03-05-2012, 01:25 PM
DC MOTORS AND GENERATORS
25741_ENERGY_CONVERSION_21.ppt (Size: 470.5 KB / Downloads: 111)
DC MOTORS AND GENERATORS
1. The Equivalent Circuit of a DC Motor
2. The Magnetization Curve of a DC Machine
3. Separately Excited and Shunt DC Motors
- The Terminal Characteristics of a Shunt DC Motor
- Nonlinear Analysis of a Shunt DC Motor
- Speed Control of Shunt DC Motors
- The Effect of an Open Field Circuit
4. The Permanent-Magnet DC Motor
5. The Series DC Motor
- Induced Torque in a Series DC Motor
- The Terminal Characteristic of a Series DC Motor
- Speed Control of Series DC Motors.
6. DC Motor Starters
- DC Motor Problems on Starting
- DC Motor Starting Circuits
7. Introduction to DC generators
8. Separately Excited Generator
- Terminal Characteristic of a separately Excited DC Generator
- Control of Terminal Voltage
- Nonlinear Analysis of a Separately Excited DC generator
INTRODUCTION
DC motors are compared by their speed regulation:
SR= [ωnl-ωfl]/ωfl x 100%
It is a rough measure of shape of motor’s torque-speed characteristic
A positive regulation means speed drops with increasing load & a negative speed regulation means speed increases with increasing load
Magnitude of S.R. approximately show how steep is the slope of torque-speed
Dc motors driven from a dc power supply (unless specified) and input voltage assumed constant)
Five major types of dc motor:
1- separately excited dc motor 2-shunt dc motor
3-permnent-magnet dc motor 4- series dc motor 5-compounded dc motor
DC MOTOREQUIVALENT CIRCUIT
A simplified equivalent circuit eliminating the brush voltage drop and combining Radj with the field resistance shown in (b)
Some of the few variations and simplifications:
1- brush drop voltage is often only a very tiny fraction of generated voltage in the machine. where it is not too critical, brush drop voltage may be left out or included in the RA.
2- internal resistance of field coils is sometimes lumped together with variable resistor and total is called RF
3- Some generators have more than one field coil, all of which appear on the equivalent circuit