by Lisa Meiman
Or really big football players. Towers grow there, too.
About three dozen steel lattice structures in Upper Great
Plains are going through growth spurts this year to raise the energized lines
to the appropriate safe distance from the ground.
New technology, adapted from the lifting technique that
moves houses, can add several feet to a tower’s height without removing the
conductor, needing cranes or involving a significant number of workers and
heavy equipment.
From Aug. 5 to 18, UGP completed test lifts on two towers
with their Canada-based contractor, AmpJack, to determine if AmpJack’s patented
technology is an adequate solution for the other 35 towers in need of a raise.
“We were extremely pleased,” said Upper Great Plains General
Engineer Cody Kinsley out of Huron, South Dakota. “By adding in a 5- or
8-foot section to the existing tower, we are meeting our compliance
requirements while realizing significant cost savings compared to traditional
tower-raising techniques.”
To raise a lattice structure, one jack is clamped to each of
the four legs and surrounded by temporary support framing at the waist of the
structure. The tower is separated and lifted by the jacks. Then, the new
section, designed by Western and built by AmpJack, is bolted into the gap, and
the jacks and support framing are removed. “In the end, it looks like the rest
of the tower except shiny and newer,” said Headquarters Civil Engineer Cody
Neyens, who designed the new sections. Raising one tower takes a crew of
five people about two days, including set up, raising the tower and tear down.
Western and AmpJack plan to raise towers through September and October.
This emerging technology is revolutionary for the energy
industry, but still has its limitations. “The technology only works for
double-circuit steel lattice structures. The structure also has to have the
capacity to bear more load,” said Neyens. “These UGP structures did, but that’s
not typically the norm. Structures are built for exactly what’s needed.”
Need for growth
In October 2010, the North American Electric Reliability
Corporation released the Facility Ratings Alert, requiring utilities to prove
their facility ratings, or capacity at which the transmission equipment
operates, were based on actual field conditions—not just design. One of the key
limiting factors in facility ratings is ground clearance.
UGP and most other regions hired contractors with
LIDAR-equipped aircraft to map their entire transmission systems from the air.
Sure enough, there were several spans of transmission lines that were out of
compliance, their conductors too close to the ground at maximum operating
capability.
“There are a number of reasons why spans didn’t have
appropriate ground clearances,” said Neyens. “Some of these towers are 50 years
old or more; things change. Conductors could have stretched under heavy
loading; something in the topography changed, like a farmer could have built a berm
or a road had been raised; or survey data was not accurate at the time of
design or construction of the line.”
Western got to work modifying the structures in a variety of
ways, including:
Sliding the conductor from one span to another. This was ultimately used as a temporary solution due to the tension imbalance it created at the structure.
Installing floating dead-end assemblies, which, in essence, bend the insulator at a 90-degree angle and then connect the conductor to the end, raising the conductor about six feet.
Excavating the ground beneath the span.
Replacing towers with taller ones.
Reconductoring.
But with more than one-third of the transmission lines and
more than one-third of Western’s 1.3 million square-mile territory, UGP had
more work than the other regions and was looking for a more efficient and
cost-effective solution.
“From the onset, it was UGP’s opinion that some structure
modifications were temporary, but the anticipated costs for structure
replacements required out-year planning in the budgetary cycle. At this time,
we became aware of Ampjack lifting technique and its potential to solve our
problem at significant cost savings” said Kinsley. After a technical review in
Canada, UGP knew it had found a viable solution and contracted with AmpJack to
provide the same service to lines in North Dakota, South Dakota and Iowa.
Many utilities and groups are paying close attention to how
this emerging technology works out with UGP being one of the early adopters in
America. “Raising the towers like this is unique. We’re willing to be a best
practice participant for NERC and [Federal Energy Regulatory Commission] and
share our experience with others in the industry,” said Kinsley.
What really gets engineers excited
Finding inadequate ground clearances was only the most
immediate benefit of using LIDAR to record UGP’s 115-kilovolt and above lines.
The deliverable for the work was raw data that could be imported into Western’s
Power Line Systems Computer-Aided Design and Drafting software, or PLS-CADD.
Using the LIDAR data, PLS-CADD creates a two-dimensional
ground surface overlaid with images and accurate models of the transmission
line wire system. An accompanying tower program adds detailed 3-D tower
information. The renderings can be rotated on any axis to provide the viewer
infinite profiles of the landscape.
The main benefit is improved situational awareness. “It’s an
exact replica of the line,” said Kinsley. “This work used to be done by hand
and then digitized. It’s much more accurate than drawings. We can quickly get
changes and modifications to the field.”
Neyens added, “This tool is very powerful. It doesn’t just
help with compliance. When we have maintenance issues or storms, we have an
exact model of the system. We can tell the field immediately what size towers
are needed, where they need to be sited and other information so we can replace
and rebuild faster.”
PLS-CADD is also modeling software that can predict outcomes
of environmental conditions or help deduce what happened in the past. In June,
massive storms took down more than 100 structures in UGP, including 52 structures
along a line more than 100 miles long. “Some of those structures were
practically new, only being replaced only a few years ago due to severe
weather. We wanted to know what is unique about that segment. What is happening
there? Can we improve the structures or siting to make sure it doesn’t happen
again? This software enabled UGP identify weak points and make system
improvements,” said Kinsley.
“We’re
now realizing how many side benefits this tool has. Before LIDAR and PLS-CADD
models, UGP would have never used an emerging technology such as AmpJack; there
were just too many unknowns. What started as a NERC alert now has the UGP
transmission system positioned for our piece of the energy frontier,” he
concluded.
More photos available on Flickr.