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

http://www.electrical4u.com/voltage-regulation-of-transformer/

http://www.electrical4u.com/voltage-or-electric-potential-difference/


Variable loss

Copper loss or I2R 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 = I22 (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 = PNZ / 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 = PNZ / 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.

http://en.wikipedia.org/wiki/Power_station

http://en.wikipedia.org/wiki/Reactive_power

http://en.wikipedia.org/wiki/Fault_(power_engineering)


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

http://en.wikipedia.org/wiki/Ground_(electricity)

http://en.wikipedia.org/wiki/Electric_potential

http://en.wikipedia.org/wiki/Electric_shock

Two marks

Engineering

Transcript of Two marks