Comprehensive Guide to Electrical Machines and Power Systems
Core and Shell Construction (Building Construction)
Core Construction:
Definition: The core construction method involves creating a central core within a building, which houses the primary structural and service elements.
Components: Includes stairwells, elevators, restrooms, and mechanical spaces.
Benefits: Provides stability and strength to the building, allows for open and flexible floor spaces.
Shell Construction:
Definition: The shell construction method refers to the outer building envelope, including walls, roof, windows, and doors.
Components: Excludes interior finishes and non-structural elements.
Benefits: Protects the interior spaces from external elements, provides the aesthetic look of the building.
Three-Phase Induction Motor
Construction:
Stator: Consists of laminated steel cores with windings placed in slots, connected to a three-phase power supply.
Rotor: Can be a squirrel-cage type (consisting of aluminum or copper bars short-circuited by end rings) or a wound type (with windings connected to slip rings).
Working:
Magnetic Field Generation: When the stator windings are energized with a three-phase AC supply, a rotating magnetic field (RMF) is produced.
Induced Current in Rotor: The RMF induces current in the rotor bars.
Torque Production: The interaction between the RMF and the induced current generates a force that produces torque, causing the rotor to turn.
2 Wattmeter Method for 3Φ Balanced Delta Connected Load
Circuit: Similar setup as the star connection, but the load is connected in delta.
Phasor Diagram: Represents line voltages and currents in a delta configuration.
Operation: Wattmeters measure the power in the lines.
Formula: Ptotal = W1 + W2
Star-Delta Connection (Three-Phase Motor)
Star Connection:
Configuration: One end of each phase winding is connected to form a neutral point, and the other ends are connected to the power supply.
Voltage: Line voltage is √3 times the phase voltage.
Current: Line current equals phase current.
Usage: Often used for starting the motor to reduce the initial inrush current.
Delta Connection:
Configuration: The ends of each phase winding are connected in a closed loop.
Voltage: Line voltage equals phase voltage.
Current: Line current is √3 times the phase current.
Usage: Used for running the motor at full load.
Stepper Motor
Construction:
Stator: Has multiple poles with windings around them.
Rotor: Can be a permanent magnet or a variable reluctance type with teeth to interact with the magnetic field from the stator.
Working:
Electromagnetic Pulses: When current is supplied to the stator windings in a specific sequence, magnetic fields are generated.
Stepwise Movement: The rotor aligns with these fields, causing it to rotate in discrete steps.
Precision Control: The rotation angle and speed are controlled by the frequency and sequence of the input pulses, allowing precise positioning without feedback systems.
Core Type vs. Shell Type Transformers
Core Type:
- Magnetic circuit is a closed loop
- Efficient and compact
- Flux linkage is high
Shell Type:
- Magnetic circuit is an incomplete loop
- Less efficient and larger in size
- Flux linkage is low
Comparison Between Series and Parallel Resonance Circuits
Series Resonance:
Configuration: R, L, C in series.
Impedance: Minimum at resonance.
Current: Maximum at resonance.
Voltage across L and C: High at resonance.
Applications: Filters, tuning circuits.
Parallel Resonance:
Configuration: R, L, C in parallel.
Impedance: Maximum at resonance.
Current: Minimum at resonance.
Voltage across L and C: Same as source voltage.
Applications: Frequency selection, tank circuits.
2 Wattmeter Method for 3Φ Balanced Star Connected Load
Circuit: Two wattmeters are connected to two phases (A and B), and the common point to the third phase (C).
Phasor Diagram: Shows phase voltages and currents, indicating their phase relationships.
Operation:
- Wattmeter 1 measures power between phase A and neutral.
- Wattmeter 2 measures power between phase B and neutral.
Total Power: Ptotal = W1 + W2
Double Field Revolving Theory (Single-Phase Induction Motor)
- Pulsating magnetic field produces two rotating fields:
- One clockwise (F1)
- One counterclockwise (F2)
- Resultant torque = T1 + T2
- Motor rotates in the direction of the resultant torque
Principle of Operation of Three-Phase Induction Motor
- Three-phase current produces a rotating magnetic field
- Field induces an EMF in the rotor, causing it to rotate
- Rotor rotation is in the direction of the rotating magnetic field