Sunday, February 28, 2010

Electrical Q & A



Why copper is called variable loss & core loss is constant loss? 
Latest Answer: Iron loss-When an electric current flows through a copper conductor (or any conductor), some energy is converted to heat. i(square)*r...this equation is obvious that iron loss depends on flowing current. Core loss-Magnetic loss...composed of hysterisis ...

Iron loss-When an electric current flows through a copper conductor (or any conductor) some energy is converted to heat. i(square)*r...this equation is obvious that iron loss depends on flowing current. 
Core loss-Magnetic loss...composed of hysterisis loss eddy current loss... 
Doesnt depend on electrical component....The losses same even with or without load. hence know as constant losses.


Actually current is nothing its simply flow of charges.earthing is a wire which is common to all the points in a circuit used to complete the circuit it is compulsory .while grounding is used to pass leakage of charges to the ground it is used for safety measure but not compulsory.
Earthing is connecting the neutral point in 3 phase circuits to ground.
Grounding is connecting an electrical equipment individually to ground.




Change in Frequency
Why do we maintain 50hz frequency? What happens when we change this frequency to any other value?

If the question is for changing the frequency of Power supply to Induction Motors then it will lead to (1) Increased Iron losses (2) run at a differenct speed close to its new synchronous speed (120F/P) (3) lead to reduction in Torque capacity.

It has been set as standard 50Hz for india and 60Hz at many other places. Either you believe this or not but FREQUENCY IS NEVER CONSTANT. It keeps on changing with load at the generation unit. As the load increases freq decreases this is only because of the change in torque angle due to change in load to fulfill the requirement of the load we provide more input and hence freq. changes normal to 50Hz. this constant frequency is useful for parallal operation of generators such as in power grids. Any change in freq. of two units will cause harmonics and heavy transients which may cause critical damage! To avoid this all the power generation units or power plants are synchronized with each other having const freq 50 Hz. if any power plant looses its synchronism it is notified immediately or it will be disconnected from every other unit!! to avoid losses!

An Inductive Load say Induction Motor connected to an Alternator requires Active (KW) & Reactive Power (KVAr) both. This Motor receives Apparent Power (KVA --> KW + KVAr) from the Alternator. Active Power is what the Motor is delivering through its shaft and the reactive Power is what it is consuming internally to deliver the rated Output.

So if Motor Power Factor is 0.8 then it is said that


Motor is coverting 80 of its Input Apparent Power into Mechnical Output consuming remaining 20 Apparent Power internally. So the motor is demanding 20 reactive power being generated by the alternator.

If the Power Factor of Motor is improved to 0.95 by means of External Capacitor then it should be understood that out of 20 of reactive Power required by the Motor 15 is supplied by external Capacitor and remaining 5 is being supplied by Alternator. so the Apparent Power Output of the Alternator reduces whereas Active Power Output remains constant as Motor KW.

The alternator is always generating the real power along with the reactive power. This will never consume the reactive power. The induction generator only consume the reactive power. The output reactive power of the alternator is decided by the type of load. . .

RE: Reactive Power Relation with Alternator
If syn m/c is under excited that means it is not able to produce reactive power itself which is required so it will take reactive power i.e. act as induction generator.


why frequency is 50 hZ

Hi The frequency of the generated voltage basically depends on:

1). The speed of the Rotor (Field Winding) of the generator/alternator

2). No. of Poles of the alternator.

By increasing both factors we can increase the generated frequency of the system but in increasing the frequency cost also increasees thats why both factors are limited by the other physical factors and cost. As explained:

1). The speed of the Rotor is limited by the capacity of the 'Prime Mover' which is revolving it and by the strength of the material by which Rotor is made of (otherwise it may bent at high speeds)

2). The no. of Poles are limited by the growing size of the machine.

But simulteneously we can't take very low frequency also as the AC has quite large advantages over DC system.

So The conclusion is that the frequency band of Around 50-60 Hz is an optimized value of the frequency in both respects i.e. Cost of generation and advantage of frequency.

EDDY CURRENT LOSSES

As frequency increases eddy current and hysteriss losses increasesand hence power loss also increases.



Alternator
Why alternator is operated at lagging power factor?
How alternator responses with changing the load?

Since the Synchronous generator having the property of supplying the reactive power along with the real power this can be operated in lagging power factor only. Suppose if it want to work with leading power factor means it should absorbed reactive power supplied by the capacitive load. The induction generator only having the property of observing the reactive power for its excitation purpose. If the load of the generator changes suddenly means from that instant itself the generator will take care of that load. But to balance the power the generator speed either increase or decrease. This reduction in speed will affect the frequency. 

What is the diffrence between Altrnator & Generator? Outline its working principal.


1.Alternators are used in automobiles to charge the battery and to power all the car's electric systems when its engine is running. Alternators have the great advantage over direct-current generators of not using a commutator which makes them simpler lighter and more rugged than a DC generator. The stronger construction of alternators allows them to turn at higher speed allowing an automotive alternator to turn at twice engine speed improving output when the engine is idling. The availability of low-cost solid-state diodes from about 1960 allowed auto manufacturers to substitute alternators for DC generators. Automotive alternators use a set of rectifiers (diode bridge) to convert AC to DC. To provide direct current with low ripple automotive alternators have a three-phase winding.

2.Alternator puts out voltage when it needed. But generator puts out voltage all the time.

3.Alternator produces Alternating Current.But Generator produces Direct Current.

4.Alternator consist no commutator and due to absense of commutator it's simpler than generator.

5.Alternator construction is more stronger than dc generator.

6.Alternator use only those energy which is needed.So it save energy.Where Generator use all those energy which is supplied.There is no save of energy.So using alternator is more profitable than generator in the purposes.


Transformer Sound
Why do you get a typical sound when the transformer is put into operation?

Transformer noise is caused by the phenomenon magnetostriction. When a piece of any magnetic sheet is placed in the magnetic field it gets magnetised and elongate. But when the magnetic field is removed it is again comes to its original shape and because of this elongating and again coming back to shape produces noise which in known as transformer noise this phenomenon occurs in the core of a transformer which produces noise.

If we are connecting a 50 hz transformer to a 60 hz transformer then there hystersis and eddy current both losses increases considerably (for detail check effect of frequency on transformer losses).


Explain why the secondary terminal of current transformer should not be lift open circuited.

Normally in a potential transformer the primary current depends on the secondary side load. But in current transformer the primary current does not depends on the secondary side load of current transformer. That will purely depends on the line where it is connected in series. So to equalise the primary MMF and secondary MMF of the current transformer there should be a load in the secondary of current transformer. Suppose in the case of no load condition there will be a heavy repeated accumulation of MMF will be restrained in the current transformer core. This will provide a heavy shock if anybody touches the secondary of current transformer.

If the secondary of CT is left opened there wont be any current flow in secondary thus increasing iron loss (eddy hysteresis). This results in wastage of power in form of heat in th core. It also leads to saturation of the core.


Why there is 220v in 1-phase but 440v in 3-phase?

The Phase voltage of an generator is 220 - 230 V but the Phase to phase 
voltage (Line Voltage) will be 400 V.


Voltage of 

R - Phase-230

Y - Phase-230

B - Phase-230


but


RY-400V

BY-400V

RB-400V


Because 

Line Voltage will be Root3 Times of the phase voltage 

In case off 3 phase Equipments we will take only line voltage for operating 
mode. But in single phase will take only Phase voltage


Lightening is an an electricity charge that happens when two different charges clash in the clouds. This contains no current because it discharges to the nearest low resistance objects.


Sub-Station Label
Why the Substaions are labled as 11KV/33KV or 66/11KV etc instead of label with the POWER TRANSFORMERS Rating (In MVA/KVA)?

All electrical equipments operated depend on voltage.
In substations we can
get same ratio transformers with various power ratings.
Ex:
400/200KV with 800MVA
315 MVA

Power ratings
are depend on load.
If we have small rating TR we connect less load

High rating means we can connect high load
So the substations are labeled like 132/11kV
like that.





Power factor is the ratio of Active ppwer to apparent power in sysytem,It is an index to see how much of the energy is actually being utilized to do useful work
We know power factor(ie.Current lags or leads behind voltage by some angle and cos of that angle is power factor)...If the power factor drops below 1 the current consumed increases with the decrease in power factor...(for instance load with pf 0.2 consumes more current than that with 1)...This lagging or leading of current is mainly due to the storage of charges by the capacitors and inductors....Power factor is useful because they are helpful in analysying the percentage of useful power of all the power supplied...
Power factor also gives the idea about the active power and recative power. If power factor is high its active power is higher in comparision with reactive power also if power factor is higher then the corresponding current rating will be lower so for same rating of machine we need lower current rating coil.





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terrorism

terrorism /t'erərɪzəm/ 
  1. Terrorism is the use of violence, especially murder and bombing, in order to achieve political aims or to force a government to do something.N-UNCOUNT disapproval

Web definitions

  • the calculated use of violence (or the threat of violence) against civilians in order to attain goals that are political or religious or ...
    • http://wordnetweb.princeton.edu/perl/webwn?s=terrorism
  • State terrorism refers to acts of terrorism conducted by governments. Like the definition of terrorism and that of state-sponsored terrorism, the definition of state terrorism remains controversial and without international consensus.
    • http://en.wikipedia.org/wiki/Terrorism_(state)
  • Terrorism is a policy or ideology of violenceTerrorism in asymmetrical conflict: ideological and structural aspects, By Ekaterina Stepanova, Stockholm International Peace Research Institute, Oxford University Press US, 2008 ISBN 0199533555, 9780199533558 186 pages, page 28, "the Russian ...
    • http://en.wikipedia.org/wiki/Terrorism
  • The word "terrorism" is politically and emotionally charged,Hoffman, Bruce "Inside Terrorism" Columbia University Press 1998 ISBN 0-231-11468-0. Page 32. See review in The New York Times and this greatly compounds the difficulty of providing a precise definition. ...
    • http://en.wikipedia.org/wiki/Terrorism_(definitions_of)
  • terror - panic: an overwhelming feeling of fear and anxiety
  • terror - a person who inspires fear or dread; "he was the terror of the neighborhood"
  • terror - a very troublesome child
  • terror - the use of extreme fear in order to coerce people (especially for political reasons); "he used terror to make them confess"
    • http://wordnetweb.princeton.edu/perl/webwn?s=terror
  • terrorist - a radical who employs terror as a political weapon; usually organizes with other terrorists in small cells; often uses religion as a cover for ...
    • http://wordnetweb.princeton.edu/perl/webwn?s=terrorist
  • The Terrorists (Swedish title: Terroristerna) is a 1975 novel by Sjöwall and Wahlöö in their detective series revolving around Martin Beck and his team. The Terrorists was unfinished at the time of Per Wahlöö's death in June 1975; the manuscript was completed by Maj Sjöwall alone.
    • http://en.wikipedia.org/wiki/The_Terrorists
  • The Terrorist is a young adult novel by Caroline B. Cooney, published in 1997. It deals with Laura Williams, a sixteen-year-old American who attends an international school in London. When her younger brother, Billy, is killed by a terrorist bomb, Laura becomes obsessed with revenge. ...
    • http://en.wikipedia.org/wiki/The_Terrorist_(novel)
  • Terrorist is a real-time, two player strategy game developed by Steven Pederson of Edu-Ware Services in 1980 for the Apple II. ...
    • http://en.wikipedia.org/wiki/Terrorist_(computer_game)
  • Terrorist is the 2nd album by Norwegian black metal artist Nattefrost.
    • http://en.wikipedia.org/wiki/Terrorist_(album)
  • The Terrorist (Theeviravaathi) is a Tamil Indian film directed by Santosh Sivan. The film portrays a period in the life of a nineteen-year-old ...
    • http://en.wikipedia.org/wiki/The_Terrorist_(film)
  • Terrorist is the 22nd novel written by John Updike.
    • http://en.wikipedia.org/wiki/Terrorist_(novel)
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Saturday, February 27, 2010

technology

Technology refers to methods, systems, and devices which are the result of scientific knowledge being used for practical purposes


Technology is the usage and knowledge of tools, techniques, and crafts, or is systems or methods of organization, or is a material product (such as clothing) of these things. The word technology comes from the Greek technología (τεχνολογία) — téchnē (τέχνη), 'craft' and -logía (-λογία), the study of something, or the branch of knowledge of a discipline.


The Merriam-Webster dictionary offers a definition of the term: "the practical application of knowledge especially in a particular area" and "a capability given by the practical application of knowledge".[1] 
Ursula Franklin, in her 1989 "Real World of Technology" lecture, gave another definition of the concept; it is "practice, the way we do things around here".[9] The term is often used to imply a specific field of technology, or to refer to high technology or just consumer electronics, rather than technology as a whole.[10] Bernard Stiegler, in Technics and Time, 1, defines technology in two ways: as "the pursuit of life by means other than life", and as "organized inorganic matter."[11]



Science, engineering and technology

The distinction between science, engineering and technology is not always clear. Science is the reasoned investigation or study of phenomena, aimed at discovering enduring principles among elements of the phenomenal world by employing formal techniques such as the scientific method.[15] Technologies are not usually exclusively products of science, because they have to satisfy requirements such as utility, usability and safety.
Engineering is the goal-oriented process of designing and making tools and systems to exploit natural phenomena for practical human means, often (but not always) using results and techniques from science. The development of technology may draw upon many fields of knowledge, including scientific, engineering, mathematical, linguistic, and historical knowledge, to achieve some practical result.
Technology is often a consequence of science and engineering — although technology as a human activity precedes the two fields. For example, science might study the flow of electronsin electrical conductors, by using already-existing tools and knowledge. This new-found knowledge may then be used by engineers to create new tools and machines, such assemiconductors, computers, and other forms of advanced technology. In this sense, scientists and engineers may both be considered technologists; the three fields are often considered as one for the purposes of research and reference.[16]
The exact relations between science and technology in particular have been debated by scientists, historians, and policymakers in the late 20th century, in part because the debate can inform the funding of basic and applied science. In immediate wake of World War II, for example, in the United States it was widely considered that technology was simply "applied science" and that to fund basic science was to reap technological results in due time. An articulation of this philosophy could be found explicitly in Vannevar Bush's treatise on postwar science policy, Science—The Endless Frontier: "New products, new industries, and more jobs require continuous additions to knowledge of the laws of nature... This essential new knowledge can be obtained only through basic scientific research." In the late-1960s, however, this view came under direct attack, leading towards initiatives to fund science for specific tasks (initiatives resisted by the scientific community). The issue remains contentious—though most analysts resist the model that technology simply is a result of scientific research.[17][18]

 
technology /tekn'ɒlədʒi/

Synonyms:
noun: technics, engineering, technique

technologies plural;
  1. Technology refers to methods, systems, and devices which are the result of scientific knowledge being used for practical purposes.N-VAR
    • Technology is changing fast.
    • They should be allowed to wait for cheaper technologies to be developed.
    • ...nuclear weapons technology.
    • technologist N-COUNT /tekn'ɒlədʒɪst/

      technologists plural;
      1. ...the scientists and technologists that we will need for the future.

Web definitions

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Electrical Engineering Definition

Engineering is the work involved in designing and constructing engines and machinery, or structures such as roads and bridges.
Engineering is also the subject studied by people who want to do this work. N-UNCOUNT
  • ...the design and engineering of aircraft and space vehicles.
  • ...graduates with degrees in engineering.

  1. electrical engineering is the designing, constructing, and maintenance of electrical devices.
  2. The branch of engineering that deals with the technology of electricity, especially the design and application of circuitry and equipment for power generation and distribution, machine control, and communications.
  3. Electrical engineering emerged as a discipline in 1864 when James Clerk Maxwell summarized the basic laws of electricity in mathematical form and predicted that radiation of electromagnetic energy would occur in a form that later became known as radio waves. The need for electrical engineers was not felt until the invention of the telephone(1876) and the incandescent lamp (1878). N-UNCOUNT

Web definitions

Electrical engineering, often referred to as the electrical and electronic engineering (EEE), is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. It is a very broad area that encompasses the design and study of various electrical & electronic systems, such as electrical circuits, generators, motors, transformers, magnetic devices & materials, otherelectromagnetic/electromechanical devices, electronic devices, electronic circuits, electronic materials, optical fibers, optoelectronic devices,computer systems, radio, television, telephony, telecommunications, wireless, microwave systems, mobile telephony, radar, datacommunication, computer networking, nanotechnology, photonics, MEMs, etc.

Electrical engineering may or may not include electronic engineering. Where a distinction is made, usually outside of the United States, electrical engineering is considered to deal with the problems associated with large-scale electrical systems such as power transmission andmotor control, whereas electronic engineering deals with the study of small-scale electronic systems including computers and integrated circuits.[1] Alternatively, electrical engineers are usually concerned with using electricity to transmit energy, while electronic engineers are concerned with using electricity to transmit information.


Electricity has been a subject of scientific interest since at least the early 17th century. The first electrical engineer was probably William Gilbert who designed the versorium: a device that detected the presence of statically charged objects. He was also the first to draw a clear distinction between magnetism and static electricity and is credited with establishing the term electricity.[2] 
In 1775 Alessandro Volta's scientific experimentations devised the electrophorus, a device that produced a static electric charge, and by 1800 Volta developed the voltaic pile, a forerunner of the electric battery.[3]
However, it was not until the 19th century that research into the subject started to intensify. Notable developments in this century include the work of Georg Ohm, who in 1827 quantified the relationship between the electric current and potential difference in a conductor,
 Michael Faraday, the discoverer of electromagnetic induction in 1831, and 
James Clerk Maxwell, who in 1873 published a unified theory of electricity and magnetism in his treatise Electricity and Magnetism.[4]

Thomas Edison built the world's first large-scale electrical supply network


In 1882, Edison switched on the world's first large-scale electrical supply network that provided 110 volts direct current to fifty-nine customers in lower Manhattan.



 In 1884 Sir Charles Parsons invented the steam turbine which today generates about 80 percent of theelectric power in the world using a variety of heat sources. 



In 1887, Nikola Tesla filed a number of patents related to a competing form of power distribution known as alternating current. In the following years a bitter rivalry between Tesla and Edison, known as the "War of Currents", took place over the preferred method of distribution. AC eventually replaced DC for generation and power distribution, enormously extending the range and improving the safety and efficiency of power distribution.


The efforts of the two did much to further electrical engineering—Tesla's work on induction motors and polyphase systems influenced the field for years to come, while Edison's work on telegraphy and his development of the stock ticker proved lucrative for his company, which ultimately became General Electric. However, by the end of the 19th century, other key figures in the progress of electrical engineering were beginning to emerge.[8]


Control

Main article: Control engineering

Control systems play a critical role inspace flight
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 electrical circuits, digital signal processors,microcontrollers and PLCs (Programmable Logic Controllers). 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.




 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.[11] 
In 1895, Guglielmo Marconi furthered the art of hertzian wireless methods. 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).[12]
 In 1920 Albert Hull developed the magnetron which would eventually lead to the development of the microwave oven in 1946 by Percy Spencer.[13][14] 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.[15]
In 1941 Konrad Zuse presented the Z3, the world's first fully functional and programmable computer.[16] 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 missions and the NASA moon landing.[17]
The invention of the transistor in 1947 by William B. Shockley, John Bardeen and Walter Brattain 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.[18] Starting in 1968, Ted Hoff and a team at Intel invented the first commercial microprocessor, which presaged the personal computer. The Intel 4004 was a 4-bit processor released in 1971, but in 1973 the Intel 8080, an 8-bit processor, made the first personal computer, the Altair 8800, possible.[19]





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