Software for Education and Industry
Three phase induction motors are the workhorse of industry. It has been estimated that 70% to 80% of all electricity in the world is consumed by these motors. They are truly elegant machines in that there are no moving parts except the rotor, and there are no brushes, commutators, or slip rings to wear out.
This computer program explains How
To Control 3 Phase Induction Motors in easy to understand
text, graphics, and pictures. The program explains:
This program requires no installation on your computer. Simply double-click on the Table of Contents.html file or any other .html file on the CD and your web browser will run the program.
Table of Contents
2. Why Not Just Use a Switch?
3. Manual Motor Starters
4. NEMA Size Motor Starters
5. Magnetic Motor Starters
6. Motor Starting Circuit
7. Motor Starting Circuit Explained
8. Reversing Motor Starters
9. Reversing Motor Starter Schematic
10. Controlling Motor Speed
11. Multi-Speed Motor Starters
12. Variable Speed Motor Starters
13. Variable Speed Drives (VFDs)
14. Variable Speed Drive Features
15. Motor Starting Characteristics
16. Reduced Voltage Starters
17. Primary Resistor Starters
18. Autotransformer Starters
19. Wye-Delta Starters
20. Part Winding Starters
21. Solid State Starters
Electrical drawings usually show schematic diagrams, not pictorial diagrams. The pictorial diagram below is the same as the one seen on the previous page.
The schematic diagram below is how the same circuit would be shown on an electrical drawing. In addition, a control transformer has been added to the circuit so that the pushbutton and coil of the motor starter are 120VAC instead of 480VAC, because it is generally considered safer to have 120VAC on a pushbutton than 480VAC.
Example screen showing reversing motor control
When the Reverse pushbutton is pressed, the R coil is energized sending power to the motor through the red power contacts. Phases A, B, and C are applied to the motor as shown below, reversing the direction of the motor rotation.
Example screen showing Variable
These drives have become available in only the last few years due to the development of IGBTs (insulated gate bipolar transistors) like the one shown below.
The IGBT is essentially a power transistor capable of switching at very high speeds.