DC Equipment and Controls

Table of Contents

Chapter 1: DC Power in Industry

Topics: DC generators and motors; Rectifiers; SCR speed control; Storage batteries; Electroplating; Electrolytic refining; Arc welding

Learning Objectives:

• List the advantages of dc over ac.
• List the brush problems caused by eddy currents.
• Name three types of batteries commonly used in the plant.
• Explain how the electroplating process works.
• Explain the difference between straight polarity and reversed polarity in arc welding.

Chapter 2: DC Electromagnets

Topics: Magnetic forces and fields; Magnetic shielding; Solenoids; Residual magnetism; Relays; Polarized relays; Protecting relay contacts

Learning Objectives:

• State the definition of residual magnetism.
• Explain the effects of distance on magnetic field strength.
• Discuss the characteristics and uses of solenoids.
• Discuss the characteristics of relays.

Chapter 3: DC Generators

Topics: Parts and action of DC generators; Armature reaction; Commutation; Interpoles; Types of generators; Losses; Parallel operation

Learning Objectives:

• Explain the function of each of the main parts of the dc generator.
• Explain how to increase the number of pulses during each rotation of an armature.
• Demonstrate how to combine the shunt field and series field to produce a compound generator.
• State the reasons why electrical losses, magnetic losses, and mechanical losses occur in the dc generator.

Chapter 4: DC Motors

Topics: CEMF; Armature reaction; Self-induction and commutation; Interpoles; Torque; Speed regulation; Shunt, series, and compound motors

Learning Objectives:

• Explain what happens during self-induction and commutation.
• Define CEMF.
• State the difference between speed regulation and speed control.
• Name the kinds of dc motors.
• Explain the different operating characteristics of series, shunt, and compound motors.

Chapter 5: DC Armatures

Topics: Windings; Armature, copper, eddy-current, and hysteresis loss; Commutation; Armature maintenance

Learning Objectives:

• Name the basic parts of an armature assembly.
• Describe the main differences between a lap winding and a wave winding.
• List the characteristics of a single-reentrant simplex-lap winding.
• State the definition of copper loss, eddy-current loss, and hysteresis loss.
• Demonstrate how to perform preventive maintenance on an armature.

Chapter 6: DC Relays

Topics: Operating characteristics; Shunt, series, lockout, and inductive time-delay relays; Magnetic blowout coils; Dynamic braking

Learning Objectives:

• Name three factors that determine the performance and reliability of a relay.
• Name the six types of commonly used relays.
• Explain the operation of each type of relay.
• Explain dynamic braking.
• Describe how a disc brake is attached to a motor.

Chapter 7: DC Controllers

Topics: Classification; Factors affecting motor speed; Protection; Temperature compensation; Manual starters; Overload reset; Magnetic and drum controllers

Learning Objectives:

• List the kinds of functions performed by motor-control devices.
• Name the types of motor controllers and discuss their operating characteristics.
• Explain how each of the three kinds of thermal overload relays works.
• Name the kinds of resets for overload relays.

Chapter 8: DC Power Supplies

Topics: Electron emission; Electron tubes; Vacuum-tube diode and rectifier; Mercury-vapor diodes; Semiconductors; Checking diodes; Identifying replacement semiconductors

Learning Objectives:

• Discuss the operating principles of vacuum tubes and rectifiers
• Name the four types of filters commonly used in rectifier circuits.
• Identify a mercury-vapor diode.
• List common causes of semiconductor failure.
• State the criteria for selecting replacement semiconductors.

Chapter 9: Silicon Controlled Rectifiers

Topics: Principles of SCRs; Pulse timing in DC circuits; Trigger pulses; SCR motor control; AC and DC applications; AC-DC conversion

Learning Objectives:

• State the definition of a silicon controlled rectifier.
• Explain how an SCR works.
• Explain how to increase the effective current and the power delivered to a motor by an SCR motor control.
• List four dc applications of SCRs.
• List four ac applications of SCRs.

Chapter 10: Maintenance of DC Equipment

Topics: Inspection; Replacing field coils; DC motor controllers; Relay contacts; Commutation; Brush selection and care; Maintaining relays and armatures

Learning Objectives:

• Explain how to test field coils to determine the condition of the insulation.
• List the signs of a short-circuited field coil in a machine.
• Explain how to replace a field coil in a machine.
• Discuss how to maintain relay control.
• Name the criteria for satisfactory commutation.

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