I wrote this some time ago. Maybe some of you would find it helpful. LIGHTNING PROTECTION: We have seen many stations that have sustained substantial equipment damage from power surges. Not surges from the power company, but lightning caused surges. At most of the stations we visited, lightning has reduced asset value, crippled coverage, and affected programming. How is this possible? Modern solid state equipment, its chips composed of microscopic silicon traces, are very sensitive to power surges induced by lightning into power lines, phone lines, or any other wires. A stoke need not directly hit the wire. It need only be nearby. A strike to ground miles away can induce high voltages into nearby wires, which can then be carried from afar into equipment. Many of the inspected stations have lost thousands of dollars of equipment, audience reach, and production capacity, losses that are largely preventable. Although some stations have some degree of lightning damage protection, few have exhaustive damage control. It is a shame most stations are not fitted with, or aware of how to prevent lightning damage. Transmitter towers, poking into the sky, naturally attract bolts from the blue. Power lines and phone lines, also stick up into the sky, are strung along power poles, will pick up surges from miles away, and can conduct kilo volt blasts into exposed studio or transmitter equipment. Studios also need protection. Besides power and telephone lines, studios, remote from transmitters usually have a smaller tower used to support studio to transmitter links. Towers attract direct lightning strikes. When a stations FM transmitter power amplifiers has turned to toast, the station will be broadcasting instead, at greatly reduced power, on their low power “exciter”. An exciter is device used to create the signal that is supposed to be amplified before being sent out to an antenna. FM power power amplifiers cost thousands of dollars, and are expensive and difficult to repair. Surely a high degree of protection is good investment. Some stations have lost use of their device, called a hybrid, used to place telephone calls on air. Note we have included a page on telephone line entry protection. However, additional protectors should be installed directly to the case of well grounded telephone to air equipment. A typical grounding improvement program might cost $2,000 USD in material and copper and several man days to install. In addition, special devices may be needed at a transmitter or atop a tower to prevent lightning strikes. Certain rules should be followed at studios: 1. Where practical, the studio and transmitter building should have a heavy copper wire running all the way around the perimeter. 2. Every tower, where practical, should have several radial wires, at least three, at least 4 feet, and up to 15 feet in length, with ground rods at the end of each wire, and one at the base of the tower. AM towers already have ground radials, but tower base ground rods should be added if not already present. 3. Where electricity enters the building, another ground should run from the electrical box down to another ground rod, and a bond run to the studio ground grid. 4. #3 above applies to telephone. 5. Any co-axial cables running down the tower must be electrically bonded to the tower before the run over to the building. If the cable is electrical, surge protection should be used to shunt surges into the tower in an attempt to keep them from heading off to the building. 6. The cable should have at least one loop, maybe three or 4, just before the cable enters the building. 7. Every cable entering the building must be connected to the perimeter ground. The perimeter ground should spider into the building, bonding to everything electronic; mixers, computers, radios connected to other gear, STL transmitters, and audio hybrids used to put telephone calls on air. That means a ground wire will be connected to every piece of equipment or the rack into which it is mounted. Stand alone computers will have a ground wire running to and screwed into the computer case. The station will not rely on the electrical system ground. When equipment is mounted in an equipment rack, the rack must be well bonded, and if there is any question about the contact, an additional wire will be run to equipment in the rack. 8. Antennas up in the air, on a tower, or sitting on the roof, also must be bonded. If the station uses wi-fi over the air for internet, that equipment must also be connected to ground. You cannot have too many grounds, 9 The phone line may have an outside on the wall surge protector, but that is not enough. Buy special low voltage inside protection to go on the wires just before they connect to the device used to put phone calls on air. 10. Transmitters are a special problem. Besides all the above rules, and in addition to the power surge protection you will be placing in the breaker or fuze panel, you should put a ferrite impedance bead on the power line after it leave the main breaker panel. Then you will have a smaller disconnect switch mounted to the transmitter, and besides the ground you already know the transmitter needs, the new panel will also will have surge production. Finally, we have to note that mobile wireless companies have towers, transmitters and phone lines. I have no doubt that experts can be found who work in country for cellular companies. Local people should be found and their help sought. A few of many links found on the internet. I have not explored it much, but the link below looks to be very helpful. It is not intended for a broadcast audience. As mobile phone systems are far more exposed to lightning, all broadcasters probably have a lot they could learn from them. gpr-expert/cell-site.htm smithsinterconnect/Companies/Protection/Polyphaser/about.html protectiongroup/Home hubersuhner/mozilla/hs-rf-lightning-protectors
Posted on: Thu, 04 Sep 2014 06:46:09 +0000
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