Industrial Electricity Vol 2

Table of Contents

Chapter 1: Principles of Three-Phase Circuits

Topics: Three-phase alternators; Y- and delta-connected alternators; Power in three-phase circuits; Load connections; Measuring power

Learning Objectives:

• List the main advantages of the three-phase ac system.
• State the definition of phase sequence.
• Demonstrate how to calculate the RMS power in a single-phase circuit.
• Explain how to measure the total power consumed by the load in a three-phase circuit.
• List the functions of an instrument transformer.

Chapter 2: Transformer Operations

Topics: Transformer designation, insulation, cooling, and polarity; Single-and three-phase transformer connections; Installing transformers

Learning Objectives:

• Name general kinds of transformers.
• List the temperature limits for each class of transformer insulation.
• Explain how oil-immersed transformers are cooled.
• Name the common methods of connecting three single-phase transformers for threephase operation.
• Explain how to select the correct location for a transformer.

Chapter 3: Principles of Three-Phase Motors

Topics: Induction motors; Squirrel-cage rotors; Pole-phase relationships; Torque, rotor speed, slip, frequency, resistance, reactance, and power factor

Learning Objectives:

• Describe a squirrel-cage rotor.
• List the factors that determine the strength of the magnetic field in an induction motor.
• Discuss pole-phase relationships.
• Demonstrate how to reverse the rotation direction of the magnetic field.
• Discuss the relationship between rotor speed and frequency.

Chapter 4: Maintaining Three-Phase Motors

Topics: Cleaning; Care of stator and rotor windings; Air gap; Overload and single-phase operation; Motor shaft currents; Bearings; Maintenance schedule

Learning Objectives:

• List the steps in measuring the resistance of the insulation on motor windings.
• Explain how to raise the temperature of a motor winding.
• List the steps in lubricating motor bearings.
• List the conditions that must exist before you can lubricate bearings.

Chapter 5: Three-Phase Motor Controllers

Topics: Limitations; Full-voltage and across-the-line starting; Reducing starting current; Primary- and secondary-resistance starters; Maintenance; Multiple start-stop controls; Across-the-line reversing starters; Plugging control; Jogging; Controlling surge and backspin

Learning Objectives:

• Explain how a motor starter works.
• Explain the difference between open transition and closed transition.
• Name the common kinds of reduced-voltage starters.
• List the steps in inspecting motor starters.
• Explain how to select the best motor starter for a particular application.
• Explain the difference between low-voltage release and low-voltage protection.
• Describe the plugging process.
• Explain how to prevent backspin.

Chapter 6: Motor Starters

Topics: Motor controllers; Controller enclosures; Starters; Magnetic controls; Interlocks, Reversing and combination starters

Learning Objectives:

• Describe the difference between a manual starter and a magnetic starter.
• Explain the function of a shading coil in a magnetic starter.
• Explain the effects of low voltage on a controller.
• State the reason why holding-circuit interlocks are required on magnetic starters and contactors.
• Demonstrate how to reverse the shaft rotation of a three-phase motor.

Chapter 7: Switches and Controls

Topics: Pushbuttons; Selector switches; Wall boxes; Contact blocks; Indicating lights; Circuit diagrams; Legend plates

Learning Objectives:

• Discuss the characteristics of industrial switches and controls.
• Identify the five most commonly used NEMA pushbutton stations.
• Demonstrate how to mount an oil-tight control station both vertically and horizontally.
• Explain the difference between standard and press-to-test indicating lights.
• Explain how a three-wire control circuit works.

Chapter 8: Control Relays

Topics: Contact operation; Mountings, enclosures, terminals, and definitions; NEMA classes; Causes of failure

Learning Objectives:

• State the definition of a relay
• Explain the function of relay contacts.
• Select the best relay for use where large movement of the contacts or high contact force is required.
• List the advantages of a reed relay.
• Tell why industrial relays usually have double-break contacts.

Chapter 9: Motor Control Centers

Topics: Features and advantages; MCC bus; NEMA standards; Enclosure construction; Wiring; Circuit protection; Installation

Learning Objectives:

• Define the term motor control center.
• Name the main advantages and disadvantages of back-to-back MCC construction.
• Explain how to install an MCC.
• Define a note, a caution, and a warning as each relates to MCC equipment.
• List the checks to conduct prior to releasing an MCC for plant operation.

Chapter 10: Troubleshooting with Electrical Schematics

Topics: Symbols; Elementary diagrams; Power control and motor-starting circuits; Identifying conductors; Control panel layout; Sequence of operation

Learning Objectives:

• Identify a control relay on an electrical schematic.
• State the NEC requirements for fuses in ungrounded conductors.
• Explain component numbering on electrical schematics.
• Explain how conductors in a motor-control circuit are identified.

Chapter 11: Troubleshooting Control Circuits

Topics: Control-circuit functions; Conditions of protection; Troubleshooting pushbutton, sequence/control, motor, and overload circuits

Learning Objectives:

• Explain how severe three-phase voltage unbalance affects a three-phase motor.
• List the advantages of inherent protection.
• Explain how undervoltage release works.
• Describe how to troubleshoot a motor circuit.

Chapter 12: Troubleshooting Combination Starters

Topics: Using relay-troubleshooting charts; Latching-relay and timing-relay checks; Replacing relay coils; Troubleshooting control circuits, starters, and relays

Learning Objectives:

• List the reasons why a magnet coil burns or short-circuits.
• List the steps in troubleshooting a defective motor.
• Explain how a mechanical latching relay works.
• Explain how an electronic timing relay operates.

Chapter 13: Troubleshooting Control Devices

Topics: Reversing controllers; Using a checking-sequence chart; Autotransformer starters; Multispeed motor starter controls

Learning Objectives:

• Demonstrate how to reverse the rotation of a three-phase induction motor.
• Explain the function of limit switches in reversing-motor applications.
• Describe how to use a checking-sequence chart.
• Select the best starter for use where it is undesirable to put a heavy load on the power supply.
• Explain how to change the speed of a squirrel-cage motor.

Chapter 14: Troubleshooting Special Controls

Topics: Selenium rectifiers; Testing rectifier diodes and three-phase rectifiers; Control-system logic; Static control; Time delay element

Learning Objectives:

• Explain the effects of age on a selenium rectifier.
• Name the protective devices used in electrical systems and pneumatic systems.
• State the definition of a bistable device.
• List the functions of a static control device.

Chapter 15: Troubleshooting AC Motors

Topics: Grounded stator windings; Short-circuited and reversed phases; Open circuits; Incorrect voltage connections

Learning Objectives:

• Identify various kinds of three-phase motor failures.
• Demonstrate how to conduct a balanced-current test on a three-phase, Y-connected winding.
• List the symptoms of a reversed phase in a three-phase winding.
• Explain how to identify external leads that have become defaced.
• Demonstrate how to test for an open circuit in a split-phase motor

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