Transmission towers: The power-packed transporters

Let’s take a stroll down memory lane. As children, while traveling long by train or car, you felt amazed by the giant robot-like structures that wove strings of imagination in your mind linked to your favourite cartoon characters. A villain who grew suddenly to a 100 ft in the Power Rangers series or Jerry running to the top to save himself from Tom — your genre could change but the central prop didn’t.

 

Well, as much as we enjoyed putting our imagination to work it’s time to come back to the real world. By now, you’d have understood that we are talking about transmission towers. 

 

A transmission tower is a metallic structure which supports high-voltage conductors of overhead power lines. It starts as a series of such towers from the generating station switchyard owing to the high voltage and runs right up to the source substations and satellite substations of cities, towns, villages, etc. — basically the populated areas. The job is to transfer electricity by means of the conductors on them. The size, electrical load, configuration and types of transmission towers vary. Let’s delve deeper into it.

 

Contents:

HISTORY

UP ABOVE THE WORLD SO HIGH BUT WHY?

TYPES AND APPLICATIONS

 

HISTORY

 

13 is not always a unlucky number. Sometimes it’s the foundation for the future. The first transmission tower series came to existence in North America in the form of a 13 mile long power transmission tower network in 1889. Thanks to the trio of James Clerk Maxwell, Lord Kelvin and Oliver Heaviside, the generating station at Willamette Falls in Oregon City got connected with downtown Portland. The distance seems short today but it was the beginning for the giant transmission grids today.

 

UP ABOVE THE WORLD SO HIGH BUT WHY?

 

Transmission towers are somewhere between 55 to 150 ft high. But why so? The reason is simple — to be out of reach of people and allow free passage to vehicles below. The towers carry extremely high voltage. While domestically we use 240 V and 120 V appliances, these towers carry between 23,000 V and 7,65,000 V. If the voltage at home gives you a nasty shock, imagine the impact – any living creature will be toast within milliseconds.

 

TYPES AND APPLICATIONS

 

Broadly, transmission towers can be best classified as under, although there can be alternative classifications too:

 

  1. Suspension tower
    These are the ones we see the most — the ones in a straight line at intervals. There might be a slight bend to a maximum of 5 degree angle. Thus, they exist only to maintain the weight of the conductor in a straight line. They are cheaper to construct, the most common and abundantly used.
  2. Tension tower
    When there’s a deviation of more than 5 degrees, tension or angle towers come to play. These function as a junction of the conducting line network to deviate from the straight line. The piece of line from one angle tower to another angle tower is called ‘section’ and the length of the section may vary as per the geographical location. These are heavier and costlier than suspension towers. 

Based on the angle, there are three types of angle towers-
– 0-10 degree tension towers (TD1)
– 10- 30 degree tension towers (TD3)
– 30-60 degree tension towers (TD6)

    3. Transposition tower
In a transmission tower system, unwanted voltage gets induced in neighbouring wires due to the unsymmetrical spacing of wires across the line. It is hence necessary to change the position of the conductors at intervals to avoid an unbalanced voltage drop. Transposition towers do exactly that in a transmission system. For example, the bottom wire becomes the top one while the top one becomes the middle one and so on. This maintains the capacitance (the amount of electric charge stored on a conductor) between conductors, as well as between conductors and ground thereby keeping things even.

   4. Special tower
  When towers get customized based on locations, transmission tower design saves the day with special towers. These are much costlier because their customization       and making varies as per the requirements and specifications. Long span river crossings, valley crossings, power lines under existing power lines call for special       towers.

 

 Transmission towers are risky. Yet you’d often see birds sitting atop wires and might be wondering: what if they create risks of short circuits? But again, these risks   have been considered from day one. Besides, many transmission towers are also harnessed for weather forecasting by placing equipment like an anemometer, etc.  All towers have to withstand various natural calamities too because they exist in remote areas and are open to the elements. This calls for some serious engineering  where civil, mechanical, and electrical engineering concepts are equally applicable. Thanks to able engineers,  transmission towers today can span virtually all  terrains and adverse conditions to reach electricity where needed.