Met Tower Erection Report- Hibbing
The day started early, with the Department of Commerce crew rolling into the HPU office at 9:30 a.m. Mike Taylor instantly wanted to know what time the sun went down and how many HPU staff could help out!
We got to the site about 10 a.m. and started to unload. Gordon phones his guys to come help.
First task was to lay out the 15 or so sections of 6” pipe (they are in 10’ or 5’ lengths) and start fitting them together. The bottom end was inserted into the center plate at the already marked center point for the tower (luckily Jim Markovich of HPU and his crew had installed and marked all the anchors and the center point). Blocks of wood were inserted underneath at 10 foot intervals to keep the pipe off the ground. Jeff made sure to assemble the 10 foot and 5 foot sections in proper order so that the guy wire attachment points were located at the proper position up the tower.
Next the guy wires from each of the guy points was unraveled and extended to the guy anchors. The anchors were placed several weeks before by the utility crew, they used their 12,000 pound bearing capacity larger ground anchors. Typically a smaller screw in anchor or dead-man anchor is used, and two of them are placed at each corner.
The gin pole was assembled on top of the met tower and ropes were extended from the top of the gin pole to the side anchor. Each of the side anchor wires was looped through the anchor and secured with two wire rope clips.
Now the entire tower has been assembled on the ground. The instruments are attached to the tower using hose clamps and 3 foot long aluminum booms. There is one anemometer placed on top of the tower and then three more placed at 39m, 30m and 20m heights. Wind direction sensors were placed at 40m and 20 m. The wires from each sensor were uncoiled and run down the tower, tape was applied every three feet to keep them organized and in place. There were numerous attempts to get the wire strung properly so as not to get hung up in the guy wires, a few times rerouting the wires and we were ready to attach the winch and start pulling (note that we had to physically lift the gin pole the first ten feet off the ground before the winch could effectively start pulling it up)
Close-up of met instruments on the top of the tower. Note there is a lightning rod with separate copper conductor attached to the top and then connected to a 6’ long copper rod pounded into the ground at the base of the tower.
The next picture shows the first attempt at tipping up the gin pole, some wires were crossed and had to be moved. Also one wire pulled a wind vane sensor off as it was pulled up in the air by the gin pole. We lowered the gin pole and fixed the boom, then raised it again. Crews on either side tightened all the side anchor guy wires at this point before the tower was picked up off the ground.
Next the gin pole is pulled farther and the tower starts rising off the ground. More visual inspections reveal additional guy wires that must be untangled before the tower can be raised further. Several guys argue about who knows what they are doing:
Below’s a picture showing a closeup of the winch anchor and winch in operation. At this point the truck is starting to roll, and another truck is brought over and chained to the truck with the winch.
Finally all is clear and the tower is winched to within 5 degrees of vertical. The North side (what was the anchor under the tower) wires are tightened somewhat and then the tower is tipped a little further till the gin pole is nearly horizontal and the tower is starting to rest on those North wires. The South wires are taken from the gin pole top one at a time and attached to the South anchor. This is a good time to be thankful for little wind.
All the anchors are slowly tightened while eyeing the tower for straightness. Several rounds of tightening and eyeballing straightness are needed, with the end result not perfect but good enough for our year’s worth of wind monitoring.
The last job is to wire the logger and set the parameters. This requires a special electronic interface from NRG Systems called the Term Reader. Mike sets the parameters to read wind speed in miles per hour, and to record data once every ten minutes. It’s getting cloudy and cold, everyone agrees a job well done and goes on their merry way!
