energy conversion

Generators and Motors

Are rotating electrical machines that convert mechanical energy input to usable electrical energy

Generators

Yoke

Pole and Pole Shoe

Field Winding

Armature

Commutator

Brushes

Main Parts

Main Parts

• Support the field

coil and spread

the flux over large

area

• It is cylindrical

in shape to

which even

number of

poles is bolted

Yoke Field Winding

Pole and Pole Shoe

It is cylindrical in shape to which even number of poles is bolted

• A cylindrical core

• Made of sheet steel

laminations and

insulated from each

other by a thin layer of

paper and varnish to

reduce iron loss

Armature

Main Parts

Cylindrical in shape and consists of segments of hard drawn copper . A mica strip insulates each segment from each other. Windings of armature are terminated on it

Main Parts

• Used to connect the external circuit to the

armature

Commutator

Brushes

General Types of AC Armature Winding

Lap Winding Wave Winding

Type of winding which

coil end are connected

to commutator segments

that are near to one

another.

Type of winding which

the coil ends are

connected to

commutator segments

that are of some

distance from one

another; nearly 360

degrees

Parallel Paths

a = Armature current paths for both DC motor and DC generator

M = plex or degree of multiplicity of the winding P = number of poles

a = mP a = 2m

For Lap

WindingFor Wave

Winding

Parallel Paths

Winding m

Simplex 1

Duplex 2

Triplex 3

Quadruplex 4

Voltage across the armature of the DC generatorAC not DC

General Voltage of a DC Generator

(EMF)

Commutation

responsible in converting the generated AC voltage in the armature to DC

the reversal of current in the coil passes through the brush position

Commutator

General Voltage of a DC Generator

(EMF)

Eg =ZPΦN

X 10-8 V60a

Eg = generated voltage/induced voltage Φ = flux per pole, lines or maxwells N = speed of rotation of the armature; rpm Z = number of active conductors a = number of parallel paths

Armature Reaction

When the generator is loaded, the armature conductor carries current and hence current carrying conductors produce a magnetic flux of its own which affects the flux created by the main poles.

Effects of Armature Reaction

Field Strength in the gap is weakened under the leading pole tips and strengthens under the trailing pole tips.

Magnetic field of the machine is distorted.

Neutralizes the cross-magnetizing effects of armature reaction

Connected in series with armature such that the current in it flows in opposite direction to that flowing in armature conductors directly below the pole shoes

Compensating Windings

A better method of providing commutating field.

Does not reduce armature reaction

Interpoles

Types of DC Generators

SeriesShunt

Self Excited GeneratorSeparately Excited

DC Generator

Compound

Long Shunt Short Shunt

Separately Excited DC Generator

Ia = ILIf = V/Rf

Eg = VT + Va + Vbc

Eg = VT + Ia( ra + rbc )

The field winding is energized from an external DC source is called “exciter”. The exciter maybe a battery or another DC generator.

The field winding is energized by its own armature( shunt, series or compound)

Self Excited DC Generator

Shunt Generator

Ia = ISH +ILIf = VT/RSH

Eg = VT + Va + Vbc

Eg = VT + Ia( ra + rbc )


Series Generator

Ia = IS = ILEg = VT + Va +Vs + Vbc

Eg = VT + Ia( ra + Rs + rbc )

Compound Generator

Long Shunt

Ia = ISH = IS = ILISH = VT/RSH

Eg = VT + Va + VS + Vbc

Eg = VT + Ia(ra + rbc + RS)


Compound Generator

Short Shunt


IS = ILIa = ISH + ILEg = Va + Vbc + VSH

Eg = VT + Va + VS + Vbc

Eg = VT + Ia(ra + rbc) + IsRs


Where:Eg = generated voltage/induced voltage of the generator Ia = armature current; AIL = load current / line current; AISH = shunt field current; AIS = series field current; Ara = armature winding resistance; ΩRbc = brush contact resistance; ΩRSH = shunt field resistance; ΩRS = series field resistance; ΩRL = Load resistance; Ω


VT = load voltage / terminal voltage; VVSH = shunt field winding resistance drop; VVS = series field winding resistance drop; VVa = armature winding resistance drop; VVbc = brush contact resistance drop; V

Losses in DC Generator

Losses due to current in the various windings of the machine

Armature copper loss

Field copper loss

Brush contact loss

Copper Loss


Iron Loss

Magnetic or core losses

Hysteresis Loss

Eddy Current Loss


Mechanical Losses

Air friction of rotating armature

Bearing friction

Brush friction

Machine designed to generate alternating curves

Alternators

Operating Principle

When the rotor rotates, the stator conductors are cut by the

magnetic flux, hence they have induced emf produced in

them. Because of the magnetic poles are alternately N and

S poles, they have induced an emf and hence current in the

armature conductors, which first flow in one direction and

then in the other. Hence an alternating emf is produced in

the stator conductors whose frequency depends on the

number of poles moving past in a conductor in one second

and whose direction is given by Flemings’s Right hand Rule.

Alternators

Frequency of the Generated Voltage

f =P(rpm)

Hertz120

Where:

F = frequency, Hz

P = no. of poles

rpm = speed of rotation

Where:E = total generated voltage, VN = no. of turns per coilΦ = flux per pole, maxwellskd = distribution factorkp = pitch factor

Note:For full winding, kp = 1For concentric winding, kd = 1

Alternators

E = 4.44NΦkdkp x 10-8 V

Generated Voltage

of an Alternator

Alternators

Effects of Various Types of Load

on the Alternator Terminal Voltage

Resistive Loads

Capacitive Loads

Inductive Loads

Resistive Loads Incandescent

lamps, heating devices or loads with unity power factor

8% to 20% drop in terminal voltage below its no-load value

Alternators

Inductive Loads

• Induction motors,

electrical

welders,

fluorescent

lighting or loads

with lagging

power factor.

• 25% to 50% drop

in terminal

voltage below

the no-load value

Capacitive Loads

• Capacitor devices

or special types of

synchronous

motor or loads

with leading power

factor.

• Tend to raise or

increase the

terminal voltage of

the alternator

above the no load

value.

Rotating electrical machines that convert electrical energy into mechanical energy

It has a reverse operation with generators

The presence of back emf causes the armature current to automatically changes with the increase of load on the motor. If there is no back emf, the armature may take very high current and winding may be damaged (like during starting, the current is high

Motors

Utilizes DC energy as input to produce mechanical actions

Ec =ZPΦN

X 10-8 V60a

DC Motors

Counter EMF of MotorsWhere:

Ec = back emf or counter emf,V

P = no. of poles

Φ = flux per pole, lines or

maxwells

N = speed of rotation of the

armature; rpm

Z = number of active conductors

a = number of parallel paths

Types of DC Motors

Shunt

Series

Compound

Its field winding is connected across the armature

Nearly constant or adjustable

Medium starting torque

Used for fan, blower, pump, grinder, etc

Note:

To reverse the direction of rotation, interchange the brush or reverse the connection of the shunt field

Never open the field circuit while the motor is operating for it will “race” or “run away”

Shunt Motor

Shunt Motor

IL = Ia + ISH

ISH = Vs/RSH

Ec = Vs – Va – Vbc

Ec = Vs – Ia(ra + rbc)

The field winding is connected in series with the armature

Variable speed High starting torque Used for elevators, crane, conveyor, hoist, gear drive,

etc.

Note:To reverse the direction of rotation, interchange the

brushesNever start this series motor without load or remove the

load while operating for it will “race” or “run away”.

Series Motor

Series Motor

IL = Is = IaEc = Vs - Va - Vbc - VSF

Ec = Vs – IL(ra + rbc + Rs)

Variable-speed or adjustable speed

Has a series and shunt field coils similar to compound generator

High starting torque

Used for elevators, conveyor, crane, milling machine, punching machine, etc

Compound Motor

Torque Developed in the Armature

T = 9.55 (

Ia x Ec

)N-m T = kIaΦ

N

Where:T = torque developed, N-mN = speed of rotation, rpmΦ = flux per pole, weber

K = proportinality constant

Mechanical Power Output

HP = 2πNT

HP = 2πNT

33,000 44,760

Where:

HP = horsepower

Percentage rise in the speed of the motor when the mechanical load is removed

%NR = NNL - NFL

x 100%NFL

Speed Regulations

• Where:

• NNL = no-load speed

• NFL = full-load speed

An Arc machine that operates at synchronous speed and converts electrical energy to mechanical energy

Synchronous Motors

Stator

Houses 3 phase armature windings in the slots of the core and receives power from 3-phase supply

Rotor

Has a number of alternate N and S poles. The rotor poles are excited by an exciter, which is a DC generator, mounted on the rotor shaft

Parts of Synchronous Motors

Under-excitation

the field excitation that the back emf is less than the applied voltage. The motor has lagging power factor

Normal Excitation

Operates at almost unity power factor

Over-Excitation

Operates in leading power factor

Characteristics of Synchronous Motors

Used where a constant speed is required

Used in power factor correction in the factories

Uses of Synchronous Motors

When a 3-phase supply is applied to the stator, a rotating magnetic field is produced. This rotating magnetic field produces induced emfin the rotor windings that cause induced current to circulate.

Induction Motors

Principles of Induction Motors

By Lenz’s Law, the induced current tends to oppose the action producing it and therefore circulate in such a manner that a torque is produced. However, the rotor not rotate as fast as the rotating magnetic field.

Principles of Induction Motors

Induction Motors

The speed at which the rotating flux rotates

Speeds of Induction Motors

Synchronous Speed Rotor Speed Slip

• Actual speed of the motor

• It cant be calculated but it can be measured using tachometer or speedometer

• The difference between the synchronous speed and the actual speed

Squirrel Cage Motor

Used where low power needed and speed control is needed Slip Ring

Used only when high starting torque is required

Types of Induction Motors

Advantages of Induction Motors

Requires minimum care

and maintenance

High efficiency

Good power factor

Self-starting

Simple in construction,

robust and almost

unbreakable

Disadvantages of Induction Motors

Speed cannot be varied

without loss of

efficiency

Speed decreases with

the increase load

Has inferior starting

torque

Converters

and

Rectifiers

Methods of Converting AC to DC

Motor-Generator Set

An AC and DC generator

mechanically coupled; AC

motor can be synchronous

or induction motor

Rotary Converters

Single machine with one

armature and one field

Combines the function of a

synchronous motor and DC

generator

Methods of Converting AC to DC

Motor Converters

Rectifiers

consists of ordinary slip

ring induction motor

coupled both mechanically

and electrically to a DC

generator

Converts AC to

unidirectional current by

virtue of permitting flow of

currents in only one

direction

Applications of Generators and Motors

Trade name for rotating amplifiers

Quick response DC generator, output of which is controlled by a very small field power

Power amplifier; most suitable use as an exciter in a closed loop control system

Amplidyne


Generator employing silicon rectifiers as static commutation devices

Aircraft generator

Brushless Generators


Rotary transformer

A composite machine having a single magnet frame but two separate armature windings, one acting as a generator and the other as a motor, and independent commutators

Dyna-motor


A single-stage rotating amplifier relying on the use of positive feedback

Rototrol Magnicon

• Trade name for rotating amplifiers with cross field excitation


Converts thermal energy into electric by breaking a stream of hot ionized gas

Plasma hydrodynamic generator

Magnetohydrodynamic Generator


A stream of gas is ionized, the positive ions being carried away by the stream while the electrons are collected by an electrode ring causing a current to flow through a wire between the ring and a collecting grid

Electrohydrodynamic Generator


Rotating amplifier

Similar to the nature of amplidyne

Metadyne Generator


An induction motor and a synchronous converter mechanically and electrically coupled

Converts AC to DC

Motor Converter


A converter consisting of an AC motor directly coupled to a DC generator

No electrical connection between the two machines

Motor Generator


A converter based on electronic devices of the semiconductor, mercury arc or gaseous type, usually in combination with a transformer

Static Converter


Thermal-electrical conversion device

Thermocouple Generator

Transformers

It is an AC device that transfers power from one circuit to another without rotating and change of frequency

The windings are placed on outside of the core

Transformer Construction

Core Type

The windings are placed on inside of the core such that the magnetic circuit completely surrounds the winding

Transformer Construction

Shell Type

Parameters of Transformer

Equivalent Circuit of an ideal Transformer

For Ideal Transformers

Pp = PS


Voltage Ratio a = EP

=NP

ES NS

1=

IP=

NS

a IS NP

Impedance Ratio

Current Ratio

a² =ZP

= (NP

) ²ZS NS


Where

A = ratio of transformer/ turn ratio

EP = primary line (impressed) voltage

ES = secondary line (impressed) voltage

NP = no. of primary turn

NS = no. of secondary turn

IP = primary line current

IS = secondary line current

Losses in Transformers

Hysteresis Eddy Current

Iron Losses Copper Losses

Losses in Transformers

Hysteresis

Heating loss due to the collision of iron’s magnetic particles when it aligned to the external magnetic induction

Eddy Current

Loss due to eddy

current(eddy currents are

currents circulating around

the magnetic core of the

transformer

Condition for Maximum Efficiency

Copper Loss = Core Loss

Transformer

Open Circuit Test or No-load Test

Determine the no-load loss or core loss

Transformer

Short Circuit Test or Impedance test

Equivalent impedance, leakage reactance and total resistance of the transformer as referred to the winding in which the measuring instruments are placed

Rated or Full-load copper loss

Autotransformer

Has only one winding which performs

the function of both primary and

secondary winding. These

transformers are used as regulating

transformers where only a small

variation of voltage is required

Electrolysis and Batteries

Electrolysis

The conduction of electric current

through the solution of an electrolyte

together with the resulting chemical

changes

Important Terms

Anode

Cathode

Ions

Anions

Cations

plate or electrode connected to the + terminal

plate or electrode connected to the - terminal

The electrolyte gets chemically decomposed

Ions having + charge

Ions having - charge

The mass of an ion set free by a current in the process of electrolysis is proportional to the quantity of charge that has passed through the electrolyte

Faraday’s Law of Electrolysis

First Law

W α Q α It W = ZIt

Where

W = mass of ion liberated

I = current in amperes

t = time in seconds

Z = a constant value that depends upon the nature of substance

When the same current passes through several electrolyte for the same time, the mass of various ions deposited at each of the electrodes are proportional to their chemical equivalents

m1=

E1=

Z1

m2 E2 Z2

Faraday’s Law of Electrolysis

Second Law

Where

m1 & m2 = mass of ion deposited or liberated

E1 & E2 = chemical equivalent weights (atomic weight / valency)

Z1 & Z2 = electromechanical equivalent

Applications of Electrolysis

Electroplating

Depositing a thin layer of precious metal (silver,

gold) over an inferior metal

Extraction and Purification of Metals

Battery

Primary Cells Secondary Cells

Chemical action not

reversible

An assembly of voltaic primary and secondary cell

Also known as

accumulators

or storage

batteries

Uses acid as an

electrolyte

Uses alkali as an

electrolyte

Acid Cells

Alkali Cells

Local Action

The continuous dissolution of the zinc rod even

when the cell is not connected to the external circuit

This is due to impurities present in commercial zinc. The impurities

form small tiny cells, which are short circuited by the main body of

the zinc rod

Can be minimized by using amalgamated zinc

The collection of hydrogen bubbles on the surface of the copper plate

Polarization

Effects of Polarization

The bubbles act as insulators and hence increase the internal

resistance of the cell

Sticking H2 ions on the +Ve plate exert repulsive

force on the other H2 ions coming towards the Cu

plate. Minimized by surrounding the cathode by

depolarizers, which oxidizes H2 bubbles as soon as

they are produced

Charging the Battery

Process of reversing the current flow through the battery to restore the battery to its original position

5 Types of Charge

1. Initial Charge

2. Normal Charge

3. Equalizing Charge

4. Floating Charge

5. Fast Charge

List of Batteries and their Corresponding Output

Primary

Alkaline Mn02 1.15 V

Carbon Zinc 1.5 V

Electrolyte 2.8 V

Leclanche 1.2 V

Li-organic 2.8 V

Magnesium 1.5 V

Manganeses dioxide (alkaline) 1.5 V

Mercad 0.85 V

Mercury 1.2 V

Mercuric Oxide 1.35 V

Silver Oxide 1.5 V

Solid 1.9 V

Zinc-Air 1.1 V

Zinc-Chloride 1.5 V

List of Batteries and their Corresponding Output

Secondary

Edison 1.2 V

Lead - Acid 2.1 V

Manganese Dioxide (alkaline) 1.5 V

Nickel - Cadmium 1.25 V

Nickel - Hydrogen 1.2 V

Nickel - Iron 1.2 V

Silver - Cadmium 1.05 V

Silver - Zinc 1.5 V

Zinc - Chloride 2.0 V

Zinc - Nickel Oxide 1.6 V

Most Commonly Used Cells

Primary

Type Voltage (V) Remarks

Carbon - Zinc 1.5

used for flash lights

and toys; low cost

and low current

capacity

Zinc - Chloride 1.5higher current

capacity

Manganese Alkaline 1.5

hydroxide electrolyte

and high current

capacity

Silver Oxide 1.5 hydroxide electrolyte

Lithium 2.8 long life, high cost

Most Commonly Used Cells

Secondary

Type Voltage (V) Remarks

Lead Acid 2.1 wet electrolyte

Silver - Zinc 1.5

rechargeable dry cell,

high current

capacity

Silver - Cadmium 1.05rechargeable dry cell,

high efficiency

Nickel - Cadmium 1.25rechargeable dry

battery

Review

Questions

1. A 4-pole DC generator with duplex lap winding has 48 slots and four elements per slot. The flux per pole is 2.5 x 106 maxwells and it runs at 1500 rpm. What is the output voltage?

a. 60

b. 360

c. 225

d. 120

Review Questions

2. Find the frequency in kilocycles per second in the armature of a 10 pole, 1200 rpm generator?

a. 100

b. 1000

c. 10

d. .1

Review Questions

3. What is the voltage regulation when the full load voltage is the same as no-load voltage assuming a perfect voltage source?

a. 100%

b. 10%

c. 1%

d. 0%

Review Questions

4. In DC motors, the emf developed which opposes to the supplied voltage

a. Residual emf

b. Coercive emf

c. Induced emf

d. Counter emf

Review Questions

5. What will happen to a DC series motor when its load is removed?

a. the motor will stop

b. the motor speed remains the same

c. the torque remains the same

d. the motor will over speed

Review Questions

6. The armature of a DC generator is laminated to _________.

a. Reduce the bulk

b. Provide passage for cooling air

c. Reduce eddy current losses

d. Insulate the core

Review Questions

7. Which of the following helps in reducing the effect of armature reaction in DC generators?

1. Interpoles

2. Compensating Windings

a. 1 only

b. 2 only

c. Both 1 & 2

d. Neither 1 & 2

Review Questions

8. The loss in DC generator that varies with the load is ___________.

a. Copper loss

b. Eddy current Loss

c. Hysteresis Loss

d. Windage Loss

Review Questions

9. Magnetic field in a DC generator is produced by _________.

Electromagnets Permanent Magnets Iron Core Steel Laminations

a. 1 onlyb. 2 onlyc. 1 & 2 onlyd. 1,2,3 & 4

Review Questions

10. In DC generator, the cause of rapid brush wears maybe _________.

Severe sparking Rough commutation surface Imperfect contact Slots disorientation

a. 1,2 & 3 onlyb. 1,2 & 4 onlyc. 2,3 & 4 onlyd. 1,2,3 and 4

Review Questions

11. Which of the following components of a DC generator plays vital role for providing direct current of a DC generator

a. Dummy coils

b. Commutator

c. Eye bolt

d. Equalizer ring

Review Questions

12. Find the voltage regulation of a generator when full load voltage is 110 V and the no load voltage is 120 V.

a. 1%

b. 9.09%

c. 90.9%

d. 10%

Review Questions

13. Where does voltage generated in a DC generator depends?

Field resistance Speed Flux Field current Armature resistance

a. 1,2 and 3 onlyb. 2 and 3 onlyc. 2,3 and 4 onlyd. 1,3 and 5 only

Review Questions

14. Generators are often preferred to be run in parallel because of ___________.

Great reliability

Meeting greater load demands

Higher efficiency

a. 1,2 and 3

b. 1 and 2 only

c. 1 and 3 only

d. 2 and 3 only

Review Questions

15. DC generator preferred for charging automobile batteries is __________.

a. Shunt generator

b. Long shunt compund generator

c. Series generator

d. Any of these

Review Questions

16. The purpose of providing dummy coils in a generator is __________.

a. To reduce eddy current losses

b. To enhance flux density

c. To amplify voltage

d. To provide mechanical balance for the rotor

Review Questions

17. Which of the following generating machine will offer constant voltage on all loads?

a. Self excited generator

b. Separately excited generator

c. Level compounded generator

d. All of the above

Review Questions

18. A DC generator works on the principle of

a. Lenz’s Law

b. Ohm’s Law

c. Faraday’s Law of Electromagnetism Induction

d. None of the above

Review Questions

19. With a DC generator, which of the following regulation is preferred?

a. 100% regulation

b. Infinite regulation

c. 50% regulation

d. 1% regulation

Review Questions

20. The purpose of an amperite regulator

a. Power regulation

b. Loss regulation

c. Current regulation

d. Voltage regulation

Review Questions

21. The only purpose of a DC generator that has been modified to function as an amplidyne is to

a. Serve as a booster

b. Serve as a regualtor

c. Serve as a meter

d. Serve as power amplifier

Review Questions

22. A simple method of increasing the voltage of a DC generator is ________

a. Increase the length of the armature

b. Decrease the length of the armature

c. Increase the speed of rotation

d. Decrease the speed of rotation

Review Questions

23. A 4-pole lap wound armature has 120 slots and 4 conductors per slot. The flux per pole is 50 mWb and it generates 240 volts. Find the speed.

a. 1200 rpm

b. 800 rpm

c. 600 rpm

d. 300 rpm

Review Questions

24. The power stated on the nameplate of any motor is always the ________

a. Gross Power

b. Output power at the shaft

c. Power drawn in kVA

d. Power drawn in kW

Review Questions

25. A DC motor is used to ___________

a. Generate power

b. Change mechanical to electrical energy

c. Change electrical to mechanical energy

d. Increase energy put to it

Review Questions

26. A DC motor is still used in industrial applications because it

a. Is cheap

b. Is simple in construction

c. Provides fine speed control


Review Questions

27. Carbon brushes are preferable to copper brushes because

They have longer life They reduce armature reaction They have lower resistance They reduce sparking

a. 1 and 2 onlyb. 2 and 3 onlyc. 3 and 4 onlyd. 1 and 4 only

Review Questions

28. The field poles and armature of a DC machine are laminated to ________

a. Reduce the weight of the machine

b. Decrease the speed

c. Reduces eddy current

d. Reduce armature reaction

Review Questions

29. Steam turbo alternators are much smaller in size than water turbine alternators for a given output. This is so because _________.

Steam turbo alternators are built with smaller capacities Steam turbo alternators run at high speed Steam turbo alternators have long rotors

a. 1 & 2 onlyb. 1 & 3 onlyc. 2 & 3 onlyd. 1,2 and 3

Review Questions

30. When the speed of a DC motor increases, its armature current ________

a. Increases

b. Decreases

c. Remains constant


Review Questions

31. The amount of the back emf of a shunt motor will increase when __________

a. Load is increased

b. The field is weak

c. The field is strengthened


Review Questions

32. The speed of a DC motor is ________

a. Directly proportional to the flux per pole

b. Inversely proportional to the flux per pole

c. Inversely proportional to the applied voltage


Review Questions

33. The torque developed by a DC motor is directly proportional to ______

a. Flux per pole x armature current

b. Armature resistance x applied voltage

c. Armature resistance x armature current


Review Questions

34. The speed of a _______ motor is practically constant

a. Cumulatively compounded

b. Series

c. Differentially compounded

d. Shunt

Review Questions

35. ________ motor is a variable speed motor.

a. Series Motor

b. Shunt Motor

c. Cumulatively Compounded

d. Differentially Compunded

Review Questions

36. What do you call an electromagnet with its core in a form of a magnetic ring?

a. Paraboloid

b. Solenoid

c. Toroid

d. Motor

Review Questions

37. The working principle of a transformer is ________

a. Self induction

b. Static induction

c. Mutual induction

d. Dynamic induction

Review Questions

38. A type of transformer that is protect technicians from deadly electrical shock is called a/an ______

a. Absorber transformer

b. Step down transformer

c. Step up transformer

d. Isolation transformer

Review Questions

39. What is the typical use of an autotransformer?

a. Toy transformer

b. Control transformer

c. Variable transformer

d. Isolating transformer

Review Questions

40. Synchronous motor is capable of beig operated at _________

a. Lagging pf only

b. Unity pf only

c. Leading pf only

d. All of the above

Review Questions

energy conversion

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