Power Distribution Systems Overview

Power Distribution Systems

• Power distribution systems are the final stage of electricity delivery, bringing power from the transmission system to consumers.
• Distribution systems operate at lower voltage levels than transmission systems, typically between 11 kV and 415 V.
• The key purpose of distribution systems is to deliver electricity reliably and efficiently to consumers, maintaining consistent voltage levels, protecting the system from faults, and facilitating integration of distributed energy resources.

Components of a Distribution System

• Sub-transmission systems deliver energy from bulk power sources to distribution substations.
• They operate at voltages between 12.47 kV and 245 kV.
• Distribution substations contain transformers, voltage regulating apparatus, buses, and switchgear, reducing the sub-transmission voltage to a lower primary system voltage for local distribution.
• Primary feeders, operating between 4.16 kV and 34.5 kV, distribute energy from the substation to load centers, branching into sub-feeders and laterals.
• Distribution transformers, in ratings of 10 to 500 kVA, connect to primary feeders, sub-feeders, and laterals for voltage reduction.
• Secondary circuits distribute energy from distribution transformers to consumers through service drops, reducing the distribution voltage to the utilization voltage.
• Service drops connect the distributor to the consumer's meter, typically using a small cable.

Feeders and Distributors

• Feeders are conductors that connect the substation to the distribution area.
• They are overhead lines or underground cables and do not have any tappings.
• The primary concern in designing feeders is their current carrying capacity.
• Distributors are conductors with tappings that supply power to consumers.
• They can be overhead or underground lines, but often smaller and lighter than feeders.
• Voltage drop along the length of the distributor is a primary concern in their design.

Classification of Distribution Systems

• Classified based on:
  • Number of wires: Two-wire, three-wire, and four-wire systems.
  • Scheme of connections: Radial, ring (loop), and interconnected distribution systems.
  • Nature of current: AC and DC distribution systems.
  • Type of construction: Overhead and underground systems.

Connection Schemes

• Radial Distribution System:

  • Single path between each distributor and substation.
  • Simple and most widely used due to its low cost and easy maintenance.
  • Disadvantage: Power disruption impacts all consumers along the single path.

• Ring Distribution System:

  • The feeder forms a closed loop around the distribution area, allowing for redundant power supply.
  • Offers increased reliability as each distributor is fed by two feeders.
  • Enables power supply to continue even if there is a fault on one section of the feeder.
  • Advantages: Less voltage fluctuations, less use of conductor material.
  • Disadvantage: Increased complexity and cost compared to the radial system.

• Interconnected Distribution System:

  • Feeder is powered by two or more substations.
  • Provides high levels of reliability and flexibility in power supply.

Power Distribution Systems

• Power distribution systems deliver electricity from the transmission system to individual consumers.
• The system operates at lower voltage levels than transmission systems, typically in the range of 11 kV to 415 V.
• The network structure of the system comprises overhead or underground lines branching out from substations to reach diverse customer locations.
• Power distribution systems ensure consistent voltage levels within acceptable ranges and protect the system from faults and overloads.
• The distribution system also facilitates the integration of distributed energy resources like solar panels and wind turbines.

Distribution System Components

• Sub-transmission system delivers energy from bulk power sources to distribution substations at a voltage level between 12.47 and 245 kV.
• Distribution substations reduce the sub-transmission voltage to a lower primary system voltage for local distribution using power transformers, voltage-regulating apparatus, buses, and switchgear.
• Primary feeders distribute energy from the low-voltage bus of the substation to its load center at a voltage level of 4.16–34.5 kV.
• Distribution transformers with ratings from 10 to 500 kVA are connected to primary feeders, sub-feeders, and laterals.
• Secondary circuits distribute energy from the distribution transformer to consumers through service drops, reducing the distribution voltage to the utilization voltage.
• Service drops are small cables that connect the distributor to the consumer's meter.

Feeders and Distributors

• Feeders connect the substation (generating station) to the area where power is to be distributed.
  • They are typically overhead lines or underground cables.
  • The current in a feeder remains the same throughout its length.
  • The main consideration in feeder design is the current carrying capacity.
• Distributors are conductors from which tappings are taken for consumer supply.
  • They can be overhead or underground lines but are often smaller and lighter than feeders.
  • The current through a distributor is not constant because tappings are taken at various places along its length.
  • The main consideration in distributor design is the voltage drop along its length.

Classification Of Distribution System

• Number Of Wires
  • Two Wire System: Used for small loads and residential areas.
  • Three Wire System: Offers voltage flexibility and is more efficient for larger loads like commercial buildings.
  • Four Wire System: Allows for both single-phase and three-phase loads.
• Scheme Of Connection:
  • Radial Distribution System: Power flows along a single path, making it simple and cost-effective but susceptible to power outages if a fault occurs.
  • Ring or Loop Distribution System: Offers redundancy with two possible power paths, increasing reliability but requiring more complex design and increased cost.
  • Interconnected Distribution System: Supplied by two or more substations, enhancing reliability by providing alternative power sources.
• Nature Of Current:
  • AC Distribution System: The most common distribution system, using alternating current.
  • DC Distribution System: Used for specialized applications like battery banks and emergency power systems.
• Type Of Construction:
  • Overhead System: Uses poles and wires above ground, cost-effective and easier to install.
  • Underground System: Wires are buried below ground, enhancing aesthetics and reducing interference from environmental factors but more expensive to install and maintain.

Connection Schemes in Distribution System

• Radial Distribution System:
  • The simplest and most widely used distribution system.
  • Characterized by a single path for power flow between the substation and the distributor.
  • Offers low cost, simple design, and easy maintenance.
  • Disadvantage: single path can result in complete power loss if interrupted.
• Ring Distribution System:
  • Offers redundancy with a loop-shaped feeder that connects to the substation at both ends.
  • Distributors are tapped from the feeder at multiple points.
  • Advantages: increased reliability due to alternative paths for power flow, reduced voltage fluctuations.
  • Disadvantage: increased design complexity and cost compared to radial systems.
• Interconnected Distribution System:
  • Supplied by two or more substations.
  • Provides alternative power sources, enhancing reliability.
  • Offers flexibility in power flow and increased capacity.
  • Requires complex control and coordination systems.

This quiz covers the fundamentals of power distribution systems, detailing their role in electricity delivery from transmission to consumers. It includes information on voltage levels, key components, and the functionality of distribution substations. Test your understanding of how power is distributed reliably and efficiently.