ELECTRONICS

Electronics Is The Branch Of Science That Deals With The Study Of Flow And Control Of Electrons (electricity) And The Study Of Their Behavior And Effects In Vacuums, Gases, And Semiconductors, And With Devices Using Such Electrons.

1.What is Electronic?

The study and use of electrical devices that operate by controlling the flow of electrons or other
electrically charged particles.

2.What is communication?

Communication means transferring a signal from the transmitter which passes through a medium then the
output is obtained at the receiver. (or)communication says as transferring of message from one place to
another place called communication.

3.Different types of communications? Explain.

Analog and digital communication.
As a technology, analog is the process of taking an audio or video signal (the human voice) and translating
it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the
audio or video data is represented by a series of "1"s and "0"s.
Digital signals are immune to noise, quality of transmission and reception is good, components used in
digital communication can be produced with high precision and power consumption is also very less when
compared with analog signals.

4.What is sampling?

The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.

5.State sampling theorem.

It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is
equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist
rate.

6.What is cut-off frequency?

The frequency at which the response is -3dB with respect to the maximum response.

7.What is pass band?

Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.

8.What is stop band?

A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone
circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.

9.Explain RF?

Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This
range corresponds to frequency of alternating current electrical signals used to produce and detect radio
waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to,
RF usually refers to oscillations in electrical circuits or electromagnetic radiation.

10.What is modulation? And where it is utilized?

Modulation is the process of varying some characteristic of a periodic wave with an external signals.
Radio communication superimposes this information bearing signal onto a carrier signal.
These high frequency carrier signals can be transmitted over the air easily and are capable of travelling
long distances.
The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the
information bearing signal. Modulation is utilized to send an information bearing signal over long
distances.

11.What is demodulation?

Demodulation is the act of removing the modulation from an analog signal to get the original baseband
signal back. Demodulating is necessary because the receiver system receives a modulated signal withspecific characteristics and it needs to turn it to base-band.

12.Name the modulation techniques.

For Analog modulation--AM, SSB, FM, PM and SM
Digital modulation--OOK, FSK, ASK, Psk, QAM, MSK, CPM, PPM, TCM, OFDM

13.Explain AM and FM.

AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in
accordance with the information bearing signal.
FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in
accordance with the information bearing signal.

14.Where do we use AM and FM?

AM is used for video signals for example TV. Ranges from 535 to 1705 kHz.
FM is used for audio signals for example Radio. Ranges from 88 to 108 MHz

15.What is a base station?

Base station is a radio receiver/transmitter that serves as the hub of the local wireless network, and may
also be the gateway between a wired network and the wireless network.

16.How many satellites are required to cover the earth?

3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span
of the satellite is about 15 years.

17.What is a repeater?

A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher
power, or onto the other side of an obstruction, so that the signal can cover longer distances without
degradation.

18.What is an Amplifier?

An electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an
applied signal.

19.Example for negative feedback and positive feedback?

Example for –ve feedback is ---Amplifiers And for +ve feedback is – Oscillators

20.What is Oscillator?

An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of
oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while
relaxation oscillators have waveforms with sharp changes.

21.What is an Integrated Circuit?

An integrated circuit (IC), also called a microchip, is an electronic circuit etched onto a silicon chip. Their
main advantages are low cost, low power, high performance, and very small size.

22.What is crosstalk?

Crosstalk is a form of interference caused by signals in nearby conductors. The most common example is
hearing an unwanted conversation on the telephone. Crosstalk can also occur in radios, televisions,
networking equipment, and even electric guitars.

23.What is resistor?

A resistor is a two-terminal electronic component that opposes an electric current by producing a voltage
drop between its terminals in proportion to the current, that is, in accordance with Ohm's law:
V = IR.

24.What is inductor?

An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An
inductor can take many forms.

25.What is conductor?

A substance, body, or device that readily conducts heat, electricity, sound, etc. Copper is a good conductor
of electricity.

26.What is a semi conductor?

A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that
of an insulator(An Insulator is a material that resists the flow of electric current. It is an object intended to
support or separate electrical conductors without passing current through itself); it can vary over that wide
range either permanently or dynamically.

27.What is diode?

In electronics, a diode is a two-terminal device. Diodes have two active electrodes between which the
signal of interest may flow, and most are used for their unidirectional current property.

28.What is transistor?

In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic
signals. The transistor is the fundamental building block of computers, and all other modern electronic
devices. Some transistors are packaged individually but most are found in integrated circuits.

29.What is op-amp?

An operational amplifier, often called an op-amp , is a DC-coupled high-gain electronic voltage amplifier
with differential inputs[1] and, usually, a single output. Typically the output of the op-amp is controlled
either by negative feedback, which largely determines the magnitude of its output voltage gain, or by
positive feedback, which facilitates regenerative gain and oscillation.

30.What is a feedback?

Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the
input. This is often used to control the dynamic behavior of the system.

31.Advantages of negative feedback over positive feedback.

Much attention has been given by researchers to negative feedback processes, because negative feedback
processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a
system and can lead a system away from equilibrium states, possibly causing quite unexpected results.

32.What is Barkhausen criteria?

Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations.
“Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the
transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network ( the
magnitude of the loop gain ) are less than unity”.
The condition of unity loop gain -A? = 1 is called the Barkhausen criterion. This condition implies that
A?= 1and that the phase of - A? is zero.

33.What is CDMA, TDMA, FDMA?

Code division multiple access (CDMA) is a channel access method utilized by various radio
communication technologies. CDMA employs spread-spectrum technology and a special coding scheme
(where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same
physical channel. By contrast, time division multiple access (TDMA) divides access by time, while
frequency-division multiple access (FDMA) divides it by frequency.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate
with each other. To avoid confusion, people could take turns speaking (time division), speak at different
pitches (frequency division), or speak in different directions (spatial division). In CDMA, they would
speak different languages. People speaking the same language can understand each other, but not other
people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the
same channel, but only users associated with a particular code can understand each other.

34.Explain different types of feedback

Types of feedback:
Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation).
Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the
result that fluctuations are attenuated.
Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as "cumulative
causation", is a feedback loop system in which the system responds to perturbation (A perturbation means
a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as
the perturbation. In contrast, a system that responds to the perturbation in the opposite direction is called a
negative feedback system.
Bipolar feedback: which can either increase or decrease output.

35.What are the main divisions of power system?

The generating system, transmission system, and distribution system

36.The generating system, transmission system, and distribution system

An instrumentation amplifier is a differential op-amp circuit providing high input impedances with ease of
gain adjustment by varying a single resistor.

37.What is meant by impedance diagram?

The equivalent circuit of all the components of the power system are drawn and they are interconnected is
called impedance diagram.

38.What is the need for load flow study?

The load flow study of a power system is essential to decide the best operation existing system and for
planning the future expansion of the system. It is also essential for designing the power system.

39.What is the need for base values?

The components of power system may operate at different voltage and power levels. It will be convenient
for analysis of power system if the voltage, power, current ratings of the components of the power system
is expressed with reference to a common value called base value.

40.what is the principle of motor?

Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting
movement is called as torque.

41.Types of dc generator?

DC Generators are classified into two types 1) separately excited DC generator 2)self excited DC
generator, which is further classified into; 1)series 2)shunt and 3)compound(which is further classified into
cumulative and differential).

42.Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor?

DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors
on load, but can not start the DC series motor without load.

43.Define stepper motor. What is the use of stepper motor?

The motor which work or act on the applied input pulse in it, is called as stepper motor. This stepper motor is
under the category of synchronous motor, which often does not fully depend of complete cycle. It likes to
works in either direction related to steps. for this purpose it mainly used in automation parts.

44.What is 2 phase motor?

A two phase motor is a motor with the starting winding and the running winding have a phase split. e.g;ac
servo motor. where the auxiliary winding and the control winding have a phase split of 90 degree.

45.Which type of A.C motor is used in the fan (ceiling fan, exhaust fan, pedestal fan, bracket fan etc) which are find in the houses

Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

46.Give two basic speed control scheme of DC shunt motor?

1. By using flux control method: in this method a rheostat is connected across the field winding to control
the field current. so by changing the current the flux produced by the field winding can be changed, and
since speed is inversely proportional to flux speed can be controlled

2.armature control method: in this method a rheostat is connected across armature winding by varying the
resistance the value of resistive drop(IaRa) can be varied, and since speed is directly proportional to
Eb-IaRathe speed can be controlled.

47.Difference between a four point starter and three point starter?

The shunt connection in four point starter is provided separately form the line where as in three point
starter it is connected with line which is the drawback in three point starter.

48.What is the difference between synchronous generator & asynchronous generator?

In simple, synchronous generator supply's both active and reactive power but asynchronous
generator(induction generator) supply's only active power and observe reactive power for magnetizing.
This type of generators are used in windmills.

49.Why syn. generators are used for the production of electricity?

Synchronous machines have capability to work on different power factor (or say different imaginary power
varying the field EMF. Hence syn. generators r used for the production of electricity.

50.Why is the starting current high in a DC motor?

In DC motors, Voltage equation is V=Eb-IaRa (V = Terminal voltage, Eb = Back emf in Motor, Ia =
Armature current,Ra = Armature resistance). At starting, Eb is zero. Therefore, V=IaRa, Ia = V/Ra ,where
Ra is very less like 0.01ohm.i.e, Ia will become enormously increased.

51.What are the advantages of star-delta starter with induction motor?

The main advantage of using the star delta starter is reduction of current during the starting of the motor.
Starting current is reduced to 3-4 times Of current of Direct online starting.(2). Hence the starting current
is reduced , the voltage drops during the starting of motor in systems are reduced.

52.Why series motor cannot be started on no-load?

Series motor cannot be started without load because of high starting torque. Series motor are used in
Trains, Crane etc.

53.Mention the methods for starting an induction motor?

The different methods of starting an induction motor
DOL: direct online starter
Star delta starter
Auto transformer starter
Resistance starter
Series reactor starter

54.What are Motor Generator Sets and explain the different ways the motor generator set can be used ?

Motor Generator Sets are a combination of an electrical generator and an engine mounted together to form
a single piece of equipment. Motor generator set is also referred to as a genset, or more commonly, a
generator The motor generator set can used in the following different ways:
1.Alternating current (AC) to direct current (DC)
2.DC to AC
3.DC at one voltage to DC at another voltage
4.AC at one frequency to AC at another harmonically-related frequency

55.Which type of motor is used in trains, what is the rating of supply used explain Working principal?

Dc series is in the trains to get high starting torque while starting of the trains and operating voltage is
1500v dc.

56.What are the Application of DC Motors in Thermal Power Plant?

In thermal power plants dc motors are employed for certain control and critical emergency operations
which are supplied by dedicated batteries. DC motors operate as backup drives for normal ac drive systems
when ac power supply to the plant is lost.In thermal power plant, the dc motors finds applications for performing control functions such as

Turbine governor motor
Governor limit setting
Motor operated rheostats
Emergency lubrication for the turbines (main, boiler feed pumps)
Generator (H2 oil seal).
DC motor operated valves
DC motors employed in thermal plants are classified in to two types based on the type of application.
DC motors carrying out Control function
Dc motors carrying out Emergency function
Control functions: This category consists of the turbine governor motor, governor limiting setting, motor
operated rheostats, etc. These motors are small, about 1/8 hp or less. They are operated quite infrequently
for short duration.

Emergency functions: This category consists of turbine-generator emergency (lubrication) bearing oil
pumps and emergency seal oil pumps. Such pumps may also be provided for steam turbine drives of feed
water pumps, fans, and other large loads. The lack of lubrication during a shutdown without ac power will
ruin the linings of the bearings and damage the shaft.
Hydrogen seal oil pump is provided to prevent the escaping of hydrogen (for large turbine-generators
hydrogen cooling is provided for efficient cooling) from the casing by providing a tight seal with high
pressure oil

57.What are the Advantages & Disadvantages of Synchronous motors?

Advantage or Merits:
One of the major advantage of using synchronous motor is the ability to control the power factor. An over
excited synchronous motor can have leading power factor and can be operated in parallel to induction
motors and other lagging power factor loads thereby improving the system power factor.

In synchronous motor the speed remains constant irrespective of the loads. This characteristics helps in
industrial drives where constant speed is required irrespective of the load it is driving. It also useful when
the motor is required to drive another alternator to supply at a different frequency as in frequency changes.

Synchronous motors can be constructed with wider air gaps than induction motors which makes these
motors mechanically more stable.

In synchronous motors electro-magnetic power varies linearly with the voltage.

Synchronous motors usually operate with higher efficiencies ( more than 90%) especially in low speed and
unity power factor applications compared to induction motors

Disadvantages or Demerits:
Synchronous motors requires dc excitation which must be supplied from external sources.

Synchronous motors are inherently not self starting motors and needs some arrangement for its starting
and synchronizing.

The cost per kW output is generally higher than that of induction motors.

These motors cannot be used for variable speed applications as there is no possibility of speed adjustment
unless the incoming supply frequency is adjusted (Variable Frequency Drives).

Synchronous motors cannot be started on load. Its starting torque is zero.

These motors have tendency to hunt.

When loading on the synchronous motor increases beyond its capability, the synchronism between rotor
and stator rotating magnetic field is lost and motor comes to halt.

Collector rings and brushes are required resulting in increase in maintenance.

Synchronous motors cannot be useful for applications requiring frequent starting or high starting torques
required.

58.What are the different operation regions of the SCR?

SCR or thyristor will have three regions of operations based on the mode in which the device is connected
in the circuit.
Reverse blocking region: When the cathode of the thyristor is made positive with respect to the anode and
no gate signal is applied. In this region scr exhibits the reverse blocking characteristics similar to diode.
Forward blocking region: In this region the anode of the thyristor is made positive with respect to the
cathode and no gate signal is applied to the thyristor. A small leakage current flow in this mode of
operation of the thyristor
Forward conduction region: when the forward voltage applied between the anode and cathode increases at
particular break over voltage avalanche breakdown takes place and thyristor starts conducting current in
forward direction. By this type of triggering the device damages the scr. Hence a gate signal is applied
before the forward break over voltage to trigger the scr.

59.What is Latching current?

Gate signal is to be applied to the thyristor to trigger the thyristor ON in safe mode. When the thyristor
starts conducting the forward current above the minimum value, called Latching current, the gate signal
which is applied to trigger the device in no longer require to keep the scr in ON position.

60.What is Holding current ?

When scr is conducting current in forward conduction state, scr will return to forward blocking state when the
anode current or forward current falls below a low level called Holding current
Note: Latching current and Holding current are not same. Latching current is associated with the turn on
process of the scr whereas holding current is associated with the turn off process. In general holding current
will be slightly lesser than the latching current.

61.Why thyristor is considered as Charge controlled device?

During the triggering process of the thyristor from forward blocking state to forward conduction state through
the gate signal, by applying the gate signal (voltage between gate and cathode) increases the minority carrier
density in the p-layer and thereby facilitate the reverse break over
of the junction J2 and thyristor starts conducting. Higher the magnitude of the gate current pulse, lesser is the
time required to inject the charge and turning on the scr. By controlling the amount of charge we can control
the turning on time of the scr.

62.What is the relation between the gate signal and forward break over voltage (VBO)?

Thyristor can be triggered by increasing the forward voltage between anode and cathode, at forward break
over voltage thyristor starts conducting. However this process may damage the thyristor, so thyristor is
advices to trigger on through the gate pulse. When a gate signal is applied thyristor turns on before
reaching the break over voltage. Forward voltage at which the thyristor triggers on depends on the
magnitude of the gate current. Higher is the gate current lower is the forward break over voltage.

63.What are the different losses that occur in thyristor while operating?

Different losses that occur are
Forward conduction losses during conduction of the thyristor
Loss due to leakage current during forward and reverse blocking.
Power loss at gate or Gate triggering loss.
Switching losses at turn-on and turn-off.

64.What are the advantages of speed control using thyristor?

Advantages :

1. Fast Switching Characteristics than MOSFET, BJT, IGBT

2. Low cost 3. Higher Accurate.

65.What happens if I connect a capacitor to a generator load?

Connecting a capacitor across a generator always improves power factor, but it will help depends up on the
engine capacity of the alternator, other wise the alternator will be over loaded due to the extra watts
consumed due to the improvement on pf. Secondly, don't connect a capacitor across an alternator while it
is picking up or without any other load.

66.Why the capacitors works on ac only?

Generally capacitor gives infinite resistance to dc components (i.e., block the dc components). it allows the
ac components to pass through.

67.Explain the working principal of the circuit breaker?

Circuit Breaker is one which makes or breaks the circuit. It has two contacts namely fixed contact &
moving contact under normal condition the moving contact comes in contact with fixed contact thereby
forming the closed contact for the flow of current. During abnormal & faulty conditions (when current
exceeds the rated value) an arc is produced between the fixed & moving contacts & thereby it forms the
open circuit Arc is extinguished by the Arc Quenching media like air, oil, vacuum etc.

68.What is the difference between Isolator and Circuit Breaker?

Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for
the reason of any maintenance on downstream circuits. it is manually operated and does not contain any
solenoid unlike circuit breaker. it should not be operated while it is having load. first the load on it must be
made zero and then it can safely operated. its specification only rated current is given. But circuit breaker
is onload automatic device used for breaking the circuit in case of abnormal conditions like short circuit,
overload etc., it is having three specification 1 is rated current and 2 is short circuit breaking capacity and 3
is instantaneous tripping current.

69.What is the difference between earth resistance and earth electrode resistance?

Only one of the terminals is evident in the earth resistance. In order to find the second terminal we should
recourse to its definition: Earth Resistance is the resistance existing between the electrically accessible part
of a buried electrode and another point of the earth, which is far away.
The resistance of the electrode has the following components:
(A) the resistance of the metal and that of the connection to it.
(B) the contact resistance of the surrounding earth to the electrode.

70.What is use of lockout relay in ht voltage?

A lock-out relay is generally placed in line before or after the e-stop switch so the power can be shut off at
one central location. This relay is powered by the same electrical source as the control power and is
operated by a key lock switch. The relay itself may have up to 24 contact points within the unit itself. This
allows the control power for multiple machines to be locked out by the turn of a single key switch.

71.What is the power factor of an alternator at no load?

At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it
should be zero lagging like inductor.

72.How to determine capacitor tolerance codes?

In electronic circuits, the capacitor tolerance can be determined by a code that appears on the casing. The
code is a letter that often follows a three-digit number (such as 130Z).The first two are the 1st and 2nd
significant digits and the third is a multiplier code. Most of the time the last digit tells you how many zeros
to write after the first two digits and these are read as Pico-Farads.

73.Why most of analog o/p devices having o/p range 4 to 20 mA and not 0 to 20 mA?

4-20 mA is a standard range used to indicate measured values for any process. The reason that 4ma is
chosen instead of 0 mA is for fail safe operation .For example- a pressure instrument gives output 4mA to
indicate 0 psi, up to 20 mA to indicate 100 psi, or full scale. Due to any problem in instrument (i.e) broken
wire, its output reduces to 0 mA. So if range is 0-20 mA then we can differentiate whether it is due to
broken wire or due to 0 psi.

74.Two bulbs of 100w and 40w respectively connected in series across a 230v supply which bulb will glow bright and why?

Since two bulbs are in series they will get equal amount of electrical current but as the supply voltage is
constant across the bulb(P=V^2/R).So the resistance of 40W bulb is greater and voltage across 40W is
more (V=IR) so 40W bulb will glow brighter.

75.What is meant by knee point voltage?

Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a
CT. It is the voltage at which a CT gets saturated.(CT-current transformer).

76.What is reverse power relay?

Reverse Power flow relay are used in generating station's protection. A generating stations is supposed to
fed power to the grid and in case generating units are off, there is no generation in the plant then plant may
take power from grid. To stop the flow of power from grid to generator we use reverse power relay.

77.What are the advantage of free wheeling diode in a Full Wave rectifier?

It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it
reduces the voltage spike seen in a inductive load.

78.what is the full form of KVAR?

We know there are three types of power in Electrical as Active, apparent & reactive. So KVAR is stand
for ``Kilo Volt Amps with Reactive component.

79.What is a System?

When a number of elements or components are connected in a sequence to perform a specific function, the
group of elements that all constitute a System

80.What is Control System?

In a System the output and inputs are interrelated in such a manner that the output quantity or variable is
controlled by input quantity, then such a system is called Control System.
The output quantity is called controlled variable or response and the input quantity is called command
signal or excitation.

81.What are different types of Control Systems?

Two major types of Control Systems are 1) Open loop Control System 2) Closed Loop Control Systems
Open loop Control Systems: The Open loop Control System is one in which the Output Quantity has no
effect on the Input Quantity. No feedback is present from the output quantity to the input quantity for
correction.
Closed Loop Control System: The Closed loop Control System is one in which the feedback is provided
from the Output quantity to the input quantity for the correction so as to maintain the desired output of the
system.

82.What is a feedback in Control System?

The Feedback in Control System in one in which the output is sampled and proportional signal is fed back to
the input for automatic correction of the error ( any change in desired output) for further processing to get
back the desired output.

83.Why Negative Feedback is preferred in the Control System?

The role of Feedback in control system is to take the sampled output back to the input and compare output
signal with input signal for error ( deviation from the desired result).Negative Feedback results in the better
stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations.
Hence in control systems negative feedback is considered.

84.What is the effect of positive feedback on stability of the system?

Positive feedback is not used generally in the control system because it increases the error signal and drives
the system to instability. But positive feedbacks are used in minor loop control systems to amplify certain
internal signals and parameters

85.What is Latching current?

Gate signal is to be applied to the thyristor to trigger the thyristor ON in safe mode. When the thyristor
starts conducting the forward current above the minimum value, called Latching current, the gate signal
which is applied to trigger the device in no longer require to keep the scr in ON position.

86.What is Holding current ?

When scr is conducting current in forward conduction state, scr will return to forward blocking state when
the anode current or forward current falls below a low level called Holding current
Note: Latching current and Holding current are not same. Latching current is associated with the turn on
process of the scr whereas holding current is associated with the turn off process. In general holding
current will be slightly lesser than the latching current.

87.Why thyristor is considered as Charge controlled device?

During the triggering process of the thyristor from forward blocking state to forward conduction state
through the gate signal, by applying the gate signal (voltage between gate and cathode) increases the
minority carrier density in the p-layer and thereby facilitate the reverse break over of the junction J2 and
thyristor starts conducting. Higher the magnitude of the gate current pulse, lesser is the time required to
inject the charge and turning on the scr. By controlling the amount of charge we can control the turning on
time of the scr.

88.What are the different losses that occur in thyristor while operating?

Different losses that occur are
a)Forward conduction losses during conduction of the thyristor
b)Loss due to leakage current during forward and reverse blocking.
c)Power loss at gate or Gate triggering loss.
d)Switching losses at turn-on and turn-off.

89.What is meant by knee point voltage?

Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a
CT. It is the voltage at which a CT gets saturated.(CT-current transformer).

90.What is reverse power relay?

Reverse Power flow relay are used in generating stations protection. A generating stations is supposed to
fed power to the grid and in case generating units are off, there is no generation in the plant then plant may
take power from grid. To stop the flow of power from grid to generator we use reverse power relay.

91.What will happen if DC supply is given on the primary of a transformer?

Mainly transformer has high inductance and low resistance. In case of DC supply there is no inductance
,only resistance will act in the electrical circuit. So high electrical current will flow through primary side
of the transformer. So for this reason coil and insulation will burn out.

92.What is the difference between isolators and electrical circuit breakers? What is bus-bar?

Isolators are mainly for switching purpose under normal conditions but they cannot operate in fault
conditions .Actually they used for isolating the CBs for maintenance. Whereas CB gets activated under
fault conditions according to the fault detected. Bus bar is nothing but a junction where the power is
getting distributed for independent loads.

93.What are the advantage of free wheeling diode in a Full Wave rectifier?

It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it
reduces the voltage spike seen in a inductive load.

94.Mention the methods for starting an induction motor?

The different methods of starting an induction motor:
a)DOL:direct online starter
b)Star delta starter
c)Auto transformer starter
d)Resistance starter
e)Series reactor starter

95.What is the power factor of an alternator at no load?

At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it
should be zero lagging like inductor.

96.What is the function of anti-pumping in circuit breaker?

When breaker is close at one time by close push button,the anti pumping contactor prevent re close the
breaker by close push button after if it already close.

97.What is stepper motor. what is its uses?

Stepper motor is the electrical machine which act upon input pulse applied to it. it is one type of
synchronous motor which runs in steps in either direction instead of running in complete cycle. so, in
automation parts it is used.

98.There are a Transformer and an induction machine. Those two have the same supply. For which device the load current will be maximum? And why?

The motor has max load current compare to that of transformer because the motor consumes real
power..and the transformer is only producing the working flux and its not consuming.. hence the load
current in the transformer is because of core loss so it is minimum.

99.What is SF6 Circuit Breaker?

SF6 is SulpherhexaFlouride gas..if this gas is used as arc quenching medium in a Circuit breaker means
SF6 CB.

100.What is ferrantic effect?

Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage.

101.What is meant by insulation voltage in cables? explain it?

It is the property of a cable by virtue of it can withstand the applied voltage without rupturing it is known
as insulation level of the cable.

102.What is the difference between MCB & MCCB, Where it can be used?

MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small
current rating circuit. MCCB molded case circuit breaker and is thermal operated for over load current and
magnetic operation for instant trip in short circuit condition. under voltage and under frequency may be
inbuilt. Normally it is used where normal current is more than 100A.

103.Where should the lighting arrestor be placed in distribution lines?

Near distribution transformers and out going feeders of 11kv and incoming feeder of 33kv and near power
transformers in sub-stations.

104.Define IDMT relay?

It is an inverse definite minimum time relay. In IDMT relay its operating is inversely proportional and also
a characteristic of minimum time after which this relay operates. It is inverse in the sense ,the tripping time
will decrease as the magnitude of fault current increase.

105.What are the transformer losses?

TRANSFORMER LOSSES - Transformer losses have two sources-copper loss and magnetic loss. Copper
losses are caused by the resistance of the wire (I2R). Magnetic losses are caused by eddy currents and
hysteresis in the core. Copper loss is a constant after the coil has been wound and therefore a measurable
loss. Hysteresis loss is constant for a particular voltage and current. Eddy-current loss, however, is
different for each frequency passed through the transformer.

106.what is the full form of KVAR?

We know there are three types of power in Electricals as Active, apparent & reactive. So KVAR is stand
for ``Kilo Volt Amps with Reactive component.

107.What is the difference between selection and insertion sorting?

In insertion sorting elements are added to the sorted sequence in an arbitrary order. In selection sorting, the
elements are added to the sorted sequence in order so they are always added at one end.

108.What is merge sorting?

Merging is the sorting algorithm which combines two or more sorted sequences into a single sorted
sequence. It is a divide and conquer algorithm, an O(n log n) comparison-based sorting algorithm. Most
implementations produce a stable sort, meaning that the implementation preserves the input order of equal
elements in the sorted output.

109.Which are the main steps of a merge sorting algorithm?

Sorting by merging is a recursive, divide-and-conquer strategy. The basic steps to perform are the
following:
a) divide the sequence into two sequences of length
b) recursively sort each of the two subsequences
c) merge the sorted subsequences to obtain the final result

110.Provide a short description of binary search algorithm.

Binary search algorithm always chooses the middle of the remaining search space, discarding one half or
the other, again depending on the comparison between the key value found at the estimated position and
the key value sought. The remaining search space is reduced to the part before or after the estimated
position.

111.Two bulbs of 100w and 40w respectively connected in series across a 230v supply which bulb will glow bright and why?

Since two bulbs are in series they will get equal amount of electrical current but as the supply voltage is
constant across the bulb(P=V^2/R).So the resistance of 40W bulb is greater and voltage across 40W is
more (V=IR) so 40W bulb will glow brighter.

112.Why temperature rise is conducted in bus bars and isolators?

Bus bars and isolators are rated for continuous power flow, that means they carry heavy currents which
rises their temperature. so it is necessary to test this devices for temperature rise.

113.What is Automatic Voltage regulator(AVR)?

AVR is an abbreviation for Automatic Voltage Regulator. It is important part in Synchronous Generators,
it controls the output voltage of the generator by controlling its excitation current. Thus it can control the
output Reactive Power of the Generator.

114.Difference between a four point starter and three point starter?

The shunt connection in four point stator is provided separately form the line where as in three point stater
it is connected with line which is the drawback in three point stator

115.Why the capacitors works on ac only?

Generally capacitor gives infinite resistance to dc components(i.e., block the dc components). it allows the
ac components to pass through.

116.How many types of cooling system it transformers?

1. ONAN (oil natural, air natural)
2. ONAF (oil natural, air forced)
3. OFAF (oil forced, air forced)
4. ODWF (oil direct, water forced)
5. OFAN (oil forced, air forced)

117.Operation carried out in Thermal power stations?

The water is obtained in the boiler and the coal is burnt so that steam is obtained this steam is allowed to
hit the turbine , the turbine which is coupled with the generator generates the electricity.

118.What is 2 phase motor?

A two phase motor is a motor with the starting winding and the running winding have a phase split. e.g;ac
servo motor. where the auxiliary winding and the control winding have a phase split of 90 degree.

119.What is the principle of motor?

Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting
movement is called as torque.

120.What is meant by armature reaction?

The effect of armature flu to main flux is called armature reaction. The armature flux may support main
flux or opposes main flux.

121.What is the difference between synchronous generator & asynchronous generator?

In simple, synchronous generator supply's both active and reactive power but asynchronous
generator(induction generator) supply's only active power and observe reactive power for magnetizing.
This type of generators are used in windmills.

122.What is MARX CIRCUIT?

It is used with generators for charging a number of capacitor in parallel and discharging them in series. It
is used when voltage required for testing is higher than the available.

123.What are the advantages of speed control using thyristor?

Advantages :
1. Fast Switching Characteristics than Mosfet, BJT, IGBT
2. Low cost
3. Higher Accurate.

124.What is ACSR cable and where we use it?

ACSR means Aluminum conductor steel reinforced, this conductor is used in transmission & distribution.

125.What is the one main difference between UPS &inverter ? And electrical engineering & electronics engineering ?

Uninterrupted power supply is mainly use for short time .means according to ups VA it gives backup. ups
is also two types : on line and offline . online ups having high volt and amp for long time backup with high
dc voltage. but ups start with 12v dc with 7 amp. but inverter is start with 12v,24,dc to 36v dc and 120amp
to 180amp battery with long time backup.

126.What will happen when power factor is leading in distribution of power?

If their is high power factor, i.e. if the power factor is close to one:
a)Losses in form of heat will be reduced,
b)Cable becomes less bulky and easy to carry, and very cheap to afford, &
c)It also reduces over heating of transformers.

127.What are the advantages of star-delta starter with induction motor?

(1). The main advantage of using the star delta starter is reduction of current during the starting of the
motor. Starting current is reduced to 3-4 times Of current of Direct online starting.(2). Hence the starting
current is reduced , the voltage drops during the starting of motor in systems are reduced.

128.Why Delta Star Transformers are used for Lighting Loads?

For lighting loads, neutral conductor is must and hence the secondary must be star winding. and this
lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary
we use delta winding in the primary. So delta / star transformer is used for lighting loads.

129.Why computer humming sound occurred in HT transmission line?

This computer humming sound is coming due to ionization (breakdown of air into charged particles) of air
around transmission conductor. This effect is called as Corona effect, and it is considered as power loss.

130.What is rated speed?

At the time of motor taking normal current (rated current)the speed of the motor is called rated speed. It is
a speed at which any system take small current and give maximum efficiency.

131.If one lamp connects between two phases it will glow or not?

If the voltage between the two phase is equal to the lamp voltage then the lamp will glow. When the
voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow
depending on the type of lamp.

132.Can a class or a struct have multiple constructors?

Yes, a class or a struct can have multiple constructors. Constructors in C# can be overloaded.