An electric tower or a transmission tower is a tall structure, mostly a steel lattice tower which is used to support the overhead power lines. They carry heavy electrical transmission conductors at a proper height from the ground and these transmission lines must be able to withstand strong wind and snow load. In order to withstand these natural forces, its design must be done considering the structural and electrical requirements. Transmission lines can carry electricity over long distances at high voltages, the size and height of the tower is depended upon the stresses to which they are exposed
What are the elements of a transmission line tower
Tower top
The tower top is used to carry earth shield wire and this is connected at the tip of the tower and also known as earth wire
Cross arm
Cross arm is used to hold insulators and the insulators are used to carry transmission conductors. The dimension of the cross arm depended upon the level of voltage to be transmitted.
Cage of transmission tower
It is the portion between the tower body and the peak of the transmission tower. Mostly the earth shield wire will be connected to this tip peak
Insulator string
Insulator string is used to carry transmission lines, the number of the insulated string is depended upon the level of transmission voltage to be transmitted, so if the voltage level increase then the number of insulators will increase in a string.
Cage of transmission tower
It is the main structure of the transmission tower which provides support to the whole body of the transmission tower.
Transmission tower body
It is the portion from the bottom cross arms up to the ground level is called the transmission tower body. This portion of the tower plays a major role to maintain the required ground clearance of the bottom conductor of the transmission line.
How can we determine the height of the tower
The height of the tower is determined by certain factors they are minimum permissible ground clearance, maximum sag, the vertical spacing between conductors, and vertical clearance between the ground wire and top conductor.
What is a stub-cleat arrangement
The anchoring arrangement of transmission tower legs consisting of inclined angle with bearing cleats at the end, all embedded in the concrete foundation is called the stub or stub-cleat arrangement. A stub should be set in a manner so that the distance between the stubs, their alignment and slope are as per design and drawing
What are the conductors which are used in transmission power lines
Conductors are used to transmitting electrical power in a transmission system, mostly the conductors are made up of aluminum with a steel core. These conductors are bare and the air around them provides insulation. The conductors which are used are created by twisting several wires together, bundled conductors are used on high voltage power lines to reduce energy losses, audible noise, and radio interference. A conductor bundle is a series of two, three or four conductors which are kept apart by a spacer, spacer damper can separate bundled conductors and controls vibration caused by wind and ice buildup.
Classification of transmission line tower
Lattice structure
The lattice structure is self-supporting and then have been used since the beginning of the electrical transmission, most of the power companies use this lattice structure for power transmission. These structures can be erected in places where it is hard to fix the transmission towers because the tower members can be easily transported. Lattice structures are light and are cost-effective. It has one disadvantage that is it needs more right of way, right of way is the stretch of land acquired along the route length of line keeping the towers in the middle of row width. Lattice structure consists of a steel framework comprised of many structural components bolted or welded together.
Tubular pole structure
In places where the lattice structure can’t be used tubular pole structure is used and tubular structure is used by some power companies for high and extra tension transmission lines and this type of pole structure installation is costly but requires less time the tubular structure can be a single tubular form or H-form and it can be used to carry two or more circuits and this type of tower can be used in populated area. The tubular steel structure is less massive than other towers so it can be used in many places without using much space, and they are used more in urban centers it is suitable for voltage range from 110-315 KV
Both the tubular and lattice structures are used to carry either one or two electrical circuits which are referred to as a single structure and double structure circuit. The double structure circuit holds the conductor in a vertical or stacked configuration, whereas the single structure holds the conductor horizontally. Because of the vertical configuration the double circuit structure is taller than the single circuit structure.
Waist type tower
This type of tower is used for voltage ranging from 110-735 kV, they can be easily assembled and these towers are suitable for power lines that cross very uneven terrain.
Guyed V tower
This tower is designed for voltage ranging from 230-735 kV, this type of tower is more economical than the double circuit and waist type tower.
Guyed cross rope suspension tower
Because of its simple design, this tower is easy to assemble and its voltage range is up to 735 kV. This type requires less galvanized steel than the guyed-V tower making it lighter and less costly.
