MODULE-1

ROTATING ELECTRICAL MACHINESROTATING ELECTRICAL MACHINESBASIC & GENERAL CONCEPTS

LECTURE- 2

PROF. S. S. MURTHY

LECTURE 2

DEPARTMENT OF ELECTRICAL ENG.IIT DELHI.

C S SMACHINES AND PARTS

STAMPINGS

WINDINGWINDING

GSWINDINGS

WINDINGS/ COILSWINDINGS/ COILS

COILS

FRAMEFRAME

UNWOUND STATOR POLE-DC M/C OR SYNCH M/C

CO OCOMMUTATOR

COMMUTATOR IN MAKINGCOMMUTATOR IN MAKING

COMMUTATOR AND BRUSHESCOMMUTATOR AND BRUSHES

S GSSLIP RINGS

STATOR OF DC MACHINE

WOUND STATOR POLES

STATOR OF TURBO GENERATORSTATOR OF TURBO GENERATOR

HYDRO GENERATOR- STATOR SEGMENT

HYDRO GENERATOR

C C O OCYLINDRICAL ROTOR

S O O OSALIENT POLE ROTOR

ROTOR OF BRUSHLESS SYNCH MACHINEROTOR OF BRUSHLESS SYNCH MACHINE

PARTS OF IND MOTORPARTS OF IND. MOTOR

PARTS OF IND. MOTOR

STATOR ROTORBEARING

ENDPLATES

SQ. CAGE ROTOR

DIE CAST ROTOR IN MAKING

CUT VIEW OF IND. MOTOR

SQIRREL CAGE ROTORSQIRREL CAGE ROTOR

SHAFT INSERTEDIN ROTORIN ROTOR

HALF WOUND STATOR OF IND. MOTOR

END WINDING CONNECTIONS

WINDING INSERTIONS IN STATOR

PART WOUND STATORPART WOUND STATOR

STATOR OF 3-PH. IND. MOTORSTATOR OF 3 PH. IND. MOTOR

3 PH INDUCTION MOTOR3-PH. INDUCTION MOTOR

3- PHASE3- PHASEINDUCTION MOTOR

S STERMINALS AND SHAFT

VE

RTIC

AAL A

XIS

MOO

TOR

AC MachinesAC Machines

A.C. MACHINES ARE OF TWO PRINCIPLE VARIETIES NAMELYPRINCIPLE VARIETIES NAMELY

3 - Φ MACHINES1- Φ MACHINES

3 Φ hi3 – Φ machines

THERE ARE TWO TYPES OF 3 – ΦMACHINESMACHINES

SYNCHRONOUS MACHINES1. SYNCHRONOUS MACHINES 2. ASYNCHRONOUS OR INDUCTION

MACHINESMACHINES

SYNCHRONOUS MACHINESMACHINES

THE STATOR IS NORMALLY THE ARMATURE CARRYING 3-PHASE BALANCED WINDING EACH DISPLACED BY 120 DEGREES AND ROTOR IS THE FIELD. HOWEVER LOW POWERED SYNCHRONOUS GENERATORS ARE ALSO MADE WITH THE STATOR AS THE FIELD AND THE ROTOR ASSTATOR AS THE FIELD AND THE ROTOR AS ARMATURE HAVING 3-PHASE WINDING, THE POWER BEING EXTRACTED THROUGH SLIP RINGSRINGS.

THERE ARE TWO TYPES OF ROTORS NAMELY

SALIENT POLE ROTOR CYLINDRICAL ROTORCYLINDRICAL ROTOR

IN BOTH TYPES OF ROTORS, THE FIELD WINDING IS EXCITED BY D CFIELD WINDING IS EXCITED BY D.C THROUGH A PAIR OF SLIP RINGS.

THEORETICALLY A SALIENT POLE MACHINE CAN ALSO BE CONCEIVED AS HAVING LIMITED NUMBER OF SLOT AND TEETH EQUAL TO NUMBER OF POLES, TEETH FORMING POLES AND SLOTS AS INTERPOLAR SPACE HOUSING FIELD COILSFIELD COILS.

S O C S O O O CTHUS A UNIFORMLY CUT 36 SLOT ROTOR CAN BE EMPLOYED AS A 36 POLE MACHINE BY PLACING A COIL ON EACH TOOTHPLACING A COIL ON EACH TOOTH.

SINCE THE AVAILABLE COIL SPACE IS LIMITED

A li i f h h hiApplications of the synchronous machine

THE MAJOR APPLICATION OF THE SYNCHRONOUSTHE MAJOR APPLICATION OF THE SYNCHRONOUS MACHINE IS IN “GENERATING” OPERATION (I.E. AS ALTERNATOR), AS THE BULK OF THE ELECTRICAL POWER GENERATED IN THE WORLD IS THROUGH SYNCHRONOUS GENERATORS DRIVEN MAINLY BY HYDRO OR STEAM TURBINES.

HOWEVER LIMITED APPLICATION OF SYNCHRONOUS MOTORS CAN BE FOUND IN CONSTANT SPEED DRIVES, AND IN POWER SYSTEMS TO IMPROVE POWERAND IN POWER SYSTEMS TO IMPROVE POWER FACTOR BY USING IT AS LEADING PF LOAD.

Induction (Asynchronous) Machines

The stator would be identical to aThe stator would be identical to a synchronous machine having 3-phase distributed windings placed in slots formed in a laminated core.

The rotor is normally short circuited, except in what is known as doublyexcept in what is known as doubly fed machine.

Rotor currents in an induction machine are induced by the statormachine are induced by the stator MMF.There are two types of rotors

Squirrel Cage rotorSquirrel Cage rotor Slip ring or Wound rotor

S i l tSquirrel cage rotors

SQUIRREL CAGE ROTORS EFFECTIVELY FORM ASQUIRREL CAGE ROTORS EFFECTIVELY FORM A MULTIPHASE (EQUAL TO THE NUMBER OF BARS) SHORT CIRCUITED WINDING, EACH PHASE CONSISTING OF A HALF TURNCONSISTING OF A HALF TURN.

CURRENT IN THE END WINDING WOULD BE THE INSTANTANEOUS SUM OF CORRESPONDING BAR CURRENTS.

ONE DISADVANTAGE OF SUCH ROTORS IS THE ABSENCE OF CONTROLLABILITY IN THE ROTOR TOABSENCE OF CONTROLLABILITY IN THE ROTOR TO OBTAIN DESIRED PERFORMANCE.

Sli i d tSlip ring or wound rotors

SLIP RING OR WOUND ROTORS ON THE OTHER HAND, HAVE 3-PHASE BALANCED DISTRIBUTED WINDINGS BROUGHT OUT TO EXTERNAL CIRCUITSWINDINGS BROUGHT OUT TO EXTERNAL CIRCUITS THROUGH

SLIP RINGS.

ROTOR IS EXTERNALLY SHORT CIRCUITED.

CONTROL OF MOTOR THROUGH ROTOR IS POSSIBLE BY CONNECTING SUITABLE ELECTRICALPOSSIBLE BY CONNECTING SUITABLE ELECTRICAL CONTROLLERS AT THE SLIP RING TERMINALS.

A li ti f I d ti tApplications of Induction motors

IT IS THE MOST COMMONLY USED ELECTRIC DRIVEIT IS THE MOST COMMONLY USED ELECTRIC DRIVE IN THE INDUSTRY AND AGRICULTURE, AND IT IS ESTIMATED THAT MORE THAN 70% OF ELECTRICAL ENERGY GENERATED IN THE WORLD IS CONSUMED BY INDUCTION MOTORS.INDUCTION MOTORS ARE NORMALLY USED FOR NEAR CONSTANT SPEED APPLICATION SUCH AS

COMPRESSORSPUMPSPUMPSMACHINE TOOLS ETC.

Applications of Induction motors contdApplications of Induction motors contd…

THEY ARE WIDELY USED INTHEY ARE WIDELY USED IN

PETROCHEMICAL INDUSTRIES,

CHEMICAL PROCESS INDUSTRIESCHEMICAL PROCESS INDUSTRIES,

STEEL MILLS,

THERMAL POWER PLANTSTHERMAL POWER PLANTS,

TEXTILE MILLS,

IRRIGATION PUMPSIRRIGATION PUMPS.

Induction Generator (special application)Asynchronous machine can also be operated as a y pgenerator by driving the rotor above the synchronous speed so that the direction of induced current reverses with respect to the voltage causingreverses with respect to the voltage, causing Generator action.Such generators are finding increased application these days in small Hydro and Wind energy conversion systems.Due to rugged brushless rotor they offer certainDue to rugged brushless rotor, they offer certain advantages over alternators for operation in remote unattended regions.

1 – Φ machines1 Φ machines

1 BASICALLY TWO TYPES1. BASICALLY TWO TYPES1. INDUCTION2 SYNCHRONOUS2. SYNCHRONOUS

1 Φ INDUCTION MACHINES1 – Φ INDUCTION MACHINES1. SPLIT PHASE2. CAPACITOR START3. CAPACITOR START AND RUN4. SHADED POLE

1 – Φ machines1 Φ machines

1 – Φ Synchronous1 Φ Synchronous

RELUCTANCE MOTORS1. RELUCTANCE MOTORS2. HYSTERESIS MOTORS

S G S G O3. SINGLE PHASE GENERATOR

Electric and Magnetic CircuitgANY MACHINE CONSISTS OF MASS OF COPPER AND IRON, RESPECTIVELY FORMING THE ELECTRIC AND MAGNETIC CIRCUITSCIRCUITS.

CORE: THE HIGH PERMEABILITY PART OF THE MACHINE CONSISTING OF FERROMAGNETIC MATERIAL AND MEANT TO CARRY FLUX WITH LEAST RELUCTANCE IS KNOWN AS CORE.

WINDINGS: CONDUCTING PARTS OF THE MACHINE MEANT FOR CARRYING CURRENTS ARE KNOWN AS WINDINGS.

COILS ARE OF DIFFERENT SHAPES • CIRCULAR

SQUARE• SQUARE• RECTANGULAR • DIAMOND SHAPED

Motoring and Generating action

ALL ELECTRICAL ROTATING MACHINES NORMALLY OPERATE EITHER AS

MOTOR

GENERATOR

IN A MOTOR ELECTRICAL ENERGY IS FED AS INPUT AND MECHANICAL ENERGY IS TAKEN AS OUTPUTAND MECHANICAL ENERGY IS TAKEN AS OUTPUT. REVERSE PROCESS TAKES PLACE IN A GENERATOR.

THE DIRECTION OF FLOW OF ELECTRICAL AND MECHANICAL ENERGY IS REVERSE BETWEEN A MOTOR AND GENERATOR WHILE THE DIRECTION OFMOTOR AND GENERATOR, WHILE THE DIRECTION OF LOSSES REMAINS THE SAME.

GENERATING AND O O GMOTORING

Access Points for Energy Input gy pand Output

SLIP RINGS:

THESE ARE CIRCULAR BRASS OR COPPER RINGS FIXED TO AND INSULATED FROM THERINGS FIXED TO AND INSULATED FROM THE SHAFT.

EACH SLIP RING IS ELECTRICALLY CONNECTED TO A TERMINAL OF THE ROTOR WINDING SUCHTO A TERMINAL OF THE ROTOR WINDING SUCH THAT CURRENT CAN BE INJECTED OR EXTRACTED THROUGH THE STATIONARY BRUSHES RESTING ON THE ROTOR SLIP RINGS.

COMMUTATORSTHESE ARE COPPER STRIPS FIXED TO ANDTHESE ARE COPPER STRIPS FIXED TO AND INSULATED FROM THE ROTOR SHAFT, ELECTRICALLY CONNECTED TO THE ENDS OF A ROTOR COILROTOR COIL.

STATIONARY BRUSHES COME IN TO CONTACT WITH DIFFERENT COMMUTATOR SEGMENTS AS THE ROTOR MOVES.

CURRENT IN THE WINDING AND THE VOLTAGE ACROSS IT TO ALTERNATE AT A FREQUENCY DECIDED BY THE SHAFT SPEEDDECIDED BY THE SHAFT SPEED

CO OCOMMUTATOR

COMMON PHENOMENON IN ALL ELECTRICAL MACHINES

SUPPLY SYSTEM / LOADSUPPLY SYSTEM / LOADMECHANICAL LOAD / INPUTCURRENT CARRYING CONDUCTORCURRENT CARRYING CONDUCTORFLUX CARRYING COREELECTROMAGNETIC FIELDELECTROSTATIC FIELD MAGNETIC FIELD ENERGYELECTRIC FIELD ENERGYLOSSES, NOISE, VIBRATIONS ETC

INTRODUCTION TO CONVENTIONAL MACHINESMACHINES

CONVENTIONAL ROTATINGCONVENTIONAL ROTATING MACHINES ARE BROADLY CLASSIFIED ACCORDING TO THECLASSIFIED ACCORDING TO THE TYPE OF MAIN ELECTRIC SUPPLY AS

1 D C MACHINES1. D.C. MACHINES 2. A.C. MACHINES

Cl ifi ti f DC hiClassification of DC machinesPERMANENT MAGNET MACHINEWOUND FIELD OR ELECTROMAGNET MACHINE

THERE ARE MAINLY TWO WAYS OF EXCITING THE WOUND FIELD WINDINGS.

SEPARATE EXCITATION1. SEPARATE EXCITATION 2. SELF EXCITATION

SELF EXCITATION CONSISTS OFSELF EXCITATION CONSISTS OFSHUNT SERIESSERIES COMPOUND ARRANGEMENTS

C CDC MACHINE

D C MACHINES Wound fieldD.C. MACHINES - Wound field

THE STATOR COMPRISES THE FIELDTHE STATOR COMPRISES THE FIELD STRUCTURE WITH PROTRUDING POLES ALSO CALLED SALIENT POLES FIXED TO THE YOKE HELICAL COIL WINDINGS ARETHE YOKE. HELICAL COIL WINDINGS ARE USED AS FIELD WINDINGS AND ARE PLACED ON THE POLES.

ROTOR FORMS THE ARMATURE, WHOSE CORE IS HAVING UNIFORMLY DISTRIBUTED SLOTS CARRYINGDISTRIBUTED SLOTS CARRYING ARMATURE WINDING, WHOSE COIL ENDS ARE CONNECTED TO COMMUTATOR SEGMENTSSEGMENTS.

STATIONARY BRUSHES CONNECTED TO EXTERNAL NETWORK COME INTO CONTACT WITH DIFFERENTCONTACT WITH DIFFERENT COMMUTATOR SEGMENTS AND THUS WITH DIFFERENT ARMATURE COILS

O O O O ODUE TO THE ROTOR ROTATION.

DC MACHINE AS A GENERATORDC MACHINE AS A GENERATOR

WHEN THE FIELD WINDINGS AREWHEN THE FIELD WINDINGS ARE EXCITED AND THE ARMATURE AT ANY SPEED VOLTAGES AREANY SPEED, VOLTAGES ARE INDUCED IN ARMATURE CONDUCTORSCONDUCTORS.MAGNITUDE AND DIRECTION OF VOLTAGE ARE DEPENDENT ON ITSVOLTAGE ARE DEPENDENT ON ITS POSITION WITH REFERENCE TO THE FIELD STRUCTURETHE FIELD STRUCTURE.

CONDUCTOR AT ANY FIXED POSITION BELOW A POLE WILL ALWAYS ATTAIN THEBELOW A POLE WILL ALWAYS ATTAIN THE SAME POTENTIAL WHICH IS COLLECTED AT THE BRUSH THROUGH THE APPROPRIATE COMMUTATOR SEGMENT.

THUS EACH BRUSH WILL ALWAYS BE AT ATHUS EACH BRUSH WILL ALWAYS BE AT A FIXED POTENTIAL.

THE COMMUTATOR WORKS AS A MECHANICAL RECTIFIER CHANGING THE ALTERNATING VOLTAGE AT THE WINDINGSALTERNATING VOLTAGE AT THE WINDINGS TO A D.C VOLTAGE AT THE BRUSHES.

DC MACHINE AS A MOTORDC MACHINE AS A MOTOR

D.C CURRENT IS FED TO THE ARMATURE THROUGH THE BRUSHES AND THESE CURRENT CARRYING ARMATURECURRENT CARRYING ARMATURE CONDUCTORS EXPERIENCE FORCE IN THE MAGNETIC FIELD PRODUCED BY THE FIELDMAGNETIC FIELD PRODUCED BY THE FIELD WINDING.

THUS A TORQUE IS DEVELOPED AT THE SHAFT WHICH IS AVAILABLE FOR EXTERNAL MECHANICAL LOADS.

Types of DC motorsSh t• Shunt

• Series

Types of DC motorsC d M hi• Compound Machines

• Cumulative compound• Differential compound

• Universal motorsUniversal motors

Characteristics of DC motors

A li ti f DC tApplications of DC motorVARIABLE SPEED OPERATIONS:VARIABLE SPEED OPERATIONS:

MACHINE TOOLS CEMENT MILLSPAPER MILLS TEXTILE MILLS MININGMINING STEEL MILLSLIFTSLIFTSCRANES ELEVATORS ELECTRIC TRACTION ETC.

Applications of DC generatorApplications of DC generator

D.C GENERATORS HAVE CONSIDERABLY REDUCED APPLICATION IN RECENT YEARS DUE TO THE ADVENT OF SOLID STATE POWER CONVERTER, WHICH GIVES REQUIRED D C VOLTAGE FROM THE A CREQUIRED D.C VOLTAGE FROM THE A.C SUPPLY.

WELDING LOW POWER WIND ELECTRIC GENERATIONGENERATION BATTERY CHARGING AT REMOTE LOCATIONS FOR DEFENCE /COMMUNICATION USING DIESEL ENGINE DRIVEN GENERATORS