Success Story: Health Assessment of Transmission Line Towers

When it comes to any infrastructure asset, regular maintenance is critical to ensure its optimal performance. This is especially true for complex infrastructure assets deployed by Utility companies that warrant the need for expert testing and maintenance carried out by specialists.

In this post, we will cover how SCOPE’s services vertical – ISOSCELES Sales & Services Pvt. Ltd. (ISSPL), successfully carried out measurement of critical parameters of 861 Transmission Line Towers of Power Grid Corporation of India Ltd. (PowerGrid).

Tower Foot Resistance Measurement Basics

High voltage Transmission Lines demand robust Earthing mechanisms with no tolerance to failure during operation.

Lightning strikes to tall structures like Transmission Towers can cause electrical power systems to transmit currents and voltages so high that insulation can fail and heavily damage the connected electrical equipment.

Earthing systems play a pivotal role by dissipating these high currents to the earth in a controlled manner thereby ensuring the safety of the electrical equipment and enabling uninterrupted power supply.

Since all Transmission Towers are electrically interconnected through Ground Wires that act as lightning rods protecting the transmission lines from atmospheric discharges, regularly testing the grounding resistance/impedance of Transmission Towers becomes important.

ISSPL’s Mandate

PowerGrid empaneled ISSPL to facilitate testing of critical parameters of their 400kV Double Circuit Lines spread across 861 Transmission Towers on the Farakka-Kahalgaon, Kahalgaon-Maithon and Chaibasha-Rourkela belt.

ISSPL was entasked with end-to-end project execution including making available skilled service engineers for testing, arranging the requisite T&M equipment, organising logistics and submitting pass/fail reports.

T&M Kits Used

To ensure flawless test results, ISSPL Team deployed the below-mentioned advanced T&M Kits:

1) Megabras TM25R and TM25M High-Frequency Earth Ground Testers

2) Megabras MTD20KWe Digital Earth Tester

3) Sonel CMP 200 Digital Clamp-on AC Leakage Current Meter

Challenges Faced

Testing Transmission Towers is a tricky affair with multiple external factors amplifying project complexities. The three major challenges that our ISSPL Team faced during this project execution were:

1. Safety Hazards

With many Transmission Towers located on mountaintops surrounded by dense forests infested with poisonous snakes and other dangerous animals, reaching these Towers was a challenge in itself.

Most of the Towers situated between Rourkela and Chaibasa were located in remote forest areas that demanded the Testing Engineers to walk 2-3 kms from the main road to reach each Tower. The situation was further compounded by the fact that the distance between each Tower spanned 10-15 kms that made testing an arduous process.

Similarly, many Towers were partially submerged in shallow waters and dense mud that amplified the risks of accidental electrocution. Since there is always a high possibility of current leakage under Transmission Towers, the Test Engineers had to ensure that they were always equipped with protective equipment like safety shoes, rubber gloves, helmets, etc.

Furthermore, with 25+ years in service, the ageing Towers posed a high risk of loose metal pieces that could fall anytime. Adhering to the strict environment, health and safety (EHS) regulations, the ISSPL team ensured the successful completion of this project without any accident.

2. Unfavourable Weather Conditions

As mandated by PowerGrid, ISSPL carried out TFR Testing in the months of September and October. The preceding rains had created a high moisture environment that made TFR testing difficult.

One of the key factors that affect Tower Footing Resistance is Soil Resistivity that plays a critical role in determining the resistance of the Tower’s charging electrodes. The Soil Resistivity values significantly differ during dry and wet seasons.

To ensure accurate TFR values, the ISSPL Team had to factor in multiple elements like the type of electrodes, the depth at which the electrodes were installed, soil type, its temperature, moisture content, etc.

3. Resistance From Local Farmers

Considering the high risk of accidental current leakage, various government regulations discourage farmers from cropping in the vicinity of Transmission Towers and award crop compensation to farmers on whose land the Towers are erected. Despite this, farming near Transmission Towers continues unabated across India.

The ISSPL Team faced a similar issue as large parcels of land near PowerGrid’s Transmission Towers were covered in Kharif crops ready for harvesting. The local farmers strongly resisted ISSPL’s Testing Engineers from entering their land where the Towers were erected. At other places, testing was made difficult as the Tower footings were submerged in crop water.

Summing Up

Despite all the aforementioned operational challenges, the ISSPL Team succeeded in completing the project within the agreed timeline.

To learn more about ISSPL’s Transmission Tower Testing capabilities, please write to us as marketing@scopetnm.com.

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