How an engineer conquers the world with true passion?

Engineer

Engineers design materials, structures, and systems while considering the limitations imposed by practicality, regulation, safety, and cost. The word engineer (from the Latin ingeniator) is derived from the Latin words ingeniare ("to contrive, devise") and ingenium ("cleverness").The foundation education of an engineer is typically a 4-year bachelor's degree or in some countries, a master's degree in an engineering discipline plus 4–6 years peer-reviewed professional practice culminating in a project report or thesis. Engineers who seek a professional engineer license in N. America will be required to take further exams in ethics, law and professional practice.

The work of engineers forms the link between scientific discoveries and their subsequent applications to human and business needs and quality of life.

Definition

In 1960, the Conference of Engineering Societies of Western Europe and the United States of America defined "professional engineer" as follows:

A professional engineer is competent by virtue of his/her fundamental education and training to apply the scientific method and outlook to the analysis and solution of engineering problems. He/she is able to assume personal responsibility for the development and application of engineering science and knowledge, notably in research, design, construction, manufacturing, superintending, managing and in the education of the engineer. His/her work is predominantly intellectual and varied and not of a routine mental or physical character. It requires the exercise of original thought and judgement and the ability to supervise the technical and administrative work of others. 

Roles and expertise

Design

Engineers develop new technological solutions. During the engineering design process, the responsibilities of the engineer may include defining problems, conducting and narrowing research, analyzing criteria, finding and analyzing solutions, and making decisions. Much of an engineer's time is spent on researching, locating, applying, and transferring information.Indeed, research suggests engineers spend 56% of their time engaged in various information behaviours, including 14% actively searching for information.

Engineers must weigh different design choices on their merits and choose the solution that best matches the requirements. Their crucial and unique task is to identify, understand, and interpret the constraints on a design in order to produce a successful result.

Analysis

Engineers conferring on prototype design, 1954

Engineers apply techniques of engineering analysis in testing, production, or maintenance. Analytical engineers may supervise production in factories and elsewhere, determine the causes of a process failure, and test output to maintain quality. They also estimate the time and cost required to complete projects. Supervisory engineers are responsible for major components or entire projects. Engineering analysis involves the application of scientific analytic principles and processes to reveal the properties and state of the system, device or mechanism under study. Engineering analysis proceeds by separating the engineering design into the mechanisms of operation or failure, analyzing or estimating each component of the operation or failure mechanism in isolation, and recombining the components. They may analyze risk.

Specialization and management

NASA Launch Control Center Firing Room 2 as it appeared in the Apollo era

Most engineers specialize in one or more engineering disciplines. Numerous specialties are recognized by professional societies, and each of the major branches of engineering has numerous subdivisions. Civil engineering, for example, includes structural and transportation engineering and materials engineering include ceramic, metallurgical, and polymer engineering. Mechanical engineering cuts across just about every discipline since its core essence is applied physics. Engineers also may specialize in one industry, such as motor vehicles, or in one type of technology, such as turbines or semiconductor materials.

Several recent studies have investigated how engineers spend their time; that is, the work tasks they perform and how their time is distributed among these. Research suggests that there are several key themes present in engineers’ work: (1) technical work (i.e., the application of science to product development); (2) social work (i.e., interactive communication between people); (3) computer-based work; (4) information behaviours. Amongst other more detailed findings, a recent work sampling study found that engineers spend 62.92% of their time engaged in technical work, 40.37% in social work, and 49.66% in computer-based work. Furthermore, there was considerable overlap between these different types of work, with engineers spending 24.96% of their time engaged in technical and social work, 37.97% in technical and non-social, 15.42% in non-technical and social, and 21.66% in non-technical and non-social.

The time engineers spend engaged in such activities is also reflected in the competencies required in engineering roles. In addition to engineers’ core technical competence, research has also demonstrated the critical nature of their personal attributes, project management skills, and cognitive abilities to success in the role.

Ethics

The Challenger disaster is held as a case study of engineering ethics.

Engineers have obligations to the public, their clients, employers, and the profession. Many engineering societies have established codes of practice and codes of ethics to guide members and inform the public at large. Each engineering discipline and professional society maintains a code of ethics, which the members pledge to uphold. Depending on their specializations, engineers may also be governed by specific statute, whistleblowing, product liability laws, and often the principles of business ethics.

An engineer receiving his Order of the Engineer ring

Some graduates of engineering programs in North America may be recognized by the Iron Ring or Engineer's Ring, a ring made of iron or stainless steel that is worn on the little finger of the dominant hand. This tradition began in 1925 in Canada with The Ritual of the Calling of an Engineer, where the ring serves as a symbol and reminder of the engineer's obligations to the engineering profession. In 1972, the practice was adopted by several colleges in the United States including members of the Order of the Engineer.

Education

Main article: Engineering education

Most engineering programs involve a concentration of study in an engineering specialty, along with courses in both mathematics and the physical and life sciences. Many programs also include courses in general engineering and applied accounting. A design course, often accompanied by a computer or laboratory class or both, is part of the curriculum of most programs. Often, general courses not directly related to engineering, such as those in the social sciences or humanities, also are required.

Accreditation is the process by which engineering programs are evaluated by an external body to determine if applicable standards are met. The Washington Accord serves as an international accreditation agreement for academic engineering degrees, recognizing the substantial equivalency in the standards set by many major national engineering bodies. In the United States, post-secondary degree programs in engineering are accredited by the Accreditation Board for Engineering and Technology.

Regulation

In many countries, engineering tasks such as the design of bridges, electric power plants, industrial equipment, machine design and chemical plants, must be approved by a licensed professional engineer. Most commonly titled Professional Engineer is a license to practice and is indicated with the use of post-nominal letters; PE or P.Eng. These are common in North America, as is European Engineer (EUR ING) in Europe. The practice of engineering in the UK is not a regulated profession but the control of the titles of Chartered Engineer (CEng) and Incorporated Engineer (IEng) is regulated. These titles are protected by law and are subject to strict requirements defined by the Engineering Council UK. The title CEng is in use in much of the Commonwealth.

Many skilled / semi-skilled trades and engineering technicians in the UK call themselves engineers. A growing movement in the UK is to legally protect the title 'Engineer' so that only professional engineers can use it; a petition was started to further this cause.

In the United States, licensure is generally attainable through combination of education, pre-examination (Fundamentals of Engineering exam), examination (Professional Engineering Exam), and engineering experience (typically in the area of 5+ years). Each state tests and licenses Professional Engineers. Currently, most states do not license by specific engineering discipline, but rather provide generalized licensure, and trust engineers to use professional judgment regarding their individual competencies; this is the favoured approach of the professional societies. Despite this, however, at least one of the examinations required by most states is actually focused on a particular discipline; candidates for licensure typically choose the category of examination which comes closest to their respective expertise.

In Canada, the profession in each province is governed by its own engineering association. For instance, in the Province of British Columbia an engineering graduate with four or more years of post graduate experience in an engineering-related field and passing exams in ethics and law will need to be registered by the Association for Professional Engineers and Geoscientists (APEGBC) in order to become a Professional Engineer and be granted the professional designation of P.Eng allowing one to practice engineering.

In Continental Europe, Latin America, Turkey and elsewhere the title is limited by law to people with an engineering degree and the use of the title by others is illegal. In Italy, the title is limited to people who both hold an engineering degree and have passed a professional qualification examination (Esame di Stato). In Portugal, professional engineer titles and accredited engineering degrees are regulated and certified by the Ordem dos Engenheiros. In the Czech Republic, the title "engineer" (Ing.) is given to people with a (masters) degree in chemistry, technology or economics for historical and traditional reasons. In Greece, the academic title of "Diploma Engineer" is awarded after completion of the five-year engineering study course and the title of "Certified Engineer" is awarded after completion of the four-year course of engineering studies at a Technological Educational Institute (TEI).

Perception

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The perception and definition of the term 'engineer' varies across countries and continents.

19th century engineer Isambard Kingdom Brunel by the launching chains of the SS Great Eastern

UK

British school children in the 1950s were brought up with stirring tales of "the Victorian Engineers", chief amongst whom were the Brunels, the Stephensons, Telford and their contemporaries. In the UK, "engineering" was more recently perceived as an industry sector consisting of employers and employees loosely termed "engineers" who included the semi-skilled trades. However, the 21st-century view, especially amongst the more educated members of society, is to reserve the term Engineer to describe a university-educated practitioner of ingenuity represented by the Chartered (or Incorporated) Engineer. However, a large proportion of the UK public still sees Engineers as semi-skilled tradespeople with a high school education.

France

In France, the term 'ingénieur" (engineer) is not a protected title and can be used by anyone, even by those who do not possess an academic degree.

However, the title "Ingénieur Diplomé" (Graduate Engineer) is an official academic title that is protected by the government and is associated with the "Diplôme d'Ingénieur", which is one of the most prestigious academic degrees in France. Anyone misusing this title in France can be fined a large sum and jailed, as it is reserved for graduates of French engineering grandes écoles that provide highly intensive training in science and engineering. Among such institutions, the most renown (and hardest to gain admission) are Ecole Centrale Paris (Centrale), Ecole des Mines de Paris (Mines Paristech), Ecole Nationale Supérieure d'Arts et Métiers, Ecole Polytechnique, and Ecole des Ponts ParisTech. Engineering schools which were created during the French revolution have a special reputation among the French people, as they helped to make the transition from a mostly agricultural country of late 18th century to the industrially developed France of the 19th century. A great part of 19th century France's economic wealth and industrial prowess was created by engineers that have graduated from Ecole Centrale Paris, Ecole des Mines de Paris, or Ecole Polytechnique. This was also the case after the WWII when France had to be rebuilt.

North America

In the US and Canada, engineering is a regulated profession whose practice and practitioners are licensed and governed by law. A 2002 study by the Ontario Society of Professional Engineers revealed that engineers are the third most respected professionals behind doctors and pharmacists.

Auto rice milling machinery in Bangladesh

Asia, Africa, and Middle East

In the Indian subcontinent, RuB, Middle East, Africa, and China, engineering is one of the most sought after undergraduate courses, inviting thousands of applicants to show their ability in highly competitive entrance examinations.

In Egypt, the educational system makes engineering the second-most-respected profession in the country (after medicine); engineering colleges at Egyptian universities require extremely high marks on the General Certificate of Secondary Education (Arabic: الثانوية العامة‎‎ al-Thānawiyyah al-`Āmmah)—on the order of 97 or 98%—and are thus considered (along with the colleges of medicine, natural science, and pharmacy) to among the pinnacleكليات القمة kullīyāt al-qimmah).

In the Philippines and Filipino communities overseas, engineers who are either Filipino or not, especially those who also profess other jobs at the same time, are addressed and introduced as Engineer, rather than Sir/Madam in speech or Mr./Mrs./Ms. (G./Gng./Bb. in Filipino) before surnames. That word is used either in itself or before the given name or surname.

Corporate culture

In companies and other organizations, there is sometimes a tendency to undervalue people with advanced technological and scientific skills compared to celebrities, fashion practitioners, entertainers, and managers. In his book, The Mythical Man-Month, Fred Brooks Jr says that managers think of senior people as "too valuable" for technical tasks and that management jobs carry higher prestige. He tells how some laboratories, such as Bell Labs, abolish all job titles to overcome this problem: a professional employee is a "member of the technical staff." IBM maintain a dual ladder of advancement; the corresponding managerial and engineering or scientific rungs are equivalent. Brooks recommends that structures need to be changed; the boss must give a great deal of attention to keeping his managers and his technical people as interchangeable as their talents allow.

A scholarly article on audio engineer?

An audio engineer at an audio console

An audio engineer (also sometimes recording engineer or a vocal engineer) works on the recording, manipulating the record using equalization and electronic effects, mixing, reproduction, and reinforcement of sound. Audio engineers work on the "...technical aspect of recording—the placing of microphones, pre-amp knobs, the setting of levels. The physical recording of any project is done by an engineer ... the nuts and bolts."Many audio engineers creatively use technologies to produce sound for film, radio, television, music, electronic products and computer games.Audio engineers also set up, sound check and do live sound mixing using an audio console and a sound reinforcement system for music concerts, theatre, sports games and corporate events.

Alternatively, the term "audio engineer" can refer to a scientist or professional engineer who holds a B.Sc. or M.Sc. who designs, develops and builds new audio technologies working within the field of acoustical engineering.

Audio engineering concerns the creative and practical aspects of sounds including speech and music, as well as the development of new audio technologies and advancing scientific understanding of audible sound.

Research and development

Research and development audio engineers invent new technologies, equipment and techniques, to enhance the process and art of audio engineering. They might design acoustical simulations of rooms, shape algorithms for audio signal processing, specify the requirements for public address systems, carry out research on audible sound for video game console manufacturers, and other advanced fields of audio engineering. They might also be referred to as acoustic engineers.

Education

Audio engineers working in research and development may come from backgrounds such as acoustics, computer science, broadcast engineering, physics, acoustical engineering, electrical engineering and electronics. Audio engineering courses at university or college fall into two rough categories: (i) training in the creative use of audio as a sound engineer, and (ii) training in science or engineering topics, which then allows students to apply these concepts while pursuing a career developing audio technologies. Audio training courses give you a good knowledge of technologies and their application to recording studio and sound reinforcement systems, but do not have sufficient mathematical and scientific content to allow you to get a job in research and development in the audio and acoustic industry.

Noted audio engineer Roger Nichols at a vintage Neve recording console.

Audio engineers in research and development usually possess a bachelor's degree, master's degree or higher qualification in acoustics, physics, computer science or another engineering discipline. They might work in acoustic consultancy, specializing in architectural acoustics.[8] Alternatively they might work in audio companies (e.g. headphone manufacturer), or other industries that need audio expertise (e.g., automobile manufacturer), or carry out research in a university. Some positions, such as faculty (academic staff) require a Doctor of Philosophy. In Germany a Toningenieur is an audio engineer who designs, builds and repairs audio systems.

Sub-disciplines

The listed subdisciplines are based on PACS (Physics and Astronomy Classification Scheme) coding used by the Acoustical Society of America with some revision.

Audio signal processing

Main article: Audio signal processing

Audio engineers develop algorithms to allow the electronic manipulation of audio signals. These can be processed at the heart of much audio production such as reverberation, Auto-Tune or perceptual coding (e.g. mp3 or Opus). Alternatively, the algorithms might carry out echo cancellation on Skype, or identify and categorize audio tracks through Music Information Retrieval (e.g., Shazam).

Architectural acoustics

Acoustic diffusing mushrooms hanging from the roof of the Royal Albert Hall.

Architectural acoustics is the science and engineering of achieving a good sound within a room. For audio engineers, architectural acoustics can be about achieving good speech intelligibility in a stadium or enhancing the quality of music in a theatre. Architectural Acoustic design is usually done by acoustic consultants.

Electroacoustics

The Pyramid Stage

Electroacoustics is concerned with the design of headphones, microphones, loudspeakers, sound reproduction systems and recording technologies. Examples of electroacoustic design include portable electronic devices (e.g. mobile phones, portable media players, and tablet computers), sound systems in architectural acoustics, surround sound in movie theater and vehicle audio.

Musical acoustics

Main article: Musical acoustics

Musical acoustics is concerned with researching and describing the science of music. In audio engineering, this includes the design of electronic instruments such as synthesizers; the human voice (the physics and neurophysiology of singing); computer analysis of audio; music therapy, and the perception and cognition of music.

Psychoacoustics

Psychoacoustics is the scientific study of how humans respond to what they hear. At the heart of audio engineering are listeners who are the final arbitrator as to whether an audio design is successful, such as whether a binaural recording sounds immersive.

Speech

The production, computer processing and perception of speech is an important part of audio engineering. Ensuring speech is transmitted intelligibly, efficiently and with high quality; in rooms, through public address systems and through mobile telephone systems are important areas of study.

Practitioner

Mixing sound live

Producer, engineer, and mixer Phil Ek has described audio engineering as the "technical aspect of recording—the placing of microphones, the turning of pre-amp knobs, the setting of levels. The physical recording of any project is done by an engineer ... the nuts and bolts." A variety of terms are used to describe audio engineers who install or operate sound recording, sound reinforcement, or sound broadcasting equipment, including large and small format consoles. Terms such as "audio technician," "sound technician," "audio engineer," "audio technologist," "recording engineer," "sound mixer" and "sound engineer" can be ambiguous; depending on the context they may be synonymous, or they may refer to different roles in audio production. Such terms can refer to a person working in sound and music production; for instance, a "sound engineer" or "recording engineer" is commonly listed in the credits of commercial music recordings (as well as in other productions that include sound, such as movies). These titles can also refer to technicians who maintain professional audio equipment. Certain jurisdictions specifically prohibit the use of the title engineer to any individual not a registered member of a professional engineering licensing body.

In German, the "Tontechniker" (audio technician) is the one who operates the audio equipment and the "Tonmeister" (sound master) is a person who creates recordings or broadcasts of music, who is both deeply musically trained (in classical and non-classical genres), and who also has a detailed theoretical and practical knowledge of virtually all aspects of sound.

Education and training

Audio engineers come from backgrounds and/or postsecondary training in fields such as audio, fine arts, broadcasting, music, or electrical engineering. Training in audio engineering and sound recording is offered by colleges and universities. Some audio engineers are autodidacts with no formal training, but who have attained professional skills in audio through extensive on-the-job experience.

Training and background

Audio engineers must have extensive knowledge of audio engineering principles and techniques. They have to understand, to name a few, how to mic different instruments and amplifiers, what types of mics to use, where to place the mics, how to attenuate "hot" instrument signals that are overloading and clipping the channel, how to prevent audio feedback, how to set the audio compression for different instruments and vocals, and how to prevent unwanted distortion of the sound. However, to be a professional sound engineer, an individual needs more than just technical knowledge. She or he must also understand the types of sounds and tones that rock and pop music bands and other musical ensembles expect in different genres. This knowledge of musical styles is typically learned from years of experience listening to and mixing bands in recording and/or live sound contexts. A sound engineer must know, for example, the difference between creating the powerful drum sound that a heavy metal drummer will want for her kit, versus a drummer from a Beatles tribute band.

Practitioners

At the front of house position, mixing sound for a band

In the recording studio environment, a sound engineer records, edits, manipulates, mixes, or masters sound by technical means to realize the creative vision of the artist and record producer. While usually associated with music production, an audio engineer deals with sound for a wide range of applications, including post-production for video and film, live sound reinforcement, advertising, multimedia, and broadcasting. In larger productions, an audio engineer is responsible for the technical aspects of a sound recording or other audio production, and works together with a record producer or director, although the engineer's role may also be integrated with that of the producer. In smaller productions and studios the sound engineer and producer are often the same person.

In typical sound reinforcement applications, audio engineers often assume the role of producer, making artistic and technical decisions, and sometimes even scheduling and budget decisions.

Role of women

According to Women's Audio Mission (WAM), a nonprofit organization based in San Francisco dedicated to the advancement of women in music production and the recording arts, less than 5% of the people creating sound and media are women. "Only three women have ever been nominated for best producer at the Brits or the Grammys" and none won either award. "Women who want to enter the [producing] field face a boys' club, or a guild mentality". The UK "Music Producers' Guild says less than 4% of its members are women" and at the Liverpool Institute of Performing Arts, "...only 6% of the students enrolled on its sound technology course are female."

Women's Audio Mission was started in 2003 to address the lack of women in professional audio by training over 6,000 women and girls in the recording arts and is the only professional recording studio built and run by women. Notable recording projects atInclude the Grammy Award-winning Kronos Quartet, Angelique Kidjo (2014 Grammy winner), author Salman Rushdie, the Academy Award-nominated soundtrack to “Dirty Wars”, Van-Ahn Vo (NPR’s top 50 albums of 2013), Grammy-nominated St. Lawrence Quartet, and world music artists Tanya Tagaq and Wu Man.

One of the first women to produce, engineer, arrange and promote music on her own rock and roll music label was Cordell Jackson (1923-2004). Trina Shoemaker is a mixer, record producer and sound engineer who became the first woman to win the Grammy Award for Best Engineered Album in 1998 for her work on The Globe Sessions.

Gail Davies was the '...first female producer in country music, delivering a string of Top 10 hits in the '70s and '80s including "Someone Is Looking for Someone Like You," "Blue Heartache" and "I'll Be There (If You Ever Want Me)."  When she moved to Nashville in 1976, men "...didn't want to work for a woman" and she was told women in the city were "...still barefoot, pregnant and [singing] in the vocal booth." 

Wendy Waldman, who became a producer after Davies, saw that Davies had a difficult time. When Jonell Polansky arrived in Nashville in 1994, with a degree in electrical engineering and recording experience in the Bay Area, she was told "...[y]ou're a woman, and we already had one"–a reference to Waldman.  KK Proffitt, who is a studio "owner and chief engineer" states that men in Nashville do not want to have women in the recording booth. At a meeting of the Audio Engineering Society, Proffitt was told to "shut up" by a male producer when she raised the issue of updating studio recording technologies.Proffitt said she finds "...finds sexism rampant in the industry". 

What is Power electronics?

Definition

Power electronics is the application of solid-state electronics to the control and conversion of electric power. It also refers to a subject of research in electronic and electrical engineering which deals with the design, control, computation and integration of nonlinear, time-varying energy-processing electronic systems with fast dynamics.

The first high power electronic devices were mercury-arc valves. In modern systems the conversion is performed with semiconductor switching devices such as diodes, thyristors and transistors, pioneered by R. D. Middlebrook and others beginning in the 1950s. In contrast to electronic systems concerned with transmission and processing of signals and data, in power electronics substantial amounts of electrical energy are processed. An AC/DC converter (rectifier) is the most typical power electronics device found in many consumer electronic devices, e.g. television sets, personal computers, battery chargers, etc. The power range is typically from tens of watts to several hundred watts. In industry a common application is the variable speed drive (VSD) that is used to control an induction motor. The power range of VSDs start from a few hundred watts and end at tens of megawatts.

The power conversion systems can be classified according to the type of the input and output power

AC to DC (rectifier)
DC to AC (inverter)
DC to DC (DC-to-DC converter)
AC to AC (AC-to-AC converter)

Devices

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The capabilities and economy of power electronics system are determined by the active devices that are available. Their characteristics and limitations are a key element in the design of power electronics systems. Formerly, the mercury arc valve, the high-vacuum and gas-filled diode thermionic rectifiers, and triggered devices such as the thyratron and ignitron were widely used in power electronics. As the ratings of solid-state devices improved in both voltage and current-handling capacity, vacuum devices have been nearly entirely replaced by solid-state devices.

Power electronic devices may be used as switches, or as amplifiers. An ideal switch is either open or closed and so dissipates no power; it withstands an applied voltage and passes no current, or passes any amount of current with no voltage drop. Semiconductor devices used as switches can approximate this ideal property and so most power electronic applications rely on switching devices on and off, which makes systems very efficient as very little power is wasted in the switch. By contrast, in the case of the amplifier, the current through the device varies continuously according to a controlled input. The voltage and current at the device terminals follow a load line, and the power dissipation inside the device is large compared with the power delivered to the load.

Several attributes dictate how devices are used. Devices such as diodes conduct when a forward voltage is applied and have no external control of the start of conduction. Power devices such as silicon controlled rectifiers and thyristors (as well as the mercury valve and thyratron) allow control of the start of conduction, but rely on periodic reversal of current flow to turn them off. Devices such as gate turn-off thyristors, BJT and MOSFET transistors provide full switching control and can be turned on or off without regard to the current flow through them. Transistor devices also allow proportional amplification, but this is rarely used for systems rated more than a few hundred watts. The control input characteristics of a device also greatly affect design; sometimes the control input is at a very high voltage with respect to ground and must be driven by an isolated source.

As efficiency is at a premium in a power electronic converter, the losses that a power electronic device generates should be as low as possible.

Devices vary in switching speed. Some diodes and thyristors are suited for relatively slow speed and are useful for power frequency switching and control; certain thyristors are useful at a few kilohertz. Devices such as MOSFETS and BJTs can switch at tens of kilohertz up to a few megahertz in power applications, but with decreasing power levels. Vacuum tube devices dominate high power (hundreds of kilowatts) at very high frequency (hundreds or thousands of megahertz) applications. Faster switching devices minimize energy lost in the transitions from on to off and back, but may create problems with radiated electromagnetic interference. Gate drive (or equivalent) circuits must be designed to supply sufficient drive current to achieve the full switching speed possible with a device. A device without sufficient drive to switch rapidly may be destroyed by excess heating.

Practical devices have non-zero voltage drop and dissipate power when on, and take some time to pass through an active region until they reach the "on" or "off" state. These losses are a significant part of the total lost power in a converter.

Power handling and dissipation of devices is also a critical factor in design. Power electronic devices may have to dissipate tens or hundreds of watts of waste heat, even switching as efficiently as possible between conducting and non-conducting states. In the switching mode, the power controlled is much larger than the power dissipated in the switch. The forward voltage drop in the conducting state translates into heat that must be dissipated. High power semiconductors require specialized heat sinks or active cooling systems to manage their junction temperature; exotic semiconductors such as silicon carbide have an advantage over straight silicon in this respect, and germanium, once the main-stay of solid-state electronics is now little used due to its unfavorable high temperature properties.

Semiconductor devices exist with ratings up to a few kilovolts in a single device. Where very high voltage must be controlled, multiple devices must be used in series, with networks to equalize voltage across all devices. Again, switching speed is a critical factor since the slowest-switching device will have to withstand a disproportionate share of the overall voltage. Mercury valves were once available with ratings to 100 kV in a single unit, simplifying their application in HVDC systems.

The current rating of a semiconductor device is limited by the heat generated within the dies and the heat developed in the resistance of the interconnecting leads. Semiconductor devices must be designed so that current is evenly distributed within the device across its internal junctions (or channels); once a "hot spot" develops, breakdown effects can rapidly destroy the device. Certain SCRs are available with current ratings to 3000 amperes in a single unit.

Solid-state devices

Device Description Ratings

Diode Uni-polar, uncontrolled, switching device used in applications such as rectification and circuit directional current control. Reverse voltage blocking device, commonly modeled as a switch in series with a voltage source, usually 0.7 VDC. The model can be enhanced to include a junction resistance, in order to accurately predict the diode voltage drop across the diode with respect to current flow. Up to 3000 amperes and 5000 volts in a single silicon device. High voltage requires multiple series silicon devices.
Silicon-controlled rectifier (SCR) This semi-controlled device turns on when a gate pulse is present and the anode is positive compared to the cathode. When a gate pulse is present, the device operates like a standard diode. When the anode is negative compared to the cathode, the device turns off and blocks positive or negative voltages present. The gate voltage does not allow the device to turn off.[4] Up to 3000 amperes, 5000 volts in a single silicon device.
Thyristor The thyristor is a family of three-terminal devices that include SCRs, GTOs, and MCT. For most of the devices, a gate pulse turns the device on. The device turns off when the anode voltage falls below a value (relative to the cathode) determined by the device characteristics. When off, it is considered a reverse voltage blocking device.
Gate turn-off thyristor (GTO) The gate turn-off thyristor, unlike an SCR, can be turned on and off with a gate pulse. One issue with the device is that turn off gate voltages are usually larger and require more current than turn on levels. This turn off voltage is a negative voltage from gate to source, usually it only needs to be present for a short time, but the magnitude s on the order of 1/3 of the anode current. A snubber circuit is required in order to provide a usable switching curve for this device. Without the snubber circuit, the GTO cannot be used for turning inductive loads off. These devices, because of developments in IGCT technology are not very popular in the power electronics realm. They are considered controlled, uni-polar and bi-polar voltage blocking.
Triac The triac is a device that is essentially an integrated pair of phase-controlled thyristors connected in inverse-parallel on the same chip. Like an SCR, when a voltage pulse is present on the gate terminal, the device turns on. The main difference between an SCR and a Triac is that both the positive and negative cycle can be turned on independently of each other, using a positive or negative gate pulse. Similar to an SCR, once the device is turned on, the device cannot be turned off. This device is considered bi-polar and reverse voltage blocking.
Bipolar junction transistor (BJT) The BJT cannot be used at high power; they are slower and have more resistive losses when compared to MOSFET type devices. To carry high current, BJTs must have relatively large base currents, thus these devices have high power losses when compared to MOSFET devices. BJTs along with MOSFETs, are also considered unipolar and do not block reverse voltage very well, unless installed in pairs with protection diodes. Generally, BJTs are not utilized in power electronics switching circuits because of the I2R losses associated with on resistance and base current requirements. BJTs have lower current gains in high power packages, thus requiring them to be set up in Darlington configurations in order to handle the currents required by power electronic circuits. Because of these multiple transistor configurations, switching times are in the hundreds of nanoseconds to microseconds. Devices have voltage ratings which max out around 1500 V and fairly high current ratings. They can also be paralleled in order to increase power handling, but must be limited to around 5 devices for current sharing.
Power MOSFET The main benefit of the power MOSFET is that the base current for BJT is large compared to almost zero for MOSFET gate current. Since the MOSFET is a depletion channel device, voltage, not current, is necessary to create a conduction path from drain to source. The gate does not contribute to either drain or source current. Turn on gate current is essentially zero with the only power dissipated at the gate coming during switching. Losses in MOSFETs are largely attributed to on-resistance. The calculations show a direct correlation to drain source on-resistance and the device blocking voltage rating, BVdss.
Switching times range from tens of nanoseconds to a few hundred microseconds, depending on the device. MOSFET drain source resistances increase as more current flows through the device. As frequencies increase the losses increase as well, making BJTs more attractive. Power MOSFETs can be paralleled in order to increase switching current and therefore overall switching power. Nominal voltages for MOSFET switching devices range from a few volts to a little over 1000 V, with currents up to about 100 A or so. Newer devices may have higher operational characteristics. MOSFET devices are not bi-directional, nor are they reverse voltage blocking.

Insulated-gate bipolar transistor (IGBT) These devices have the best characteristics of MOSFETs and BJTs. Like MOSFET devices, the insulated gate bipolar transistor has a high gate impedance, thus low gate current requirements. Like BJTs, this device has low on state voltage drop, thus low power loss across the switch in operating mode. Similar to the GTO, the IGBT can be used to block both positive and negative voltages. Operating currents are fairly high, in excess of 1500 A and switching voltage up to 3000 V. The IGBT has reduced input capacitance compared to MOSFET devices which improves the Miller feedback effect during high dv/dt turn on and turn off.[6]
MOS-controlled thyristor (MCT) The MOS-controlled thyristor is thyristor like and can be triggered on or off by a pulse to the MOSFET gate.[6] Since the input is MOS technology, there is very little current flow, allowing for very low power control signals. The device is constructed with two MOSFET inputs and a pair of BJT output stages. Input MOSFETs are configured to allow turn on control during positive and negative half cycles. The output BJTs are configured to allow for bidirectional control and low voltage reverse blocking. Some benefits to the MCT are fast switching frequencies, fairly high voltage and medium current ratings (around 100 A or so).
Integrated gate-commutated thyristor (IGCT) Similar to a GTO, but without the high current requirements to turn on or off the load. The IGCT can be used for quick switching with little gate current. The devices high input impedance largely because of the MOSFET gate drivers. They have low resistance outputs that don't waste power and very fast transient times that rival that of BJTs. ABB Group company has published data sheets for these devices and provided descriptions of the inner workings. The device consists of a gate, with an optically isolated input, low on resistance BJT output transistors which lead to a low voltage drop and low power loss across the device at fairly high switching voltage and current levels.
An example of this new device from ABB shows how this device improves on GTO technology for switching high voltage and high current in power electronics applications. According to ABB, the IGCT devices are capable of switching in excess of 5000 VAC and 5000 A at very high frequencies, something not possible to do efficiently with GTO devices.

DC/AC converters (inverters)

DC to AC converters produce an AC output waveform from a DC source. Applications include adjustable speed drives (ASD), uninterruptable power supplies (UPS), active filters, Flexible AC transmission systems (FACTS), voltage compensators, and photovoltaic generators. Topologies for these converters can be separated into two distinct categories: voltage source inverters and current source inverters. Voltage source inverters (VSIs) are named so because the independently controlled output is a voltage waveform. Similarly, current source inverters (CSIs) are distinct in that the controlled AC output is a current waveform.

Being static power converters, the DC to AC power conversion is the result of power switching devices, which are commonly fully controllable semiconductor power switches. The output waveforms are therefore made up of discrete values, producing fast transitions rather than smooth ones. The ability to produce near sinusoidal waveforms around the fundamental frequency is dictated by the modulation technique controlling when, and for how long, the power valves are on and off. Common modulation techniques include the carrier-based technique, or Pulse-width modulation, space-vector technique, and the selective-harmonic technique.

Voltage source inverters have practical uses in both single-phase and three-phase applications. Single-phase VSIs utilize half-bridge and full-bridge configurations, and are widely used for power supplies, single-phase UPSs, and elaborate high-power topologies when used in multicell configurations. Three-phase VSIs are used in applications that require sinusoidal voltage waveforms, such as ASDs, UPSs, and some types of FACTS devices such as the STATCOM. They are also used in applications where arbitrary voltages are required as in the case of active filters and voltage compensators.

Current source inverters are used to produce an AC output current from a DC current supply. This type of inverter is practical for three-phase applications in which high-quality voltage waveforms are required.

A relatively new class of inverters, called multilevel inverters, has gained widespread interest. Normal operation of CSIs and VSIs can be classified as two-level inverters, due to the fact that power switches connect to either the positive or to the negative DC bus. If more than two voltage levels were available to the inverter output terminals, the AC output could better approximate a sine wave. It is for this reason that multilevel inverters, although more complex and costly, offer higher performance.

Each inverter type differs in the DC links used, and in whether or not they require freewheeling diodes. Either can be made to operate in square-wave or pulse-width modulation (PWM) mode, depending on its intended usage. Square-wave mode offers simplicity, while PWM can be implemented several different ways and produces higher quality waveforms.

Voltage Source Inverters (VSI) feed the output inverter section from an approximately constant-voltage source.

The desired quality of the current output waveform determines which modulation technique needs to be selected for a given application. The output of a VSI is composed of discrete values. In order to obtain a smooth current waveform, the loads need to be inductive at the select harmonic frequencies. Without some sort of inductive filtering between the source and load, a capacitive load will cause the load to receive a choppy current waveform, with large and frequent current spikes.

There are three main types of VSIs:

Single-phase half-bridge inverter
Single-phase full-bridge inverter
Three-phase voltage source inverter

Single-phase half bridge inverter

The single-phase voltage source half-bridge inverters, are meant for lower voltage applications and are commonly used in power supplieshalf-bridge inverter

Low-order current harmonics get injected back to the source voltage by the operation of the inverter. This means that two large capacitors are needed for filtering purposes in this design.
Inverters can use several modulation techniques to control their switching schemes. The carrier-based PWM technique compares the AC output waveform, vc, to a carrier voltage signal, vΔ. When vc is greater than vΔ, S+ is on, and when vc is less than vΔ, S- is on. When the AC output is at frequency fc with its amplitude at vc, and the triangular carrier signal is at frequency fΔ with its amplitude at vΔ, the PWM becomes a special sinusoidal case of the carrier based PWM.This case is dubbed sinusoidal pulse-width modulation (SPWM).For this, the modulation index, or amplitude-modulation ratio, is defined as ma = vc/v∆ .

The normalized carrier frequency, or frequency-modulation ratio, is calculated using the equation mf = f∆/fc .

If the over-modulation region, ma, exceeds one, a higher fundamental AC output voltage will be observed, but at the cost of saturation. For SPWM, the harmonics of the output waveform are at well-defined frequencies and amplitudes. This simplifies the design of the filtering components needed for the low-order current harmonic injection from the operation of the inverter. The maximum output amplitude in this mode of operation is half of the source voltage. If the maximum output amplitude, ma, exceeds 3.24, the output waveform of the inverter becomes a square wave.

As was true for PWM, both switches in a leg for square wave modulation cannot be turned on at the same time, as this would cause a short across the voltage source. The switching scheme requires that both S+ and S- be on for a half cycle of the AC output period. The fundamental AC output amplitude is equal to vo1 = vaN = 2vi/π .

Its harmonics have an amplitude of voh = vo1/h.

Therefore, the AC output voltage is not controlled by the inverter, but rather by the magnitude of the DC input voltage of the inverter.

Using selective harmonic elimination (SHE) as a modulation technique allows the switching of the inverter to selectively eliminate intrinsic harmonics. The fundamental component of the AC output voltage can also be adjusted within a desirable range. Since the AC output voltage obtained from this modulation technique has odd half and odd quarter wave symmetry, even harmonics do not exist. Any undesirable odd (N-1) intrinsic harmonics from the output waveform can be eliminated.

Single-phase full-bridge inverter

 Carrier and Modulating Signals for the Bipolar Pulsewidth Modulation Technique
The full-bridge inverter is similar to the half bridge-inverter, but it has an additional leg to connect the neutral point to the load.
To avoid shorting out the voltage source, S1+ and S1- cannot be on at the same time, and S2+ and S2- also cannot be on at the same time. Any modulating technique used for the full-bridge configuration should have either the top or the bottom switch of each leg on at any given time. Due to the extra leg, the maximum amplitude of the output waveform is Vi, and is twice as large as the maximum achievable output amplitude for the half-bridge configuration.

States 1 and 2 from Table 2 are used to generate the AC output voltage with bipolar SPWM. The AC output voltage can take on only two values, either Vi or –Vi. To generate these same states using a half-bridge configuration, a carrier based technique can be used. S+ being on for the half-bridge corresponds to S1+ and S2- being on for the full-bridge. Similarly, S- being on for the half-bridge corresponds to S1- and S2+ being on for the full bridge. The output voltage for this modulation technique is more or less sinusoidal, with a fundamental component that has an amplitude in the linear region of less than or equal to one[8] vo1 =vab1= vi • ma.

Unlike the bipolar PWM technique, the unipolar approach uses states 1, 2, 3 and 4 from Table 2 to generate its AC output voltage. Therefore, the AC output voltage can take on the values Vi, 0 or –V . To generate these states, two sinusoidal modulating signals, Vc and –Vc, are needed.

Vc is used to generate VaN, while –Vc is used to generate VbN. The following relationship is called unipolar carrier-based SPWM vo1 =2 • vaN1= vi • ma.

The phase voltages VaN and VbN are identical, but 180 degrees out of phase with each other. The output voltage is equal to the difference of the two phase voltages, and do not contain any even harmonics. Therefore, if mf is taken, even the AC output voltage harmonics will appear at normalized odd frequencies, fh. These frequencies are centered on double the value of the normalized carrier frequency. This particular feature allows for smaller filtering components when trying to obtain a higher quality output waveform.

As was the case for the half-bridge SHE, the AC output voltage contains no even harmonics due to its odd half and odd quarter wave symmetry.

Three-phase voltage source inverter

 Three-Phase Square-Wave Operation a) Switch State S1 b) Switch State S3 c) S1 Output d) S3 Output
Single-phase VSIs are used primarily for low power range applications, while three-phase VSIs cover both medium and high power range applications.
Switches in any of the three legs of the inverter cannot be switched off simultaneously due to this resulting in the voltages being dependent on the respective line current's polarity. States 7 and 8 produce zero AC line voltages, which result in AC line currents freewheeling through either the upper or the lower components. However, the line voltages for states 1 through 6 produce an AC line voltage consisting of the discrete values of Vi, 0 or –Vi.

For three-phase SPWM, three modulating signals that are 120 degrees out of phase with one another are used in order to produce out of phase load voltages. In order to preserve the PWM features with a single carrier signal, the normalized carrier frequency, mf, needs to be a multiple of three. This keeps the magnitude of the phase voltages identical, but out of phase with each other by 120 degrees.The maximum achievable phase voltage amplitude in the linear region, ma less than or equal to one, is vphase = vi / 2. The maximum achievable line voltage amplitude is Vab1 = vab • √3 / 2

The only way to control the load voltage is by changing the input DC voltage.

Current source inverters

 Synchronized-Pulse-Width-Modulation Waveforms for a Three-Phase Current Source Inverter a) Carrier and Modulating Signals b) S1 State c) S3 State d) Output Current

Current source inverters convert DC current into an AC current waveform. In applications requiring sinusoidal AC waveforms, magnitude, frequency, and phase should all be controlled. CSIs have high changes in current overtime, so capacitors are commonly employed on the AC side, while inductors are commonly employed on the DC side. Due to the absence of freewheeling diodes, the power circuit is reduced in size and weight, and tends to be more reliable than VSIs. Although single-phase topologies are possible, three-phase CSIs are more practical.

In its most generalized form, a three-phase CSI employs the same conduction sequence as a six-pulse rectifier. At any time, only one common-cathode switch and one common-anode switch are on.

As a result, line currents take discrete values of –ii, 0 and ii. States are chosen such that a desired waveform is outputted and only valid states are used. This selection is based on modulating techniques, which include carrier-based PWM, selective harmonic elimination, and space-vector techniques.

Carrier-based techniques used for VSIs can also be implemented for CSIs, resulting in CSI line currents that behave in the same way as VSI line voltages. The digital circuit utilized for modulating signals contains a switching pulse generator, a shorting pulse generator, a shorting pulse distributor, and a switching and shorting pulse combiner. A gating signal is produced based on a carrier current and three modulating signals.

A shorting pulse is added to this signal when no top switches and no bottom switches are gated, causing the RMS currents to be equal in all legs. The same methods are utilized for each phase, however, switching variables are 120 degrees out of phase relative to one another, and the current pulses are shifted by a half-cycle with respect to output currents. If a triangular carrier is used with sinusoidal modulating signals, the CSI is said to be utilizing synchronized-pulse-width-modulation (SPWM). If full over-modulation is used in conjunction with SPWM the inverter is said to be in square-wave operation.

The second CSI modulation category, SHE is also similar to its VSI counterpart. Utilizing the gating signals developed for a VSI and a set of synchronizing sinusoidal current signals, results in symmetrically distributed shorting pulses and, therefore, symmetrical gating patterns. This allows any arbitrary number of harmonics to be eliminated. It also allows control of the fundamental line current through the proper selection of primary switching angles. Optimal switching patterns must have quarter-wave and half-wave symmetry, as well as symmetry about 30 degrees and 150 degrees. Switching patterns are never allowed between 60 degrees and 120 degrees. The current ripple can be further reduced with the use of larger output capacitors, or by increasing the number of switching pulses.

The third category, space-vector-based modulation, generates PWM load line currents that equal load line currents, on average. Valid switching states and time selections are made digitally based on space vector transformation. Modulating signals are represented as a complex vector using a transformation equation. For balanced three-phase sinusoidal signals, this vector becomes a fixed module, which rotates at a frequency, ω. These space vectors are then used to approximate the modulating signal. If the signal is between arbitrary vectors, the vectors are combined with the zero vectors I7, I8, or I9.[8] The following equations are used to ensure that the generated currents and the current vectors are on average equivalent.

Multilevel inverters

FIGURE 10: Three-Level Neutral-Clamped Inverter
A relatively new class called multilevel inverters has gained widespread interest. Normal operation of CSIs and VSIs can be classified as two-level inverters because the power switches connect to either the positive or the negative DC bus.[9] If more than two voltage levels were available to the inverter output terminals, the AC output could better approximate a sine wave.[8] For this reason multilevel inverters, although more complex and costly, offer higher performance.[9] A three-level neutral-clamped inverter is shown in Figure 10.

Control methods for a three-level inverter only allow two switches of the four switches in each leg to simultaneously change conduction states. This allows smooth commutation and avoids shoot through by only selecting valid states.[9] It may also be noted that since the DC bus voltage is shared by at least two power valves, their voltage ratings can be less than a two-level counterpart.

Carrier-based and space-vector modulation techniques are used for multilevel topologies. The methods for these techniques follow those of classic inverters, but with added complexity. Space-vector modulation offers a greater number of fixed voltage vectors to be used in approximating the modulation signal, and therefore allows more effective space vector PWM strategies to be accomplished at the cost of more elaborate algorithms. Due to added complexity and number of semiconductor devices, multilevel inverters are currently more suitable for high-power high-voltage applications.[9] This technology reduces the harmonics hence improves overall efficiency of the scheme.

Protective devices and power systems in practice?

Protective devices

Introduction

Power systems contain protective devices to prevent injury or damage during failures. The quintessential protective device is the fuse. When the current through a fuse exceeds a certain threshold, the fuse element melts, producing an arc across the resulting gap that is then extinguished, interrupting the circuit. Given that fuses can be built as the weak point of a system, fuses are ideal for protecting circuitry from damage. Fuses however have two problems: First, after they have functioned, fuses must be replaced as they cannot be reset. This can prove inconvenient if the fuse is at a remote site or a spare fuse is not on hand. And second, fuses are typically inadequate as the sole safety device in most power systems as they allow current flows well in excess of that that would prove lethal to a human or animal.

Fuse plus circuit breaker

The first problem is resolved by the use of circuit breakers—devices that can be reset after they have broken current flow. In modern systems that use less than about 10 kW, miniature circuit breakers are typically used. These devices combine the mechanism that initiates the trip (by sensing excess current) as well as the mechanism that breaks the current flow in a single unit. Some miniature circuit breakers operate solely on the basis of electromagnetism. In these miniature circuit breakers, the current is run through a solenoid, and, in the event of excess current flow, the magnetic pull of the solenoid is sufficient to force open the circuit breaker's contacts (often indirectly through a tripping mechanism). A better design however arises by inserting a bimetallic strip before the solenoid—this means that instead of always producing a magnetic force, the solenoid only produces a magnetic force when the current is strong enough to deform the bimetallic strip and complete the solenoid's circuit.

Relays

In higher powered applications, the protective relays that detect a fault and initiate a trip are separate from the circuit breaker. Early relays worked based upon electromagnetic principles similar to those mentioned in the previous paragraph, modern relays are application-specific computers that determine whether to trip based upon readings from the power system. Different relays will initiate trips depending upon different protection schemes. For example, an overcurrent relay might initiate a trip if the current on any phase exceeds a certain threshold whereas a set of differential relays might initiate a trip if the sum of currents between them indicates there may be current leaking to earth. The circuit breakers in higher powered applications are different too. Air is typically no longer sufficient to quench the arc that forms when the contacts are forced open so a variety of techniques are used. One of the most popular techniques is to keep the chamber enclosing the contacts flooded with sulfur hexafluoride (SF6)—a non-toxic gas that has sound arc-quenching properties. Other techniques are discussed in the reference.

Residual current devices

The second problem, the inadequacy of fuses to act as the sole safety device in most power systems, is probably best resolved by the use of residual current devices (RCDs). In any properly functioning electrical appliance the current flowing into the appliance on the active line should equal the current flowing out of the appliance on the neutral line. A residual current device works by monitoring the active and neutral lines and tripping the active line if it notices a difference. Residual current devices require a separate neutral line for each phase and to be able to trip within a time frame before harm occurs. This is typically not a problem in most residential applications where standard wiring provides an active and neutral line for each appliance (that's why your power plugs always have at least two tongs) and the voltages are relatively low however these issues do limit the effectiveness of RCDs in other applications such as industry. Even with the installation of an RCD, exposure to electricity can still prove lethal.

SCADA systemsST

In large electric power systems, Supervisory Control And Data Acquisition (SCADA) is used for tasks such as switching on generators, controlling generator output and switching in or out system elements for maintenance. The first supervisory control systems implemented consisted of a panel of lamps and switches at a central console near the controlled plant. The lamps provided feedback on the state of plant (the data acquisition function) and the switches allowed adjustments to the plant to be made (the supervisory control function). Today, SCADA systems are much more sophisticated and, due to advances in communication systems, the consoles controlling the plant no longer need to be near the plant itself. Instead it is now common for plants to be controlled with equipment similar (if not identical) to a desktop computer. The ability to control such plants through computers has increased the need for security—there have already been reports of cyber-attacks on such systems causing significant disruptions to power systems.

Power systems in practice

Despite their common components, power systems vary widely both with respect to their design and how they operate. This section introduces some common power system types and briefly explains their operation.

Residential power system

Residential dwellings almost always take supply from the low voltage distribution lines or cables that run past the dwelling. These operate at voltages of between 110 and 260 volts (phase-to-earth) depending upon national standards. A few decades ago small dwellings would be fed a single phase using a dedicated two-core service cable (one core for the active phase and one core for the neutral return). The active line would then be run through a main isolating switch in the fuse box and then split into one or more circuits to feed lighting and appliances inside the house. By convention, the lighting and appliance circuits are kept separate so the failure of an appliance does not leave the dwelling's occupants in the dark. All circuits would be fused with an appropriate fuse based upon the wire size used for that circuit. Circuits would have both an active and neutral wire with both the lighting and power sockets being connected in parallel. Sockets would also be provided with a protective earth. This would be made available to appliances to connect to any metallic casing. If this casing were to become live, the theory is the connection to earth would cause an RCD or fuse to trip—thus preventing the future electrocution of an occupant handling the appliance. Earthing systems vary between regions, but in countries such as the United Kingdom and Australia both the protective earth and neutral line would be earthed together near the fuse box before the main isolating switch and the neutral earthed once again back at the distribution transformer.

There have been a number of minor changes over the year to practice of residential wiring. Some of the most significant ways modern residential power systems tend to vary from older ones include:

For convenience, miniature circuit breakers are now almost always used in the fuse box instead of fuses as these can easily be reset by occupants.

For safety reasons, RCDs are now installed on appliance circuits and, increasingly, even on lighting circuits.

Dwellings are typically connected to all three-phases of the distribution system with the phases being arbitrarily allocated to the house's single-phase circuits.

Whereas air conditioners of the past might have been fed from a dedicated circuit attached to a single phase, centralised air conditioners that require three-phase power are now becoming common.

Protective earths are now run with lighting circuits to allow for metallic lamp holders to be earthed.

Increasingly residential power systems are incorporating microgenerators, most notably, photovoltaic cells.

Commercial power systems

Commercial power systems such as shopping centers or high-rise buildings are larger in scale than residential systems. Electrical designs for larger commercial systems are usually studied for load flow, short-circuit fault levels, and voltage drop for steady-state loads and during starting of large motors. The objectives of the studies are to assure proper equipment and conductor sizing, and to coordinate protective devices so that minimal disruption is cause when a fault is cleared. Large commercial installations will have an orderly system of sub-panels, separate from the main distribution board to allow for better system protection and more efficient electrical installation.

Typically one of the largest appliances connected to a commercial power system is the HVAC unit, and ensuring this unit is adequately supplied is an important consideration in commercial power systems. Regulations for commercial establishments place other requirements on commercial systems that are not placed on residential systems. For example, in Australia, commercial systems must comply with AS 2293, the standard for emergency lighting, which requires emergency lighting be maintained for at least 90 minutes in the event of loss of mains supply. In the United States, the National Electrical Code requires commercial systems to be built with at least one 20A sign outlet in order to light outdoor signage. Building code regulations may place special requirements on the electrical system for emergency lighting, evacuation, emergency power, smoke control and fire protection.

Components of electrical engineering?

Definition of electrical engineering

Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics, and electromagnetism. This field first became an identifiable occupation in the later half of the 19th century after commercialization of the electric telegraph, the telephone, and electric power distribution and use. Subsequently, broadcasting and recording media made electronics part of daily life. The invention of the transistor, and later the integrated circuit, brought down the cost of electronics to the point they can be used in almost any household object.

Electrical engineering has now subdivided into a wide range of subfields including electronics, digital computers, power engineering, telecommunications, control systems, radio-frequency engineering, signal processing, instrumentation, and microelectronics. Many of these subdisciplines overlap and also overlap with other engineering branches, spanning a huge number of specializations such as hardware engineering, power electronics, electromagnetics & waves, microwave engineering, nanotechnology, electrochemistry, renewable energies, mechatronics, electrical materials science, and many more.

Electrical engineers typically hold a degree in electrical engineering or electronic engineering. Practicing engineers may have professional certification and be members of a professional body. Such bodies include the Institute of Electrical and Electronics Engineers (IEEE) and the Institution of Engineering and Technology (professional society) (IET).

Electrical engineers work in a very wide range of industries and the skills required are likewise variable. These range from basic circuit theory to the management skills required of a project manager. The tools and equipment that an individual engineer may need are similarly variable, ranging from a simple voltmeter to a top end analyzer to sophisticated design and manufacturing software.

More modern developments

Guglielmo Marconi known for his pioneering work on long distance radio transmission
During the development of radio, many scientists and inventors contributed to radio technology and electronics. The mathematical work of James Clerk Maxwell during the 1850s had shown the relationship of different forms of electromagnetic radiation including possibility of invisible airborne waves (later called "radio waves"). In his classic physics experiments of 1888, Heinrich Hertz proved Maxwell's theory by transmitting radio waves with a spark-gap transmitter, and detected them by using simple electrical devices. Other physicists experimented with these new waves and in the process developed devices for transmitting and detecting them. In 1895, Guglielmo Marconi began work on a way to adapt the known methods of transmitting and detecting these "Hertzian waves" into a purpose built commercial wireless telegraphic system. Early on, he sent wireless signals over a distance of one and a half miles. In December 1901, he sent wireless waves that were not affected by the curvature of the Earth. Marconi later transmitted the wireless signals across the Atlantic between Poldhu, Cornwall, and St. John's, Newfoundland, a distance of 2,100 miles (3,400 km).

In 1897, Karl Ferdinand Braun introduced the cathode ray tube as part of an oscilloscope, a crucial enabling technology for electronic television. John Fleming invented the first radio tube, the diode, in 1904. Two years later, Robert von Lieben and Lee De Forest independently developed the amplifier tube, called the triode.

In 1920, Albert Hull developed the magnetron which would eventually lead to the development of the microwave oven in 1946 by Percy Spencer. In 1934, the British military began to make strides toward radar (which also uses the magnetron) under the direction of Dr Wimperis, culminating in the operation of the first radar station at Bawdsey in August 1936.

A replica of the first working transistor.

In 1941, Konrad Zuse presented the Z3, the world's first fully functional and programmable computer using electromechanical parts. In 1943, Tommy Flowers designed and built the Colossus, the world's first fully functional, electronic, digital and programmable computer. In 1946, the ENIAC (Electronic Numerical Integrator and Computer) of John Presper Eckert and John Mauchly followed, beginning the computing era. The arithmetic performance of these machines allowed engineers to develop completely new technologies and achieve new objectives, including the Apollo program which culminated in landing astronauts on the Moon.
Solid-state transistors
The invention of the transistor in late 1947 by William B. Shockley, John Bardeen, and Walter Brattain of the Bell Telephone Laboratories opened the door for more compact devices and led to the development of the integrated circuit in 1958 by Jack Kilby and independently in 1959 by Robert Noyce. Starting in 1968, Ted Hoff and a team at the Intel Corporation invented the first commercial microprocessor, which foreshadowed the personal computer. The Intel 4004 was a four-bit processor released in 1971, but in 1973 the Intel 8080, an eight-bit processor, made the first personal computer, the Altair 8800, possible.

Subdisciplines

Electrical engineering has many subdisciplines, the most common of which are listed below. Although there are electrical engineers who focus exclusively on one of these subdisciplines, many deal with a combination of them. Sometimes certain fields, such as electronic engineering and computer engineering, are considered separate disciplines in their own right.

Power

Main article: Power engineering
Power pole

Power engineering deals with the generation, transmission, and distribution of electricity as well as the design of a range of related devices. These include transformers, electric generators, electric motors, high voltage engineering, and power electronics. In many regions of the world, governments maintain an electrical network called a power grid that connects a variety of generators together with users of their energy. Users purchase electrical energy from the grid, avoiding the costly exercise of having to generate their own. Power engineers may work on the design and maintenance of the power grid as well as the power systems that connect to it. Such systems are called on-grid power systems and may supply the grid with additional power, draw power from the grid, or do both. Power engineers may also work on systems that do not connect to the grid, called off-grid power systems, which in some cases are preferable to on-grid systems. The future includes Satellite controlled power systems, with feedback in real time to prevent power surges and prevent blackouts.

Control

Main article: Control engineering

Control systems play a critical role in spaceflight.
Control engineering focuses on the modeling of a diverse range of dynamic systems and the design of controllers that will cause these systems to behave in the desired manner. To implement such controllers, electrical engineers may use electronic circuits, digital signal processors, microcontrollers, and programmable logic controls (PLCs). Control engineering has a wide range of applications from the flight and propulsion systems of commercial airliners to the cruise control present in many modern automobiles. It also plays an important role in industrial automation.

Control engineers often utilize feedback when designing control systems. For example, in an automobile with cruise control the vehicle's speed is continuously monitored and fed back to the system which adjusts the motor's power output accordingly. Where there is regular feedback, control theory can be used to determine how the system responds to such feedback.

Electronics

Main article: Electronic engineering

Electronic components

Electronic engineering involves the design and testing of electronic circuits that use the properties of components such as resistors, capacitors, inductors, diodes, and transistors to achieve a particular functionality. The tuned circuit, which allows the user of a radio to filter out all but a single station, is just one example of such a circuit. Another example (of a pneumatic signal conditioner) is shown in the adjacent photograph.

Prior to the Second World War, the subject was commonly known as radio engineering and basically was restricted to aspects of communications and radar, commercial radio, and early television.Later, in post war years, as consumer devices began to be developed, the field grew to include modern television, audio systems, computers, and microprocessors. In the mid-to-late 1950s, the term radio engineering gradually gave way to the name electronic engineering.

Before the invention of the integrated circuit in 1959, electronic circuits were constructed from discrete components that could be manipulated by humans. These discrete circuits consumed much space and power and were limited in speed, although they are still common in some applications. By contrast, integrated circuits packed a large number—often millions—of tiny electrical components, mainly transistors, into a small chip around the size of a coin. This allowed for the powerful computers and other electronic devices we see today.

Microelectronics

Main article: Microelectronics

Microprocessor

Microelectronics engineering deals with the design and microfabrication of very small electronic circuit components for use in an integrated circuit or sometimes for use on their own as a general electronic component. The most common microelectronic components are semiconductor transistors, although all main electronic components (resistors, capacitors etc.) can be created at a microscopic level. Nanoelectronics is the further scaling of devices down to nanometer levels. Modern devices are already in the nanometer regime, with below 100 nm processing having been standard since about 2002.

Microelectronic components are created by chemically fabricating wafers of semiconductors such as silicon (at higher frequencies, compound semiconductors like gallium arsenide and indium phosphide) to obtain the desired transport of electronic charge and control of current. The field of microelectronics involves a significant amount of chemistry and material science and requires the electronic engineer working in the field to have a very good working knowledge of the effects of quantum mechanics.

Signal processing

Main article: Signal processing

A Bayer filter on a CCD requires signal processing to get a red, green, and blue value at each pixel.
Signal processing deals with the analysis and manipulation of signals. Signals can be either analog, in which case the signal varies continuously according to the information, or digital, in which case the signal varies according to a series of discrete values representing the information. For analog signals, signal processing may involve the amplification and filtering of audio signals for audio equipment or the modulation and demodulation of signals for telecommunications. For digital signals, signal processing may involve the compression, error detection and error correction of digitally sampled signals.

Signal Processing is a very mathematically oriented and intensive area forming the core of digital signal processing and it is rapidly expanding with new applications in every field of electrical engineering such as communications, control, radar, audio engineering, broadcast engineering, power electronics, and biomedical engineering as many already existing analog systems are replaced with their digital counterparts. Analog signal processing is still important in the design of many control systems.

DSP processor ICs are found in every type of modern electronic systems and products including, SDTV | HDTV sets, radios and mobile communication devices, Hi-Fi audio equipment, Dolby noise reduction algorithms, GSM mobile phones, mp3 multimedia players, camcorders and digital cameras, automobile control systems, noise cancelling headphones, digital spectrum analyzers, intelligent missile guidance, radar, GPS based cruise control systems, and all kinds of image processing, video processing, audio processing, and speech processing systems.

Telecommunications

Main article: Telecommunications engineering

Satellite dishes are a crucial component in the analysis of satellite information.
Telecommunications engineering focuses on the transmission of information across a channel such as a coax cable, optical fiber or free space. Transmissions across free space require information to be encoded in a carrier signal to shift the information to a carrier frequency suitable for transmission; this is known as modulation. Popular analog modulation techniques include amplitude modulation and frequency modulation. The choice of modulation affects the cost and performance of a system and these two factors must be balanced carefully by the engineer.

Once the transmission characteristics of a system are determined, telecommunication engineers design the transmitters and receivers needed for such systems. These two are sometimes combined to form a two-way communication device known as a transceiver. A key consideration in the design of transmitters is their power consumption as this is closely related to their signal strength. If the signal strength of a transmitter is insufficient the signal's information will be corrupted by noise.

Instrumentation

Main article: Instrumentation engineering

Flight instruments provide pilots with the tools to control aircraft analytically.
Instrumentation engineering deals with the design of devices to measure physical quantities such as pressure, flow, and temperature. The design of such instrumentation requires a good understanding of physics that often extends beyond electromagnetic theory. For example, flight instruments measure variables such as wind speed and altitude to enable pilots the control of aircraft analytically. Similarly, thermocouples use the Peltier-Seebeck effect to measure the temperature difference between two points.

Often instrumentation is not used by itself, but instead as the sensors of larger electrical systems. For example, a thermocouple might be used to help ensure a furnace's temperature remains constant.For this reason, instrumentation engineering is often viewed as the counterpart of control engineering.

Computers

Main article: Computer engineering

Supercomputers are used in fields as diverse as computational biology and geographic information systems.
Computer engineering deals with the design of computers and computer systems. This may involve the design of new hardware, the design of PDAs, tablets, and supercomputers, or the use of computers to control an industrial plant. Computer engineers may also work on a system's software. However, the design of complex software systems is often the domain of software engineering, which is usually considered a separate discipline. Desktop computers represent a tiny fraction of the devices a computer engineer might work on, as computer-like architectures are now found in a range of devices including video game consoles and DVD players.

Related disciplines

The Bird VIP Infant ventilator
Mechatronics is an engineering discipline which deals with the convergence of electrical and mechanical systems. Such combined systems are known as electromechanical systems and have widespread adoption. Examples include automated manufacturing systems, heating, ventilation and air-conditioning systems, and various subsystems of aircraft and automobiles.

The term mechatronics is typically used to refer to macroscopic systems but futurists have predicted the emergence of very small electromechanical devices. Already, such small devices, known as Microelectromechanical systems (MEMS), are used in automobiles to tell airbags when to deploy, in digital projectors to create sharper images, and in inkjet printers to create nozzles for high definition printing. In the future it is hoped the devices will help build tiny implantable medical devices and improve optical communication.

Biomedical engineering is another related discipline, concerned with the design of medical equipment. This includes fixed equipment such as ventilators, MRI scanners, and electrocardiograph monitors as well as mobile equipment such as cochlear implants, artificial pacemakers, and artificial hearts.

Aerospace engineering and robotics an example is the most recent electric propulsion and ion propulsion.

Education

Main article: Education and training of electrical and electronics engineers

Oscilloscope

Electrical engineers typically possess an academic degree with a major in electrical engineering, electronics engineering, electrical engineering technology, or electrical and electronic engineering. The same fundamental principles are taught in all programs, though emphasis may vary according to title. The length of study for such a degree is usually four or five years and the completed degree may be designated as a Bachelor of Science in Electrical/Electronics Engineering Technology, Bachelor of Engineering, Bachelor of Science, Bachelor of Technology, or Bachelor of Applied Science depending on the university. The bachelor's degree generally includes units covering physics, mathematics, computer science, project management, and a variety of topics in electrical engineering. Initially such topics cover most, if not all, of the subdisciplines of electrical engineering. At some schools, the students can then choose to emphasize one or more subdisciplines towards the end of their courses of study.

Typical electrical engineering diagram used as a troubleshooting tool
At many schools, electronic engineering is included as part of an electrical award, sometimes explicitly, such as a Bachelor of Engineering (Electrical and Electronic), but in others electrical and electronic engineering are both considered to be sufficiently broad and complex that separate degrees are offered.

Some electrical engineers choose to study for a postgraduate degree such as a Master of Engineering/Master of Science (M.Eng./M.Sc.), a Master of Engineering Management, a Doctor of Philosophy (Ph.D.) in Engineering, an Engineering Doctorate (Eng.D.), or an Engineer's degree. The master's and engineer's degrees may consist of either research, coursework or a mixture of the two. The Doctor of Philosophy and Engineering Doctorate degrees consist of a significant research component and are often viewed as the entry point to academia. In the United Kingdom and some other European countries, Master of Engineering is often considered to be an undergraduate degree of slightly longer duration than the Bachelor of Engineering rather than postgraduate.

Practicing engineers

Belgian electrical engineers inspecting the rotor of a 40,000 kilowatt turbine of the General Electric Company in New York City
In most countries, a bachelor's degree in engineering represents the first step towards professional certification and the degree program itself is certified by a professional body. After completing a certified degree program the engineer must satisfy a range of requirements (including work experience requirements) before being certified. Once certified the engineer is designated the title of Professional Engineer (in the United States, Canada and South Africa), Chartered Engineer or Incorporated Engineer (in India, Pakistan, the United Kingdom, Ireland and Zimbabwe), Chartered Professional Engineer (in Australia and New Zealand) or European Engineer (in much of the European Union).

The IEEE corporate office is on the 17th floor of 3 Park Avenue in New York City
The advantages of certification vary depending upon location. For example, in the United States and Canada "only a licensed engineer may seal engineering work for public and private clients". This requirement is enforced by state and provincial legislation such as Quebec's Engineers Act. In other countries, no such legislation exists. Practically all certifying bodies maintain a code of ethics that they expect all members to abide by or risk expulsion. In this way these organizations play an important role in maintaining ethical standards for the profession. Even in jurisdictions where certification has little or no legal bearing on work, engineers are subject to contract law. In cases where an engineer's work fails he or she may be subject to the tort of negligence and, in extreme cases, the charge of criminal negligence. An engineer's work must also comply with numerous other rules and regulations such as building codes and legislation pertaining to environmental law.

Professional bodies of note for electrical engineers include the Institute of Electrical and Electronics Engineers (IEEE) and the Institution of Engineering and Technology (IET). The IEEE claims to produce 30% of the world's literature in electrical engineering, has over 360,000 members worldwide and holds over 3,000 conferences annually. The IET publishes 21 journals, has a worldwide membership of over 150,000, and claims to be the largest professional engineering society in Europe. Obsolescence of technical skills is a serious concern for electrical engineers. Membership and participation in technical societies, regular reviews of periodicals in the field and a habit of continued learning are therefore essential to maintaining proficiency. An MIET(Member of the Institution of Engineering and Technology) is recognised in Europe as an Electrical and computer (technology) engineer.

In Australia, Canada, and the United States electrical engineers make up around 0.25% of the labor force.

Tools and work

From the Global Positioning System to electric power generation, electrical engineers have contributed to the development of a wide range of technologies. They design, develop, test, and supervise the deployment of electrical systems and electronic devices. For example, they may work on the design of telecommunication systems, the operation of electric power stations, the lighting and wiring of buildings, the design of household appliances, or the electrical control of industrial machinery.

Satellite communications is typical of what electrical engineers work on.
Fundamental to the discipline are the sciences of physics and mathematics as these help to obtain both a qualitative and quantitative description of how such systems will work. Today most engineering work involves the use of computers and it is commonplace to use computer-aided design programs when designing electrical systems. Nevertheless, the ability to sketch ideas is still invaluable for quickly communicating with others.

The Shadow robot hand system
Although most electrical engineers will understand basic circuit theory (that is the interactions of elements such as resistors, capacitors, diodes, transistors, and inductors in a circuit), the theories employed by engineers generally depend upon the work they do. For example, quantum mechanics and solid state physics might be relevant to an engineer working on VLSI (the design of integrated circuits), but are largely irrelevant to engineers working with macroscopic electrical systems. Even circuit theory may not be relevant to a person designing telecommunication systems that use off-the-shelf components. Perhaps the most important technical skills for electrical engineers are reflected in university programs, which emphasize strong numerical skills, computer literacy, and the ability to understand the technical language and concepts that relate to electrical engineering.

A laser bouncing down an acrylic rod, illustrating the total internal reflection of light in a multi-mode optical fiber.
A wide range of instrumentation is used by electrical engineers. For simple control circuits and alarms, a basic multimeter measuring voltage, current, and resistance may suffice. Where time-varying signals need to be studied, the oscilloscope is also an ubiquitous instrument. In RF engineering and high frequency telecommunications, spectrum analyzers and network analyzers are used. In some disciplines, safety can be a particular concern with instrumentation. For instance, medical electronics designers must take into account that much lower voltages than normal can be dangerous when electrodes are directly in contact with internal body fluids. Power transmission engineering also has great safety concerns due to the high voltages used; although voltmeters may in principle be similar to their low voltage equivalents, safety and calibration issues make them very different. Many disciplines of electrical engineering use tests specific to their discipline. Audio electronics engineers use audio test sets consisting of a signal generator and a meter, principally to measure level but also other parameters such as harmonic distortion and noise. Likewise, information technology have their own test sets, often specific to a particular data format, and the same is true of television broadcasting.

Radome at the Misawa Air Base Misawa Security Operations Center, Misawa, Japan
For many engineers, technical work accounts for only a fraction of the work they do. A lot of time may also be spent on tasks such as discussing proposals with clients, preparing budgets and determining project schedules.[76] Many senior engineers manage a team of technicians or other engineers and for this reason project management skills are important. Most engineering projects involve some form of documentation and strong written communication skills are therefore very important.

The workplaces of engineers are just as varied as the types of work they do. Electrical engineers may be found in the pristine lab environment of a fabrication plant, the offices of a consulting firm or on site at a mine. During their working life, electrical engineers may find themselves supervising a wide range of individuals including scientists, electricians, computer programmers, and other engineers.

Electrical engineering has an intimate relationship with the physical sciences. For instance, the physicist Lord Kelvin played a major role in the engineering of the first transatlantic telegraph cable. Conversely, the engineer Oliver Heaviside produced major work on the mathematics of transmission on telegraph cables. Electrical engineers are often required on major science projects. For instance, large particle accelerators such as CERN need electrical engineers to deal with many aspects of the project: from the power distribution, to the instrumentation, to the manufacture and installation of the superconducting electromagnets.Courtesy of wikipedia...