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Lightning Loops?




 
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Author Topic: Lightning Loops?  (Read 15505 times)
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Bill, KD0HG
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« Reply #50 on: July 10, 2012, 10:43:03 AM »

The transmitter is a Harris DX-50, and its VSWR trip was working FB as of last week. (I know, I accidentally tripped it during a pattern change test- LOL) There is also a VSWR trip test built into the transmitter. I've seen the box trip offline due to a nearby lightning strike maybe a mile away. Also, the logging in the remote control indicated a VSWR trip and power shutdown about the time the fire started. The tower ATU was a Kintronics inside a steel enclosure. Completely melted, the coils of copper tubing lying in the rubble were inside the steel enclosure. While there are a few thermocouple meters lying around, we always use the modern Delta ammeters built into the gear. About 32 amps of aref into that tower.

This is the worst damage I have ever seen, it's gotta be the result of one of those dreaded positive lightning bolts..?
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WA1GFZ
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« Reply #51 on: July 10, 2012, 11:40:26 AM »

looks like the resistance of the tower is a lot lower than the resistance of the ground system.
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W8IXY
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« Reply #52 on: July 10, 2012, 01:02:58 PM »

That damage looks "appropriate" considering the occasion.  I assume that the coil of copper tubing seen in the wreckage was once part of the tuning network.  Looks like the EMF in the lightning just literally sucked the coil together.   I have worked on several station's ATU's after a lightning hit and am reminded each time of the force generated by a lightning bolt.  G3 and G4 mica capacitors were vaporized-all that was left were the end plates.  The edge wound inductors were sucked together like a slinky.  The thermocouple base current meter was nowhere to be seen except for the two brass bolts that used to connect to it.

I built and still maintain a 6 tower 50kw site that, when we built it, installed a "cage" at the top of each tower (260') and after 13 years, have never suffered a direct hit that damaged anything in the ATU or tuning houses.  I've been inside the transmitter building during storms and have occasionally heard a few "snaps" from inside the phasor during thunderstorms, but nothing that appeared (or sounded like) a direct hit.   Like Bill's site, we also have a Harris DX-50 as the main, and the only thing that's happened to the transmitter in 13+ years is a few VSWR trips during storms.

When we built it, we used all state of the art techniques, perimeter straps,  120 1/2 wave radials for each tower, etc.  Aside from needing to replace a few contacts from the ATU contactors, so far at least, lightning has not caused any serious damage or taken the station off the air. 

Geez, I hope I haven't spooked it now.   Lips sealed  .....I'm getting too old and fat to climb around that much any more.

73
Ted W8IXY
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KA3EKH
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« Reply #53 on: July 10, 2012, 02:09:23 PM »

Looking at picture number one it looks like you can see the remains of the signal turn loop in the feed from the ATU building to the tower. So much for the inductance of the one turn protecting the ATU, with the lightning melting the ATU and all that how did the tower lighting circuit do? Can see the Austin ring looks ok. Do you have regular lights or LEDS on the tower? Have recently changed out all the side markers on my towers to LED lights and was wondering how they would do in a direct strike on the tower.
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Bill, KD0HG
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« Reply #54 on: July 10, 2012, 05:29:29 PM »

Looking at picture number one it looks like you can see the remains of the signal turn loop in the feed from the ATU building to the tower. So much for the inductance of the one turn protecting the ATU, with the lightning melting the ATU and all that how did the tower lighting circuit do? Can see the Austin ring looks ok. Do you have regular lights or LEDS on the tower? Have recently changed out all the side markers on my towers to LED lights and was wondering how they would do in a direct strike on the tower.

The Austin transformer is torched. The top support became unwelded from the core/winding from the blast. You can see the metal from the top support melted and dripped down the side of the coil which is now dangling by its wires. Tower has regular incandescent beacon lighting, The lighting control box has the front cover blown off of it. The whole enchilada is destroyed. Well, maybe the light bulbs on the stick survived...

Bill


* Austin.jpg (158.05 KB, 1024x768 - viewed 391 times.)
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #55 on: July 11, 2012, 11:49:33 AM »



Don't want to throw gas on the fire, but from the pic of the tower bottom, the concrete form that the tower rests on is leaning off to the side at a pretty decent angle... fyi.

                                    _-_- bear
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_-_- bear WB2GCR                   http://www.bearlabs.com
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