Two marks

Prepared by D.BALAJI & R. MUTHUNAGAI AP/EEE
Manakula Vinayagar Institute of Technology
(Affiliated to Pondicherry University)
Kalitheerthalkuppam, Mannadipet Commune, Pondicherry– 605107.
EC T32 - ELECTRICAL ENGINEERING
1. What is a transformer?
Transformer is a static piece of apparatus by means of which an electrical power is
transformed from one alternating current circuit to another with the desired change in voltage
and current, without any change in its frequency.
2. Can you apply D.C. supply to a single-phase transformer?
The D.C. supply cannot be used for the transformers. Because transformer works on the principle
of mutual induction, for which current in one coil must change uniformly. If D.C. supply is given, the
current will not change due to constant supply and transformer will not work.
3. What are the main parts of a transformer?
 Winding (or) Coil
o Primary winding
o Secondary winding
 Magnetic core
4. How we can identify Primary & Secondary windings?
 The winding which is connected across the supply is called as “Primary winding”.
 The winding which is connected across the load is called as “Secondary winding”.
5. Give the emf equation of a transformer and define each term.
Emf induced in primary coil E1 = 4.44 fφ mN1 volt
Emf induced in secondary coil E2 = 4.44 fφ mN2 volt
Where, f is the frequency of AC input
Φ m is the maximum value of flux in the core
N1, N2 are the number of primary and secondary turns.
6. Does the transformer draw any current when secondary is open? Why?
Unit-I (Transformers)
Principle of operation – Single Phase transformer – Equivalent circuit – Regulation – Losses and
Efficiency – Introduction to 3 phase transformers – Autotransformers.

Yes, it (primary) will draw the current from the main supply in order to magnetize the
core and to supply iron and copper losses on no load. There will not be any current in the
secondary since secondary is open.
7. Why transformers are rated in KVA?
Copper loss of a transformer depends on current and iron loss on voltage. Hence total
losses depend on Volt- Ampere and not on the power factor. That is why the rating of
transformers is in KVA and not in kW.
8. What are the applications of step-up and step-down transformers?
Step-up transformers are used in generating stations. Normally the generated voltage
will be either 11 kV or 22 kV. This voltage is stepped up to 110 kV or 220 kV or 400 kV and
transmitted through transmission lines. (In short it may be called as sending end).
Step-down transformers are used in receiving stations. The voltage are again stepped
down to 11 kV or 22 kV and transmitted through feeders.(In short it may be called as receiving
end). Further these 11 kV or 22kV are stepped down to 3 phase 400 V by means of a distribution
transformer and made available at consumer premises. The transformers used at generating
stations and receiving stations are called power transformers.
9. How transformers are classified?
According to their construction as
 Core
 Shell
 Berry
According to their input supply as
 Single phase transformer
 Three phase transformer
According to their output voltage as
 Step up transformer
 Step down transformer
10. Compare between core and shell type transformer
Core Type Transformer Shell type transformer
The core has only one magnetic
circuit. It has two magnetic circuits.
Core has two limbs. Core has three limbs.
It has less mechanical protection to
coil.
It has better mechanical protection to
coil.

It has better cooling since more
surface is exposed to atmosphere. Cooling is not very effective.
Natural cooling is provided. Natural cooling cannot provide
This transformer is easy to repair. This transformer is not easy to repair.
The winding is surrounded
considerable part of core.
Core is surrounded considerable part
of winding of transformer.
13. Define voltage regulation of a transformer.
The voltage regulation is the percentage of voltage difference between no load and full
load voltages of a transformer with respect to its full load voltage.
(Or)
It is defined as ratio of difference between no load voltage of the transformer and load
voltage of transformer to no load voltage of transformer. Mathematically it can be expressed as
% Voltage Regulation = [(E2 – V2) / E2 ]* 100
Where, E2 = no load voltage, V2 = loaded voltage
14. An 1100/400 V, 50 Hz single phase transformer has 100 turns on the secondary
winding. Calculate the number of turns on its primary.
We know V1 / V2 = k = N2 / N1
Substituting 400/1100 = 100/N1
N1 = 100/400 x 1100,
N1= 275 turns.
15. What is the function of laminated core?
To provide magnetic coupling between Primary & Secondary coil.
16. Why the core is laminated?
Usually core is laminated in order to reduce eddy current losses.
17. What will be the Primary- secondary turns & EMF’s in case of step-down transformers?
 Primary turns (N1) > Secondary turns (N2 ) [ N1 > N2 ]
 Primary EMF (E1 ) > Secondary EMF (E2 ) [ E1 > E2 ]
18. What are the losses in Transformers?
Constant losses
 Iron loss or core loss
 Hysteresis loss
 Eddy current loss

Variable loss
 Copper loss or I2
R loss
19. How to eliminate hysteresis & eddy current losses?
 Laminated core is used to reduce eddy current losses.
 Silicon steel core is used to reduce Hysteresis losses.
20. What is the principle of operation of a transformer?
Transformer works under the principle of Faraday’s Laws of electromagnetic mutual
induction. That is, when two coils are inductively coupled and if current in one coil is changed
uniformly then e.m.f. gets induced in the other coil.
21. Define efficiency of a transformer?
% Efficiency (η) = (output power / input power) * 100
Where, Input power = Output power + Total losses.
22. List some applications of some transformer?
 It is used in rectifier network.
 It is also used in furnaces, welding.
 Electronic good require less voltage by using transformers.
 For traction systems & testing units, transformers are also used.
23. How will you determine equivalent circuits in constants in a transformer?
Equivalent circuit constant are found by conducting O.C & S.C test.
Ro Xo – found from O.C test
R1 & X1 or R2 & X2 - found from S.C test
24. What are the 3 Transformer connections?
 Star – Star connection (λ – λ )
 Star – Delta connection (λ – Δ )
 Delta – Delta connection (Δ – Δ)
 Delta – Star connection (Δ – λ)
Other than the above, there are 2 more connections, they are
 Open delta (or) V – V connection
 Scott (or) T-T connection
29. What are the types of three phase transformer according to construction?
Similar to single phase transformer, three phase transformers are also classified as
 Core type
 Shell type
30. Define Auto transformer and what principle it works?

 It is a one winding transformer and has single winding act as Primary & Secondary.
 Primary & Secondary windings are not electrically isolated from each other.
 Operation similar to two winding transformer.
It works on the principle of induction and conduction.
31. What is the condition for maximum efficiency in a transformer?
 Core loss = Copper loss
 WC = I2
2
(R02)
32. Difference between auto transformer & two winding transformer?
 Auto transformer has single winding which act as both primary & secondary
 Secondary voltage levels can be varied from zero to its max value in case auto
transformer but it is not possible in 2 winding transformer.
 Copper used in auto transformers is comparatively less than 2 winding
transformer.

33. What is meant by Voltage transformation ratio?
It is ratio of secondary induced e.m.f. to primary induced e.m.f. is known as
voltage transformation ratio denoted as K.
K = (N2/N1) = E2/E1
34. What is meant by ideal transformer and what its properties?
An ideal transformer is an imaginary transformer; here primary applied voltage is same as the
secondary induced e.m.f. as there is no voltage drop. That is, its efficiency is 100 percentages.
Its properties are,
 It has no losses
 Its windings have zero resistance
 Leakage flux is zero
 Permeability of core is so high
35. What are the advantages of autotransformer?
 Copper required is less
 Efficiency is higher compared to two winding transformer
 The size and cost is less compared to two winding transformer
 Resistance and leakage reactance is less
 Copper losses is less
 VA rating is more compared to two winding transformer.
36. What are the applications of autotransformer?
 For safety starting the machines like induction and synchronous motor
 To give a small boost to distribution cable to compensate for voltage drop
 As a furnace transformer to supply power to the furnace
 For interconnecting the system which are operated roughly at same voltage level.

37. What are the limitations of autotransformer?
 Low impedance hence high short circuit currents for short circuits on secondary side
 No electrical separation between primary and secondary which is risky in case of high
voltage levels
 Economical only where the voltage ratio is less than 2
38. Draw the equivalent circuit of transformer.
1. Define a pole pitch.
It may be defined as the distance between the two adjacent poles i.e. the periphery of
armature divided by the number of poles.
2. What is the principle of DC motor?
DC Motor:
 DC motor is a machine which converts electrical energy in to mechanical
energy
 Its action is based on the principle that when a current carrying conductor
placed in a magnetic field, it experiences force in it.
Unit-II (D.C. MACHINES)
Construction, Principles of operation of DC Generators – types -EMF equation – No load and Load
characteristics of series and shunt generators – DC motor – Torque – Speed – Torque characteristics of
series and shunt motors – Speed control methods and application

3. What is the principle of DC generator?
DC Generator:
 DC Generator is a machine which converts mechanical energy in to electrical energy.
 Energy conservation based on the production of dynamically induced EMF according
to Faraday’s law of electromagnetic induction. It states that whenever the number of
magnetic lines of force linking with a coil or circuit changes, an e.m.f. gets induced in
that coil or circuit.
4. What are the constructional parts of DC machine?
 Yoke
 Pole shoe & pole core
 Pole coils (or) field coils
 Armature core
 Armature windings
 Commutator
 Brushes
 Bearings
 Shaft
5. What is the function of brushes in DC machine?
The function of brushes is to collect current from commutator and make it available to
the stationary external circuit. It connects the stationary external circuit to rotating commutator.
6. Which type of material is used in brushes?
Brushes are usually made up to carbon.
7. What is armature reaction? What are its effects?
When the generator is loaded, the armature carries the current. The armature current sets up
its own magnetic field. The effect of this armature flux on the distribution of main field flux is
called armature reaction. Its two effects are,
(i) It reduces the generated voltage by distorting the main flux
(ii) It causes sparking at the brushes.
8. How to reduce armature reaction?
Armature reaction is reduced by providing inter poles (or) commutating poles, &
compensating windings in the DC machine
9. What are the types of armature windings in a DC machine?
Armature windings is of two types
 Lap winding ( A=P)

 Wave winding (A=2)
10. How can we find out the direction of a DC motor & define Fleming’s left hand rule?
The direction of the DC motor is found by using Fleming’s Left hand rule
DEFINITION:
Stretch the thumb, Forefinger & middle finger of the left hand rule are
mutually perpendicular to each other thumb represents the direction of the force experienced by
the conductor, forefinger represents the direction of the magnetic field & middle finger
represents the direction of current.
11. How can we find out the direction of induced EMF in DC generators? Define Fleming’s
right hand rule?
The direction of the DC generator is found by using Fleming’s right hand rule.
DEFINITION:
Stretch the thumb, Forefinger & middle finger of the Right Hand Rule are
mutually perpendicular to each other thumb represents the direction of the motion of conductor ,
forefinger represents the direction of the magnetic flux lines & middle finger represents the
direction of the induced EMF.
12. Define excitation?
Sending current through the field winding for producing magnetic flux (or) energize the
field winding is called excitation.
13. What are the types of excitations?
 Self excitations
 Separately excitations
14. What is the difference between self and separately excited DC generators?
In Self excited DC generators, its field winding is excited by the e.m.f. induced by the
DC generators In Separately excited DC generators, field winding is excited by a separate DC
source.
15. Why O.C.C curve of a DC shunt generator not starts from Zero (or) Origin?
Due to residual magnetism some amount of e.m.f. is present in the generator even the
field current is zero, So that the O.C.C. curve is not starts from origin.
16. What are the types of DC motors?
DC motors
 DC series motor
 DC shunt motor
 DC compound motor
DC compound motor is classified in to two types
 Long shunt DC motor

 Short shunt DC motor
(Or)
 Cumulatively compound DC motor
 Differentially compound DC motor.
17. What are the types of DC generators?
DC generators
 DC series generator
 DC shunt generator
 DC compound generator
DC compound generator is classified in to two types
 Long shunt DC compound generator
 Short shunt DC compound generator
(Or)
 Cumulatively compound
 Differentially compound
18. What are the losses in DC machine?
 Copper losses
 Rotational losses
Rotational losses are classified in two types
 Iron (or) Core losses
 Mechanical Losses
Iron (or) Core losses are classified in two types
 Hysteresis Loss
 Eddy current Loss
Mechanical Losses are classified in three types
 Brush friction loss
 Bearing friction loss
 Windage (or) air friction loss
19. What is the EMF equation of DC generator?
E = PNZ / 60 A, Volts
Where, E = Induced EMF in Volts
P = No. of poles
N = Speed rotation in RPM
Z = Total no. of armature conductors
A = No. of parallel paths
20. List the applications of DC motor?
 Shunt motor - Centrifugal Pumps, Reciprocating pumps, lathe, milling & drilling
machines
 Series motor – Cranes, hoists, trolleys & electric locomotives

 Cumulative compound – Rolling Mills, punches, shears & elevators
 Differential compound – not suitable for any practical application
21. List the applications of DC shunt generator?
 Separately Exited generator - Electro plating & Electro-refining of materials
 Shunt generator - Battery charging & ordinary lighting purposes
 Series generator – boosters on dc feeders, welding generator and arc lamps
 Compound generator – domestic lighting purposes & transmit energy over long distance.
22. What is the expression for speed in a DC motor?
N  [V- IaRa] or [V- Ia(Ra+Rse)]/ (Or) N  Eb/
Where, N = Speed in RPM
V = Supply voltage in RPM
 = Flux in Weber’s
Eb = Back EMF in volts
23. What is the expression for Torque in a DC motor?
T  Ia = For shunt motors
T  Ia2 = for series & compound motor
24. What is the use of Swinburne’s test?
 Simple method for finding losses
 From the losses, efficiency at any desired load can be predetermined in advance.
 Power required for this test is very less.
 This test is applicable to shunt & compound Machines.
25. How the direction of the DC motor reversed?
 By reversing either field current (or) armature current
 Interchanging the polarity of supply.
26. List some applications of DC series generator?
 Boosters
 For supplying Arc lamps etc.,
27. Define residual e.m.f?
The e.m.f which is produced due to residual magnetic flux is called residual e.m.f.
28. What are the conditions for building up of e.m.f in DC shunt generator?
 Field magnets should have residual magnetism to initiate the building up process.
 Flux produced by the field coil must be in same direction of the residual magnetic
flux.

 Shunt field resistance should be greater than the Critical field resistance, etc.
30. What is back e.m.f in D.C motors?
After a motoring action, there exists a generating action. Due to this induced e.m.f. in
armature conductors and results to set up a current through armature which is in opposite
direction to supply voltage by Lenz’s law. So as this e.m.f always opposes the supply voltage, it
is called back e.m.f and denoted as Eb.
Eb = PNZ / 60 A, Volts
31. Write the voltage equation of a d.c. motor?
V=Eb+ IaRa+ brush drop
32. What is the commutator and what its function?
Commutator is element which is placed one side of armature of machine.
Its functions are,
 To collect current from armature conductor
 To convert alternating e.m.f. to unidirectional (d.c.) e.m.f.
 To produce unidirectional torque in case of motor.
33. What are the important characteristics of dc motors?
(i) Torque – Armature current characteristics (T Vs Ia) (or) Electrical characteristics
(ii) Speed – Armature current characteristics (N Vs Ia)
(iii) Speed – Torque characteristics (N Vs T) (or) Mechanical characteristics
34. What are the necessary conditions for the generator to be self-excited?
o The field connections must be proper to help residual magnetism
o The field resistance must be less than critical resistance
o The direction of rotation of generator must be proper to help the residual flux.
1. What is a three phase induction motor?
It is a three phase AC motor in which electrical energy is converted into mechanical energy.
2. How does 3 phase induction motor differ from the DC machine?
An induction motor differs from the dc machine in the following ways;
1. It has a small air-gap, where as the air gap is large in DC machines.
2. Commutator is not present in the induction motor.
3. An induction motor has a speed limitation.
4. An induction motor consists of laminated stator.
3. What are different parts of a 3 phase induction motor?
Unit-III (A.C. MACHINES)
Principle of operation of 3-phase Induction Motor – Torque, slips characteristics- Speed control
methods – Single-phase Induction motor starting methods – Principle of operation of Alternators.

A three phase induction motor mainly consists of the following two parts namely stator
and rotor. Stator is the stationary part and Rotor is the rotating part.
4. What is the principle of an Induction motor?
It works under the principle of Faradays law of Electromagnetic Mutual Induction similar
to two winding Transformer. Due to interaction between stator and rotor flux, rotor experiences
mechanical force and it rotates.
5. List out the types of induction motors according to rotor construction?
 Squirrel cage induction motor (mostly 90% of usage)
 Slip ring Induction motor (rarely used, construction is difficult)
6. Why it is called as Induction motor?
In DC motor, electric power is conducted directly to the rotating part (armature). Hence
DC motors are called as Conduction motor. But in AC motors the rotor doesn’t receive electric
power by conduction but by Induction exactly similar to two winding transformer, it receive
electrical power from stator. That is why AC motors are called as Induction motor.
7. List the main parts of an Induction Motor?
There are two main parts.
 Stator(Stationary part)
 Rotor(Rotating part)
Two types of Rotors
 Squirrel cage Induction Motor
 Slip Ring Induction Motor
8. What is slip & Percentage Slip?
Slip is the difference in speed of stator magnetic flux & the speed of the rotor.
S = (Ns-N)/Ns
Ns = speed of the stator rotating Magnetic flux in RPM.
N = Actual speed of the rotor in RPM.
%Slip = ( (Ns-N)/Ns ) x 100%
9. List the applications of Squirrel cage Induction Motor?
 Fans
 Lathes
 Conveyors
 Drilling machine
 Blowers
10. List the applications of Slip Ring Induction Motor?
 Hoists
 Cranes
 Elevator
 Lifts
11. List the types of Single Phase Induction Motors?

 Split Phase Motor
 Capacitor start Motor
 Capacitor start & run Motors
 Shaded Pole Motors
12. List the applications of Single Phase Induction Motors?
 Washing Machines
 Domestic Refrigerators
 Centrifugal pumps
 Fans etc.
13. Induction Motor can be treated as a Rotating Transformer. Why?
Because stator act as Primary coil & rotor act as a secondary coil as similar to two
winding Transformer. By induction, rotor receives Electrical power & it will start to rotate.
Hence it is called as a Rotating Transformer.
14. What is pole pitch?
It is centre to centre distance between the two adjacent poles.
15. How we can make a Single Phase Induction Motor as a Self starting Motor?
An Extra winding called Starting or Auxiliary is connected in the stator side, the flux
produced by the starting &running winding creates rotating magnetic flux in the stator side then
the rotor starts rotating as similar to 3phase Induction Motor. In this way we can make 1phase
Induction Motor as a Self starting Motor.
16. What is the condition for Maximum Starting Torque?
Rotor Resistance (R2) = Rotor Reactance (X2)
(Or) slip at maximum Sm= R2/ X2
17. What are the windings in single Phase Induction Motor?
 Starting winding or Auxiliary winding
 Running Winding or Main winding
These 2 windings are spaced 90 degree electrical apart & are connected across supply.
18. What is the principle of operation of three Phase Induction Motor?
When a 3 Phase supply is applied to the stator, (RMF) Rotating magnetic Field (which is
rotating at synchronous speed is sets up) is developed in stator & an EMF is developed in the
stator, this rotor EMF cuts the stationary rotor conductors and produces EMF in the rotor too.
Due to interaction between stator& rotor fluxes rotor experiences forces and the rotor starts
rotating.
19. What are End rings?
 Squirrel Cage Rotor consists of a laminated cylindrical core with no of parallel slots.
 For each slot, one bar is placed which are short circuited (or) joined at each end by metal
rings called “END RINGS”
20. What is meant by Synchronous Speed?

When a 3Phase supply is applied to the stator Windings, Rotating Magnetic Flux (RMF)
is sets up. The RMF rotates at a constant speed known as “Synchronous Speed (Ns)”.
Synchronous speed is given by Ns = (120f/p)
f = frequency of the supply in HZ
p = No. of poles.
21. What is RMF?
When a 3Phase supply is applied to the stator Windings which produces Magnetic Flux
is sets up whose having constant magnitude but rotating at Synchronous Speed (Ns), this
Magnetic Flux is called as “Rotating Magnetic Flux (RMF)”
22. What is the formula Frequency of Rotor Current?
Rotor Frequency Current f’ = Sf
S= Slip
f = frequency of the supply
23. List the types of 3Phase Induction Motor Starters?
 DOL(Direct On-Line Starter)
 Auto-Transformer Starter
 Star-Delta Starter
 Rotor Resistance Starter(for Slip Ring Induction Motor) etc
24. What are the Speed controls Methods of 3phase Induction Motor?
 Control from stator side
1. By changing applied voltage(V)
2. By changing applied Frequency(f)
3. By changing No of Poles(P)
 Control from Rotor side
1. Rotor Rheostat Control
2. By operating two Motors is Concatenation (or) Cascade
3. By injecting slip frequency to rotor circuit
4.
25. Why the Stator Core is laminated in 3Phase Induction Motor & specifies its thickness?
 Generally Stator Core is build up of silicon steel laminations in order to
reduce Hysteresis & Eddy Current Losses.
 Thickness of the Laminations is 0.4 to 0.5mm.
26. What are the limitations of shaded pole single phase induction motor?
 Starting torque is poor
 Power factor is very low
 Due to cu losses in shading ring efficiency is very low
 Speed reversal is very difficult
 Size and power rating is very small
27. Why the Rotors of Induction Motor are skewed?

 To reduce the Humming Effect
 To Avoid magnetic locking
28. Where the coppers bars & double layer windings are placed in an Induction Motors?
 In a Squirrel Cage Induction Motors, copper bars are placed in the rotor slots & it
is short circuited through end rings.
 In Slip Ring Induction Motors, 3phase double layer windings are placed in rotors.
29. List the differences between Squirrel Cage & Slip Ring Induction Motors?
 Rotor Construction is simple in Squirrel Cage type but complicated in case of Slip
Ring Induction Motors.
 Copper bars are placed in the rotor slots in Squirrel Cage but in Slip Ring
Induction Motors, 3phase double layer windings are placed in rotors.
 Efficiency is Squirrel Cage type higher than Slip Ring Induction Motors.
 Starting Torque of Squirrel Cage Induction Motors is less than Slip Ring
Induction Motors.
30. What is the use of Centrifugal switch in 1phase Induction Motors?
It is used for disconnecting starting winding under normal running conditions.
31. What is the use of shading coil in the shaded pole motor?
In shaded pole motors the necessary phase –splitting is produced by induction. These
motors have salient poles on stator and a squirrel cage type rotor. The poles are shaded i.e. each
pole carries a copper band one of its unequally divided part is called shading band. When single
phase ac supply is given to the stator winding due to shading provided to the poles a rotating
magnetic field is generated
32. Why capacitor – start induction motors advantageous?
In capacitor start induction motors capacitor is connected in series with the auxiliary
winding. When speed of the motor approaches to 75 to80%of the synchronous speed the starting
winding gets disconnected due to the operation of the centrifugal switch the capacitor remains in
the circuit only at start. The starting torque is proportional to phase angle and hence such motors
produce very high starting torque.
33. List out 4 applications of shaded pole induction motor?
Shaded pole motors have very low starting torque, low power factor and low efficiency.
The motors are commonly used for small fans, toy motors, advertising displays, film projectors,
record players, gramophones, hair dryers, photocopying machines etc.
34. Is single phase induction motor self starting? Why?
Due to cutting of flux, e.m.f gets induced in the rotor which circulates rotor current .the
rotor current produces rotor flux. This flux interacts with forward component Φf to produce a
torque in one particular direction say anticlockwise direction. While rotor flux interacts with
backward component Φb to produce a torque in the clockwise direction. So if anti clock wise
torque is positive then clockwise torque is negative thus net torque experienced by the rotor is

zero at start. Hence net torque experienced by rotor is zero at start and so single phase induction
motor is not self starting.
35. How to start squirrel cage motor?
Squirrel cage motors are started with the help of DOL starter, auto-transformer and star-delta
starter. These starters are starting the motor with limiting the starting current.
36. Define voltage regulation of alternator.
The voltage regulation of an alternator is defined as the change in its terminal voltage
when full load is removed, keeping field excitation and speed constant, divided by rated terminal
voltage.
% Regulation = [Eph-Vph]/Vph * 100
Where, Vph- rated terminal voltage
Eph – no load induced e.m.f.
37. What are the two types of rotors used in alternator?
Salient pole type and smooth cylindrical type
38. What are the applications of alternator?
Alternators used in central power stations also control the field current to
regulate reactive power and to help stabilize the power system against the effects of
momentary faults.
1. What is servomotor?
The motors used in automatic control systems or in servomechanism are called
servomotors. They are used to convert electrical signal into angular motion.
It is built like a series d.c motor with the difference that both its stator and armature are
laminated. They can be used either on d.c or a.c supply although the speed and power are greater
on direct current. They cannot be satisfactorily made to run at less than about 2000 rpm.
2. What are the types of servo motor?
 1.A.C .servo motor
 2..DC .Servo motor
i) Armature controlled
ii) Field controlled.
3. Give some applications of Servo motor.
Unit-IV (SPECIAL MACHINES)
Servo motor – DC and AC servomotors; stepper motors – variable reluctance and
permanent magnet stepper motors; single phase synchronous motor – reluctance motor and
hysteresis motor – universal motor – Repulsion motor –synchronous motor.

The major applications of servomotor are
 Radar
 Tracking and guidance system
 Process controller
 Computer and machine tools
4. How universal motor different from dc series motor?
Universal motor is built like a series d.c motor with the difference that both its stator and
armature are laminated.
5. Define stepper motor.
These motors are also called stepping motors or step motors. The name stepper is used
because this motor rotates through a fixed angular step in response to each input current pulse
received by its controller.
6. Define step angle.
The angle through which the motor shaft rotates for each command pulse is called the
step angle (φ)
φ = Step Angle
Ns = Number of poles on stator
Nr = Number of poles on rotor
7. State the applications of stepper motor.
 Computer peripherals like printers, tape and floppy disc drives
 Numerical control of machine tools
 Robotics
 Watches and spacecrafts
 X-Y recorders and plotters
8. What are the types of stepper motor?
 Variable reluctance stepper motor
 Permanent magnet stepper motor
 Hybrid stepper motor
9. What are the advantages of variable reluctance stepper motor?
The variable reluctance motor has the following advantages
 High torque to inertia ratio

 Fast acceleration
 Fast dynamic response
 Simple and low cast machine
 Rotor construction is robust due to absence of brushes
10. Define holding torque.
Holding torque is the maximum load torque which the energized stepper motor can
withstand without slipping from equilibrium position.
11. Compare variable reluctance and permanent magnet stepper motor.
S. No Variable Reluctance Stepper Motor Permanent Magnet Stepper Motor
1 The Rotor is not magnetized The Rotor is magnetized
2 High torque to inertia ratio Low torque to inertia ratio
3 Fast acceleration Slow acceleration
4 Fast dynamic response Very slow dynamic response
12. What is universal motor and what are its features?
A universal motor is a special type of motor which is designed to run on either DC or
single phase AC supply.
Its features are high starting torque, can run at high speed, and are lightweight and
compact. They are commonly used in portable power tools and equipment, as well as many
house hold appliances.
13. Give the application of universal motor.
 Domestic appliances like food processors, vacuum cleaners and Mixes etc
 Industrial sewing machine
 Electric hand drills
 Hand dryers
 Electric shavers
14. State the advantage of universal motors.
 Produce high speed from 3600 rpm to 25000 rpm
 High power output in small physical sizes
 High torque at low loads
 Variable speed by adjustable governor
15. State the disadvantage of universal motor.
 Relatively high noise level at high speed
 Requirement of careful balancing to avoid vibration
 Requirement of reduction gearing in most portable tools

16. Give the types of universal motor.
 Concentric winding type
 Non-concentric winding type
17 .Write the applications of synchronous motor?
a. Used for power factor improvement in sub-stations and in industries.
b. Used in industries for power applications.
c. Used for constant speed drives such as motor-generator set, pumps and compressors
18. List four applications of reluctance motors.
This motor is used in signaling devices, control apparatus, automatic regulators, recording
instruments, clocks and all kinds of timing devices, teleprinters and gramophones.
19. What is hybrid stepper motor?
A hybrid stepper motor combines the features of both Permanent Magnet and
Variable Reluctance stepping motors.
20. What are the advantages of hybrid stepper motor?
 Less tendency to resonate.
 Higher holding torque capability.
 High stepping rate capability.
21. What are the disadvantages of hybrid stepper motor?
1. Higher inertia and weight due to presence of rotor magnet.
2. Performance affected by change in magnetic strength.
22. What are the different modes of excitation in a stepper motor?
1. 1-phase on or full step operation.
2. 2- phase on mode.
3. Half step operation.
4. Micro stepping operation.
23. What is meant by full step operation?
It is the one-phase on mode operation. It means, at that time only one winding is
energized. By energizing one stator winding, the rotor rotates some angle. It is the full step
operation.
24. What is meant by half step operation?
It is the alternate one phase on and 2 phase on mode operation. Here the rotor rotate
an each step angle is half of the full step angle.
25. What are the advantages of reluctance motor?
 No dc supply is necessary for rotor
 Constant speed characteristics
 Robust construction
 Less maintenance
26. Write some advantages of hysteresis motor over induction motor?

 As rotor has no teeth, no winding, there are no mechanical vibrations
 Operation is quiet and noiseless
 Suitability to accelerate high inertia loads
 Possibility of multispeed operation by employing gear train
27. Write some applications of hysteresis motor?
 Sound recording instruments
 Sound producing equipments
 High quality record players
 Tape recorders
 Electric clocks
 Teleprinters and timing devices
28. State the limitations of the reluctance motor.
 Less efficiency
 Poor power factor
 Need of very low inertia rotor
 Less capacity to drive the loads
1. What is meant by air conditioning?
It involves the control of the temperature, humidity and motion of air in an enclosure. It
has filters for removing lint and dust and may include equipment for services such as removing
odours or killing bacteria.
(Or)
The technique of maintaining of air condition inside a building in such a way that
produce comfort to human beings, ensures trouble free operation of delicate equipment or helps
in industrial manufacturing operation is called air conditioning.
2. What are the types of air conditioning system?
 Unitary air conditioning system
 Central air conditioning system
 Unitary-central air conditioning system
3. What are the processes involved in air conditioning?
 Control of temperature
 Cleanliness
 Humidity
 Circulation of air
4. Define plane angle.
Unit-V (UTILISATION)
Domestic wiring – principle of electrical heating – The laws of illumination – Electric lamps –
Photometers – Electroplating – Electric Traction – Air conditioning – Earthing.

When two straight lines lying in the same plane meets at a point, there will be an angle
between these converging lines at the meeting point. This angle is termed as Plane Angle. In the
figure AOB is the plane angle. The plane angle is represented by radians.
5. What is radian?
The plane angle is represented in radians and from the above figure radians is given as
Radians =
6. What is solid angle?
The angle subtended by a point in space by an area, is termed as solid angle. This solid angle
represents the volume which is enclosed by numerous lines lying on the surface and meeting at a
point. It is usually denoted by the symbol
2
Unit for solid angle is STERADIAN.
7. Define Mean horizontal candle power [MHCP].
The mean or average of the candle power in all directions on a horizontal plane passing
through the source of light is called mean horizontal candle power.
8. Define LUX.
It is defined as the luminous flux falling per square metre on the surface which is everywhere
perpendicular to the rays of light from a source of one candle power and one metre away from it.
9. Define Lumen.

It is the unit of luminous flux and is defined as the luminous flux per unit angle from a
source of 1 candle power.
Lumens = Candle power x solid angle
= CP x ω
In the same way we can represent the candle power in terms of lumens and angular velocity as
C.P. =
10. Define illumination.
When the light falls upon any surface, the phenomenon is called is called illumination. (Or)
The number of lumens, falling on the surface, per unit area. E = F/A lumens/m2
or lux
11. Define Mean Spherical candle power. [MSCP]
The mean or average of candle power of a source of light in all directions in all planes is
called MSCP.
12. Define Mean Hemispherical candle power. [MHSCP]
The mean or average of candle power in all directions within the hemisphere either above the
horizontal plane or below the horizontal plane
13. What are the two laws of illumination?
 Inverse square law
 Lambert’s cosine law.
14. State Inverse square law.
The law states that illumination of a surface is inversely proportional to the square of the
distance of the surface from the source of light. Under this condition the source is a point source.
15. State Lambert’s cosine law.
This law states that illumination at any point on a surface is proportional to the cosine of the
angle between the normal at that point and the direction of luminous flux.
16. Define Luminous Intensity.
It is the measure of luminous flux in lumens emitted per unit solid angle by a point source and
is denoted by ‘I’.

I = its unit is candela or lumen/steradian.
17. What are the various types of arc lamps?
 Carbon arc lamp
 Flame arc lamp
 Magnetic arc lamp
18. What are the advantages of dielectric heating?
 Possibility of applying accurate quality of heat
 Increase in production
 High uniformity and quality of the products
 Improvement in working condition
 Limited space requirement
 Easy maintenance
19. Mention any two advantages of electrical heating
 Cleanliness
 Absence of flue gases
 Ease of control
 Cheap furnaces
20. What is meant by electric traction?
Electric traction is meant for locomotion in which the driving (tractive) force is obtained
from electric motors or traction motors. It involves utilization of electric power for traction
systems i.e., for railways, trams, trolleys etc.
21. What are the types of electric traction?
 DC traction
 AC traction
 Multi system
22. State any two advantages of electric traction.
The four advantages of electric traction are
 Initial and running cost of the system are low
 High efficiency
 The wearing of track is minimum
 There is no expensive wear and tear.
23. Define electro plating
Electro plating is defined as art of depositing a superior or a more noble metal on an
inferior or a base metal by means of electrolysis of an aqueous solution of a suitable electrolyte.
24. What are the uses of electro plating?
Electro plating are used as the
 Protection of metals against correction
 Giving a shiny appearance to articles

 Giving reflecting properties to the reflectors
 Replacing worn out material
25. What is meant by photometer?
An instrument that measures luminous intensity or brightness, luminous flux, light distribution,
color, etc., usually by comparing the light emitted bytwo sources, one source having certain
specified standard characteristics.
26. How light sources are classified?
 Arc lamps
 High temperature lamps
 Gaseous discharge lamps
 Fluorescent type lamps

27. What is meant by earthing? What are its types?
An earthing system or grounding system is circuitry which connects parts of the electric
circuit with the ground, thus defining the electric potential of the conductors relative to the
Earth's conductive surface. If a fault within an electrical device connects a live supply conductor
to an exposed conductive surface, anyone touching it while electrically connected to the earth
will complete a circuit back to the earthed supply conductor and receive an electric shock.
Types of earthing are
 Pipe earthing
 Plate earthing

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