UNIT – II ELECTRICAL MACHINES

Types of Electrical Machines There are basic three rotating machines, 1.DC Machines i. Shunt ii. Series iii. Compound 2.Synchronous Machines (A.C) i. Salient Pole type ii. Non Salient Pole type 3.Induction Machines (A.C) i. Squirrel Cage type ii. Slip Ring type

Construction of DC Machines: Yoke

Various parts of DC machines: 1.Magnetic Frame or Yoke 2.Pole cores and pole shoes 3.Pole coils or field coils 4.Armature Core 5.Armature Windings or conductors 6.Commutator 7.Brushes and Bearings Change in flux linkages of a coil may occur in two ways: The coil remains stationary withy respect to flux, but flux through it changes with time. This induced emf is known as statically induced emf. E.g. Transformers. Flux remains constant and stationary but coil moves relative to it. This induced emf is known as dynamically (or motional) induced emf. E.g. Generators.

EMF Equation of DC Machines:

MOTOR CHARACTERISTICS SERIES MOTOR 1.Armature Torque and armature current i.e.,Ta /Ia characteristics. It is known as electrical characteristics. 2. Speed and armature current i.e, N/Ia Characteristics 3. Speed and armature torque i.e, N/Ta Characteristics. It is known as mechanical characteristics. Voltage Equation, V=Eb+Ia(Ra+Rse)+Vbrush 1 2 3

SHUNT MOTOR 1.Armature Torque and armature current i.e.,Ta /Ia characteristics 2.Speed and armature current i.e.,N /Ia characteristics 3. Speed and Armature Torque i.e.,N /Ta characteristics Voltage Equation, V=Eb+IaRa+Vbrush 2 3 1 2

Cummulatively compound Differentially compound COMPOUND MOTOR Cummulatively compound Differentially compound Long shunt compound motor, V=Eb+Ia(Ra+Rse)+Vbrush Short Shunt compound motor, V=Eb+IaRa+IseRse+Vbrush

COMPOUND MOTOR Speed and Armature current, i.e N/Ia characteristics Armature torque and Armature current, i.e Ta/Ia characteristics 2 1

APPLICATIONS OF DC MOTOR Shunt Motor: Its an constant speed motor. Where the speed is required to remain almost constant from no load to full load. Industrial use: Lathes, drills, boring mills, shapers, spinning machine, etc., Series Motor: Its an variable speed motor. Where large starting torque is required. Where the load is subjected to heavy fluctuations and the speed is automatically required to reduce at high torque and vice versa. Industrial Use: Electric traction, cranes, elevator, air compressor, vacuum cleaner, hair drier, etc., Compound Motor: Differential Compound motors are rarely used because of their poor torque characteristics. However, cummulative compound motors are used where constant speed is required with irregular loads (or) suddenly applied heavy loads. Industrial Use: Presses, reciprocating machines, etc.,

GENERATOR CHARACTERISTICS APPLICATIONS OF DC GENERATOR Shunt generators-Charging of car batteries, supplying fields of synchronous machines. Series generators used as boosters for adding a voltage to the transmission line and to compensate the voltage drop. Compound generators to maintain better voltage regulation GENERATOR CHARACTERISTICS The three most important characteristics or curves of a d.c generator are 1. No-load saturation characteristic (E0/If) 2. Internal or Total characteristic (E/Ia) 3. External characteristic (V/I)

SERIES GENERATOR: Genereted, Eg=V+Ia(Ra+Rse)+Vbrush

SHUNT GENERATOR: Genereted, Eg=V+IaRa+Vbrush

COMPOUND GENERATOR: Long shunt compound motor, Eg=V+Ia(Ra+Rse)+Vbrush Short Shunt compound motor, Eg= V+IaRa+IseRse+Vbrush

SPEED CONTROL OF DC MOTOR 1.Shunt Motor Flied (or) Flux control method Armature control method Voltage control method Multiple voltage control method Ward Leonord method 2. Series Motor Flux control method Field divertor Armature divertor Tapped field control method Paralleling field coils Variable resistance in series with armature

TRANSFORMER CONSTRUCTION

Transformer is a static piece of apparatus is used to transfer the a Transformer is a static piece of apparatus is used to transfer the a.c power from one circuit (primary) to another (secondary) circuit without any change in frequency and only desirable change in voltage and current.

Classification of Transformer: Duty they perform Power transformer – for transmission and distribution purpose Current transformer – instrument transformer Potential transformer – instrument transformer 2. Construction Core type transformer Shell type transformer Berry core type transformer 3. Voltage output Step down transformer Step up transformer Auto transformer 4. Application Welding transformer Furnace transformer

5. Cooling Duct type transformer Oil immersed Self cooled Forced air cooled Water cooled Forced oil cooled 6. Input supply Single phase transformer Three phase transformer Star-star Star-Delta Delta-delta Delta-star open delta scott connection

CORE TYPE TRANSFORMER SHELL TYPE TRANSFORMER CONSTRUCTION OF TRANSFORMERS:

EQUIVALENT CIRCUIT OF TRANSFORMER: ‘

TYPES OF LOSSES IN TRANSFORMER: 1.Core loss (or) Iron loss a. Hysteresis loss b. Eddy current loss 2. Copper loss 3. Stray loss 4. Dielectric loss

DOUBLE REVOLVING FIELD THEORY

Torque-Speed Characteristics:

Single Phase Induction Motor stator

Squirrel cage rotor

SINGLE PHASE INDUCTION MOTOR The single phase induction motor are classified according to the starting methods, Resistance start (split phase) induction motor Capacitor start induction motor Capacitor run induction motor Capacitor start capacitor run motor Shaded pole induction motor

RESISTANCE START (SPLIT PHASE) INDUCTION MOTOR Phasor Diagram

SPEED-TORQUE CHARACTERISTICS

APPLICATIONS It is mainly used for loads that require low or medium starting torque. The applications are Fans Blowers Centrifugal Pumps Washing Machines

CAPACITOR START INDUCTION MOTOR PHASOR DIAGRAM

SPEED-TORQUE CHARACTERISTICS

APPLICATIONS It is mainly used for high starting loads. The applications are Compressor Pumps Conveyors Refrigerators Air Conditioning Equipments Washing Machines

CAPACITOR RUN INDUCTION MOTOR

SPEED-TORQUE CHARACTERISTICS

ADVANTAGES High power factor at full load High full load efficiency Increased pull out torque Low full load line current APPLICATIONS Fans Blowers Centrifugal Pumps

CAPACITOR START CAPACITOR RUN MOTOR

SPEED-TORQUE CHARACTERISTICS

ADVANTAGES High starting torque High efficiency High power factor APPLICATIONS It is mainly used for low noise and high starting torque applications, such as Compressors Pumps Conveyors Refrigerators

SHADED POLE INDUCTION MOTOR

SPEED-TORQUE CHARACTERISTICS

DISADVANTAGES Low efficiency Low power factor Very low starting torque APPLICATIONS The main applications of these motors are for load requiring low starting torque such as Fans Blowers Turn tables Hair driers Motion picture projectors