Fig. 1: The insulator on the northeast leg sustained the most serious damage.
Crawford Broadcasting Director of Engineering Cris Alexander wrote in depth in the Aug. 17, 2011, issue of Radio World Engineering Extra about the replacement of a self-supporting tower’s insulators. The article caught the attention of North Carolina contract engineer Tim Walker, who experienced a similar situation at WMVA(AM) in Martinsville, Va.
In December of 1994, an overnight ice storm deposited approximately 1cm of rime ice on the members of the station’s 425-foot self-supporting tower, constructed in 1950. As if ice weren’t enough, high winds followed.
The next morning station personnel noticed that three of the four base insulators were cracked or completely broken. Fig. 1 shows the northeast insulator, with a portion of the cracked porcelain lying on top of the cement pier.
Fig. 2: Here we see Sky Tower Service’s temporary repair to support and restrain the northeast leg.
Fortunately Sky Tower Service of Lynchburg, Va., was in the area to perform maintenance on a nearby tower. The crew responded immediately and secured the tower leg, which was supported by the demolished insulator.
Fig. 3: Porcelain insulators can also crack, as seen in the northwest leg.
The temporary repair to the northeast tower leg can be seen in Fig. 2. The support foot, under the jack on the right, was left over from previous tower work.
Sky Tower Service then replaced the broken insulator with an on-site spare insulator assembly that the station had in storage. Over the course of the following months, the damaged insulators were shipped to LeRoy, N.Y., for evaluation by Lapp Insulators Co.
Tim’s frightening experience suggests one more thing to check after ice and windstorms.
Not only can the stresses of an ice storm cause major insulator failure, as seen in Fig. 1, but insulators should be checked for hairline cracks, clearly seen on the northwest leg’s insulator, Fig. 3. Damage to the southeast leg’s insulator, Fig. 4, was almost as bad.
It would be interesting to model this damage, given that the most serious breaks occurred on the northeast and southeast legs. Curiously, there was no damage to the fourth insulator. Could the ice and wind direction have contributed to the severe insulator damage on one side? We’ll leave that answer for the mechanical engineers.
Fig. 4: The damage to the southeast insulator was almost as bad as that suffered by the northeast leg.
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HCJB’s Alan Shea, CSRE, CBNT and N2UDV, offers a worthy comment about the use of Sharpie brand markers to indicate critical adjustment locations on satellite dishes, as we described in the Nov. 16 Workbench.
Alan notes that vandals often carry Sharpies to create graffiti; someone intent on ruining your day conceivably could make spurious marks on your dish settings just to confuse you.
That’s why he keeps a bottle of red nail polish in his tool bag. For critical situations he recommends real “thread lock,” but for marking the settings/locations of set screws, nuts and other adjustments, the nail polish is king. Most vandals aren’t into carrying red nail polish around. Now that black nail polish is so popular, you might consider that color, too.
Frankly, Alan says he would use both a Sharpie Industrial marker and red nail polish for his dish settings. He says Sharpie Industrials can be found at most home improvement stores or online.
By the way, if the bottle of nail polish isn’t made of plastic, you might want to seal it in a small plastic sandwich bag. If your tool bag is anything like mine, there’s way too much stuff rolling around in it. Save your tools from being “painted” and use a sealed bag.
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You know, Alan’s idea of red nail polish can be applied elsewhere.
It’s customary to use colored cable for stereo analog pairs, where the color helps distinguish “left” from “right.” But if your plant uses conventional Belden 8451 (black) shielded audio cable, a red dot of nail polish atop the connector feeding your “right” audio signal can guard against audio mix-ups. (Red and Right both begin with “R.”)
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Author John Bisset has spent 43 years in the broadcasting industry and is still learning. He is SBE Certified and is a past recipient of the SBE’s Educator of the Year Award.