
- Electrical Machines - Home
- Basic Concepts
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- Concept of Induced EMF
- Fleming's Left Hand and Right Hand Rules
- Transformers
- Electrical Transformer
- Construction of Transformer
- EMF Equation of Transformer
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- 3-Phase Transformer Principle
- 3-Phase Induction Motor Torque-Slip
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- Transformer DC Supply Issue
- Equivalent Circuit Transformer
- Simplified Equivalent Circuit of Transformer
- Transformer No-Load Condition
- Transformer Load Condition
- OTI WTI Transformer
- CVT Transformer
- Isolation vs Regular Transformer
- Dry vs Oil-Filled
- 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
- Quick Guide
- Resources
- Discussion
Construction of Synchronous Machine
Like any other rotating electrical machine, a synchronous machine (generator or motor) has two essential parts namely,
Stator − It is a stationary part of the machine and carries the armature winding.
Rotor − It is the rotating part of the machine. The rotor of a synchronous machine produces the main field flux.
In this chapter, let's discuss how the Stator and Rotor of a Synchronous Machine is constructed.
Stator Construction
The stator of a synchronous machine includes various parts like frame, stator core, stator windings and cooling mechanisms, etc. The frame is the outer part of the machine, and made up of cast iron for small-sized machines, and of welded steel for large-sized machines. The frame encloses the whole machine assembly and protects it from mechanical and environmental impacts.

The stator core is a hollow cylinder which is made up of high-grade silicon steel laminations. The silicon steel laminations reduce the hysteresis and eddy-current losses in the machine. A number of evenly spaced slots are provided on the inner periphery of the stator core. A three-phase winding is put in these slots. When current flows through the stator winding, it produces a sinusoidal magnetic field and hence the EMF.
Rotor Construction
In synchronous machines, there are two types of rotor constructions used namely, salient-pole rotor and cylindrical rotor.
Salient-Pole Rotor
The term salient means projecting. Hence, a salient-pole rotor is one that consists of field poles projecting out from the surface of the rotor core as shown in Figure-2.

Since the rotor is subjected to a changing magnetic field, therefore it is made up of thin steel lamination to reduce the eddy current loss. The field poles of same dimensions are constructed by stacking laminations of the required length and then riveted together. After wounding the field coils around each pole core, poles are fitted to a steel spider keyed to the rotor shaft.
At the outer end of each pole, damper bars are provided to dame out the oscillations of rotor during sudden changes in the load. Though, the synchronous machines using the salient-pole rotor have a non-uniform air gap, where the air gap is minimum under the pole centers and it is maximum in between the field poles. The pole face (outer end of the pole) is so shaped that length of the radial air-gap increases from the pole center to the pole tip so it can result a sinusoidal distribution of flux in the air-gap. This will ensure the smooth operation of synchronous machine.
In the salient-pole rotor, the individual field coils are connected in series so that they can give alternate north and south poles. The ends of the field coils are connected to a source of DC supply though brushes and slip-rings.
The synchronous machines having salient-pole rotor usually have a large number of field poles, and operate at lower speeds. These machines have a larger diameter and a shorter axial-length.
Cylindrical Rotor
This type of synchronous machine rotor construction has a smooth cylindrical structure. In case of cylindrical rotor, there are no physical poles projecting outward. The cylindrical rotor is made from slid forgings of high-grade Ni-Cr-Mo steel.
On the outer periphery of the rotor, evenly spaced slots are cut in about two-third part of the rotor and theses slots are parallel to the rotor shaft. The field windings are placed in these slots. The field windings are excited from a source of DC supply. The un-slotted part of the rotor forms pole-faces.

The synchronous machines that use cylindrical rotor have a smaller diameter and longer axial length. The cylindrical rotor construction limits the effect of centrifugal forces. Consequently, the cylindrical rotor construction is mainly used in high-speed synchronous machines. Also, this rotor construction provides a greater mechanical strength and permits relatively more accurate dynamic balancing to the machine.
The major advantage of having a synchronous machine using cylindrical rotor is that it makes less mechanical losses. Since the cylindrical rotor provides a uniform air-gap in the machine, hence their operation is less noisy.