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Questions and Answers
What are some factors that arrangements in distribution systems depend on?
What is the purpose of an express feeder in a distribution system?
What is the significance of a three-phase mainline in a distribution system?
What is meant by a 'voltage class' in distribution systems?
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Which voltage class is most widely used by utilities according to the text?
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What is the line-to-ground voltage of a 12.47 kV system?
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In distribution systems, what type of feeder serves areas close to the substation?
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A secondary network is used to supply high-density load areas in downtown sections of cities.
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Network transformers in a secondary network system are not protected by network protectors.
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A primary feeder is connected to a common secondary main through one or more distribution transformers.
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In a secondary network system, a forced or scheduled outage of a primary feeder can result in customer outages.
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The common secondary main is always divided into sections, where each section is fed by one distribution transformer and isolated from adjacent sections by insulators.
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Fuses are never installed along a continuous secondary main, which results in banking of distribution transformers.
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The highest degree of reliability is not required in high-density load areas in downtown sections of cities.
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The common secondary main is always a continuous line without any sections or isolation between them.
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Revenues do not justify the cost of a secondary network system in high-density load areas in downtown sections of cities.
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A forced or scheduled outage of a primary feeder in a secondary network system can result in customer outages.
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Study Notes
Overview of Distribution System
- The distribution system is the electrical system between the distribution substation (fed by transmission system) and the consumers' meters.
- It distributes electric power for local use.
Components of a Distribution System
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Distribution Substation: an electrical system that transfers power from transmission system to the distribution system of a certain area.
- Includes step-down transformers that decrease subtransmission voltages to primary distribution voltages for local distribution.
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Feeders: conductors that connect the distribution substation to the area where power is to be distributed.
- The current in a feeder remains the same throughout its length because no tapping is taken from it.
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Distribution Transformers: step-down transformers in which primary and secondary are delta and star connected respectively.
- Output voltage of distribution transformer is 440 V in three-phase system and 230 V in single-phase system.
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Distributors: conductors from which tapping are taken for supply to the consumers.
- Current being not same throughout its length due to tapping.
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Primary Distribution Configurations: three types - Radial, Loop (Ring), and Network.
- Radial system: simplest distribution circuit, lowest initial cost, but has limitations (e.g., fault on the feeder or distributor cuts off supply to consumers).
- Loop system: provides two-way feed from the substation, maintaining adequate voltage, but difficult to maintain voltage everywhere on the primary grid.
- Network system: increases service reliability, but requires more substation, more costly and complicated operation.
Primary Voltage Levels
- Most primary distribution voltages are between 4 and 35 kV.
- Four major voltage classes: 5, 15, 25, and 35 kV.
- Industry practice: voltages are given as line-to-line voltages.
Electric Power System
- Major components: Generation Sector, Transmission Sector, Distribution Sector, and Load Sector.
- Generation Sector: power generating plants convert other forms of energy into electric energy.
- Transmission Sector: transport of electricity from one region to another through high voltage overhead transmission lines.
- Distribution Sector: transport of electricity from the lower voltage distribution lines to homes, businesses, and other load centers.
- Load Sector: power required of or consumed by a circuit.
- Supply Sector: suppliers refer to any person licensed by the ERC to sell, broker, market, or aggregate electricity to end-users.
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Description
This quiz covers an overview of the distribution system, including the distribution sector, supply sector, and load sector in electricity distribution. Topics include transport of electricity, suppliers licensed by ERC, and end-users.
