Tales of disaster – Page 9 – Engineering Radio

Storm Preparation

With Hurricane Irene taking aim at the northeast, now is the time to make preparations for bad weather. This is the five-day forecast:

Now, five-day forecasts are notoriously inaccurate. There are too many variables to make it accurate and even the most seasoned meteorologist will admit, it is an educated guess. However, the large semi-transparent disk is almost always accurate. Therefore, it seems we may be in for a bit of a storm this weekend, with the eastern end of Long Island and Newport/Providence RI in the landfall area. The Bridgeport, CT stations will likely see the worst of it if the storm follows the predicted course.

Having a good disaster recovery program in place reduces much of the pre-storm work. This includes backup equipment and personnel allocations to keep the stations on the air and provide valuable information during the event. Wherever and whenever our clients allow us, we make sure that these systems are properly designed, installed, and working. When trouble is milling about offshore in the form of a Hurricane, then we make a few final preparations, both personally and for the clients:

Top off all generator fuel tanks and test them. This includes my home generator.
Make sure all loose items are secured.
Make sure other redundant systems; backup transmitters, backup STLs, and backup transmitter sites are in order and ready to be deployed.
Check the personal safety items; first aid kit, rain gear, flashlight batteries, work gloves, eye protection, hard hat, some type of energy food, and extra water are in the truck.
Get out a clean sleeping bag and a set of clean dry clothes and put them in the truck.
Gas up the chain saw and put it in the truck with extra gas, bar oil, and blade sharpener.

During the event, it is important to recognize when a situation is too dangerous to proceed and wait for the danger to subside. Examples of this are local flooding of roadways, downed power lines, high winds, and or electrical storms while working at transmitter sites.

Radio may have lost much of its relevance as an entertainment medium, however, there is still one thing it does very well; broadcast emergency communications and information to the public.

Update: As of 5 am 8/25 it looks as if the hurricane is making a b-line toward Bridgeport, CT. Most of the computer models are now in agreement which means the forecast is getting a better handle on the variables and is becoming more accurate. Strength is still somewhat debatable, but even a Category 1 storm could do significant damage. We shall see.

Update 2: As of 5 pm 8/26, Irene is still on course for the greater NYC/Long Island sound area. As much as possible, preparations are complete. There are some things that cannot be helped, like the height above the mean sea level of the WICC and WEBE transmitter sites (10 feet) or the lack of a generator at WXPK studios, etc. Estimates are for Hurricane-force winds by this time tomorrow, so the only thing left to do now is get a good night’s sleep. Tomorrow may be one of those long days.

Here is an interesting thing; several people have suggested that IBOC signals on both AM and FM NYC stations be turned off so that smaller local stations will be listenable to local residents in NJ and Long Island. A secondary consideration would be the amount of power IBOC uses and the possibility of backup generators running out of fuel to run something that has little or no audience. If that isn’t telling….

It should be interesting.

WICC WEBE damaged tower removal

Damaged in last year’s F1 tornado, this thirty-foot Rohn 25-G tower needed to be removed from the roof. It actually went faster than I thought it would, the worst part being moving the 4-foot tower sections down to the salvage truck via elevator. Naturally, the day we choose to do this is the same day that one of the two elevators servicing the seventh floor is out of order.

Damaged Rohn 25G STL tower on roof of studio — Damaged Rohn 25G STL tower on the roof of the studio

This was the same tornado that picked up a twenty-ton rooftop air conditioner and deposited it in the parking lot. Luck would have it that no one was killed or injured.

Using a circular saw with a metal blade, a sawsall and a hand grinder, the tower was cut up into four foot sections. The sections, brackets, and tower base were taken to the scrap yard and disposed of.

Tower and transmission lines ready to be removed from the roof

There were several lengths of unused 7/8 inch foam coax, broken antennas, RG-59- RG-58, RG-6, rotor cable, etc that we cleaned off of the roof and tower.

A good little project to have completed.

The studio build-out for WEBE is also nearly done. August will mark one year of our company’s involvement at WICC/WEBE. I was looking around today and comparing the difference between when we started to now. Many things have been done.

Transmitter trips main breaker

Received a call last night, after a particularly bad thunderstorm, that WGHQ in Kingston, NY was off the air. Earlier in the day, the transmitter had tripped the main breaker after a thunderstorm. I arrived at the transmitter site and found the breaker tripped again. Once the breaker was reset, the transmitter came back on and ran without any overload indications. The transmitter is a 10-year-old Nautel ND-5.

I was thinking of breaker fatigue as the breaker is the original 1960 breaker installed when the building was built. I reset the breaker and turned the power output down to 3 KW, thinking the reduced load might not trip the breaker until we could get a replacement. The transmitter was on the air running as I was about to lock up and go home when I heard, but more felt through the floor, a THUMP! There I stood and watched the transmitter go dark.

At least it happened when I was there looking at it. Because of the lightning, I was thinking of something in the output network. I reset the breaker and once again, no faults, and the transmitter came back on. Strange. Obviously some sort of power supply issue. Here are the clues:

The B- voltage was right where it should be at 72 volts.
All other readings, reflected power, forward power, and power supply current are normal before and after the breaker trip
No fault lights
The service panel breaker, which was tripping, is rated for 70 amps, and the transmitter front panel breaker which did not trip, is 50 amps.

The Nautel factory rep was thinking either breaker fatigue or the big transformer in the base of the transmitter had gone bad. According to him, no one had ever heard of a transformer going bad in these transmitters, which makes a certain amount of sense. Unlike a tube transmitter, which steps the B+ voltage up several times, these transmitters reduce the B- voltage by about 2/3rds or so. With a step-up situation, a surge would be multiplied many times and could very easily punch a hole in the transformer’s secondary winding insulation. I have, in fact, experienced this on at least two occasions.

That leaves the wiring between the transmitter and the service panel. I double-checked the panel breaker with my volt meter to ensure that the voltage was indeed off. Then I removed each phase from the connection lugs in the transmitter and tested the wire to ground with my Fluke 77 DVM. Sure enough, two of the phases showed resistance of 1.2 and 1.7 MΩ to ground where it should have been infinite. Further, when I took the cover off of the service panel, I found a dead mouse. Unfortunately, I didn’t have any #4 THHN, and all the home improvement stores were closed by that time, so it had to wait until morning.

The thunderstorm seems to be a coincidence.

After we pulled the wire out of the conduit, we found this:

mouse chewed feces encrusted electrical cable — Mouse chewed feces encrusted electrical cable

It is a little hard to see, but that shiny spot is copper. The cable jacket is chewed back quite a ways and the entire thing is encrusted in mouse feces and urine. I love to work on stuff like this. LOVE IT! Hantavirus, here we come! That reminds me, I need to get some of those blue latex exam gloves and throw them in the truck… Anyway, far back in the conduit running through the concrete floor where it bends to go up to the service panel, the mice apparently had a nest. They got into the conduit under the transmitter, where it transitioned from 3-inch rigid to 1 1/4-inch flexible metal without the benefit of a junction box or proper fitting.

We pulled new copper conductors in and installed a proper junction/transition between the 3-inch and 1 1/4-inch conduit. The service panel was also missing several knockouts of various sizes, which were sealed with knockout seals. The transmitter was back on the air at full power about 16 hours after it went off. Unfortunately, the station has no back up transmitter, so they were off for that period of time. Perhaps now they will look into a backup transmitter or at least an exterminator, but probably not.

All is not well in Paradise

If one considers paradise an FM35A. Going through another iteration of blown transmitter fuses for WEBE, Bridgeport, CT. Yesterday, I spent the afternoon examining the transmitter and found several interesting things:

Fresh arc tracks on the PA cavity and PA loading capacitor
The shoes and bars in the high-voltage contactor were severely pitted
One of the mains phases (middle) in the high voltage supply appears to be heating up, likely due to a loose connection.

I checked and re-tightened all of the mains connections. Apparently, this is an old problem, as the Allen screw was tight. Interestingly, the fuse that was blown was on the red phase, which is different from what it was last time.

I spent the afternoon filing and sanding off the arc track marks in the PA cavity. It is very important to file flat all sharp points that were the result of arcing. Any sharp points will induce corona. I also filed down all of the contacts in a high voltage contactor, which took a fair amount of time. These are soft copper shoes and bars that had so much pitting and carbon I wonder how they didn’t catch on fire. I filed them flat. We were back on the 35A transmitter at full power by 4:30 pm.

If this happens again, I will bring my megger out and check the insulation on the wire between the disconnect switch and the HV power supply.

When I left the site at 5:30, I felt like we did some good work.