This document introduces concepts related to energy conversion devices like motors and generators. It explains that motors convert electric power to mechanical power, while generators convert mechanical power to electric power using magnetic flux. It also discusses the differences between conventional and electron current flow and how to identify power sources and loads in electric circuits. Finally, it reviews sign conventions for quantities like current, voltage, and rotation to establish a reference for positive and negative values.

1. LESSON 1: INTRODUCTORY
CONCEPTS
ET 332a
Dc Motors, Generators and Energy Conversion Devices
1

2. LEARNING OBJECTIVES
After this presentation you will be able to:
 Explain the energy conversion process that
takes place in the motors and generators.
 Explain the difference between conventional
and electron current flow
 Identify power sources and loads in an electric
circuit
2

3. ENERGY CONVERSION DEVICES
Motors and Generators
Motor Action
Electric power Mechanical Power
Input Output
Electric
Energy
Mechanical
Energy
Magnetic
Flux
3

4. ENERGY CONVERSION DEVICES
4
Motors and Generators
Generator Action
Mechanical power Electric Power
Input Output
Mechanical
Energy
Electrical
Energy
Magnetic
Flux

5. REVIEW OF FUNDAMENTALS
5
Conventions and Assumptions
Conventional Vs Electron current flow
Voltage
Source
+
--
Conventional current
+ to - flow
Voltage
Source
+
--
Electron current
- to + flow
Either system is correct
Conventional current standard in power systems and ac analysis

6. REVIEW OF FUNDAMENTALS
6
Indentifying Sources and Loads
A device is a source when current flows from the
positive terminal (conventional flow)
Device
A
A
1
A2
+
-
Device A: Source
Device
A
B
1
B2
+
-
A device is a load when current flows into the
positive terminal (conventional flow)
Device B: Load

7. REVIEW OF FUNDAMENTALS
7
Reversing the direction of current or the voltage
polarity changes converts most sources to loads
Device
A
A
1
A2
-
Device A: Source
Device
A
A
1
A2
-
+ +
Reverse voltage polarity
Device A is now a load
Device
A
A
1
A2
-
Device A: Load
+
Reverse
current

8. QUANTITY SIGN CONVENTIONS
8
The + and – signs used to indicate direction of:
Current
Force
Rotatio
n
Power
Voltage
Compared to a reference direction

9. SIGN CONVENTION EXAMPLES
9
Shaft Rotation
Clockwise CW
Define clockwise as
positive (+)
rotation
Counter Clockwise CCW
Counter clockwise now
becomes negative (-)
rotation

10. SIGN CONVENTION EXAMPLES
10
Voltage measurement
Voltmeter
Reading
V
E
1
2
+
Black box
Case 1: V=E =+10 V Real polarity same as
Marked by leads
Reference relative to
black lead

11. SIGN CONVENTION EXAMPLES
11
Voltage measurement
E
1
2
+
Black box
Case 2: V=E =-10 V Real polarity opposite of
marked by leads
Voltmeter
Reading
V
Leads reversed

12. ET 332a
Dc Motors, Generators and Energy Conversion Devices
12
END LESSON 1