ROTOR LESS GENERATOR

A PROJECT REPORT

Submitted by

ANANTHARAMAN.M 41710105002

ARUN NEHRU.N 41710105003

ATTHARUDDIN.S 41710105005

In partial fulfillment for the award of the degree

Of

BACHELOR OF ENGINEERING

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

SHRI ANDAL ALAGAR COLLEGE OF ENGINEERING

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

MAMANDUR

ANNA UNIVERSITY: CHENNAI 600 025.

APRIL 2014.

ANNA UNIVERSITY: CHENNAI 600 025

BONAFIDE CERTIFICATE

Certified that this project report “ROTOR LESS GENERATOR” is the bonafide work of

“S.ATTHARUDDIN, N.ARUN NEHRU, M.ANANTHARAMAN” who carried out the

project work under my supervision.

SIGNATURE SIGNATURE

Dr.A.SOLLIAPPAN Ph.D. Mr. Mr.Kirubanandan.R M.Tech.,HEAD OF THE DEPARTMENT, ASSISTANT PROFESSOR,

Department of EEE Department of EEE,

Electrical and Electronics Engineering Electrical and Electronics Engineering

Shri Andal Alagar College of Engg. Shri Andal Alagar College of Engg.

Mamandur. Mamandur.

Submitted for the university Examination held on __________________

INTERNAL EXAMINER EXTERNAL EXAMINER

ACKNOWLEDGEMENT

At this moment we wish to record our sincere thanks to the management

“SHRI ANDAL ALAGAR COLLEGE OF ENGINEERING” for the

permission granted to carry-out this project.

Our sincere thanks to the chairperson Mrs.PREMALATHA VIJAYAKANTH,

secretary Mr.L.K.SUDHISH and correspondent for providing the facilities. We

wish to thank our principal Dr.N.KARTHIKEYAN for his encouragement during

this work.

We sincerely thank our project guide Dr.A.SOLIAPPAN Ph.D., for the effective

guidance and useful suggestions during the period of this project work.

We would also thank to Teaching and Non Teaching staff of ELECTRICAL

AND ELECTRONICS Department for providing their support in our project

work.

We would also thank to our friends and parents for their backing in our successful

completion our project. Last but not least, we thank our parents for their unstinting

faith in us and their unconditional love and support, without whom, this never

would have been possible.

ABSTRACT

The Rotor less Generator is a generator which does not have a rotating part, instead

it uses the Rotating Magnetic Field (RMF) for the production of Power. That is,

initially when the Armature is standstill the flux Rotating magnetic field cut every

solid conductor of the Armature. As a rotor (armature) conductor are stationary

and sinusoidal stator field is rotating, there will be change in flux linkage. As a

result there is a induced current in the Armature conductors as per the Faradays

law of Electromagnetic induction. Therefore the rotating magnetic field (RMF) is

employed for the generation of EMF. So that it removes the work of PRIME

MOVER in a Generating plant hence which reduces the size of the power plants,

cost and maintenance, turbine unit is removed and system is pollution free. The

output EMF can be varied by varying the supply frequency. Power electronics is

employed in controlling the supply frequency to the magnetic circuits.

CHAPTER-1

INTRODUCTION

In electricity generation, an electric generator is a device that converts

mechanical energy to electrical energy. A generator forces electric current to flow

through an external circuit. The source of mechanical energy may be a

reciprocating or turbine steam engine, water falling through a turbine or

waterwheel, an internal combustion engine, a wind turbine a hand crank,

compressed air, or any other source of mechanical energy. Generators provide

nearly all of the power for electric power grids.

The reverse conversion of electrical energy into mechanical energy is done

by an electric motor, and motors and generators have many similarities. Many

motors can be mechanically driven to generate electricity and frequently make

acceptable generators

1.1 HISTORY

Large power generation dynamos are now rarely seen due to the now nearly

universal use of alternating current for power distribution. Before the adoption of

AC, very large direct-current dynamos were the only means of power generation

and distribution. AC has come to dominate due to the ability of AC to be easily

transformed to and from very high voltages to permit low losses over large

distances.

Before the connection between magnetism and electricity was discovered,

electrostatic generators were used. They operated on electrostatic principles. Such

generators generated very high voltage and low current. They operated by using

moving electrically charged belts, plates, and disks that carried charge to a high

potential electrode. The charge was generated using either of two mechanisms:

Electrostatic induction

The triboelectric effect, where the contact between two insulators leaves

them charged.

Because of their inefficiency and the difficulty of insulating machines that

produced very high voltages, electrostatic generators had low power ratings, and

were never used for generation of commercially significant quantities of electric

power. The Wimshurst machine and Van de Graaff generator are examples of these

machines that have survived.

In 1827, Hungarian Anyos Jedlik started experimenting with the

electromagnetic rotating devices which he called electromagnetic self-rotors, now

called the Jedlik's dynamo. In the prototype of the single-pole electric starter

(finished between 1852 and 1854) both the stationary and the revolving parts were

electromagnetic. He formulated the concept of the dynamo at least 6 years before

Siemens and Wheatstone but didn't patent it as he thought he wasn't the first to

realize this. In essence the concept is that instead of permanent magnets, two

electromagnets opposite to each other induce the magnetic field around the rotor. It

was also the discovery of the principle of self-excitation.

1.2 A Brief History of Dynamos and Generators

The generator evolved from work by Michael Faraday and Joseph Henry in

the 1820s. Once these two inventors discovered and documented the phenomena of

electromagnetic induction, it lead to experimentation by others in both Europe and

North America.

1.2.1 1832 - Hippolyte Pixii (France) built the first dynamo using a commutator,

his model created pulses of electricity separated by no current. He also by accident

created the first alternator. He did not know what to do with the changing current,

he concentrated on trying to eliminate the alternating current to get DC power, this

led him to create the commutator.

1.2.2 1830s-1860s - The battery is still the most powerful way to supply electricity

for the various experimentation going on in that period. Electricity was still not

commercially viable. A battery powered electric train from Washington DC to

Baltimore failed, proving a gross embarrassment to the new field of electricity.

After m illions of dollars wasted steam still proved to be a better power source.

Electricity still needed to prove to be reliable and commercially.

He filled the magnetic field with an iron core which made a better path for

magnetic flux. This increased the power of the dynamo to the point where it was

usable for many commercial applications.

1.2.3 1870s - There was an explosion of new designs in dynamos, designs ranged a

wild assortment, only a few stood out as being superior in efficiency.

1.2.4 1877 - The Franklin Institute (Philadelphia) conducts test on dynamos from

around the world. Publicity from this event spurs development by others like Elihu

Thomson, Lord Kelvin, and Thomas Edison.

1.2.5 1878 - The Ganz Company begins to use AC generators in small commercial

installations in Budapest.

1.2.6 1880-1886 - Alternating Current systems develop in Europe with Siemens,

Sabastian Ferranti, Lucien Gaulard, and others. DC dynamos reign supreme in the

lucrative American market, many are skeptical to invest in AC. AC generators

were powerful, however the generator alone was not the biggest problem. Systems

for control and distribution of AC power needed to be improved before it could

compete with DC on a market.

1.2.7 1886-1891 - Polyphase AC generators are developed by C.S. Bradly (US),

August Haselwander (Germany), Mikhail Dolivo-Dobrovsky (Germany/Russia),

Galileo Ferraris (Italy), and others. AC systems which include better control and

powerful electric motors allow AC to compete

1.2.8 1891 - Three-Phase AC power proves to be the best system for power

generation and distribution at the International Electro-Technical Exhibition in

Frankfurt.

1.2.9 1892 - Charles P. Steinmetz presents his paper to the AIEE on hysteresis.

Steinmetz's understanding of the mathematics of AC power is published and helps

revolutionize AC power system design, including large AC Generators.

1.3 DC GENERATOR

It is based on the principle of production of dynamically (or motionally) induced

e.m.f (Electromotive Force). Whenever a conductor cuts magnetic flux,

dynamically induced e.m.f. is produced in it according to Faraday's Laws of

Electromagnetic Induction. This e.m.f. causes a current to flow if the conductor

circuit is closed.

   Hence, the basic essential parts of an electric generator are :

A magnetic field and

A conductor or conductors which can so move as to cut the flux

1.3.1 Commutator Segments

Inside a DC generator, the commutator is split into two segments. Both of

these segments are insulated so no electricity is actually transmitted directly

from one part of the commutator to the other. The loop of wire that rotates is

connected to both ends of the commutator at each end. There are also two

brushes made of carbon connected to the commutator. These carbon brushes

each have a very specific purpose--one brush is responsible for pushing the

electrical current out of the generator to whatever devices are being

powered, and the other brush pulls electrical current into the generator.

1.3.2 Carbon Brushes

All of the components on the inside of a DC generator are synced up to

operate at very specific time intervals. Once the electrical current gets going

inside of the generator, the segment of the commutator that holds all the

electricity that will be going outside of the current is always touching the

carbon brush that pushes the charge outside of the the unit. The electricity is

essentially "swept" from the commutator to the electrical devices connected

to the generator by the brush.

1.4 AC GENERATOR

A simple AC generator consists of: (a) a strong magnetic field, (b)

conductors that rotate through that magnetic field, and (c) a means by which

a continuous connection is provided to the conductors as they are rotating

the strong magnetic field is produced by a current flow through the field coil

of the rotor. The field coil in the rotor receives excitation through the use of

slip rings and brushes. Two brushes are spring-held in contact with the slip

rings to provide the continuous connection between the field coil and the

external excitation circuit. The armature is contained within the windings of

the stator and is connected to the output. Each time the rotor makes one

complete revolution, one complete cycle of AC is developed. A generator

has many turns of wire wound into the slots of the rotor.

A Delta Connection is a connection that has each coil end connected end-to-

end to form a closed loop. In a Delta Connection, the three windings are all

connected in series and form a closed circuit. A Delta Connection appears

like the Greek Letter Delta (Δ).

A Wye Connection is a connection that has one end of each coil connected

together and the other end of each coil left open for external connections. A

Wye Connection appears as the letter Y.

1.5 ROTORLESS INDUCTION GENERATOR

Current is produced in a conductor when it is moved through a magnetic

field because the magnetic lines of force are applying a force on the free

electrons in the conductor and causing them to move. This process of

generating current in a conductor by placing the conductor in a changing

magnetic field is called induction. This is called induction because there is

no physical connection between the conductor and the magnet. The current

is said to be induced in the conductor by the magnetic field. One

requirement for this electromagnetic induction to take place is that the

conductor, which is often a piece of wire, must be perpendicular to the

magnetic lines of force in order to produce the maximum force on the free

electrons. The direction that the induced current flows is determined by the

direction of the lines of force and by the direction the wire is moving in the

field.  In the animation above the ammeter (the instrument used to measure

current) indicates when there is current in the conductor.

If an AC current is fed through a piece of wire, the electromagnetic

field that is produced is constantly growing and shrinking due to the

constantly changing current in the wire. This growing and shrinking

magnetic field can induce electrical current in another wire that is held close

to the first wire. The current in the second wire will also be AC and in fact

will look very similar to the current flowing in the first wire. It is common to

wrap the wire into a coil to concentrate the strength of the magnetic field at

the ends of the coil. Wrapping the coil around an iron bar will further

concentrate the magnetic field in the iron bar. The magnetic field will be

strongest inside the bar and at its ends (poles).

CHAPTER-2

2.0 OVERVIEW OF ROTOR-LESS GENERATOR

• Principle

• Construction

• Stator

• Armature

• Working

• Control techniques

• Advantages

• Application

• Conclusion

2.1 PRINCIPLE

The electric machine works on the principle of faraday’s law of

electromagnetic induction. i.e. When a conductor placed in a rotating magnetic

field, the flux cuts the conductor and induces an EMF in the conductor ,when the

output path of the conductors are closed the current flows through it. The Output

voltage can be varied with the –

• The supply frequency

• Strength of the field

• With increase the number of Tph

2.2 Construction

The rotor less generator uses the Stator of Three Phase stator winding

The stator of the three phase winding consists of three main parts:

Stator frame

Stator core

Stator winding or field winding and

The Armature

2.2.1 Stator Winding or Field Winding

The slots on the periphery of stator core of the three phase induction motor

carries three phase windings. This three phase winding is supplied by three phase

ac supply. The three phases of the winding are connected either in star or delta

depending upon which type of starting method is used. The squirrel cage motor is

mostly started by star – delta stator and hence the stator of squirrel cage motor is

delta connected. The slip ring three phase induction motor are started by inserting

resistances so, the stator winding of slip ring induction motor can be connected

either in star or delta. The winding wound on the stator of three phase induction

motor is also called field winding and when this winding is excited by three phase

ac supply it produces a rotating magnetic field.

a) Single Phase -equivalent circuit of three phase induction stator

2.2.2 Armature coilAn armature coil consists of copper or aluminium coils wound on a non-

conducting material (insulator) to reduce the hysteresis losses. It may be star or

delta connected as per the requirements.

2.2.3 WorkingWhen an alternating supply is applied to the field or armature, the

field/armature produces a magnetic field which is electrically rotating called

Rotating magnetic field (RMF). In a 3 phase connection the rotating magnetic field

is 120` electrical. Thus producing a RMF. This RMF when passes through the

conductor ,due to the change in flux linkage an EMF induces in the conductor,

when closed the current flows. The RMF can be controlled by vvvf controller.

b) The T- equivalent stator and armature circuit:

2.3.1 Effect of 3 Phase Current Passing Through Stator Winding

When a 3 phase AC current passes through the winding, something very

interesting happens. It produces a rotating magnetic field. As shown in figure

below a magnetic field is produced which is rotating in nature.

• To understand this phenomenon much better consider a simplified 3 phase

winding with just 3 coils. A wire carrying current produces magnetic field

around it. Now for this special arrangement magnetic field produced by 3

phase A.C current will be as shown at a particular instant.

b) Magnetic field produced around the simplified winding and a single wire

With variation in A.C current, magnetic field takes a different orientation as

shown. From these 3 positions it’s clear that, it is like a magnetic field of uniform

strength rotating. Speed of rotation of magnetic field is known as synchronous

speed.

c) Rotating magnetic field produced over simplified winding

3.2 Effect of RMF on a Closed Conductor

Assume you are putting a closed conductor inside it. Since the magnetic

field is fluctuating an e.m.f will be induced in the loop according to Faraday’s law.

The e.m.f will produce a current through the loop. So the situation has become like

a current carrying loop is situated in a magnetic field. This current carrying

conductor can be taken to the load.

d) Effect of RMF on a closed conductor

DERIVATION OF AC MACHINE

1. The speed of the rotating magnetic field

ωsyn =2πf1/P/2 (rad/s)

or nsyn =60f1/P/2 (rev/min)

where

f1= is the frequency of the stator,

P = number of poles.

2. The armature speed of an induction machine is generally different from the

speed of the rotating magnetic field. The percentage difference of speed, known as

slip, is defined as

S =ωsyn-ωm/ωsyn

=nsyn-n/nsyn

where ωm and n are the speed of the armature in rad/s and rev/min, respectively.

3. The induced emf in one phase of the stator winding is

• E1 = 4.44f1N1kw1Φm

• and the emf in the armature winding

• E2s = 4.44f2N2kw2Φm

• where f1 and f2 are the frequencies of the emf's in the stator and rotor

windings, N1kw1 and N2kw2 the effective number of turns of the stator and

rotor windings, and Φm the magnitude of the rotating magnetic flux.

• Since f2=sf1, we have

• E2s=sE2

where E2 = 4.44f1N2kw2Φm is the armature when the armature is standstill.

CHAPTER-3

FIELD DESIGN

Outer

diameter

Inner

diamet

er

Stator

Bore

length

Slot

length

Slot

diameter

poles sl

ot

s

F

(H

Z)

Vph

(v)

PF H.P KW

10 8 12 6 7.5 4 24 50 415 .69 .50 .37

Table 3.1

OUTPUT EQUATION OF STATOR

Output equation of three phase machine:-

KVA rating of an 3phase machine = 3Vph*Iph*10-3

Synchronous speed = 120f/p

Frequency=NsP/120

Kw1=kd1*kp1

Φm=flux/pole

Tph=No of turns/phase

Iph=Stator current/Phase

Where,

kw1= the winding factor

Vph=voltage per phase

Iph=current per phase

F=supply frequency

P=Poles

Ns=synchronous speed

Specific Magnetic Loading= pφm=BavπDL/2

Where,

Specific Electric Loading=No of r.m.s ampere-conductor/unit of the air gap

circumference

q=3*Iph*zph/πD

Conductors/Phase Zph=Z/3

Total Conductor=Z=3ZphZph=2TphZ=6TphIphTph=πqd/6

Specific Electric Loading :

The Specific Electric loading q determines the I2R losses of the

machine and depends upon the following factors

1.Number of poles:

• Machines with smaller number of poles are high speed machines and have

a smaller armature diameter.

• Owing to the smaller dimensions great difficulty is experienced in

accommonding the copper of the windings and generally in such machines

q is lower.

2.Voltage of the machine:

• In high voltage machines a greater percentage of the slot area is occupied

by insulation.

• This allows a lesser amount a lesser amount of copper to be

accommodated.

• The value of q is thus smaller in high voltage machines.

3.Frequency:

• At lower frequencies the iron losses (consisting of hysteresis and eddy

current losses) are smaller.

• Hence proportionately more copper could be used which will increase I2R

lpsses.

• Therefore, at low frequencies, the value of q is proportionally higher.

4.Overload Capacity:

• It will be seen from calculations of slot reactance that reluctance of the

leakage flux path through the slot depends upon the ratio(slot width)/(slot

depth).

• Now greater the slot depth, lesser will be the slot reluctance hence more

the leakage flux(since φ=mmf/reluctance) and also the leakage reactance.

• In short, therfore, slot reactance increases as the depth is increased.

• Heating of the conductor in the winding wil depend upon the I2R losses,

which in turn depend upon q.

• On the other hand heat dissipated depends upon the surfaces of the

conductor.

The temperature rise of the conductors will, therefore, depend upon the

ratio, q/surface area per ampere.

If q is large,

• The surface area of the conductor per ampere has to be greater and hence

a greater amount of copper will have to be used to keep the temperature

rise within reasonable limits.

• It is normally not possible to increase the width of slot much, and so to

accommodate the greater amount of copper, the depth of slot will have to

be increased thereby increasing the slot reactance.

• The increase of reactance reduces the diameter of circle diagram=E/X, and

hence the maximum torque (or) overload capacity of machine.

• Assumptions:

• when sufficient data is not given, we shall assume the values:

• Q=25,000 amp-load/m

• Current density=3.5 A/mm2

Specific Magnetic Loading:

• The value of Bav the specific magnetic loading, should not be so high as to

cause magnetic saturation of the teeth.

If Bav is large,

• Iron loss proportional to flux density increases, hence the temperature rise

and the machine will have a low efficiency.

• For a given voltage,if the flux/pole is larger, the number of turns will have to

be less.

• This reduces the leakage reactances and increases the maximum torque by

increasing the diameter of the circle diagram.

• The magnetising current Im=(0.427p*AT/Kw1 Tph ) depending on the flux

density increases.

• The magnetising currents in such a component of current which lags upon

the applied voltage and tends to lower the power factor of the machine.

• Therefore, greater the air gap, lower will be the power factor of the

machine.

• Considering this factor the designer will have a tendency to provide a very

small air gap.

• From the above discussions, Bav and q cannot chosen arbitrarily, but

optimum values are to be used in due consideratons of above factors.

• For normal 50hz machine Bav lies between (0.3-0.6) wb/m2

• For crane, rolling mill and similar drives it may be around 0.65 wb/m2

• The specific electric loading(q) lies between (5000 to 45000) ac/m 3

• For preliminary design cosφ and n may be taken as each 0.9

Kw1, the winding factor equal the product of the distribution factor and

pitch factor.

When nothing is given, assume a phase spread of 60, whereby Kd1= 0.955

and full pitched coils whereby Kp1=1 i.e., Kw1=Kd1*Kp1=0.955*1 =0.955

Assumptions:

Q=25,000 amp-load/m

Current density=3.5 A/mm2

Magnetic Loading:

Magnetising Current

Im=(0.427p*AT/Kw1*Tph)

Assumptions:

• For Normal 50hz machine

Bav lies between (0.3 to 0.6)wb/m2

• For Preliminary design cos φ and n=0.9

Kd1=0.955

Kp1=1

Kd1=0.955

SEPERATION OF D2L PRODUCTS

• Gross Core Length=L

• Net Core Length LN=(L-nv bv )

nv = number of ventilating ducts

Bv = width of each ducts

• Net Iron Length Li=Ki(L-nv bv )

Ki=0.9

• No of turns and dimensions of stator conductors:

Since Bav=pφm/πdl

φm=flux/pole=Bavπdl/p weber

If the applied voltage/phase=Induced emf/phase

• Eph=Vph=4.44Kw1φmftph

• No of turns/phase=Tph=T1=Vph/4.44Kw1φmf

• No of stator conductors = Z = 3*Zph

= 3*2Tph=6Tph

• Stator current/phase=Iph(or)I1= H.P*746/ncosφ*3Vph

• Area of stator conductors a1=Iph/δ

δ (Current density) =(3to8)A/mm2

DESIGN OF FIELD

• Semi cored slots = less than 25 H.P

• Leakage = δπf/mp*Tph 2is inversely proportion to the number of

slots/pole/ph=m

• Stator Slot Pitch : more slots less leakage reactance

• Slot pitch =πd/slots

NOTES:

• Slots/pole/phase should not be less than 2

• Number of slots/poles/phase(m) lies between (21/2 to 5)

• Usually 3 and 4 are common

• Slot pitch = πd/s1 for mechanical should not be less than 1cm

Semi closed slots=(1.0 to 1.5 )cms

Insulations:

• Not exceeding 440v = Class A Insulation

• The slot insulation consists of lines of =MICANITE AND LEATHEROLD

each of 0.25mm thick ( above 500v)

• Slot width of stator=bss =(2-4mm)

Depth of stator core :

• Flux density in stator core Bcs =(φm/2) / dcsLi

Bcs = 0.9 and 1.4 wb/m2

MAIN DIMENSIONS

D2L= H.P*0.746/ncos φc0ns

C0=11*10-3 Kw1Bavq

C0=11*10-3*0.955*Bav*25000

C0=137.184Bav

No of poles (P)= 120f/N = 120*50/1360 =4.411

Practically, it is not possible, so select p=4

Synchronous speed in rpm (Ns)=120f/p = 120*50/4 = 1500rpm

Ns= 1500/60 =25rps

D2l=H.P*0.746/n cosφc0*ns

Bav = 0.373/0.71*0.69*11*10-3*0.955*13000*25*6.776*10-4

Bav=0.329wb/m2

Q=13059 amp – load/m

TURNS PER PHASE

flux/pole (φm) = πBavdl/p

= π*0.329*11*10-2*5.6*10-2 /4

φm= 0.00159 weber

Stator turns/phase T1 or Tph=Vph/4.44*kw1fφm

=415/4.44*0.955*50*0.0015917

Tph = 1230

No of stator slots =24 =s1

Total no of stator conductors =z1=6Tph=6*1230 =7380

Conductors/slots= 7380/24 = 307.5

OVERALL DIMENSIONS OF CONSIDER MACHINE

Diameter of the stator core = 11*10-2m

Length of the stator core (L) =5.6*10-2m

Number of stator slots (s1) =24

Stator turns per phase (T1)(Tph) =1230

Total no of stator conductors (z1)=7380

Total no of conductors/slot=307

Flux/pole(φm)=0.0015917 weber

Stator current/phase (Iph) or (I) = 0.61155 A

=0.10192 for (s=6)

Area of stator conductors(a1) = 0.2038 for (s=3)

Area of stator conductors(a2)=0.15288 for (s=4)

Area of stator conductors(a3)=0.12230 for (s=5)

Average flux density(Bav)=0.329 wb/m2

Conductors per phase(Zph)=2460

Specific electric loading=13059 amp-load/m

Slot pitch = πd/slots = π*11*10-2 = 0.01440

Induced emf/phase = Vph = Eph =415.07127 volts

Q=3*Iph*zph/πd

=3*0.6115*2460/π*11*10-2

=13059.0

Conductors/phase Zph=Z/3

Zph=2Tph

Iph=(0.76138/3)*103/415

Iph=0.61155A

MACHINE OVERALL DESIGN

Rated Frame

Size

Type ref.

B3

Operating characteristics

at rated output

With

DOL

Rotor Net

Output IEC Constructio

n

starting GD2

Kgm2

Weight

B3 construction

kg

Current

Amps.

Power Factor Startin

g

current

to rated

current

ratio

Kw HP FL 3/4L 1/2L

.37 .50 71 MA071433 1.02 .71 .62 .50 3.4 .0033 7

Table 3.2

CHAPTER-4

ARMATURE CONSTRUCTION

An armature coil consists of copper or aluminium coils wound on a non-

conducting material (insulator) to reduce the hysteresis losses. It may be star or

delta connected as per the requirements.

An armature is wound on an insulator to reduce the hysteresis loses this is because

when the supply frequency is varied with a variable frequency controller the core

of the armature will create more core losses. Hence it is wound on an insulator to

eliminate the core loss. This type of construction of an armature is only

implemented when variable frequency is used get the variable output voltage.

o Slot angle = 30 deg

o No of slots = 12

o M = n/4 = 3

DESIGN OF ARMATURE

ARMATURE 1 (LAP WINDING)

Slot

Length

(cm)

Slot

Width

(cm)

Slot

depth

(cm)

Conductor

size (swg)

Diameter

(cm)

Turns

per

phase

(Tph)

Output

Voltage

(V0)

6 0.6 0.8 32 5.6 300 8

ARMATURE 2 (WAVE WINDING)

Slot

length

(cm)

Slot width

(cm)

Slot depth

(cm)

Conductor

size (swg)

Diameter

(cm)

Turns

per

phase

(Tph)

Outpu

t

voltag

e (V0)

6 0.6 0.8 32 5.6 400 13

ARMATURE 3 (DISTRIBUTED WINDING)

Slot

length

(cm)

Slot width

(cm)

Slot depth

(cm)

Conductor

size (swg)

Diameter

(cm)

Turns

per

phase

(Tph)

Outpu

t

voltag

e (V0)

6 0.6 0.8 32 5.6 400 13

CHAPTER-5

TESTING OF MACHINES

TEST ON STATOR

Ω0=√3v0I0cosφ0

=√3*415*0.6115*0.69

Ω0=303.28734 watts

Note: watts consumed to produce the field Bav=0.329 Tesla.

Consideration 1

If a 4pole three phase 1500rpm, star connected alternators has 24slots there are

2coil slides /slot

And total 14 conductors/slot if flux/pole is 0.0015917wb

Rms value of emf in a conductor:-

P=4,Ns=1500

F=p*Ns/120=4*1500/120 = 50hz

Average value of emf in a conductor=2fφ

Therefore, rms value =1.11*2fφ

=2.22*50*0.0015917

=0.17668v

Average value of emf in a turn=4fφ

=4*50*0.0015317

=0.31834v

Now each slot has 14conductors and 2 coil slides:-

So conductor/coil side = 14/2=7

Such coil slides,so there are 7 turns

Therfore rms value of emf in a coil :-

Rms value of emf/turn*no of turns/coil

=0.31834*7

=2.22838

Now total conductors Z=conductors/coil slide * No of slots

Z=14*24

Z=336

Zph=336/3 =Z/3

Zph=112

Tph=Zph/2=112/2 =56

N=slots/pole =24/4 =6

M=n/3=6/3=2

B=180/n =180/6 =30

Kd=Sin(mβ/2)/mSinβ/2) = Sin(2*30/2)/2sin(30/2) =0.96593

Eph=4.44KckdφfTph

=4.44*1*0.96593*50*0.0015917*56

=19.22v

Consideration 2

A Simple calculation:-

Given:- 3φ,50hz,4pole star-connected stator winding 24slots with 308/slot,

φm=0.0015917

N=slots/pole=24/4=6

M=slots/pole/phase=6/3=2

β=180/6 =30

Kc=cosα/2=cos15=0.96593

Kd=0.96593

Z=slots*conductor/slot=24*308=7392

Zph=2464

Tph=1232

Eph=406.17v

Eline=Eph*√3

=703.52 volts star connected

CHAPTER – 6

VARIABLE VOLTAGE VARIABLE FREQUENCY CONTROLLER

METHOD OF OUTPUT VOLTAGE CONTROL

Supply frequency control

We are going to study supply frequency control method. we can

conveniently adjust the speed of generator by changing the frequency applied to

the generator. We could adjust generator speed by adjusting the number of poles,

but this physical change to the generator, would require rewinding, and result in a

step change to the speed. So for convenience, cost efficiency. precision, we change

the frequency.

Variable voltage variable frequency controller:

A variable frequency drive (VVVFD) is a system for controlling the

rotational speed of an alternating current (AC) electric generator by controlling the

frequency of the electrical power supplied to the generator. A variable frequency

drive a specific type of adjustable speed drive. Variable frequency drives are also

known as adjustable frequency drives (AFD),variable speed drives (VSD), AC

drives or inverter drives.

Voltage induced in stator is proportional to the product of supply frequencies

and area flux, if stator drop is neglected , terminal voltage can be considered

proportional to product of frequency and flux .Any reduction in supply

frequencies without change in terminal voltage causes an increase air gap flux.

The increase in flux will saturate the motor.

While an increase in flux beyond rated value is undesirable from the

consideration of saturation effects. A decrease in flux is avoided to retain the

torque capability of the motor. Therefore the variable frequency control below

the rated frequency is generally carried out at rated air gap flux varying the

terminal voltage with frequency so as to maintain (V/F) ratio constant at rated

value.

OPERATING PRINCIPLE

Variable frequency drives operate under the principle that the synchronous speed

of an AC motor is determined the frequency of the AC supply and the number of

poles in the stator winding, according to the relation.

R.P.M=120*f/p

Where,

RPM = Revolutions per minute

f = AC power frequency (Hertz)

p = Number of poles (an even number)