2.1.   Basic Components of Electromagnetic Relays
2.2.   Hysteresis and Coercitive Force
2.3.   Types of Magnetic Systems
2.3.1 The Clapper-Type (Attracted-Armature) Magnetic System
2.3.2. Systems with a Balanced Armature
2.3.3. Direct Motion (Solenoid-type) Systems and Their Peculiarities
2.4.   Differences Between AC and DC Relays
2.5.   Some Auxiliary Elements for Improving the Relay Operation
2.6.   What Happens When a Relay is Energized
2.7.   Windings of Relays: Types and Design Features

3 Contact Systems
3.1. Designs of Basic types of Contacts
3.2. Silver, Gold, Platinum
3.3. Contacts with Two-Stage Commutation
3.4. What is the Purpose of Contact Pressure
3.5. Self-cleaning Contacts
3.6. Self-Adjusting Contacts
3.7. When Power Does Not Equal Multiplication by Current and Voltage
3.8. Split ... Make-Before-Break... High-Frequency Contacts
3.9. Compensation for Shocks and Electro-Dynamic Forces in Contacts
3.10. Sparking Contacts and Their Control
3.11. High-Power Contact Systems
3.12. Mercury Displacement Relays

4 External Design of Relays
4.1. Environmental Impact on Relays
4.2. Wood and Cardboard: First Protection Shield for Relays
4.3. Is a Sealed Relay Always Better Than Open One?
4.4. Outlets, Terminal Sockets and Containers for Relays
4.5. Indicators of Operation and Test Buttons
4.6. Relays Which Do Not Look Like Relays at All

5 Reed Switches and Reed Switch Relays
5.1. Who invented the "Reed Switch"?
5.2. Coruscation of Ideas and Constructions
5.3. High Power Reed Switches
5.4. Membrane Reed Switches
5.5. Mercury Reed Switches
5.6. High-Voltage Reed Switches
5.7. Reed Switches with Liquid Filling
5.8. Polarized and Memory Reed Switches
5.9. Reed Switch Relays
5.10. Mercury Reed Switch Relays
5.11. Winding-Free Relays

6 High-Voltage Relays
6.1. What is a High-Voltage Relay?
6.2. Open Relays for High-Voltage Switching
6.3. Vacuum and Gas-Filled High-Voltage Low Power Relays
6.4. High Power Vacuum Relays and Contactors
6.5. High-Voltage Reed Relays
6.6. High-Voltage Interface Relays

7 Electronic Relays
7.1.Was it Thomas A. Edison Who Invented a Lamp?
7.2. Lee De Forest Radio Valve
7.3. How a Vacuum Tube Works
7.4. Relays with Vacuum Valves
7.5. Gas-Tubes with Relay Characteristics
7.6. Power Mercury Valves
7.7. Electron-Beam Switching Tubes
7.8. Semiconductor Relays
7.8.1. First Experiments and Early Semiconductor Devices
7.8.2. Semiconducting Materials and p-n-Junctions
7.8.3. Diode Switch of Electric Circuits
7.8.4. Transistors
7.8.5. Bipolar... Unijunction... Field
7.8.6. From Micromodules to Microchips
7.8.7. Transistor Devices with Relay Characteristics
7.8.8. Thyristors
7.8.8.1. Control of Thyristors on Direct Current
7.8.8.2. Control of Thyristors on Alternating Current
7.8.8.3. Diac, Triac, Quadrac
7.9. Optoelectronic Relays
7.10. Super-Power Electronic Relays
7.11. Hybrid Relays

8 Time Relays
8.l. Electromagnetic Time-Delay Relays
8.1. Capacitor Time-Delay Relays
8.3. Relays with Clockwork
8.4. Pneumatic and Hydraulic Time-Delay Relays
8.5. Electronic Time-Delay Relays
8.6. Attachments to Standard Electromagnetic Relays
8.7. Microprocessor Based Time-Delay Relays
8.8. Accelerated (Forced) Relays

9 Thermal Relays
9.1. Relays Based on a Bimetallic Thermal Element
9.2. Protective Thermal Relays
9.3. Automatic Circuit Breakers with Thermal Elements
9.4. Dilatometer Relays
9.5. Manometric Thermal Relays
9.6. Mercury Thermal Relays
9.7. Thermal Relays with Reed Switches
9.8. Semiconductor Thermal Elements and Thermal Relays

10 Current and Voltage Protection Relays

10.1. What are Protective Relays
10.2. Current and Voltage Transformers
10.3. Instantaneous Current and Voltage Relays
10.3.1. Protective Relays of the Electromagnetic Type
10.3.2. Electronic Current and Voltage Relays
10.3.3. Reed Switch Current Relays
10.4.    Current Relays with an Independent Time-Delays
10.4.1. Relays with Integrated Clockwork
10.4.2. Current Relays with Electronic Time-Delay Components
10.4.3. Electronic Current Relays with Independent Time-Delay
10.5.    Current Relays with Dependent Time-Delay
10.5.1. Relays with Liquid Time-Delay Elements
10.5.2. Induction Relays: Design and Characteristics
10.5.3. Electronic Current Relays with Dependent Characteristics
10.6.    Harmonic and Voltage Restraint Relays

11 Power and Power-Directional Relays
11.1. Induction-Type Relays
11.2. Characteristics of Power Direction Relays
11.3. Electro-Dynamic-Type Relays
11.4. Electronic Analogues of Power Direction Relays

12 Differential Relays
12.1. Principles of Differential Protection
12.2. High-Impedance Differential Relays
12.3. Biased Differential Relays
12.4. Electromagnetic Percentage Differential Relays
12.5. Induction-Type Differential Relays
12.6 Harmonic Restraint Differential Relays
12.7. Pilot-Wire Differential Relays

13 Distance Relays
13.1. Principles and Basic Characteristics of Distance Protection
13.2. System Swing
13.3. Principles of Distance Relays Construction
13.4. Why do Distance Relays Need Memory?
13.5. Distance Relays with Higher Performance
13.6. Electronic Analogues of Impedance Relays

14 Frequency Relays
14.1. Why is it Necessary to Control Frequency in Electric Networks?
14.2. Charles Steinmetz - Inventor of the Frequency Relay
14.3. Induction Frequency Relays
14.4. Resonance Relays
14.5. Electronic Frequency Relays

15 Microprocessor-Based Relays: Prospects and Challenges

15.1. Is It a Relay at All?
15.2. Advantages of Microprocessor-Based Relays
15.3. Disadvantages of Microprocessor-Based Relays
15.4. Summing Up

16 Special Types of Relays
16.1. Polarized Relays
16.2. Latching Relays
16.3. Sequence Relays
16.4. Rotary Relays
16.5. Moving-Coil Relays
16.6. Amplifier-Driven Relays
16.7. Magneto-Hydro-Dynamic Relays
16.8. Annunciator Target Relays
16.9. Flashing-Light Relays
16.10. Buchholz Relays
16.11. Safety Relays
16.12. Ground Fault Relays
16.13. Supervision Relays
16.14. Hydraulic-Magnetic Circuit Breakers

Basic Relay Terms and Definitions-Glossary
References

Things should be described as simply as possible,
but not simpler

A. Einstein