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Adjusting Power Line                                   Real-Time Measuring and Monitoring
                                                               Late last year, Sellevoll and Vestbø climbed into a helicopter and
        Sag in Real-Time                                       flew up 600 meters to the top of a mountain in Leikanger, a small
                                                               town on the northern shore of Sognefjord, the longest and deep-
                                                               est fjord in Norway and the second-longest in the world. Hanging
        -This article was originally published in the January 1, 2019 edition   above the steep, angular surface of the mountainous terrain was
                                                               a 450-meter-long section of four power lines that their customer,
        of Power magazine. Mary Jo Wagner is a Vancouver, British Columbia-  BKK Enotek, had just installed. After installing the cables, BKK
        based freelance writer with more than 20 years of experience covering   had tried to determine and set the appropriate sag levels using
        geospatial technology.
                                                               a traditional sag scope. But the precipitous landscape and the
        https://www.powermag.com/adjusting-power-line-sag-in-real-time/  span between the two towers made it too difficult to accurately
                                                               calibrate the lines.

                                                               The Geomatikk Survey crew took on the task of measuring the
                                                               sag and assisting BKK in correcting the sag elevation to meet the
                                                               height and tension tolerances. To spatially ground the project data,
                                                               Sellevoll and Vestbø used their Trimble R10 GNSS receiver and
                                                               SX10 total station technology to establish control.

                                                               Standing beneath the utility tower at one end of the line, they
                                                               aimed the SX10 directly overhead and collected a point where
                                                               the cable connects to the tower, a process they repeated for
                                                               each power line. They then set up underneath the other tower
                                                               and acquired four more connection points (Figure 2). With the
                                                               instrument’s controller, they determined a chord (straight line)
                                                               between each power line’s end points and established a vertical
                                                               offset from the chord down to the existing power line. Given the
                                                               length of the cables, their above-ground height of 25 meters (m),
                                                               and the current temperature, which was about 17C, BKK speci-
                                                               fied that each cable’s sag needed to be 6.26 m below the chord
        Getting proper sag between power line towers can be time-consuming.   at the lowest point.
        However, a new surveying tool allows workers to make adjustments in   2. Using a Trimble SX10 scanning total station to acquire needed mea-
        real-time. The method saves time and money, while also providing excel-  surements and process data, workers were able to determine needed
        lent 3-D documentation of the end result.              line adjustments in real-time. Courtesy: Geomatikk Survey
        For surveyors, the unexpected in the field is not usually welcome.
        Surprises lead to challenges to resolve, time delays, and often   “The ability to see and compare the chord line with the existing
        increased costs.                                       power line on the controller’s big screen enabled us to see in real
                                                               time how much each line was outside of tolerance,” Sellevoll said.
        But occasionally there are pleasant surprises. Like when Even   “So, when they adjusted and lifted the cable, we could monitor it
        Sellevoll, a survey engineer with Norwegian company Geomatikk   on the controller and see that it needed 50 centimeters more or 10
        Survey, set up his integrated total station and scanner instrument   centimeters more until it was in the correct position.”
        to survey a power line, and it revealed a capability he wasn’t aware
        it had. That unexpected discovery completely changed his approach   Measuring to an accuracy of plus or minus 3 centimeters, the
        to the survey assignment—in a good way.                Geomatikk Survey team determined that each of the four power

        The project required Geomatikk Survey to mea-
        sure and adjust the sag of new, high-voltage
        power lines on a mountain in Sogn og Fjordane,
        a county in western Norway (Figure 1). The
        original strategy was for Sellevoll and his col-
        league, Svein Ivar Vestbø, to use the company’s
        newly acquired Trimble SX10 scanning total
        station to acquire the needed measurements
        and process the data to calculate how much
        adjusting the lines needed. However, “When
        we pointed the SX10 at the first power line, the
        sensor automatically locked on to the line itself,
        even though there was no prism,” explained
        Sellevoll. “That was very interesting because
        we didn’t know that it would do that. What that
        meant was we could not only more easily and
        accurately survey the lines, we could adjust
        their sag in real time, directly in the field.”
        1. Simply accessing power lines in remote mountain areas can be    lines was hanging too low, between 1.5 m and 2 m below the ac-
        difficult. Courtesy: Geomatikk Survey                  ceptable sag limit. With a BKK crew positioned at the transformer
        And just like that, a project originally scheduled for several days’   station down in the valley, Sellevoll and his colleague instructed the
        work was suddenly reduced to a single day. The new technology   tensioning team via telephone.
        was not only a game-changer in the field, it is proving to be the
        business development tool it was acquired to be: an instrument to   Starting with line one, he aimed the SX10 and once it had locked
        redefine real-time surveying and to reap the revenue benefits of   onto the cable, he told the crew how much adapting it needed.
        new business opportunities.                            Then he followed the cable movements in real time, guiding the
                                                               BKK crew until the line’s sag was in the correct position.
        22 The Nevada Traverse Vol.50, No.2, 2023
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