Use of high temperature conductors in new lines

Introduction

HTLS have traditionally been used to reconductor lines which are thermally limited to enable more power to flow without increasing tower height or strengthening towers. The use and selection of these conductors is described in [1]. With regard to new lines, however, very little is written relating to the benefits of using high temperature conductors. 

This brochure describes the nature of HTC as well as the possible benefits in using these conductors for new lines.

Scope/Methodology

The scope of the brochure includes the following: Identification of new line designs where the use of HTLS conductor can be considered. Description of the advantages and disadvantages as well as provision of technical support for regulatory approval considering both environmental, safety, and economic issues.

The main tasks of the WG included the following:

1. Environmental issues

• ROW considerations
• Reduction in tower height and line visibility
• Structure geometry

2. Electrical considerations

• Thermal rating
• Line losses
• EMF
• Audible noise
• Operational constraints

3. Mechanical considerations

• Use of HTLS in bundle configuration
• Sag, tension
• Creep
• Vibration mitigation
• Hardware
• Maintenance

4. Operations and maintenance

• Tools and equipment
• Live line maintenance considerations
• Emergency operations

5. Economic considerations including overall line design

• Initial and life cycle cost
• Operational cost
• Expected life of asset.
• Review of TB 638 “Guide to overall line design” as applied to HTLS conductors.
• Inclusion of HTLS in conductor selection process

The necessary actions addressed were:

• Questionnaire/s to collect data on
  • Reasons for using HTLS conductors on new lines
  • Reasons for not using HTLS conductors on new lines.
• Detailed discussion on line losses for both “radial” and “network embedded” lines.
• Relative advantages & cost of HTLS conductor types in new line design.
• Evaluate impact of thermal rating assumptions on use of HTLS conductors.

To achieve this a survey was undertaken amongst WG members on use of these conductors on new lines as well as reasons for and against the use of these conductors. The electrical and mechanical characteristics of these conductors on a 500kV tower was then analysed and presented. This included audible noise, EMF, thermal rating and mechanical characteristics. Operational issues included experience with type 4 conductors in fire conditions as well as possible damage to conductors due to poor handling.

Description of the Technical Brochure

The brochure deals initially with the description of the conductors, the survey summary and the use of the conductors. Other items then follow describing the environmental, electrical and mechanical characteristics. An economic study is then performed in detail with a comprehensive line design comparing conventional to type 4 HTLS application. As the price of the HTC was not known a ratio was determined to indicate the price the HTC conductor could be higher than the conventional ACSR for it to be considered viable. The same set of line design options was then applied to the index as described in [2]. This provided an alternate approach to conductor selection where the options included conventional and high temperature conductors.

The description of each chapter is as follows

Chapter 1: Introduction

This includes the background and reason for the brochure, scope and types of high temperature conductors. It then describes the questionnaire and summary of the results including reasons for using HTC and reasons for not using these conductors. A section on experience on using the conductors based on input from the working members concludes the chapter.

Chapter 2: Environmental issues

The low sag conductors allow for narrower right of way as well as reduction in tower height for maximum power transfer. The benefits of this are expanded on in this chapter as well as tower spotting and structure geometry. Examples of loss calculations for AAAC and type 4 conductors are shown indicating possible differences in certain circumstances.

Chapter 3: Electrical considerations

Actual tower configurations are analysed in this chapter indicating insulation, corona effects, conductor blow out as well as audible noise and electric and magnetic fields under the line and at the edge of the ROW. Radio interference is also covered.

A separate section on thermal rating including magnetic heating, theory of conductor impedance and further explanation of line losses is given. Short circuit tests conducted on type 4 HTLS compared to ACSR is covered as well as further detailed determination of audible noise. A section on use of expanded conductor for audible noise reduction is described.

Chapter 4: Mechanical considerations

This chapter deals with sag-tension and vibration. A section on use of light weight conductors for severe cross wind conditions is described. Earth wire considerations are mentioned when used in conjunction with Type 4 HTLS.