Projects:2020s1-1540 Determining Transmission Overhead Conductor Ratings based on Line Tension

Conductor ratings are an important aspect in maintaining transmission lines, especially with the increasing number of renewable energy source and complexity of transmission lines. An accurate conductor rating can improve the capacity of the transmission line, and help prevent any damage occurring to the system.

This projects aims to develop an accurate method for converting tension to a conductor rating.

Introduction

Transmission lines are a very important infrastructure in transferring electrical power from where it is generated to the loads to be supplied. There are many factors which determine how much power can be transmitted through these transmission lines, but the predominate ones are the maximum temperature of the conductor and the minimum allowable clearance between the transmission line and the ground. If the conductor gets too hot, then there can be irreversible damage caused to the transmission line. Furthermore, the increase in temperature can cause clearance violations as the overhead conductor increases in length as the temperature increases.

A conductor rating system is employed in order to know what the maximum power which can flow through the transmission lines can be. This prevents the maximum power through the transmission lines being exceeded and hence prevents permanent damage to the transmission lines and clearance violations. Additionally, having an accurate conductor rating also allows for the full capacity of the transmission lines to be better utilised, allowing for exiting infrastructure to be taken advantage of, rather than new transmission lines being required for improved power capacity.

Objectives

• Develop a method to convert tension measurements to a conductor rating (in amps and MVA), using available parameters.
• Compare the weather station rating method with the tension rating method developed, and asses the differences between the two different approaches.
• Determine possible ways the weather station method may be improved and refined to achieve a greater correlation between the weather station and tension rating methods.

Project Team

Project Students

• Adrian Barone
• James Smithson

Supervisors

• Dr. Wen Soong
• Josh Smith (ElectraNet)
• Ellen Thomas (ElectraNet)

Aim

The aim of this project is to analyse the behaviour of overhead powerline conductors under operation and develop a method to use line tension measurements to determine a line rating.

Objectives

• Investigate the behaviour of the overhead conductors under operation such that it can be used in a line current rating system.
• Develop a tension-based method to estimate the line rating in Amperes and MVA.
• Analyse existing weather station based rating model and compare the outputs of the two rating methods (tension and weather based).
• Provide recommendations to refine the existing weather based system to achieve greater correlation between the two methods.

Method

• Convert measured tension to equivalent real-time conductor temperature using mechanical properties of the conductor.
• Use heat-balance equation with the calculated conductor temperature, ambient environmental conditions, and mechanical properties of the conductor to estimate the effective wind speed on the conductor.
• Use heat-balance equation again, using calculated estimated effective wind speed, ambient environmental conditions, mechanical properties of the conductor, and the maximum operating temperature of the conductor.
• Compare rating to the weather based rating.

Results

• Defined a method to calculate the effective wind speed experienced by the overhead conductor using line tension measurements.
• The tension based method calculates a effective wind speed which accounts for varying wind conditions across the entire transmission line.
• Determined that the estimated wind speed is a more accurate measurement of wind speed compared to measured wind speed (at a weather station) at high conductor temperatures.
• Determined that the tension based method can provide a higher degree of accuracy for the rating at high currents in comparison to the weather based method.
• The conductor temperature calculated from both the weather and tension based methods provide an important comparison to determine if the rating for both methods are accurate.

Conclusion

In conclusion, a method was developed to utilise conductor line tension measurements to determine a line rating. It was found that the tension based method could estimate the effective wind speed such that it accounted for varying wind conditions across the entire conductor. Furthermore, it was found that the tension based method had greater accuracy at high currents. Finally, an important comparison between the conductor temperatures calculated using the weather and tension based methods can be used to determine the validity of the line rating determined from both methods.