AC Distribution System

The AC Distribution System is responsible for delivering electrical power from the transmission network to the consumers. It is a network of lines, substations, and equipment designed to distribute electricity to residential, commercial, and industrial areas. Let's break down the different aspects of an AC distribution system.

4.1 Components Classification and Requirements of an Ideal Distribution System

Components Classification:

The major components of an AC distribution system include:

Transmission lines: These carry electricity from the substation to the consumers.
Substations: These step down the high voltage from transmission lines to lower distribution voltages.
Transformers: These devices step down the voltage to levels suitable for use by consumers.
Feeder Lines: These carry the electrical power from substations to local distribution points.
Distributors: These are the lines that carry electricity to the consumers from the feeder lines.
Service Lines: These connect the consumers' premises to the distribution system.

Requirements of an Ideal Distribution System:

Reliability: It should consistently supply electricity without interruptions.
Efficiency: The system should minimize power losses.
Cost-Effectiveness: The installation and maintenance costs should be low.
Flexibility: It should be adaptable to future load changes and expansions.
Safety: Protection against overcurrent, short circuits, and other faults.
Quality of Supply: The voltage and frequency should be stable.

4.2 Primary and Secondary Distribution System

Primary Distribution System:

The primary distribution system is responsible for carrying electricity from the substation to various local distribution points. It operates at a higher voltage level (typically 11 kV, 33 kV, or 66 kV).
Example: Power transmission lines that deliver electricity from a local substation to feeders.

Secondary Distribution System:

The secondary distribution system is responsible for delivering electricity from the primary system to individual consumers at lower voltages (usually 400 V or 230 V).
Example: The final network of wires that brings electricity to homes or businesses.

4.3 Feeder and Distributor

Feeder:

A feeder is a part of the primary distribution system. It carries the electrical power from a substation to distribution transformers or local distributor networks.
Characteristics:
- Operates at high voltages (11 kV, 33 kV).
- Designed to carry large amounts of power to specific areas.
- Typically connected to multiple distributors.

Distributor:

A distributor is a part of the secondary distribution system. It carries the electrical power from feeders to the consumers' premises.
Characteristics:
- Operates at lower voltages (typically 400 V).
- Supplies power to individual customers.

4.4 Factors to Be Considered in the Design of Feeder and Distributor

Load Density: Areas with higher load demand require feeders and distributors designed to handle more electricity.
Length of the Line: The longer the feeder or distributor, the more voltage drop and power loss there will be.
Cost: Both the initial installation and maintenance costs must be considered.
Reliability: Ensure that the system can handle faults and minimize service interruptions.
Safety: Proper insulation, protection devices (like fuses and circuit breakers), and clearance must be maintained.
Future Growth: Design should consider the potential for load growth in the future.

4.5 Types of Different Distribution Schemes: Radial, Ring, and Grid Layout

Radial Distribution System:
- Description: In this system, power flows in one direction from a single source to the consumers.
- Characteristics:
  - Simple design.
  - Least expensive.
  - Vulnerable to faults, as a single fault can affect a large area.
- Example: Common in rural areas.
Ring Distribution System:
- Description: In a ring system, the distribution lines are connected in a loop or ring. Power flows in both directions, providing a backup in case of a fault.
- Characteristics:
  - More reliable than the radial system.
  - Expensive to install.
- Example: Used in urban areas where reliability is important.
Grid Distribution System:
- Description: The grid system combines both radial and ring systems, with multiple interconnected feeders forming a grid.
- Characteristics:
  - Highly reliable.
  - Can handle large loads and faults efficiently.
  - Complex and expensive to build and maintain.
- Example: Large cities or industrial areas where reliability and high demand are essential.

4.6 Distribution Sub-Station

4.6.1 Classification of Distribution Substations:

Step-Down Substations: These substations reduce the voltage from the transmission level (e.g., 33 kV) to distribution voltage levels (e.g., 11 kV).
Distribution Substations: Located closer to the load centers and distribute power at lower voltages (e.g., 11 kV to 400 V).

4.6.2 Site Selection:

When selecting a site for a distribution substation, several factors must be considered:

Proximity to Load Centers: The substation should be located near the area where the demand for electricity is high.
Accessibility: The site should be easy to access for maintenance and emergency repairs.
Environmental Considerations: The site should not be prone to flooding or other natural hazards.
Safety: The site should be free from any hazards that could risk the safety of the equipment or personnel.

4.6.3 Advantages, Disadvantages, and Application of Distribution Substations:

Advantages:

Voltage Regulation: Ensures stable voltage levels for consumers.
Reliability: Helps in ensuring continuous power supply.
Cost-Effective: Reduces transmission loss by being located closer to consumers.

Disadvantages:

High Initial Investment: The construction of substations requires a significant capital investment.
Maintenance Costs: Regular maintenance is required to ensure smooth operation.

Applications:

Urban Areas: Substations are built closer to urban load centers to meet the high electricity demand.
Industrial Areas: Used to provide large amounts of power to industries.

4.7 Single Line Diagram (Layout) of 33/11 KV Substation, 11KV/400V Substation

33/11 kV Substation Layout:
- The 33/11 kV substation steps down voltage from 33 kV to 11 kV for local distribution.
- The substation typically includes transformers, circuit breakers, isolators, and busbars to regulate and distribute power.
11 kV/400 V Substation Layout:
- The 11 kV/400 V substation further steps down the voltage from 11 kV to 400 V, which is used for final distribution to consumers.
- It consists of transformer units, distribution boards, and protection devices.

4.8 Symbols and Functions of Their Components

Here are some of the common symbols used in distribution systems and their functions:

Transformer (T):
- Function: Steps up or steps down the voltage for distribution.
Circuit Breaker (CB):
- Function: Protects the system by interrupting the current flow in case of faults.
Busbar (BB):
- Function: A conductor that connects multiple circuits together and allows the distribution of power.
Switch (SW):
- Function: Used to open or close a circuit.
Isolator (IS):
- Function: Disconnects parts of the system for maintenance without affecting the entire grid.
Feeder (F):
- Function: Carries power from the substation to local distribution points.
Distributor (D):
- Function: Distributes power from feeders to end consumers.
Protection Relay (PR):
- Function: Detects faults and triggers circuit breakers to prevent damage.

Conclusion

An AC Distribution System is a critical component in the transmission of electrical power from substations to end consumers. The system's design, components, and layout are carefully planned to ensure reliability, efficiency, and safety. By understanding the components such as feeders, distributors, and substations, engineers can design better systems for both urban and rural electricity distribution.

AC Distribution System