College of Applied Engineering King Saud University, Muzahimiyah Branch Semester
ID: 2291505 • Letter: C
Question
College of Applied Engineering King Saud University, Muzahimiyah Branch Semester 2, Academic Year 1438/39 (2017/18) King Saud University Electrical Circuits and Machines (AME 3620) Assignment 3 Due date: 16/04/2018 Describe electric motors (both DC and AC). Include in your description: a) Principle of operation of electric motors b) Types of electric motors. c) Industrial and domestic uses of electric motors. You are expected to include in your description illustrations such as schematic diagrams, figures, photos, etc. You can use the internet and other resources as sources for your information. However, you should acknowledge any source you used as a reference at the end of your document. There is no recommended size for the assignment, but it should not exceed 6 pages. It is preferable to type your assignment on the computer and print it.Explanation / Answer
Let's start with some interesting fact: More than 90% of the electrcity generated is by means of conversion from mechanical energy to the electrical energy. And, again more than 70% of this total electrcity generated is covnerted from electrical energy to mechanical energy. This shows the importance of electric machines in power industry.
Electric Motors: It is a device which converts electrical energy into mechanical energy to do some useful work. DC motors would work on DC power supply and AC motors would work on AC power supply.
DC Motors: Its operation is based on the principle that when a current carrying conductor is placed in a magnetic field, the conductor experiences a mechanical force. The direction of this force is given by Fleming’s left hand rule and magnitude is given by; F = BIl newtons. Basically, there is no constructional difference between a d.c. motor and a d.c.generator. The same d.c. machine can be run as a generator or motor.
For certain applications such as in steel mills, mines and electric trains, it is advantageous to convert alternating
current into direct current in order to use d.c. motors. Because, speed/torque characteristics of d.c. motors are much more superior to that of a.c motors.
Induction Motors: The three-phase induction motors are the most widely used electric motors in industry. They run at essentially constant speed from no-load to full-load. However, the speed is frequency dependent and consequently these motors are not easily adapted to speed control. We usually prefer d.c. motors when large
speed variations are required. Nevertheless, the 3-phase induction motors are simple, rugged, low-priced, easy to maintain and can be manufactured with characteristics to suit most industrial requirements.
Like any electric motor, a 3-phase induction motor has a stator and a rotor. The stator carries a 3-phase winding (called stator winding) while the rotor carries a short-circuited winding (called rotor winding). Only the stator winding is fed from 3-phase supply. The rotor winding derives its voltage and power from the externally energized stator winding through electromagnetic induction and hence the name. The induction motor may be considered to be a transformer with a rotating secondary and it can, therefore, be described as a “transformertype” a.c. machine.
Single Phase Induction motors: These are th most familiar of all electric motors as they are extensively used in home appliances, shops, offices etc. And we have got a really good classification of it.
1. Single-phase induction motors
(i) split-phase type (ii) capacitor type (iii) shaded-pole type
2. A.C. series motor or universal motor
3. Repulsion motors
(i) Repulsion-start induction-run motor (ii) Repulsion-induction motor
4. Synchronous motors
(i) Reluctance motor (ii) Hysteresis motor
Let me know if you're not satisfied. This can be amended.