Tim Richards, ENTRUST, USA, describes the considerations at play in managing today’s transmission line infrastructure, and how the network can be properly safeguarded for the future.
Each transmission line is unique. While they share common components like poles, insulators, and wires, the terrain varies for each line’s route. These variations influence how transmission lines react to environmental conditions.
For instance, powerful storms can knock down power cables, and during prolonged dry spells, downed lines can significantly increase the risk of wildfires. Consequently, the transmission line industry must develop multiple strategies to strengthen the power grid. This will ensure that power remains on even when extreme weather causes line failures.
Significant advancements are being made by transitioning from traditional radial lines — where a single outage can leave everyone at the line’s end without power — to a more interconnected network.
In major metropolitan areas, radial lines are increasingly being replaced due to their vulnerability to disruptions.
The new network design involves interconnected lines that allow electricity to be redirected from other areas if part of the line fails, thus maintaining power supply across the network. This approach ensures that power continues uninterrupted for all connected customers.
Many transmission lines were built back in the 1940s and for some it is remarkable that they are still standing. Due to their age, the poles are often small and cracked or ‘checked.’ Since the electric codes have changed so dramatically since the 1940s, many of these poles would not be permissible in today’s regulatory environment.
Unfortunately, it is only a matter of time before a major weather event occurs that damages the line on aging infrastructure and possibly causes a cascading event of pole collapse. Poles can collapse like dominoes over a range of miles, possibly falling across buildings, roads, and railroads, causing significant danger to life and property.
ENTRUST supports utility companies that are proactively identifying aging infrastructure and helps them to prioritize portions of the transmission line for upgrade.
When assessing a transmission line for upgrade, the most important thing that utilities consider is the safety situation surrounding the lines.
Typically, electricity is sent for long distances. Most of that transmission line will cross empty landscapes but when entering the heavily populated areas of towns or cities, attention to safety rises to its highest level.
If a utility knows that they have a problem structure, but it is situated in an area that poses a very low danger to the public, they will typically adopt a watch and wait approach. If it is situated in a high fire danger area, they will likely proactively go out and strengthen all the structures in that area with extra bracing.
Occasionally, safety considerations will conflict with environmental considerations for the area, but ultimately safeguarding safety will always take precedence over environmental concerns.
Transmission lines are designed to cater for high wind loads. That means that average wood pole or steel pole strength in a transmission line will, for example, be designed to withstand a 130 mile per hour wind event.
Naturally, poles can sometimes be stronger or weaker than average. If there is a 131 mile per hour wind gust, there is a chance that the pole will fall. Winds of this strength may be only a hundred a year weather event, but with climate change we might start seeing more of those. Monitoring is showing that the frequency, but not the intensity of the storms is increasing over time. It is a risk that needs to be accepted because a system in which no pole ever fell would be prohibitively expensive for the utility and ultimately the rate payers.
The utilities also have a responsibility to keep the rate payers happy by keeping bills as low as possible. This means a great deal of cost analysis needs to take place.
To make sure that the safety of the population at large is being adhered to, a National Electric Reliability Corporation (NERC) alert was issued around 2010/2011 to all the utilities requiring that they verify that their older transmission lines still were equipped with adequate electrical clearances and met the National Electric Safety Code.
It is very possible that transmission lines located in rural, often overlooked areas, can be subject to unchecked vegetation growth that reduces clearance to ground to dangerously short distances.
At the national level, there are few mandates for action. Usually, action is more regionally dictated by the client. Many utilities observe those ice storms in Oregon or wildfires in California, and they do not want the same thing to happen to their networks. They will therefore dedicate proactive attention to their lines. They may analyze their entire area, classify certain high fire danger zones, and target those first for mitigation measures.
Understandably, homeowners living in rural, scenic areas can sometimes be very resistant to transmission lines being installed aboveground, due to the negative impact on their views. In some cases, the homeowners have even joined together to fund the installation of underground transmission lines at great personal expense.
Outside of scenic areas, underground transmission lines are becoming necessary, particularly in the northeastern USA where space for overhead lines is increasingly restricted. The major drawback of underground transmission lines is that it is truly specialty work.
Installing underground transmission lines can be more than 10 times the cost of installing overhead lines. However, it does deliver an incredibly reliable power supply as wires underground are very well protected from the elements.
Vaults are installed every so often so that the wires can be spliced together over long distances, only so much wire can be placed on a reel. Incidents are extremely rare because the wire is encapsulated extremely well, but when they do happen it is possible to work out exactly where in the line the fault occurred. There are a handful of cities across the USA that have proactively installed underground transmission lines due to their location and exposure to weather event risks, and it is a practice that ENTRUST would encourage.
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