Projects:2021s1-13005 Determining Dynamic Line Ratings of Over-Head Transmission Conductors based on Line Tension

Project Team

Team Members

• Andrew Gross
• Michael Iuliano
• Taimur Abdullah Said Al-Sanaidi

Supervisors

Principal Supervisor: Wen Soong
Co-Supervisor: David Vowles

ElectraNet Sponsors

• Josh Smithson
• Ellen Thomas

Abstract

The ratings of power line overhead conductors are dependent on the actual current flow, ambient weather conditions and conductor type. Thermal ratings have historically been calculated using a weather-based model, however, other technologies such as tension monitors to measure phase conductor tension can be utilised to derive ratings. ElectraNet installed several tension monitors in the Riverland region to support power flows over the DC interconnector to Victoria. These tension monitors can independently calculate dynamic line ratings and also verify the results produced using the existing weather based rating method. This project continues work commenced in 2020 to develop a method to convert tension measurements into ratings (in Amps and MVA) and to determine when tension delivers a superior rating outcome to weather.

Introduction

Constraints on existing transmission infrastructure is occurring due to the addition of renewable energy generation to energy networks. Operation at the maximum capacity of the conductors is an option to support additional generation on existing transmission infrastructure. The maximum current capacity, or ampacity, of overhead conductors is traditionally kept at a static, conservative level. This is done to maintain clearance levels under the conductors and prevent permanent damage. To fully utilise this infrastructure a Dynamic Line Rating, or DLR, can be used.

A form of indirect DLR finds an appropriate ampacity through a weather-based model, where weather station data is used to determine the external heating and cooling effects on the conductor. Equalising this with the temperature generated by current flow in the conductor, the ampacity is found.

This project aims to apply a direct DLR method using measured tension in conductors. The measured tension will be used to find the temperature of conductors and determine a suitable ampacity. The models will be compared, and it will be determined as to which provides a superior rating. Work will be done in reference to the ElectraNet owned and operated Robertstown-Morgan transmission line across the Mid-North and Riverland regions of South Australia. This 60km line is pertinent due to its pathing towards the MurrayLink Interconnecter, which connects the South Australian and Victorian energy grids.

The 2021 iteration of this project continues on from the work completed in the project of the same name 2020 by Adrian Barone and James Smithson.

Thermal Factors

The various effects of heating and cooling on an overhead conductor.

There are four main factors when considering the various thermal effects on an overhead conductor. These are:

• Current Heating(Joule Heating) - Due to resistive and magnetic losses of the conductor material while it is conducting current. The resistive losses are due to both the conducting material and the increase in the resistance of the conductive material as its temperature increases.
• Solar Heating - This is heating due to direct radiation from the sun. Typically, direct solar radiation is difficult to calculate as direct and diffuse solar radiation has various challenges in measuring it (expensive for sensors, need regular attention). In some cases where this data isn’t available, global solar radiation is used.
• Convective Cooling - Convective Cooling occurs per the effect of the air surrounding the conductor heating, reducing the density of the air around the conductor causing cooler air replaces it.
• Radiative Cooling - This is the effect of the material emitting thermal radiation, losing heat in the process. A simplified equation is used as the radiation loss is a small fraction of the total cooling.

We do not consider Corona Heating as it is unlikely to occur under typical operation of the conductor, nor Evaporative Cooling as while it has a significant effect on cooling, it is challenging to assess along the whole conductor and separated from wind effects, so is ignored.

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