The overhead power line (also known as overhead transmission line or OHTL) is the type of transmission line through which the electrical energy is transmitted and distributed for long distances. The range of the voltages in the overhead power line is of different values. When an electric current flows in the line. It produces a magnetic and electric field.
Power is transmitted through this type of line because it is one of the least costly methods for power transmission. The construction is very simple. depending upon the phase system, It consists of multiple not insulated conductors suspended by poles or towers. To know more about it we have to discuss some related terminologies.
Classification of overhead power linesWe discussed above that the overhead power line is the type of transmission line through which electrical energy transfers from electrical grids. We can further classify it in two categories. i.e. Voltage and length. There are different types of voltage-based transmission lines.We are including a short detail about each.
This type of overhead power line has a voltage rating below 1000 volts. this type is mostly used for commercial and residential usage.
This type of power line is rated for between 1 kV to 69 KV. It is used for power distribution between rural and urban areas.
This type of transmission line is also called sub-transmission. The rated voltage ranges from 115 KV to 138 KV.
Extra high voltage ranges from 345 to 800 KV, while Ultra-high voltage is the transmission line capable to transmit voltage above 800 KV.
Classification by lengthBased on the length these are further divided into three classes. This classification is done by the power electrical engineer to calculate track the performance.
In different regions of the world different structures of overhead transmission line are in use. The simple structure consists of a wooden pole having more than one arm. The arms are used for hanging the wires. Other structures that are common in use are tabular steel poles and concrete poles.
The wooden structure has three cross arms that are extended on one or different sides. The lattice tower consists of two forms. The first one is a pyramidal structure having cross arms extended outside, the second one is a pyramidal base having four support points extended outside.
Maintenance and inspection for OHTLOHTL contains 3 important components, Insulators, tower and conductors. Making regular electrical inspection for the OHTL network makes difference in faults and power reliability. Hereunder some inspections for overhead transmission lines. I have written a detailed article about OHTL maintenance, you can find it here for more information.
1-Insulators get dirty due to the environment pollution and dusty weather. Visual inspection could be done without power isolation. This is because you could inspect them from safe distance.
2-Cleaning insulators is one of the most important preventive maintenance. As you know that dirty insulators may pass electrical current as a flash-over. This flash-over can destroy the insulator as well as cause earth leakage fault.
Cleaning insulators process takes two forms. One is by direct contact with it and using a piece of dry and smooth clothes. In this case power must be isolated. The second way is to clean with water jet without power isolation. But only well trained persons can do this dangerous job with special precautions.
3-Sometimes the insulators get broken due to many reasons. In this case thee broken one should be replaced. Insulators replacement could be done without power isolation but with great precautions and special isolated tools.
Due to aging and windy weather besides short circuits and lightning strikes the overhead power line conductors are cut. In this case the damaged conductor could be replaced or repaired with proper connecting devices.
Poles and towers are the less affected by faults and weather. But with age it may get corroded. This is most likely to happen in high humidity environment.
OTHL vs underground cables
Electrical power transmission is done through OHTL or underground cables. The difference between them is listed below.
OHTLUnderground cablescostLOWHIGHSafetyLess safeMore safeFault detectionEasydifficultNot suitable in citiessuitable in cities