Table of Contents

1. Introduction
   • Overview
   • Objectives
   • Importance of Transmission Line Upgrading
2. Background
   • Types of Conductors
   • ACSR and HTLS Conductors
   • Comparison of ACSR and HTLS Conductors
3. Technical Properties of Conductors
   • ACSR Conductor Properties
   • HTLS Conductor Types and Properties
4. Methodology
   • Test Case Description
   • Evaluation Methods
   • Cost Components
5. Cost Calculation
   • Demolition Costs
   • Construction and Installation Costs
   • Conductor Costs
   • Energy Loss Costs
   • Land Costs
6. Results and Discussion
   • Twofold Ampacity (Plan A)
   • Fourfold Ampacity (Plan B)
   • Cost Comparisons
7. Conclusions
   • Summary of Findings
   • Recommendations
8. References

1. Introduction

Overview

The demand for reliable and efficient electricity transmission has escalated, necessitating the need for upgrading existing transmission lines. This process aims to ensure that the transmission network operates securely, reliably, and cost-effectively. Traditionally, upgrading can be achieved through network enhancement or uprating.

Objectives

This study focuses on evaluating the costs associated with uprating overhead transmission lines using Aluminum Conductor Steel Reinforced (ACSR) and High Temperature Low Sag (HTLS) conductors. By examining the costs under normal and stressed operating conditions, the study aims to provide a comprehensive cost-benefit analysis.

Importance of Transmission Line Upgrading

Upgrading transmission lines is crucial for maintaining the stability and reliability of the power grid. Enhancements usually require significant investments and lengthy regulatory processes, whereas uprating can be a more immediate and cost-effective solution.

2. Background

Types of Conductors

Conductors used in overhead transmission lines play a pivotal role in the efficiency and reliability of power transmission. Among the various types of conductors, ACSR and HTLS are commonly used due to their specific advantages and properties.

ACSR and HTLS Conductors

• ACSR (Aluminum Conductor Steel Reinforced): A widely used conductor made of aluminum and steel, known for its durability and relatively low cost.
• HTLS (High Temperature Low Sag) Conductors: Designed to operate at higher temperatures with lower sag, HTLS conductors are preferred for their high ampacity and efficiency.

Comparison of ACSR and HTLS Conductors

HTLS conductors can operate at temperatures up to 200°C, whereas ACSR conductors typically operate between 70-90°C. The higher operating temperature allows HTLS conductors to carry more current without significant sag, making them ideal for current uprating projects.

3. Technical Properties of Conductors

ACSR Conductor Properties

ACSR conductors consist of a core of steel strands surrounded by aluminum strands. The steel core provides strength, while the aluminum strands ensure good conductivity. However, the operating temperature of ACSR conductors is limited, which can restrict their ampacity.

HTLS Conductor Types and Properties

There are five main types of HTLS conductors, each with unique properties:

1. Aluminum Conductor Composite Core (ACCC): Combines high-strength composite materials with aluminum strands.
2. Aluminum Conductor Composite Reinforced (ACCR): Uses aluminum oxide fibers for reinforcement.
3. Aluminum Conductor Steel Supported (ACSS): Designed for high-temperature operation without losing mechanical properties.
4. Gap-type Thermal-resistant Aluminum Conductor Steel Reinforced (GTACSR): Features a gap between the steel core and aluminum strands to reduce sag.
5. Zirconium Thermal-resistant Aluminum Alloy Conductor Invar Reinforced (ZTACIR): Utilizes zirconium alloy for high-temperature performance.

4. Methodology

Test Case Description

The test case involves a 230-kV, double-circuit, single-bundle overhead transmission line of 11.5 km length, using 1272 MCM ACSR conductors. Two current uprating plans are considered:

• Plan A: Uprating to twin-bundle ACSR or single-bundle HTLS conductors with comparable sizes.
• Plan B: Uprating to quadruple-bundle ACSR or twin-bundle HTLS conductors with comparable sizes.

Evaluation Methods

The evaluation method focuses on calculating the total costs, including demolition, construction and installation, conductor costs, energy losses, and land costs. The assessment is conducted under normal and stressed operating conditions.

Cost Components

The cost evaluation includes the following components:

1. Demolition Cost: The cost associated with removing existing conductors, insulators, hardware, and structures.
2. Construction and Installation Costs: Costs for preliminary work, tower foundations, construction, insulator strings, accessories, grounding materials, optical fiber overhead ground wire, and conductor stringing.
3. Conductor Costs: Costs based on supplier price lists for both ACSR and HTLS conductors.
4. Energy Loss Costs: Calculated using annual power-duration curves over the economic life of the transmission line.
5. Land Costs: Considered null if the right of way is kept and negative if reduced.

5. Cost Calculation

Demolition Costs

The costs involved in disassembling existing conductors, insulators, hardware, overhead ground wires, and steel structures. These costs are significant in the initial phase of upgrading.

Construction and Installation Costs

Costs for preliminary work, tower foundations, construction, assembling insulator strings, line accessories, grounding materials, and optical fiber installation.

Conductor Costs

Estimated from public domain price lists, these costs vary significantly between ACSR and HTLS conductors.

Energy Loss Costs

Calculated using power-duration curves over the economic life of the transmission line, considering a discount rate of 8% per annum and an inflation rate of 2%.

Land Costs

Considered null if the right of way is kept, and negative if reduced.

6. Results and Discussion

Twofold Ampacity (Plan A)

The total costs for twofold current uprating under normal and stressed operations.

Cost Comparison of Twofold Current Uprating

Percentage Cost Breakdown of Twofold Current Uprating Under Normal Operation (Excluding Land Cost)

Percentage Cost Breakdown of Twofold Current Uprating Under Stressed Operation (Excluding Land Cost)

Fourfold Ampacity (Plan B)

The total costs for fourfold current uprating under normal and stressed operations.

Cost Comparison of Fourfold Current Uprating

Percentage Cost Breakdown of Fourfold Current Uprating Under Normal Operation (Excluding Land Cost)

Percentage Cost Breakdown of Fourfold Current Uprating Under Stressed Operation (Excluding Land Cost)

7. Conclusions

This work presents a cost evaluation method for current uprating of overhead transmission lines, focusing on the replacement of ACSR conductors with HTLS conductors. The analysis highlights that the cost of energy losses is the most significant factor, particularly under heavy loading conditions. Certain HTLS conductors have been identified as promising alternatives to ACSR conductors, as they offer relatively low power losses due to their moderate operating temperatures compared to other HTLS options. To mitigate excessive energy losses, it is recommended that HTLS conductors not be operated at excessively high temperatures. Instead, either ACSR or HTLS conductors should be operated below their nominal current ratings to minimize energy losses, reserving the additional current rating for contingency or emergency scenarios.

Summary of Findings

The study highlights the cost advantages of using HTLS conductors over traditional ACSR conductors for current uprating. HTLS conductors with lower operating temperatures (such as HTLS-1 and HTLS-5) offer significant savings in energy loss costs.

Recommendations

For future uprating projects, it is recommended to consider HTLS conductors due to their higher efficiency and potential for reducing overall costs. Specific conductors like HTLS-1 and HTLS-5 are particularly favorable due to their balanced performance and cost.

8. References

1. Alawar, A., Bosze, E. J., & Nutt, S. R. (2005). A composite core conductor for low sag at high temperatures. IEEE Transactions on Power Delivery, 20(3), 2193-2199.
2. Kenge, A. V., Dusane, S. V., & Sarkar, J. (2016). Statistical analysis & comparison of HTLS conductor with conventional ACSR conductor. Proceedings of the International Conference on Electrical, Electronics, and Optimization Techniques, Chennai, India.
3. Expósito, A. G., Santos, J. R., & Romero, P. C.