Overhead power line, types inspection and maintenance

Overhead power line, types inspection and maintenance
overhead power line insulators

What is overhead power line

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.

fast electrical app

Classification of overhead power lines

We 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.

  • Low Voltage overhead transmission line

This type of overhead power line has a voltage rating below 1000 volts. this type is mostly used for commercial and residential usage.

  • Medium Voltage OHTL

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.

  • High Voltage overhead power line

This type of transmission line is also called sub-transmission. The rated voltage ranges from 115 KV to 138 KV.

  • Extra-High and Ultra High Voltage

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 length

Based on the length these are further divided into three classes. This classification is done by the power electrical engineer to calculate track the performance.

  • Short overhead power line: It is the type of transmission line having a length less than 60 km.
  • Medium overhead power line: This type of transmission line having a length ranges from 80 Km to 250 km.
  • Long overhead transmission line: The type of transmission line having a length of more than 250 km.

Structure of overhead transmission line

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.

overhead power line high voltage
overhead power line high voltage

Maintenance and inspection for OHTL

OHTL 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.

  • Insulators maintenance.

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.

  • Conductors inspection and maintenance

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.

  • Towers or poles inspection

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.

OHTL Underground cables
cost LOW HIGH
Safety Less safe More safe
Fault detection Easy difficult
  Not suitable in cities suitable in cities