IMPROVING GRID RELIABILITY IN AN INCREASINGLY VOLATILE STORM ENVIRONMENT
By: Sugandh Rajpal, MS, PE, and Hunter Windle, PE
The intensity of cataclysmic storm and flooding events – including hurricanes – has increased globally. According to the Center for Climate and Energy Solutions, the upsurge in the frequency and growing ferocity of hurricanes can be attributed to warmer sea surface temperatures, sea level rise, and expanding tropical zones. The impact this weather can have on our national electricity providers is enormous.
According to the Wall Street Journal, much of the nation’s electricity system was constructed in the 1940s, and the American Society of Civil Engineers estimates that 70% of transmission and distribution lines are well into the second half of their 50-year expected lifespans. It’s no wonder that, with decades-old distribution lines, this aging network is what accounts for the majority of power outages. So whether an energy provider is responding to an actual or pending weather event, is seeking to satisfy legislative compliance, or is working to increase the resiliency of their system for the future, TTL is dedicated to failsafe and cost-effective infrastructure improvements that will keep the nation’s energy industry in peak operating condition.
CONSTRUCTABILITY IS CRITICAL IN THE DESIGN APPROACH
Constructability is a consideration for all design projects. But in the energy industry, constructability takes on a whole new meaning.
The unique locations of substations and overhead transmission lines present challenges not encountered in typical projects – marshy areas, mountainous terrain, inaccessible or remote locations – and the very distinct possibility of one stretch of transmission line encountering each one of these obstacles.
For the energy experts at TTL, an engineering design firm focused on delivering integrated infrastructure solutions for public and private clients, these challenges are not uncommon. After all, they are what come with replacing or upgrading critical energy infrastructure throughout the nation, and overcoming them is a matter of determining the proper constructability for the conditions at hand.
TTL’s approach to design begins with a thorough analysis of each unique situation to determine whether the potential solution can be constructed safely within the proposed timeframe and budget. TTL Project Manager Hunter Windle, PE, is a champion of designing
what a client needs to stabilize and secure their infrastructure while not overdesigning or exceeding the budget. “You have to find the balance between what a client wants and needs and a final, resilient, and cost-effective project that safely and reliably delivers electricity to the consumer every time,” Windle said. “Often the project objectives and desired outcomes are the easier aspects to identify, but inserting a high-value engineering solution to achieve those aspects is what TTL strives to do.”
WATER, WATER, EVERYWHERE
Designing over water is a key concern for facilities and transmission lines due to factors like wave action, depths, and lakebed variations. Open and closed bodies of water pose additional challenges including depths and varying sea levels that impact how components are installed (open body) and accessibility and maneuverability of equipment and barges (closed body).
One particularly challenging project, American Electric Power (AEP)’s Port Isabella Substation to North Padre Substation required an update of the overhead 345 kV transmission lines. While the underground line provided redundancy for weather emergencies, the capacity of the single line was insufficient to carry the full load in the event of failure. Deciding to upgrade the overwater line, AEP approached TTL to devise a cost-effective, robust solution for the transmission line replacement. Two approaches were presented to AEP:
Drilled Foundation. Drilling the foundation for each transmission pole is a conventional approach, involving drilling a hole with heavy machinery. This option is labor- and time-intensive, and risks of the hole caving in pose substantial life-safety and cost issues. Further disadvantages include the possibility of encountering obstructions, time-schedule conflicts, availability of labor and concrete, a heavily congested project area, and impact to the budget.
Driven-Pile Caissons. Caissons are the least invasive method of foundation installation in that no actual holes are required to be drilled. Instead, a pole is inserted into a concrete base and secured with anchor bolts. This method works optimally in congested areas and areas over water, is budget-friendly, and can be constructed quickly.
Of the two options, AEP selected driven-pile caissons providing the least invasive and most cost-effective solution. The caissons were installed four times faster than the conventional drilled foundation and reduced the schedule by approximately 50%.
CAISSON
cais·son /ˈkā sän,ˈkās(ə)n/ noun: a large watertight chamber, open at the bottom, from which the water is kept out by air pressure and in which construction work may be carried out under water.
WHAT LIES BENEATH
Collecting data to support the Port Isabella Substation to North Padre Substation project was essential in determining the best approach. The middle section of the transmission line crossed the bay, and collecting information in that area came with its own inherent challenges and hazards, like construction safety within a deep water zone.
While the driven-pile caisson approach was the optimum option – for both data gathering and construction – it presented several challenges requiring several TTLproposed solutions, each of which were discussed and finalized well before design began.
The TTL team studied the depth ranges, found to be between 2 feet and 13 feet, and the wave action of the location. Its findings led to an early alteration of the design to accommodate the connection between the transmission poles and the base-anchor bolt holes, providing a perfect alignment for the massive 7-foot by 60-foot caisson. In deeper water and above the high tide elevation, the team installed the caisson with a larger opening, installed the replacement transmission pole inside the caisson, and backfilled with concrete for stabilization. In shallower areas with limited space, the team used hydro-excavation –injecting high-pressure water to remove loosened soil – in order to empty the caisson cavity and allow the pole to be set inside.
Much focus was placed on the method of construction, but the team also anticipated post-construction impacts. Installing caissons produces intense vibrations which can impact surrounding infrastructure, but before-and-after photos were taken to document the existing conditions as a means to further protect AEP from unsubstantiated damage claims.
“A proper plan executed by the proper team lays out everything that will take place, and considerations for anything that could impact the project were figured out in advance,” said TTL’s Executive Vice President Sugandh Rajpal. “We also measured the strength of the vibration at multiple points to provide mathematically-sound metrics that construction was not causing any structural damage.”
While caissons are commonly used worldwide, they are most applicable in unforgiving environments. The drivenpile caisson approach resulted in no incidents or problems during the entire construction process due to TTL’s preplanning, proactive design, and implementation. Everything went according to plan and fell into place.
THE TTL TEAM
TTL has the experience, knowledge, and critical problemsolving skills to face the most challenging situations for our clients in the energy sector. Working collaboratively with the client, we work to strengthen system resiliency while providing cost-effective solutions under extreme constructability concerns. By verifying our energy clients’ facilities are resilient, they can avoid outages and keep the lights on.
For a review of your energy assets and whether they can weather any storm, or to schedule critical infrastructure repairs now, please contact TTL Executive Vice President Sugandh Rajpal, MS, PE, at srajpal@ttlusa.com or Project Manager Hunter Windle, PE, at hunter.windle@ttlusa.com.
