1.) Chapter 1 - Rotating Electrical Machines

Chapter 1

ELECTRICAL MACHINERY GENERALIZATION​

By: Joseph D. Maghanoy, M'Eng.
School of Engineering - Electrical Department
Eastern Visayas State University - Tacloban City
Leyte, Philippines

​Rotating Electrical Machines

By Joseph D. Maghanoy, M'Eng.

Armature Windings

Built of laminated steel cores with good magnetic permeability. In all motors and generators, the armature current is alternating, regardless of AC or DC type.

Generators:

AC Generator → Alternating EMF delivered directly to the load.

DC Generator → Alternating EMF is rectified by commutator and brushes into DC output.

Motors:

AC Motor → Receives AC directly and uses it in the windings to produce torque.

DC Motor → Supplied with DC at the brushes, but it flows as alternating current inside the armature winding due to the commutator.

Rotary Converter → Changes AC to DC or vice versa.

Frequency Converter → Changes the frequency of AC supply.

​Generator vs. Motor ( Comparison)

Field Structures of AC and DC Generator

Difference between AC and DC Generator

Actual Field Structures of AC and DC Generator

​Armature Windings

By Joseph D. Maghanoy, M'Eng.

Rotating Electrical Machines: Convert energy from one form to another.

Main Types:

Generator → Mechanical ➝ Electrical

Example: Power plants (turbine driving a generator).

Motor → Electrical ➝ Mechanical

Example: Electric fan, washing machine.

Other Types (less common):

Rotary Converter → Changes AC to DC or vice versa.

Frequency Converter → Changes the frequency of AC supply.

Key Point for Students:

Generators supply power, motors use power.

​Field Poles

By Joseph D. Maghanoy, M'Eng.

Field Poles

• Electromagnets (field poles) used in DC machines, AC generators, and some AC motors.

• Always in even numbers.

Construction:

• Laminated steel core (rectangular cross-section).

• Surrounded by copper coils.

• Pole shoe (wider face) spreads magnetic flux over a larger armature area.

Mounting Types:

• Stationary-field machines → Poles bolted to a yoke, projecting inward toward the armature.

• Rotating-field machines (salient poles) → Poles bolted to a hub on the shaft, projecting outward toward the stationary armature.

• High-speed alternators → Use a cylindrical (non-salient) rotor field construction.

Multiple Choice

The main function of rotating electrical machines is to:

• Store energy

• Convert energy from one form to another

• Measure electrical energy

• Control frequency

Multiple Choice

The two most common types of rotating electrical machines are:

• Transformers and rectifiers

• Generators and motors

• Converters and inverters

• Turbines and alternators

Multiple Choice

Generator action occurs only when there is:

• Voltage across the load

• Relative motion between conductor and magnetic field

• A commutator present

• Alternating supply input

Multiple Choice

In a DC generator, the armature winding:

• Is stationary inside a rotating field

• Rotates in a stationary magnetic field

• Does not carry current

• Converts AC to DC without a commutator

Multiple Choice

In AC motors, the armature winding is usually placed in the:

• Rotor

• Laminated stationary core

• Commutator

• Shaft hub

Multiple Choice

A synchronous motor is characterized by

• Slip during operation

• A DC excitation generator on the shaft

• Brushes only

• Induction without magnets

Multiple Choice

The current in all armature windings (AC and DC machines) is always:

• Direct

• Alternating

• Pulsating

• Zero

Multiple Choice

In stationary-field machines, poles are:

• Fixed on the shaft

• Bolted to a yoke ring projecting inward

• Mounted outside the casing

• Connected to slip rings

Multiple Choice

In rotating-field (salient pole) machines, poles are:

• Bolted to the yoke

• Bolted to the hub on the shaft projecting outward

• Fixed in the armature

• Eliminated entirely

Multiple Choice

Torque in a motor results from:

• Flux interaction with current in conductors

• Shaft rotation only

• Brushes sliding

• Eddy current reduction