1. EET 323 – Electrical System Design Lecture 13: Motor Circuits
Radian Belu, PhD

3. Lecture Objectives

4. Alternating Current (AC) Motors Direct Current (DC) Motors
Type of Electric Motors
Classification of Motors
Electric Motors
Alternating Current (AC) Motors
Direct Current (DC) Motors
Synchronous
Induction
Three-Phase
Single-Phase
Self Excited
Separately Excited
Series
Shunt
Compound
Electrical Equipment/
Electric Motors

5. Induction Motor Operation
3-Phase Induction Motors – The Most Common and Used Types of Electric Motor
3-Phase Induction Motors – Robust, Reliable, Standardized Construction, Economical Motor
Speed easily controllable using V/f or Field Oriented Controllers
Have replaced DC Motors in areas where traditional DC Motors cannot be used such as mining or explosive environments
Of two types depending on motor construction: Squirrel Cage or Slip Ring
Only Disadvantage: Most of them run with a lagging power factor

6. IM Construction
Stator
Rotor
Motor Control System

7. Construction
The three basic parts of an AC motor are the rotor, stator, and enclosure.
The stator and the rotor are electrical circuits that perform as electromagnets.

11. Construction (Stator Construction)
The stator is the stationary electrical part of the motor.
The stator core of a National Electrical Manufacturers Association (NEMA) motor is made up of several hundred thin laminations.
Stator laminations are stacked together forming a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core.
Electromagnetism is the principle behind motor operation. Each grouping of coils, together with the steel core it surrounds, form an electromagnet. The stator windings are connected directly to the power source.

12. Construction (Rotor Construction)
The rotor is the rotating part of the electromagnetic circuit.
It can be found in two types:
Squirrel cage
Wound rotor
However, the most common type of rotor is the “squirrel cage” rotor.

13. Construction (Rotor Construction)
Induction motor types:
Squirrel cage type:
Rotor winding is composed of copper bars embedded in the rotor slots and shorted at both end by end rings
Simple, low cost, robust, low maintenance
Wound rotor type:
Rotor winding is wound by wires. The winding terminals can be connected to external circuits through slip rings and brushes.
Easy to control speed, more expensive.

16. Rotating Magnetic Field
Balanced three phase windings, i.e. mechanically displaced 120 degrees form each other, fed by balanced three phase source
A rotating magnetic field with constant magnitude is produced, rotating with a speed
Where fe is the supply frequency and
P is the no. of poles and nsync is called the synchronous speed in rpm (revolutions per minute)

17. Rotating Magnetic Field

18. Rotating Magnetic Field

20. Single-phase Induction Motors

29. Table 6.2 is Table of NEC

38. Motor Protection
The overload elements are seized on the full-load nameplate current rating of the motor, not the full-load motor current (Table 13-2)
For continuous-duty motors, Section of the NEC requires separated overload protection not exceeding the following percentages of the full-motor ratings:

46. Table 13.2

49. Thank you for listening
THE END of the Lecture
Thank you for listening
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