The successful operation of an Overhead Distribution Lines and Transmission Lines and this also depends to a the way of mechanically design part of the over head lines. An over headline may be used to transmit or distribute electric power. While constructing an Overhead Distribution Lines, it should be ensured that mechanic strength of the line is such so as to provide against the most probable weather conditions. In general the main component of an overhead line are:
Conductors: which carry electric power from the sending end to the receiving end.
Line Supports: which may be poles or towers and keep the conductors at a suitable level above the ground.
Insulators: Insulators are connected to support the conductor which insulated from the ground.
Cross arms: which provide supports to the insulators.
Conductor materials of Overhead Distribution Lines
The conductor material which used for transmission and distribution of electric power system should have the following properties;
- High electrical conductivity.
- High tensile strength in order to hold the mechanical stress.
- Low cost so that it can be used for long distances for cheap price.
- Low specific gravity so that weight per unit volume is small.
The supporting structures for over headline conductors are ‘various types of poles and towers called line supports. In general the lire supports should have the following properties:
- High mechanical strength to withstand the weight of conductors and wind loads.
- line supports must have less weight but it must be strong
- Cheap in cost and economical to maintain.
- Longer life.
- When there are maintenance occur this must be easy to access
The line supports used for transmission and distribution of electric power are various types including,
- Wooden poles
- Steel poles
- RCC poles
- Lattice steel towers
Insulator at Overhead Distribution Lines
Insulators of overhead lines should support to the electical tower and the essential point is the current from the conductor should not contact the line support which can able to flow to earth.
So the electrical line conductor must be properly insulated form the line supports and towers. The proper insulated material mush contain following properties
- High electrical resistance
- Good relative permeability
- Dielectric Strength must be high
- Puncture ratio should also high
- Higher Mechanical Strength
There are several types of insulators in electrical systems such as
- Suspension type insulators
- Shackle type insulators
- Pin type insulators
- Strain type insulators
Cross arms provide vital role in over head distribution lines . the main purposes of overhead distribution lines are to create the line clearance each other and seperate each phases of electrical lines.