Comprehensive Guide to Distribution Line Design

Distribution Lines
Presented by:
Prof. R. S. Arora
Department of Electrical Engineering
Sanjivani K.B.P. Polytechnic, Kopargaon

Block Diagram of Electrical Power
System
The electrical power system consists of
the following main stages:
1. Generation: Power is generated at
power plants.
2. Transmission: High-voltage
transmission lines (132kV, 220kV, etc.)
transmit power over long distances.
3. Substations: Voltage is stepped
down for distribution.
4. Distribution: Further voltage
reduction (11kV, 415V) for consumer
use.
5. Consumers: Homes, industries, and
commercial establishments receive the
final supply.

Types of Distribution Lines
Primary distribution lines are high-voltage lines that carry power from
substations to distribution transformers, while Secondary distribution
lines are low-voltage lines that deliver power from those transformers to
end users.
Distribution lines are classified into:
1. Primary Distribution Lines:
• These lines operate at higher voltages.
•They carry power from the distribution substation to the distribution
transformers located on poles or in substations.
•They are designed to handle large amounts of power and are typically
overhead lines or underground cables.
•Examples of primary distribution systems include radial, ring, and
interconnected systems.

2. Secondary Distribution.
•These lines operate at lower voltages.
•They receive power from the distribution transformers and deliver it
to individual homes, businesses, and other consumers.
•They are typically overhead lines or underground cables, depending
on the location and infrastructure.
•Secondary distribution systems are often radial, but can also be part
of a network system.

Distribution lines are classified into Overhead and
Underground based on their installation method.
1.Overhead Distribution Lines
These lines are mounted on poles or towers and distribute electricity above ground.
Advantages:
•Lower installation and maintenance costs
•Easier to repair and modify
•Better heat dissipation
Disadvantages:
•Vulnerable to weather conditions (storms, lightning, etc.)
•Risk of electrical hazards and accidents
•Aesthetic concerns in urban areas
Types of Overhead Distribution Lines:
•Primary Distribution Lines: Operate at high voltage and distribute power from substations.
•Secondary Distribution Lines: Operate at lower voltage and deliver electricity to consumers.

2. Underground Distribution Lines
These lines are buried underground in conduits or directly beneath the surface.
Advantages:
• Less prone to weather-related damage
• Improved safety and aesthetics
• Reduced maintenance frequency
Disadvantages:
• Higher installation and repair costs
• Difficult to locate and repair faults
• Limited heat dissipation, requiring proper insulation
Types of Underground Distribution Lines:
• Direct Buried Cables: Placed directly in trenches with protective coverings.
• Duct System Cables: Installed inside conduits for additional protection.
• Gas-Insulated Lines (GIL): Used in high-voltage applications with a protective gas layer.

Comprehensive Guide to Distribution Line Design

Material used for distribution line HT ( 11kV) & LT (415 V)

Properties of Conductor Material used in HT/LT
distribution line (OH)
General are overhead conductors supported on cross arm insulators and open to atmosphere and are not
covered.
Sometimes power is carried by underground conductors which are covered by insulation and are buried
underground and are called as insulation Underground cables.
Conductors are the main parts of the transmission / distribution system.
Its cost is much more about 60 to 70 % of the system and therefore their size, type of material used and needed
properties must be thought for desine and deside.
Following are the main properties needed for conducting material:
1.High electricity conductivity.
2.Strength
3.Temperature co-efficient of expansion.
4.Oxidation
5.Specific gravity.
6.Cost
7.Flexibility
8.Soldarability

Types of OH conductors in HT/LT system

Cables used for Distribution Lines
Requirements of Underground cables
i. Conductor
ii. Insulation
iii. Mechanical protection
iv. Chemical/Physical stability
Construction of cables

Properties of Insulation material used for cables

Comparison between Overhead line and
Underground Cable

Methods of Cable Termination
Cable termination refers to the process of connecting the end of a cable to
a device, equipment, or another cable to ensure a secure and efficient
electrical connection. It is essential for power transmission, distribution,
and communication systems.
Following are the methods of cable termination
1. Sholdered connection
2. Wire wrapping connection
3. Crimping connection
4. Compression termination

1. Sholedercd Connection:
In a sholdered connection, the line conductors of the cables are sholdered
together to form a physical secured, low resistance termination.
Sholedered terminations are infrequently used expect when circular military type
connecters are used.
2. Wire wrapping connection:
Wire wrapping connections are connection in which uninsulated solid conductors
is wraped with the significant force above rectangular metal post for several terms.
The wrap is sufficiently tight to deform the post of result in a physically and
electrically secured connection.
This termination methods are also popular for telephone circuit distribution boxes.

3. Crimping Connection:
Crimp connections ae connection using terminals having tabular opening into
which conductors are placed.
The tube is then mechanically pressed or deform to tighten it wound to the
conductor and form a connection.
The crimping is perform typically by crimping tool specially design for termination.
4. Compression termination:
Compression termination are the termination in which uninsulated conductor is
inserted into a box and connection is then made with a screw,, flat strap or other
such mechanism that compresses the conductor and form the connection.

Materials required for Overhead Lines
1. Poles : To support conductors with the help of cross arms and insulators.
2. Isulators :To support conductor line on cross arms.
3. Bird guaeds : pin insulator are fitted wooden pieces known as bird
guards for safety to avoidearth fault short circuit due to bird sitting.
4. Line conductors : Feeders or distributors of A.C.S.R.conductors.
5. Earth wires : To avoid accidents if conductor broken and fall down.
6. Stay assembly : It gives opposite tentions to poles so that poles remain
vertical on crossings,line deviations terminal poles.
7. G.I.clamps :To support slay.
8. Anticlimbing arrangment [Guard wire] : This is G.I barbed wire to be
placed around poles atheight of 2.3 meters from ground to safeguard
against of climbing by un-authorised persons.

9. Earthing : After every 1km.The line is earthed along the pole for safety of leakage
orlightening.
10. Lightining arresters : After every 3km the L.A are provided to safe guard the from
lighteringstrokes.
11. Cross arms ; to support insulators.

Quality I.e number length ,size be mentioned

Length of line in meteres.

Span between adjacment poles[40 to 50 M]
No.of poles = length of line distance between poles

Cross arms total numbers.

Insulators-pin type,shackle type. total numbers.

Wooden bird guards.

Anticlimbing G.I barbed wire length.

Total lightening arresters.
Stay assemblies required for starting terminal poles and line deviation
places.
Toatl length of A.C.S.R conductors.
Danger plate on 11kv line pole.
Sundries charges- Labour charges.
Un-fore seen charges.

Comprehensive Guide to Distribution Line Design

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