
- Electrical Machines - Home
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- Electrical Transformer
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- 3-Phase Transformer Principle
- 3-Phase Induction Motor Torque-Slip
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- DC Machines
- Construction of DC Machines
- Types of DC Machines
- Working Principle of DC Generator
- EMF Equation of DC Generator
- Derivation of EMF Equation DC Generator
- Types of DC Generators
- Working Principle of DC Motor
- Back EMF in DC Motor
- Types of DC Motors
- Losses in DC Machines
- Applications of DC Machines
- More on DC Machines
- DC Generator
- DC Generator Armature Reaction
- DC Generator Commutator Action
- Stepper vs DC Motors
- DC Shunt Generators Critical Resistance
- DC Machines Commutation
- DC Motor Characteristics
- Synchronous Generator Working Principle
- DC Generator Characteristics
- DC Generator Demagnetizing & Cross-Magnetizing
- DC Motor Voltage & Power Equations
- DC Generator Efficiency
- Electric Breaking of DC Motors
- DC Motor Efficiency
- Four Quadrant Operation of DC Motors
- Open Circuit Characteristics of DC Generators
- Voltage Build-Up in Self-Excited DC Generators
- Types of Armature Winding in DC Machines
- Torque in DC Motors
- Swinburne’s Test of DC Machine
- Speed Control of DC Shunt Motor
- Speed Control of DC Series Motor
- DC Motor of Speed Regulation
- Hopkinson's Test
- Permanent Magnet DC Motor
- Permanent Magnet Stepper Motor
- DC Servo Motor Theory
- DC Series vs Shunt Motor
- BLDC Motor vs PMSM Motor
- Induction Motors
- Introduction to Induction Motor
- Single-Phase Induction Motor
- 3-Phase Induction Motor
- Construction of 3-Phase Induction Motor
- 3-Phase Induction Motor on Load
- Characteristics of 3-Phase Induction Motor
- Speed Regulation and Speed Control
- Methods of Starting 3-Phase Induction Motors
- More on Induction Motors
- 3-Phase Induction Motor Working Principle
- 3-Phase Induction Motor Rotor Parameters
- Double Cage Induction Motor Equivalent Circuit
- Induction Motor Equivalent Circuit Models
- Slip Ring vs Squirrel Cage Induction Motors
- Single-Cage vs Double-Cage Induction Motor
- Induction Motor Equivalent Circuits
- Induction Motor Crawling & Cogging
- Induction Motor Blocked Rotor Test
- Induction Motor Circle Diagram
- 3-Phase Induction Motors Applications
- 3-Phase Induction Motors Torque Ratios
- Induction Motors Power Flow Diagram & Losses
- Determining Induction Motor Efficiency
- Induction Motor Speed Control by Pole-Amplitude Modulation
- Induction Motor Inverted or Rotor Fed
- High Torque Cage Motors
- Double-Cage Induction Motor Torque-Slip Characteristics
- 3-Phase Induction Motors Starting Torque
- 3-phase Induction Motor - Rotor Resistance Starter
- 3-phase Induction Motor Running Torque
- 3-Phase Induction Motor - Rotating Magnetic Field
- Isolated Induction Generator
- Capacitor-Start Induction Motor
- Capacitor-Start Capacitor-Run Induction Motor
- Winding EMFs in 3-Phase Induction Motors
- Split-Phase Induction Motor
- Shaded Pole Induction Motor
- Repulsion-Start Induction-Run Motor
- Repulsion Induction Motor
- PSC Induction Motor
- Single-Phase Induction Motor Performance Analysis
- Linear Induction Motor
- Single-Phase Induction Motor Testing
- 3-Phase Induction Motor Fault Types
- Synchronous Machines
- Introduction to 3-Phase Synchronous Machines
- Construction of Synchronous Machine
- Working of 3-Phase Alternator
- Armature Reaction in Synchronous Machines
- Output Power of 3-Phase Alternator
- Losses and Efficiency of an Alternator
- Losses and Efficiency of 3-Phase Alternator
- Working of 3-Phase Synchronous Motor
- Equivalent Circuit and Power Factor of Synchronous Motor
- Power Developed by Synchronous Motor
- More on Synchronous Machines
- AC Motor Types
- Induction Generator (Asynchronous Generator)
- Synchronous Speed Slip of 3-Phase Induction Motor
- Armature Reaction in Alternator at Leading Power Factor
- Armature Reaction in Alternator at Lagging Power Factor
- Stationary Armature vs Rotating Field Alternator Advantages
- Synchronous Impedance Method for Voltage Regulation
- Saturated & Unsaturated Synchronous Reactance
- Synchronous Reactance & Impedance
- Significance of Short Circuit Ratio in Alternator
- Hunting Effect Alternator
- Hydrogen Cooling in Synchronous Generators
- Excitation System of Synchronous Machine
- Equivalent Circuit Phasor Diagram of Synchronous Generator
- EMF Equation of Synchronous Generator
- Cooling Methods for Synchronous Generators
- Assumptions in Synchronous Impedance Method
- Armature Reaction at Unity Power Factor
- Voltage Regulation of Alternator
- Synchronous Generator with Infinite Bus Operation
- Zero Power Factor of Synchronous Generator
- Short Circuit Ratio Calculation of Synchronous Machines
- Speed-Frequency Relationship in Alternator
- Pitch Factor in Alternator
- Max Reactive Power in Synchronous Generators
- Power Flow Equations for Synchronous Generator
- Potier Triangle for Voltage Regulation in Alternators
- Parallel Operation of Alternators
- Load Sharing in Parallel Alternators
- Slip Test on Synchronous Machine
- Constant Flux Linkage Theorem
- Blondel's Two Reaction Theory
- Synchronous Machine Oscillations
- Ampere Turn Method for Voltage Regulation
- Salient Pole Synchronous Machine Theory
- Synchronization by Synchroscope
- Synchronization by Synchronizing Lamp Method
- Sudden Short Circuit in 3-Phase Alternator
- Short Circuit Transient in Synchronous Machines
- Power-Angle of Salient Pole Machines
- Prime-Mover Governor Characteristics
- Power Input of Synchronous Generator
- Power Output of Synchronous Generator
- Power Developed by Salient Pole Motor
- Phasor Diagrams of Cylindrical Rotor Moto
- Synchronous Motor Excitation Voltage Determination
- Hunting Synchronous Motor
- Self-Starting Synchronous Motor
- Unidirectional Torque Production in Synchronous Motor
- Effect of Load Change on Synchronous Motor
- Field Excitation Effect on Synchronous Motor
- Output Power of Synchronous Motor
- Input Power of Synchronous Motor
- V Curves & Inverted V Curves of Synchronous Motor
- Torque in Synchronous Motor
- Construction of 3-Phase Synchronous Motor
- Synchronous Motor
- Synchronous Condenser
- Power Flow in Synchronous Motor
- Types of Faults in Alternator
- Miscellaneous Topics
- Electrical Generator
- Determining Electric Motor Load
- Solid State Motor Starters
- Characteristics of Single-Phase Motor
- Types of AC Generators
- Three-Point Starter
- Four-Point Starter
- Ward Leonard Speed Control Method
- Pole Changing Method
- Stator Voltage Control Method
- DOL Starter
- Star-Delta Starter
- Hysteresis Motor
- 2-Phase & 3-Phase AC Servo Motors
- Repulsion Motor
- Reluctance Motor
- Stepper Motor
- PCB Motor
- Single-Stack Variable Reluctance Stepper Motor
- Schrage Motor
- Hybrid Schrage Motor
- Multi-Stack Variable Reluctance Stepper Motor
- Universal Motor
- Step Angle in Stepper Motor
- Stepper Motor Torque-Pulse Rate Characteristics
- Distribution Factor
- Electrical Machines Basic Terms
- Synchronizing Torque Coefficient
- Synchronizing Power Coefficient
- Metadyne
- Motor Soft Starter
- CVT vs PT
- Metering CT vs Protection CT
- Stator and Rotor in Electrical Machines
- Electric Motor Winding
- Electric Motor
- Useful Resources
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- Discussion
Construction of Three-Phase Induction Motor
A three-phase induction motor consists of two main parts namely,
- Stator
- Rotor
There is a small air gap between the stator and rotor which ranges from 0.4 mm to 4 mm depending on the power rating of the motor.
Stator of Three Phase Induction Motor
The stator of a three-phase induction motor is a stationary part, and it consists of a cylindrical-shaped frame made up of fabricated steel. This steel frame encloses a hollow cylindrical core made up of thin laminations of silicon steel. On the inner periphery of the core, a number of evenly spaced slots are provided to place the stator winding. The silicon-steel laminations are used to reduce the hysteresis and eddy current losses.

Three windings are placed in the stator slots and are suitably connected to form a balanced three-phase delta or star connected circuit. As per the requirement of motor speed, these three-phase windings are wound for a definite number of poles. Where, greater is the number of poles, lesser is the speed of the induction motor and vice-versa.
When we fed the three-phase stator winding from a balanced three-phase supply, a rotating magnetic field of constant magnitude is produced. This rotating magnetic induces EMF in the rotor circuit by electromagnetic induction.
Rotor of Three Phase Induction Motor
The rotor is a rotating or moving part of the three-phase induction motor. It consists of a rotor core made up of thin laminations of high grade silicon steel to reduce the hysteresis and eddy-current losses. The rotor core is a hollow cylinder, mounted on a shaft. On outer periphery of the rotor core, slots are provided to place the rotor winding.
Based on the construction, the rotor of a three-phase induction motor can be of the following two types −
- Squirrel-cage rotor
- Wound rotor
Let's discuss these two types of rotors in detail.
Squirrel Cage Type Rotor
The squirrel-cage rotor consists of a laminated cylindrical core having parallel slots on its outer periphery. In case of squirrel-cage rotor, the rotor winding is made up of metal (copper or aluminium) bars. These metal bars are placed in the rotor slots and are short-circuited at each end by metal rings called end-rings as shown in Figure-2.

From Figure-2, it can be observed that the construction of this rotor resembles a squirrel cage and hence the name. Here, it is also to be noted that the rotor is not connected electrically to the supply, but it derives its voltage and power by the electromagnetic induction from the stator.
The three-phase induction motors that employ squirrel-cage rotor are known as squirrel-cage induction motors. Almost 70% to 80% three-induction motors used in industrial applications are squirrel-cage induction motors because of their simple and robust construction which enable them to operate in most adverse circumstances. Although, the induction motors that use squirrel-cage rotor have a low starting torque.
Wound Rotor or Slip Ring Rotor
The slip ring rotor consists of a laminated cylindrical armature core. The slots are provided on the outer periphery and insulated conductors are put in the slots. The rotor conductors are connected to form a 3-phase double layer distributed winding similar to the stator winding. The rotor windings are connected in star fashion (see the figure).

The open ends of the star circuit are taken outside the rotor and connected to three insulated slip rings. The slip rings are mounted on the rotor shaft with brushes resting on them. The brushes are connected to three variable resistors which are also connected in star. Here, the slip rings and brushes are used to provide a mean for connecting external resistors in the rotor circuit. The equivalent circuit of the wound rotor is shown in the figure below.

At starting, suitable values of external resistances are added into phases of the rotor winding to obtain a high starting torque. These external resistances are gradually removed from the circuit as the motor runs up to speed. The use of external resistances considerably reduces the starting current and increases the starting torque of the motor. Once the motor attains normal speed, the three carbon brushes are short-circuited so that the wound motor runs like a squirrel cage induction motor.