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Once electrical power has been produced, it must be distributed to the location where it is used. Unit III deals with electrical power distribution systems. The fundamentals of distribution systems are discussed in Section 8. This Section provides an overview of distribution systems, transformer operation, and conductor characteristics. Section 9 examines specialized power distribution equipment such as protective devices, high voltage equipment, and switch gear. Then, Section 10, Single-Phase and Three-Phase Distribution Systems, discusses the types of distribution systems used today. Ground-fault interrupters are also discussed extensively in this Section, since their use is becoming widespread in electrical power distribution systems.
Fig III shows the electrical power systems model used in this guide and the major topics of Unit III, Electrical Power Distribution Systems.
Fig III. Electrical power systems model
- Power Distribution Fundamentals (Section 8)
- Power Distribution Equipment (Section 9)
- Single-phase and Three-phase Distribution Equipment (Section 10)
UNIT OBJECTIVES
Upon completion of this unit, you should be able to:
1. List several purposes of transformers.
2. Describe the construction of a transformer.
3. Explain transformer action.
4. Calculate turns ratio, voltage ratio, current ratio, and the power and efficiency of transformers.
5. Explain the purpose of isolation transformers, autotransformers, and current transformers.
6. Explain factors that cause losses in transformer efficiency.
7. Investigate the characteristics of transformers.
8. Describe the transmission and distribution of electrical power.
9. Compare underground, overhead, and HVDC power transmission systems.
10. Explain parallel operation of electrical power systems.
11. Describe ring, radial, and network power distribution systems.
12. Explain circular mil sizing of copper and aluminum electrical conductors.
13. Calculate cross-sectional area, resistance, or ampacity of round, square, or rectangular copper or aluminum conductors.
14. Describe the types of insulation used for conductors in electrical distribution systems.
15. Describe the following equipment used at substations for electrical power distribution:
- High-Voltage Fuses
- High-Voltage Circuit Breakers
- High-Voltage Disconnect Switches
- Lightning Arrestors
- High-Voltage Insulators
- High-Voltage Conductors
- Voltage Regulators
16. Describe the following types of protective equipment used in electrical distribution systems:
- Plug Fuses
- Cartridge Fuses
- Time-Lag Fuses
- Low-Voltage Circuit Breakers
- Protective Relays
- Motor Fault Current Protection
- Overheating Protection
- Undervoltage Protection
17. Describe the following in relation to electrical power distribution systems:
- Feeder Lines
- Branch Circuits
- Safety Switches
- Distribution Panelboards
- Low-Voltage Switchgear
- Service Entrance
18. Explain the operation of single-phase/two-wire and single phase/three-wire power distribution systems.
19. Explain the operation of three-phase/three-wire, three-phase/ four-wire, and three-phase/three-wire with neutral power distribution systems.
20. Describe and sketch diagrams of delta-delta, delta-wye, wye-wye, wye-delta, and open delta three-phase transformer connection methods.
21. Describe the following in relation to grounding of electrical power systems:
- System Ground
- Equipment Ground
- Ground Fault Circuit Interrupters
22. Explain the use of the National Electric Code (NEC) as a standard for electrical power distribution design in the United States.
23. Calculate voltage drop in an electrical circuit using a conductor table or circular mil formula.
24. Calculate voltage drop in a branch circuit or feeder circuit for a single-phase or three-phase distribution system.
25. Determine grounding conductor size by using the proper tables.
26. Describe the following in relation to electrical power systems:
- Nonmetallic Sheathed Cable
- "Hot" Conductor
- Neutral Conductor
- Safety Ground
- AWG and MCM Conductor Sizing
- Metal-Clad Cable
- Rigid Conduit
- Electrical Metallic Tubing (EMT)
- Uninterruptible Power Supply (UPS)
- Power Line Filter
- Power Conditioner
- Floor-Mounted Raceway
- Conduit Connectors
- Wire Connectors
- Plastic Conduit and Enclosures
- Power Outlet Design
- International Power Sources
