Umair Questions

8/17/2019 Umair Questions

1/8

An Attenuator is an electronic device that reduces the power of a signal without

appreciably distorting its waveform.

An attenuator is effectively the opposite of an amplifier , though the two work by different

methods. While an amplifier provides gain, an attenuator provides loss, or gain less than 1.

Difference b/w pin and Scotty diode

PIN diodes: A !"# diode has a central intrinsic layer. !"# diodes are used as radio fre$uency

switches and attenuators. %hey are also used in power electronics, due to their central layer being

able to withstand high voltages.

Schottky diodes/Crystal diode& "n a Schottky diode, a semiconductor'metal (unction is formed

between a semiconductor and a metal, thus creating a Schottky barrier. %he #)type

semiconductor acts as the cathode and the metal side acts as the anode of the diode. %hisSchottky barrier results in both a low forward voltage drop and very fast switching. *sed in fast

switching applications. %hey have less losses dues to low +..D.

Peltier diodes ) %his diode is used in heat engine as a sensor for thermoelectric cooling.

Tunnel diode is the p)n (unction device with high doping that e-hibits negative resistance. %hat

means when the voltage is increased the current through it decreases. *sed in microwave +

applications

Step recovery diode: A semiconductor (unction diode having the ability to generate e-tremely

short pulses. an be used as a pulse generator.

Shockley diode: is a four)layer semiconductor diode, which was one of the first semiconductor

devices invented. "t was a 0pnpn0 diode. "t is e$uivalent to a thyristor with a disconnected gate.

*sed in switching application

Transistors:

A three terminal semiconductor device used as amplifier or as a switch

Phototransistors:

A common type of phototransistor resembles a bipolar transistor with its base lead removed andreplaced with a light)sensitive area. %his is why a phototransistor has only terminals instead of

the usual 2

Thyristor:

A thyristor is a four layer 2 (unction p)n)p)n semiconductor device consisting of at least three p)n

https://en.wikipedia.org/wiki/Electronic_devicehttps://en.wikipedia.org/wiki/Electronic_devicehttps://en.wikipedia.org/wiki/Electric_powerhttps://en.wikipedia.org/wiki/Electric_powerhttps://en.wikipedia.org/wiki/Signal_(information_theory)https://en.wikipedia.org/wiki/Signal_(information_theory)https://en.wikipedia.org/wiki/Distortionhttps://en.wikipedia.org/wiki/Waveformhttps://en.wikipedia.org/wiki/Amplifierhttps://en.wikipedia.org/wiki/Amplifierhttps://en.wikipedia.org/wiki/Gain_(electronics)https://en.wikipedia.org/wiki/Gain_(electronics)http://www.learningaboutelectronics.com/Articles/What-are-phototransistorshttp://www.electrical4u.com/thyristor-silicon-controlled-rectifier/http://www.electrical4u.com/thyristor-silicon-controlled-rectifier/http://www.electrical4u.com/theory-of-semiconductor/https://en.wikipedia.org/wiki/Electric_powerhttps://en.wikipedia.org/wiki/Signal_(information_theory)https://en.wikipedia.org/wiki/Distortionhttps://en.wikipedia.org/wiki/Waveformhttps://en.wikipedia.org/wiki/Amplifierhttps://en.wikipedia.org/wiki/Gain_(electronics)http://www.learningaboutelectronics.com/Articles/What-are-phototransistorshttp://www.electrical4u.com/thyristor-silicon-controlled-rectifier/http://www.electrical4u.com/theory-of-semiconductor/https://en.wikipedia.org/wiki/Electronic_device


2/8

(unctions, functioning as an electrical switch for high power operations. "t acts e-clusively as a

bitable switch, conducts when the gate receives a current trigger, and continuing to conduct until

the voltage across the device is not reversed 3forward)biased4.

S& can5 be turned off

6%7& can be turned off by giving a negative pulse at gate

D"A& 3A Diode4

%wo shokley diodes are connected in anti parallel fashion.

%"A&

Ss are unidirectional 3one)way4 current devices, making them useful for controlling D only.

"f two Ss are (oined in back)to)back parallel fashion (ust like two Shockley diodes were

(oined together to form a D"A, we have a new device known as the %"A

Diac use along with %"A in lamp dimmer circuits or heater input power control circuits. 7r

phase control circuits.

IGFET or MSFET is a voltage controlled field effect transistor it has a 89etal 7-ide: 6ate

electrode which is electrically insulated from the main semiconductor n)channel or p)channel by

a very thin layer of insulating material usually silicon dio-ide, commonly known as glass.

;+


3/8

What are advantages and disadvantages of @D

Advantages&

no skin effects

no charging current

only two conductors are re$uired

more power can be transmitted per conductor

less insulation is re$uired B C of A..

no problem of stability 3as no fre$uency is involved4

Disadvantages&

no reactive power can travel on the line


4/8

@A&

Advantages& no converters re$uired, voltage level can be raised ,so power transmission is

efficient, = here are cheap as that of D

Disadvantage&

Skin effect, crona effect, stability issues, interference with communication lines, more

conductors re$uired

Types o! "C Machines:

Separately E#cited "C Motor& A separately e-cited D motor the supply is given separately to

the field and armature windings. %he main distinguishing fact in these types of dc motor is that,

the armature current does not flow through the field windings

Per$anent Ma%net "C Motor: contain a permanent magnetic as field winding to produce field

flu-.

Sel! E#cited "C Motor: "n case of self e-cited dc motor, the field winding is connected either in

series or in parallel or partly in series, partly in parallel to the armature winding.

In a series &ound dc $otor' the speed varies &ith load( And operation &ise this is its $ain

di!!erence !ro$ a shunt &ound dc $otor.

Co$pound )ound "C Motor: contain both series and shunt field winding

"i!!erential Co$pound "C Motor:

Cu$ulative Co$pound "C Motor:

"C Generator:

Per$anent Ma%net "C Generator: generates very low power.

http://www.electrical4u.com/armature-winding-pole-pitch-coil-span-commutator-pitch/http://www.electrical4u.com/electric-current-and-theory-of-electricity/http://www.electrical4u.com/electric-current-and-theory-of-electricity/http://www.electrical4u.com/armature-winding-pole-pitch-coil-span-commutator-pitch/http://www.electrical4u.com/armature-winding-pole-pitch-coil-span-commutator-pitch/http://www.electrical4u.com/armature-winding-pole-pitch-coil-span-commutator-pitch/http://www.electrical4u.com/electric-current-and-theory-of-electricity/http://www.electrical4u.com/armature-winding-pole-pitch-coil-span-commutator-pitch/


5/8

Separately E#cited "C Generator:

Sel!*e#cited "C Generators:

In series &ound %enerators' the output volta%e is directly proportional &ith load current(

In shunt &ound %enerators' output volta%e is inversely proportional &ith load current(

)hich type o! A(C $otor is used in the !an +ceilin% !an' e#haust !an' padestal !an' ,racket

!an etc- &hich are !ind in the houses .

"ts Single !hase induction motor which mostly s$uirrel cage rotor and are capacitor start

capacitor run.

)hat are the Application o! "C Motors in Ther$al Po&er Plant.

D motors operate as backup drives for normal ac drive systems when ac power supply to the plant is lost.

)hy syn( %enerators are used !or the production o! electricity.

Synchronous machines have capability to work on different power factor 3or say different

imaginary power varying the field


6/8

2. ost/kwh is higher than "/9

H. an5t be used in variable speed applications...as speed can only be change by changing

the supply fre$uency.

)hy AC syste$s are pre!erred over "C syste$s.

Due to following reasons, A systems are preferred over D systems&

a. "t is easy to maintain and change the voltage of A electricity for transmission and

distribution.

b. !lant cost for A transmission 3circuit breakers, transformers etc4 is much lower than the

e$uivalent D transmission

c. +rom power stations, A is produced so it is better to use A then D instead of converting it.

1ysteresis loss in trans!or$er& @ysteresis loss is due to reversal of magnetiIation in the

transformer core.

Eddy current loss in trans!or$er& due to linkage of primary flu- with other conducting parts

like steel core or iron body or the transformer, which will result in induced emf in those parts,

causing small circulating current in them. %his current is called as eddy current.

AC Machines:

Synchronous Motor:

otors used in Synchronous alternators can be classified into

14 Salient !ole &

2( %hey are generally used in lower speed electrical machines, say 1BB !9 to 1BB !9.

3( As the rotor speed is lower, more number of poles are re$uired to attain the re$uired

fre$uency. 3#s F 1Bf / ! therefore, f F #sJp/1B i.e. fre$uency is proportional to

number of poles4. %ypically number of salient poles is between H to EB.

0( +lu- distribution is relatively poor than non)salient pole rotor.

4( Salient pole rotors generally need damper windings to prevent rotor oscillations during

operation

5( Salient pole synchronous generators are mostly used in hydro power plants.

http://www.electricaleasy.com/2014/02/AC-generator-alternator-construction-working.htmlhttp://www.electricaleasy.com/2014/02/AC-generator-alternator-construction-working.html


7/8

4 #on)Salient 3ylindrical4 !ole otors&

1. Cylindrical rotors are used in high speed electrical machines, usually 1BB !9 to

2BBB !9.

. #umber of poles is usually or H.

2. Damper windings are not needed in non*salient pole rotors.

H. +lu- distribution is sinusoidal and hence gives better emf waveform.

. Non*salient pole rotors are used in nuclear, gas and thermal power plants.

Types o! Synchronous $otor:

6eluctant Motor: An une-cited single phase synchronous motor is reluctance motor.

6epulsion Motor: An alternating)current motor having stator windings connected directly to the

source of ac power and rotor windings connected to a commutator. epulsion motors are

classified under Single !hase motors. "ts characteristics are similar to Series D motor

7niversal Motor: It construction is same as DC. Run on either DC or single phase AC

supply. Similar to Series D motor. @igh starting tor$ue and speed. Universal motors find their

use in various home appliances like vacuum cleaners, drink and food mixers, domestic

sewing machine etc.

Technical 6easons !or not usin% 1i%her Fre8uencies

. It increases series impedance in electrical transmission system. !his reduces power

transfer capa"ility so we cannot access full fruit of transmission system.

#. $armonics with higher fre%uency can carry more power and it introduces excess

heat losses.

&. As the fre%uency directly proportional to the rotating speed of alternator and it is not

practical to construct very high speed gigantic alternators.

!he MHD generation or, also known as magneto hydrodynamic power generation is a

direct energy conversion system which converts the heat energy directly into electrical

energy, without any intermediate mechanical energy conversion

http://www.brighthubengineering.com/general/44325-single-phase-motors-an-introduction/http://www.brighthubengineering.com/general/44325-single-phase-motors-an-introduction/


8/8

In conventional generator or alternator , the conductor consists of copper windings or strips

while in an '$D generator the hot ioni(ed gas or conducting fluid replaces the solid

conductor
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