, the role of electrical engineering is indispensable. As we continue to innovate and push the boundaries of technology, the importance of this field will only continue to grow.。

电气工程及其自动化专业英语作文范文Electrical Engineering and Automation: An Integral Part of Modern SocietyIntroductionElectrical Engineering and Automation, a discipline that has evolved significantly over the past few decades, has become an integral part of modern society. Its widespread applications in industry, agriculture, national defense, and various other fields have propelled it to a pivotal position in the global economy.Historical PerspectiveThe field of Electrical Engineering and Automation was first established approximately forty years ago. As a relatively new discipline, it has quickly grown to encompass a wide range of subfields and applications. From the design of switches for aerospace aircraft to the development of complex automated systems, its influence is pervasive.Core ComponentsThe core of Electrical Engineering and Automation lies in its ability to integrate electricity, machines, and intelligent systems to automate various tasks. This integration enables efficiency, precision, and safety in a wide range of applications.•Electricity and Machines: Electricity provides the power that drives machines and systems. Understanding the behavior ofelectrical circuits, voltage sources, current sources, andvarious network elements is crucial for the effective designand operation of automated systems.•Automation: Automation refers to the use of technology to control and monitor processes and machines with minimal humanintervention. It relies on sensors, actuators, and intelligentcontrollers to achieve desired outcomes.Challenges and OpportunitiesWhile Electrical Engineering and Automation offers immense opportunities for growth and development, it also poses significantchallenges. The complexity of modern systems requires a high level of technical knowledge and expertise. Additionally, the rapid pace of technological advancement requires constant updating of skills and knowledge.However, these challenges also present opportunities for innovation and growth. As new technologies emerge, there is a need for engineers and technicians who can understand and apply them effectively. This creates opportunities for those with a passion for learning and a willingness to adapt to new challenges.ConclusionIn conclusion, Electrical Engineering and Automation is a dynamic and exciting field that offers immense opportunities for growth and development. Its applications are pervasive, and its influence on society is profound. As we continue to push the boundaries of technology, Electrical Engineering and Automation will play an increasingly important role in shaping our future.。

电气工程及其自动化专业英语课程论文Document serial number【NL89WT-NY98YT-NC8CB-NNUUT-NUT108】重庆邮电大学移通学院《电气工程及其自动化专业英语》课程论文年级 2012专业电气工程与自动化姓名孙猜胜学号Three-phase asynchronous motorAbstract:The three-phase asynchronous motor is motor's one with single phase asynchronous motor, three-phase asynchronous motor operating performance is good, and can save various the structure to be simple, the manufacture is easy, firm durable, the service is convenient,cost inexpensive ,drag the ability is good,and so on a series of merits. thus becomes in each kind of electrical machinery the outputto be biggest utilizes the broadest one kind of electric motor.Key words:Moror Motor starting Star delta StartingThree-phase asynchronous motor principle:When the stator winding through into the three-phase ac three-phase symmetric arises when a synchronous speed n1 along the stator and rotor round for space in a clockwise rotation magnetic field. Because of a rotating magnetic field rotating speed to n1, rotor conductor of the static beginning, so the rotor conductor will cutthe stator and produce a rotating magnetic field induction emf (induction emf direction DingZe judge with the right hand). Because the child is short circuit loop ends conductor short meet, in therole of the induced emf, will produce the rotor conductor with induction emf direction basic consistent induced current. The rotor current-carrying conductor at stator magnetic field is the role ofthe electromagnetic force (the direction of the force with the left hand DingZe judge). The electromagnetic force of the rotor axis electromagnetic torque, drive along the rotor rotating magnetic field rotation direction.[1]Through the above analysis can be summed up the motor principle: when the three-phase motor stator winding (eachdiffer 120 KWH Angle), ventilation with three-phase ac, will producea rotating magnetic field, the rotating magnetic field cutting rotor winding, and thus to the rotor winding induced current (rotor windingis closed access), load flow of rotor stator conductor under the action of a rotating magnetic field will produce the electromagnetic force, thus in the motor shaft formed on the electromagnetic torque, driving motor rotation, and motor rotation direction and the rotating magnetic field in the same direction.Thestructureofthree-phaseasynchronousmotor:Types of three-phase asynchronous motor, but all kinds of three-phase asynchronous motor is the same basic structure, they are the stator and rotor of these two basic components, the stator and rotor has a certain air gap between. In addition, end caps, bearings, cable boxes, rings and other accessories,1).StatorpartStator is used to generate the rotating magnetic Three-phase motors generally shell, stator core, stator windings and other parts.a.Shell?Three-phase motor casing including base,end caps,bearingcaps,rings,such as junction boxes and comp onentsb. Stator CoreInduction motor stator core is part of the motor circuit from ~ thick coated with a thin insulating paint from silicon,c.ThestatorwindingsThree-phase motor stator windings are part of the circuit,there are three-phase three-phase motor windings,summetrical three-phase current access,it will have a rotating magnetic winding consists of three separate components of the winding, and each has a number of coil windings a phase of each winding, each winding in the space angle difference between the 120 ° electrical[2].2). Rotor parta. Rotor CoreWith mm thick steel from, set in the shaft, the role and the same stator core, on the one hand, as part of the motor magnetic circuit, on the one hand to place the rotor windings.b. Rotor windingsThe rotor winding induction motor winding is divided into two kinds of cage-shaped and which is divided into winding rotor asynchronous motor with cage induction motor.3). Other parts ofOther parts including the cover, fans, etc.Induction motor starting methods:There are several general methods of starting induction motors: full voltage, reduced voltage,wyes-delta,and part winding reduced voltage type can include solid state starters, adjustable frequency drives, and following is the most common method.1).Full voltageThe full voltage starting method, also known as across the line starting, is the easiest method to employ, has the lowest equipment costs, and is the most reliable. This method utilizes a control to close a contactor and apply full line voltage to the motor terminals. This method will allow the motor to generate its highest starting torque and provide the shortest acceleration method also puts the highest strain on the power system due to the high starting currents that can be typically six to seven times the normal full load current of the motor.2).AutotransformerThe motor leads are connected to the lower voltage side of the transformer. The most common taps that are used are 80%, 65%, and 50%. At 50% voltage the current on the primary is 25% of the full voltage locked rotor amps. The motor is started with this reduced voltage,and then after a pre-set condition is reached the connection is switched to line voltage. This condition could be a preset time, current level, bus volts, or motor speed. The change over can be done in either a closed circuit transition, or an open circuit transition method. In the open circuit method the connection to the voltage is severed as it is changed from the reduced voltage to the line level. Care should be used to make sure that there will not be problems from transients due to the switching. This potential problem can be eliminated by using the closed circuit transition. With the closed circuit method there is a continuous Voltage applied to the motor. Another benefit with the autotransformer starting is in possiblelower vibration and noise levels during starting.3).Star delta StartingThis approach started with the induction motor,the structure of each phase of the terminal are placed in the motor teminal box ,This allows the motor star connection in the initial start up,and then re-connected into a triangle run..The initial start time when the voltage is reduced to the original star connection,the startingcurrent and starting torque by 2/3. Depending on the applicationon,the motor switch to the triangle in the rotational speed of between 50% and the maximum be noted that the sameproblems,including the previously mentioned switch method ,if theopen circuit method,the transition may be a transient method isoften used in lesst than 600V motor,the rated voltage and higher are not suitable for star delta motor start method.[3]4).Series Resistor or Reactor StartingThis method is to use a series resistance or place in the motor loop the motor is started, a resistor to limit current and make the motor at the input voltage drop. Therefore plays a role of limitingcurrent at the small motor series resistor startup mode used more frequentlyConclusion:There are many ways asynchronous motor starting, each method hasits own benefits, according to the constraints of powersystems,equipment costs, load the boot device to select the best method.References:[1] Tang Tianhao Fundamentals of Electrical Machines and Drives [M] BeijingChina Machine Press 118-137[2] Wang Liming English for Electrical Engineering and Automation [M] BeijingTsinghua University Press 61-64[3] Stephen Electromechanics [M] America Electronic IndustryPress 340-370。

(完整word版)电气工程及其自动化专业外语作文A s a student, you will learn to apply related subjects such as computer technology，industrial electronics, instrumentation，electrical machines, robotics，power electronics，and automated control systems.作为一名学生，你将学会运用相关学科,如计算机技术，工业电子，仪器仪表，电器机械，机器人技术，电力电子和自动化控制系统。

Y ou will be able to understand written and oral instructions，as well as design, install, test，modify, troubleshoot，and repair electrical systems.您将能够理解书面和口头说明，以及设计,安装，测试，修改，故障排除和修复电力系统.U pon graduation，students of the Electrical Engineering Technology –Process Automation program can approach industrial electrical and electronic systems from the viewpoint of analysis，technical evaluation, design, and development。

The six—semester program concentrates on the in-depth study of electrical and electronic principles as they apply to automated systems using programmable logic controllers。

电气自动化专业介绍英语作文Electrical Automation Engineering.Electrical automation engineering is a branch of engineering that deals with the design, installation, and maintenance of electrical systems that are used to automate industrial processes. These systems can range from simple relay-based circuits to complex computer-controlled networks.Electrical automation engineers work in a variety of industries, including manufacturing, transportation, and utilities. They are responsible for designing and implementing electrical systems that meet the specific needs of their clients. These systems can include:Programmable logic controllers (PLCs)。

Variable frequency drives (VFDs)。

Human-machine interfaces (HMIs)。

Distributed control systems (DCSs)。

Supervisory control and data acquisition (SCADA) systems.Motion control systems.Robotics.Electrical automation engineers must have a strong understanding of electrical engineering principles, as well as a working knowledge of computer science and mechanical engineering. They must also be able to work independently and as part of a team.中文回答：电气自动化专业介绍。

重庆邮电大学移通学院《电气工程及其自动化专业英语》课程论文年级专业姓名学号Insulated-gate Bipolar Transistor Basics 【Abstract】Modern Power Electronics makes generous use of MOSFETs and IGBTs in most applications, and, if the present trend is any indication, the future will see more and more applications making use of MOSFETs and IGBTs. For high-voltage or high-power applications, it may be necessary to realize a logical switch by connecting smaller units in parallel and series to achieve high availability, high-frequency operation, and low cost due to build-in redundancy, reduced dynamic losses, and modular use of standardized units, respectively. IGBTs are very convenient to realize such units, because of quasi-linear controllability via a gate terminal. This thesis investigates control methodologies for power MOS semiconductor switches with focus on combined parallel and series connection of IGBT/diode modules. It is proposed to provide each IGBT with primary local control to monitor and adjust the IGBT's static and dynamic behavior. Secondary (global) control synchronizes the operation of multiple IGBTs. A globally synchronous clock can also be derived locally. This makes it possible to use low-cost low-bandwidth data links between series-connected units. Thereby, a flexible master- slave approach can avoid the need of dedicated global control. That is, the entire system is manageable by the local gate drive circuitry.Keywords:IGBT applications MOSFET characteristicIntroduction:The IGBT is a semiconductor device with four alternating layers (P-N-P-N) that are controlled by a metal-oxide-semiconductor (MOS) gate structure without regenerative action. This mode of operation was first proposed by Yamagami in his Japanese patent S47-21739, which was filed in 1968. This mode of operation was first experimentally reported in the lateral four layer device (SCR) by B.W. Scharf and J.D. Plummer in 1978.[1] This mode of operation was also experimentally discovered in vertical device in 1979 by B. J. Baliga.[2]The device structure was referred to as a ‘V-groove MOSFET device with the drain region replaced by a p-type Anode Region’ in this paper and subsequently as 'the insulated-gate rectifier' (IGR), the insulated-gate transistor (IGT), the conductivity-modulated field-effect transistor (COMFET) and "bipolar-mode MOSFET".[3]IGBT Fundamentals:The Insulated Gate Bipolar Transistor (IGBT) is a minority-carrier device with high input impedance and large bipolar current-carrying capability. Many designers view IGBT as a device with MOS input characteristics and bipolar output characteristic that is a voltage-controlled bipolar device. To make use of the advantages of both Power MOSFET and BJT, the IGBT has been introduced. It’s a fun ctional integration of Power MOSFET and BJT devices in monolithic form. It combines the best attributes of both to achieve optimal device characteristics.1.The main advantages of IGBT over a Power MOSFET and a BJT are:1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced.2. Low driving power and a simple drive circuit due to the input MOS gate structure. It can be easily controlled as compared to current controlled devices (thyristor, BJT) in high voltage and high current applications.3. Wide SOA. It has superior current conduction capability compared with the bipolar transistor. It also has excellent forward and reverse blocking capabilities.2.The main drawbacks are:1. Switching speed is inferior to that of a Power MOSFET and superior to that of a BJT. The collector current tailing due to the minority carrier causes the turn-off speed to be slow.2. There is a possibility of latchup due to the internal PNPN thyristor structure. The IGBT is suitable for scaling up the blocking voltage capability. In case of Power MOSFET, the on-resistance increases sharply with the breakdown voltage due to an increase in the resistively and thickness of the drift region required to support the high operating voltage.Basic Structure:An IGBT cell is constructed similarly to a n-channel vertical construction power MOSFET except the N+ drain is replaced with a P+ collector layer, thus forming a vertical PNP bipolar junction transistor. This additional P+ region creates a cascade connection of a PNP bipolar junction transistor with the surface n-channel MOSFET. Some IGBTs, manufactured without the N+buffer layer, are called non-punch through IGBTs whereas those with this layer are called punch-through IGBTs. The presence of this buffer layer can significantly improve the performance of the device if the doping level and thickness of this layer are chosen appropriately. Despite physical similarities, the operation of an IGBT is closer to that of a power BJT than a power MOSFET. It is due to the P + drain layer (injecting layer) which is responsible for the minority carrier injection into the N-drift region and the resulting conductivity modulation.IGBT Characteristics：Because the IGBT is a voltage-controlled device, it only requires a small voltage on the Gate to maintain conduction through the device unlike BJT’s which require that the Base current is continuously supplied in a sufficient enough quantity to maintain saturation.Also the IGBT is a unidirectional device, meaning it can only switch current in the “forward direction”, that is from Collector to Emitter unlike MOSFET’s which have bi-directional current switching capabilities (controlled in the forward direction and uncontrolled in the reverse direction).The principal of operation and Gate drive circuits for the insulated gate bipolar transistor are very similar to that of the N-channel power MOSFET. The basic difference is that the resistance offered by the main conducting channel when current flows through the device in its “ON” state is very much smaller in the IGBT. Because of this, the current ratings are much higher when compared with an equivalent power MOSFET.[4]The main advantages of using the Insulated Gate Bipolar Transistor over other types of transistor devices are its high voltage capability, low ON-resistance, ease of drive, relatively fast switching speeds and combined with zero gate drive current makes it a good choice for moderate speed, high voltage applications such as inpulse-width modulated (PWM), variable speed control, switch-mode power supplies or solar powered DC-AC inverter and frequency converter applications operating in the hundreds of kilohertz range. A general comparison betwe en BJT’s, MOSFET’s and IGBT’s is given in the following table.IGBT Operating area:The safe operating area is defined as the current-voltage boundary within which a power switching device can be operated without destructive failure. For IGBT, the area is defined by the maximum collector-emitter voltage V CE and collector current I C within which the IGBT operation must be confined to protect it from damage. The IGBT has the following types of SOA operations: forward-biased safe operating area , reverse-biased safe operating area and short-circuit safe operating area .1.Pulsed Collector Current (I CM ): Within its thermal limits, the IGBT can be used to a peak current well above the rated continuous DC current. The temperature rise during a high current transient can be calculated with the help of the transient thermal impedance curve or simulated in SPICE with the parameters provided in the curve. The test circuit is shown in the data sheet.2.Collector-to-Emitter Voltage (V CES ): V oltage across the IGBT should never exceed this rating, to prevent breakdown of the collector-emitter junction. The minimum value of the breakdown is stated in the Table of Electrical Characteristics.3.Maximum Gate-to-Emitter Voltage (V GE): The gate voltage is limited by the thickness and characteristics of the gate oxide layer. Though the gate dielectric rupture is typically around 80 volts, the user is normally limited to 20 or 30V to limit current under fault conditions and to ensure long term reliability.4.Clamped Inductive Load Current (I LM ):This rating is described in Section 6 and is important in most hard-switching applications. The test circuit can be found in the data sheet (it has changed over the years) and is the same as the switching loss test circuit. This circuit exposes the IGBT to the peak recovery current of the free-wheeling diode, which adds a significant component to the turn-on losses. This rating guarantees that the device can sustain high voltage and high current simultaneously, i.e. a square switching SOA. The test conditions for I LM are specified in the data sheet. This complements the information supplied by the RBSOA.References:[1] B.W. Scharf and J.D. Plummer, 1978 IEEE International Solid-State Circuits Conference, SESSION XVI FAM 16.6 "A MOS-Controlled Triac Devices"[2] B.J. Baliga, "ENHANCEMENT- AND DEPLETION-MODE VERTICAL-CHANNEL M.O.S. GA TED THYRISTORS" Electronics Letters p.645(1979)[3] A.Nakagawa et al., "High voltage bipolar-mode MOSFETs with high current capability", Ext. Abst. of SSDM, pp. 309–312(1984)[4] Ralph Locher, “Introduction to Power MOSFETs and their Applications” Fairchild Semiconductor, Application Note 558, October 1998.。

Electric Devices and SystemsAlthough transformers have no moving parts , they are essential to electromechanical energy conversion . They make it possible to increase or decrease the voltage lever that results in low costs ,and can be distributed and used safely . In addition , they can provide matching of impedances , and regulate the flow of power in a network.When we see a transformer on a utility pole all we is a cylinder with a few wires sticking out. These wires enter the transformer through bushings that provide isolation between the wires and the tank. Inside the tank these is an iron core linking coils, most probably made with copper, and insulated. The system of insulation is also associated with that of cooling the core/coil assembly. Often the insulation is paper, and the whole assembly may be immersed in insulating oil, used to both increase the dielectric strength of the paper and to transfer beat from the core-coil assembly to the outer walls of the tank to air. Figure shows the cutout of a typical distribution transformer. Few ideal versions of human constructions exist, and the transformer offers no exception. An ideal transformer is based on very simple concepts, and a large number of assumptions. This is the transformer one learns about in high school.Let us take an iron core with infinite permeability and two coils wound around it, one with N1 and the other with N2 turns, as shown in figure. Allthe magnetic flux is to remain in the iron. We assign sots at one terminal of each coil in the following fashion: if the flux in the core changes, inducing a voltage in the coils, and the dotted terminal of one coil is positive with respect its other terminal, so is the dotted terminal of the other coil. Or, the corollary to this, current into dotted terminals produces flux in the same direction,Assume that somehow a time varying flux is established in the iron. Then the flux linkages in each coil will be. Voltages will be induced in these two coil.On the other hand, currents flowing in the coils are related to the field intensity H. if currents flowing in the direction shown, i1 into the dotted terminal of coil 1, and i2 out of the dotted terminal of coil 2. we recognize that this is practically impossible, but so is the existence of an ideal transformer.Equations describe this ideal transformer, a two port network. The symbol of a network that is defined by these two equations is in the figure. An ideal transformer has an interesting characteristic. A two-port network that contains it and impedances can be replaced by an equivalent other, as discussed below. Consider the circuit in figure. Seen as a two port network. Generally a circuit on a side 1 can be transferred to side 2 by multiplying its component impedances , the voltage sources and the current sources,while keeping the topology the same. To develop the equivalent for a transformer we’ll gradually relax the assumptions that we had first imposed. First we’ll relax the assumption that the permeability of the iron is infinite. In that case equation does not revert to, but rather it becomes where is the reluctance of the path around the core of the transformer and the flux on this path. To preserve the ideal transformer equations as part of our new transformer, we can split i1 to two components: one i1, will satisfy the ideal transformer equation, and the other, i1 will just balance the right hand side. The figure shows this. We can replace the current source, i1 , with something simpler if we remember that the rate of change of flux is related to the induced voltage.Since the current i1 flows through something , where the voltage across it Is proportional to its derivative, we can consider that this something could be an inductance. This idea gives rise tothe equivalent circuit in figure,. Let us now relax the assumption that all the flux has to remain in the iron as shown in figure. Let us call the flux in the iron, magnetizing flux, the flux that leaks out of the core and links only coil 1. since links only coil 1, then it should be related only to the current there, and the same should be true for the second leakage flux.Again for a given frequency, the power losses in the core increase with the voltage. These losses cannot be allowed to exceed limit, beyond which thetemperature of the hottest spot in the transformer will rise above the point that will decrease dramatically the life of the insulation. Limits therefore are put to E1 and E2, and these limits are the voltage limits of the transformer. Similarly, winding Joule losses have to be limited, resulting in limits to the currents I1 and I2. Typically a transformer is described by its rated voltages, that give both the limits and turns radio. The ratio of the rated currents is the inverse of the ratio of the voltages if we neglect the magnetizing current. Instead of the transformer rated currents, a transformer is described by its rated apparent power.Under rated conditions, maximum current and voltage, in typical transformers the magnetizing current, does not exceed 1% of the current in the transformer. Its effect therefore in the voltage drop on the leakage inductance and winding resistance is negligible.Under maximum current, total voltage drops on the winding resistances and leakage inductances do not exceed in typical transformer 6% of the rated voltage. The effect therefore of the winding current on the voltages E1 and E2 is small, and their effect on the magnetizing current can be neglected.These considerations allow us to modify the equivalent circuit in figure, to obtain the slightly inaccurate but much more useful equivalent circuits in figures.Adjustable Speed DrivesBy definition, adjustable speed drives of any type provide a means of variably changing speed to better match operating requirements. Such drives are available in mechanical, fluid and electrical typed.The most common mechanical versions use combinations of belts and sheaves, or chains and sprockets, to adjust speed in set, selectable ratios-2:1,4:1,8:1 and so forth. Traction drives, a more sophisticated mechanical control scheme, allow incremental speed adjustments. Here, output speed is varied by changing the contact points between metallic disks, or between balls and cones. Adjustable speed fluid drives provide smooth, stepless adjustable speed control. There are three major types. Hydrostatic drives use electric motors or internal combustion engines as prime movers in combination with hydraulic pumps, which in turn drive hydraulic motors. Hydrokinetic and hydroviscous drives directly couple input and output shafts. Hydrokinetic versions adjust speed by varying the amount of fluid in a vortex that serves as the input-to-output coupler. Hydroviscous drives, also called oil shear drives, adjust speed by controlling oil-film thickness, and therefore slippage, between rotating metallic disk. An eddy current drive, while technically an electrical drive, nevertheless functions much like a hydrokinetic or hydrovidcous fluid drive in that it serves as a coupler between a prime mover and driven load. In an eddycurrent drive, the coupling consists of a primary magnetic field and secondary fields created by induced eddy currents. They amount of magnetic slippage allowed among the fields controls the driving speed.In most industrial applications, mechanical, fluid or eddy current drives are paired with constant-speed electric motors. On the other hand, solid state electrical drives, create adjustable speed motors, allowing speeds from zero RPM to beyond the motor’s base speed. Controlling the speed of the motor has several benefits, including increased energy efficiency by eliminating energy losses in mechanical speed changing devices. In addition, by reducing, or often eliminating, the need for wear-prone mechanical components, electrical drives foster increased overall system reliability, as well as lower maintenance costs. For these and other reasons, electrical drives are the fastest growing type of adjustable speed drive..There are two basic drive types related to the type of motor controlled-dc and AC. A DC direct current drive controls the speed of a DC motor by varying the armature voltage (and sometimes also the field voltage ). An alternating current drive controls the speed of an AC motor by varying the frequency and voltage supplied to the motor.Direct current drives are easy to apply and technologically straightforward, They work by rectifying AC voltage from the power line to DC voltage, then feeding adjustable voltage to a DC motor. With permanent magnet DCmotors, only the armature voltage is controlled. The more voltage supplied, the faster the armature turns. With wound-field motors, voltage must be supplied to both the armature and the field. In industry, the following three types of DC drives are most common, as shown in the figure.Drives: these are named for the silicon controlled rectifiers (also called thyristors ) used to convert AC to controlled voltage DC. Inexpensive and easy to use, these drives come in a variety of enclosures, and in unidirectional or reversing styles.Regenerative SCR Drives: Also called four quadrant drives, these allow the DC motor to provide both motoring and braking torque, Power coming back from the motor during braking is regenerated back to the power line and not lost.Pulse Width Modulated DC Drives: Abbreviated PWM and also called, generically, transistorized DC drives, these provide smoother speed control with higher efficiency and less motor heating, Unlike SCR drives, PWM types have three elements. The first converts AC to DC, the second filters and regulates the fixed DC voltage, and the third controls average voltage by creating a stream of variable width DC pulses. The filtering section and higher level of control modulation account for the PWM drive’s improved performance compared with a common SCR drive.AC drive operation begins in much the same fashion as a DC drive. Alternating line voltage is first rectified to produce DC. But because an AC motor is used, this DC voltage must be changed back, of inverted, to an adjustable-frequency alternating voltage. The drive’s inv erter section accomplishes this, In years past, this was accomplished using SCR. However, modern AC drives use a series of transistors to invert DC to adjustable-Frequency AC. An example is shown in figure.This synthesized alternating current is then fed to the AC motor at the frequency and voltage required to produce the desired motor speed. For example, a 60 Hz synthesized frequency, the same as standard line frequency in the United states, produces 100% of rated motor speed. A lower frequency produces a lower speed, and a higher frequency a higher speed. In this way, an AC drive can produce motor speeds from, approximately,15 to200% of a motor’s normally rated RPM-- by delivering frequencies of 9 HZ to 120 Hz, respectively.Today, AC drives are becoming the systems of choice in many industries,. Their use ofsimple and rugged three-phase induction motor means that AC drive systems are the most reliable and least maintenance prone of all. Plus, microprocessor advancements have enabled the creation of so-called vector drives, which provide greatly enhance response, operation down to zero speed and positioning accuracy. Vector drives, especially whencombined with feedback devices such as tachometers, encoders and resolvers in a closed-loop system, are continuing to replace DC drives in demanding applications. An Example is shown in the figure.By far the most popular AC drive today is the pulse width modulated type. Though originally developed for smaller-horsepower applications, PWM is now used in drives of hundreds or even thousands of horsepower—as well as remaining the staple technology in the vast majority of small integral and fractional horsepower ―micro‖ and ―sub-micro‖ AC drives, as shown in the figure. Pulse width modulated refers to the inverter’s ab ility to vary the output voltage to the motor by altering the width and polarity of voltage pulses, The voltage and frequency are synthesized using this stream of voltage pulses. This is accomplished through microprocessor commands to a series of power semiconductors that serve as on-off switches. Today, these switches are usually IGBTs, of isolated gate bipolar transistor. A big advantage to these devices is their fast switching speed resulting in higher pulse of carrier frequency, which minimizes motor noise.Power semiconductor devicesThe modern age of power electronics began with the introduction of thyristors in the late 1950s. Now there are several types of power devices available for high-power and high-frequency applications. The most notable power devices are gate turn-off thyristor, power darlington transistors,power mosfets, and insulated-gate bipolar transistors. Power semiconductor devices are the most important functional elements in all power conversion applications. The power devices are mainly used as switches to convert power from one form to another. They are used in motor control systems, uninterrupted power supplies, high-voltage dc transmission, power supplies, induction heating, and in many other power conversion applications. A review of the basic characteristics of these power devices is presented in this section.The thyristor, also called a silicon-controlled rectifier, is basically a four-layer three-junction pn device. It has three terminals: anode, cathode, and gate. The device is turned on by applying a short pulse across the gate and cathode. Once the device turns on, the gate loses its control to turn off the device. The turn-off is achieved by applying a reverse voltage across the anode and cathode. The thyristors symbol and its volt-ampere characteristics are shown in the figure. There are basically two classifications of thyristors: converter grade and inverter grade. The difference between a converter-grade and an inverter-grade thyristor is the low turn –off time (on the order of a few microseconds) for the latter. The converter-grade thyristors are slow type and are used in natural commutation (or phase-controlled) applications. Inverter-grade thyristors are used in forced commutation applications such as dc-dc choppers and dc-ac inverters. The inverter-grade thyristors are turned off by forcing thecurrent to zero using an external commutation circuit. This requires additional commutating components, thus resulting in additional losses in the inverter. Thyristors are highly rugged devices in terms of transient currents, di / dt, and dv/dt capability. The forward voltage drop in thyristors is about 1.5 to 2 V, and even at higher currents of the order of 100 A, it seldom exceeds 3 V. While the forward voltage determines the on-state power loss of the device at any given current, the switching power loss becomes a dominating factor affecting the device junction temperature at high operating frequencies. Because of this, themaximum switching frequencies possible using thyristors are limited in comparison with other power devices considered in this section.Thyristors have withstand capability and can be protected by fuses. The nonrepetitive surge current capability for thyristors is about 10 times their rated root mean square current. They must be protected by snubber networks for dv/dt and di/dt effects. If the specified dv/dt is exceeded, thyristors may start conducting without applying a gate pulse. In dc-to-ac conversion applications it is necessary to use an antiparalled diode of similar rating across each main thyristor. Thyristors are available up to 6000 V, 3500 A.Power mosfets are marketed by different manufacturers with differences in internal geometry and with different names such as megamos, hexfet,sipmos, and tmos. They have unique features that make them potentially attractive for switching applications. They are essentially voltage-driven rather than current-driven devices, unlike bipolar transistors.The gate of a mosfet is isolated electrically from the source by a layer of silicon oxide. The gate draws only a minute leakage current of the order of nanoamperes. Hence the gate drive circuit is simple and power loss in the gate control circuit is practically negligible. Although in steady state the gate draws virtually no current, this is not so under transient conditions. The gate-to-source and gate-to-drain capacitances have to be charged and discharged appropriately to obtain the desired switching speed, and the drive circuit must have a sufficiently to output impedance to supply the required charging and discharging currents. The circuit symbol of a power mosfet is shown in the figure.Power mosfets are majority carrier devices, and there is no minority carrier storage time. Hence they have exceptionally fast rise and fall times. They are essentially resistive devices when turned on, while bipolar transistors present a more or less constant over the normal operating range. Power dissipation in mosfets is I, and in bipolar it is Ic, and in bipolar it is Id. At low currents, therefore, a power mosfet may have a lower conduction loss than a comparable bipolar device, but at higher currents, the conduction loss will exceed that of bipolar. Also, the R increases with temperature.An important feature of a power mosfet is the absence of a secondary breakdown effect, which is present in a bipolar transistor, and as a result, it has an extremely rugged switching performance. In mosfets, R increases with temperature, and thus the current is automatically diverted away from the hot spot. The drain body junction appears as an antiparalled diode between source and drain. Thus power mosfet will not support voltage in the reverse direction. Although this in verse diode is relatively fast, it is slow by comparison with the mosfet. Recent devices have the didde recovery time as low as 100 ns. Since mosfet cannot be protected by fuses, an electronic protection technique has to be used.With the advancement in MOS technology, ruggedized MOSF are replacing the conventional MOSEFs. The need to ruggedize power MOSFETs is related to device reliability. If a MOSFET is operating within its specification range at all times, its chances for failing catastrophically are minimal. However, if its absolute maximum rating is exceeded, failure probability increases dramatically. Under actual operating conditions, a MOSFET may be subjected to transients—either externally from the power bus supplying the circuit or from the circuit itself due, for example, to inductive kicks going beyond the absolute maximum ratings. Such conditions are likely in almost every application, and in most cases are beyond a designer’s control. Rugged devices are made to be more tolerant for over-voltage transients. Ruggedness is the ability of aMOSFET to operate in an environment ofdynamic electrical stresses, without activating any of the parasitic bipolar junction transistors. The rugged device can withstand higher levels of diode recovery dv/dt and static dv/dt.译文：变压器尽管变压器没有旋转的不见，但是它在本质上还是属于几点能量交换设备。

电气专业英文作文As an electrical engineering major, I am fascinated by the way electricity powers our world. From the circuits in our phones to the power grid that keeps our cities running, electricity is everywhere and I want to understand it all.I love the hands-on aspect of electrical engineering. There's something so satisfying about designing a circuit on paper and then actually building it in the lab. It'slike bringing your ideas to life and seeing them work in the real world.One of the most challenging parts of studyingelectrical engineering is the math. It can be really tough to wrap your head around all the complex equations and calculations, but when you finally solve a difficult problem, it's incredibly rewarding.I'm also really interested in the future of electrical engineering, especially when it comes to renewable energy.I think it's so important for us to find sustainable ways to power our world, and I want to be a part of that innovation.In the end, I chose to study electrical engineering because I want to make a real impact on the world. Whether it's through designing more efficient power systems or creating new technology, I believe that electrical engineering has the potential to change the way we live for the better.。