Driving grid innovation: The importance of HTLS conductors

How? When traditional conductors heat up, the tension of overhead lines can lessen slightly (or sag), which increases the vertical drop. This is due to thermal expansion, and it needs to be controlled carefully. Proper sag improves performance under differing temperatures and reduces the risk of failure.

HTLS conductors allow for much higher thermal ratings than conventional ones. They can operate at temperatures up to 250°C (482°F), while maintaining low sag. This means we can quickly boost line capacity without raising tower heights or undertaking other structural reinforcements. 

They support more compact and efficient tower designs, which also have higher capacity. For utility companies under pressure to deliver more with less, this is a big shift in potential.

A need for deep technical experience

Installing HTLS conductors into new or existing lines requires rigorous engineering. Every project starts with a question: How do we balance technical performance, cost, and long-term reliability? 

With upgrades to existing lines, we can sometimes reuse the design bases from earlier studies. However, new lines often require a comprehensive engineering study. This is where our teams come in. Together, we explore critical decision points for clients—from initial conductor selection to final commissioning of the project. 

We do this so we can work out the best types of HTLS conductors to use in each project. It often involves advanced modeling of the overhead line’s nonlinear behaviors, assessment of structural load cases that are specific to the region, and detailed planning of how the installation should move forward. We also look at the project’s economic life cycle. This allows us to show how we’re adding value to both operators and communities.

Our team tends to look at this in four stages.

1. Different HTLS conductors for different applications

There are several types of HTLS conductors. Each of them holds its own benefits. These are: 

• ACSS (aluminium conductor steel supported): They use a high-strength annealed steel core with fully annealed aluminium strands. These HTLS conductors allow for operating temperatures up to 200°C.
• GAP-type conductors: These feature a high-temperature grease-filled gap between the steel core and thermal-resistant aluminium alloy layers. They help minimize sag even at high temperatures.
• INVAR core conductors: These use a nickel-iron alloy core with a very low coefficient of thermal expansion. This results in less sag variation with temperature, making them suitable for applications where sag control is critical.
• Composite core conductors: These have advanced cores made from carbon fiber or aluminium matrix composites. They offer high strength-to-weight ratios and extremely low thermal expansion. This allows for the highest ampacity increases and longest span lengths.

As part of this selection phase, we look at the maximum current capacity and thermal limits, and what’s right for the project. Our approach is backed by various international standards and validated industry models. We select the HTLS conductors based on their ability to boost performance and reliability.

2. Modeling for the future: Advanced and thorough analysis 

We conduct advanced modeling and analysis to reduce risk and improve asset performance. We use industry-leading software to predict how conductors will sag and behave throughout temperature extremes and through their life cycle. We also look at how lines will perform over a 10-year period or longer to understand the conductor’s “sag profile".” We make sure to account for heavy ice or wind events, which can impact how much a line sags, particularly as the weather becomes more extreme.

Based on the characteristics of the overhead line structures, terrain profile, and environmental conditions, we work out the proper sagging bases for the conductor. Knowing this, we can maintain the required ground and obstacle clearances. 

3. Getting the install right: Critical oversight

It’s also critical to provide oversight and detailed planning to produce protocols for each conductor type. Some conductors might require pretensioning to remove initial stretch and induce plastic deformation in the annealed aluminium. We provide the precise tension levels and subsequent procedures, so the final daily tension is met.

We also partner with the manufacturers of HTLS conductors. This allows us to evaluate and prescribe the use of specialised high-temperature hardware and fittings. We can provide detailed clipping instructions, accounting for insulator swing and tower deflection.

4. Value for money: Economic and life-cycle analysis

We provide cost and benefit analysis for the asset’s lifespan. This gives decision-makers a clear financial picture. We look at a huge range of capital and operational costs to work out a total cost of ownership. This includes costs related to the conductor, hardware, installation labor, and any structural modifications. 

While HTLS conductors have a higher upfront cost per metre than conventional ones, this can be offset by avoiding the need for new towers or land acquisition. And they offer a significant energy savings. The energy saved over the 30-to-40-year lifespan can be large, often outweighing the initial capital investment. A detailed analysis can help quantify this benefit for clients.

HTLS conductors: An innovative, efficient, and necessary upgrade

Using HTLS conductors is a massive enabler for the grid. But it is fundamentally a complex engineering task. 

A project needs to move from just specifications. A successful project will have

• A deep, analytical understanding of material properties
• Advanced structural dynamics
• Practical field constraints

We are excited to work with clients to provide this incredibly valuable work. It’s important to have a holistic, risk-managed framework for the overhead line’s entire life cycle.