ZAP

Thursday night five of us journeyed to Oconee County Station #8 for a training session on powerline hazards. This isn't the first time, and it won't be the last. Bruce Thaxton, Oconee County fire chief, and his firefighters put on a mighty good show and they're always generous in inviting us in.

The two-hour training was given by a Georgia Power transmission engineer. He is also a volunteer firefighter on the side, so had a nice perspective on avoiding what is invariably an issue in one form or another at just about any fire call. I want to say his name was Larry Stephens (or Stevens) but I could be wrong about that. Just leave a comment to correct me and I'll do so.

I'm certainly no transmission expert, so with the caveat that I am passing along info I took in without the vetting or skepticism of expertise, then, here's a few high points that might be generally interesting:

We got a quick course on power distribution. The pylon-supported high lines that run long distances through broad corridors are fed directly by the generating station. Those transmission lines are typically at 500,000 volts. Yikes!

Transmission lines feed into, through, or are tapped by substations - those fenced-in installations that are clearly electrical in nature. Your general neighborhood is supported by a substation of one size or another, and the voltage is stepped down to 12,000-24,000 volts here. Those are distribution lines that you see on the roadside poles that are carrying this stepped-down power.

And then there are the power poles with the cylindrical transformers closer to a structure. These step the voltage down further to the 120-240 volts that enters your house. Sometimes those transformers are ground installations, not mounted on poles.

In any event, it's the distribution lines (12-24 kv) that are most often encountered by firefighters at vehicle accidents and storm damage. A fire call to a structure will likely involve both the 12-24 kv distribution lines, as well as the 120-240v structure voltage on the other side of the transformer.

OK, that's the background. It's a typical setup for our area, and I imagine its details can differ elsewhere.

1. It goes without saying that downed power lines are dangerous. Especially when they're *not* arcing, because it's then that the unwary assume they've been de-energized. I'll get this upfront right away and not mention it again though our speaker warned us again and again - never touch a power line.

2. To me, one of the coolest things was the image of the helicopter repair of the extremely high voltage transmission lines. Larry said that it's inevitable that the local 911 will get calls from passersby reporting a helicopter caught on the overhead wires with a little man outside it trying to free it. In fact, there will be a little man outside it, on a platform attached to the landing gear. He'll be wearing a metal-impregnated suit, and will have a little metal monkey tail attached to the overhead wire. He, the platform, and the copter will all be charged to 500,000 volts. And it's ok - weird, very weird sensation, Larry said - but ok. So long as you don't touch ground, and then it's instant vaporization.

3. That's an important concept - it doesn't matter whether you're charged at 0 volts or 500,000 volts, so long as there's nowhere for the current to go. It applies to vehicle accidents involving power lines (or ladder trucks touching power lines). The tires insulate the vehicle from ground, and even if a 24,000 volt line is lying over the car, you're relatively safe - so long as you don't get out of the car.

DON'T GET OUT OF THE CAR! And no one should approach the car, either. Not until the line has been de-energized.

4. Of course it's possible in vehicle accidents that a fire may be involved, and then you really do have to get out of the car. How do you do it? VERY important: you HOP out of the car, landing with your feet together. And then you HOP away from the car until you reach someone who seems to be normal.

The reason for the initial hop out of the car is to avoid simultaneously touching the highly charged car and the ground at the same time. If you complete the circuit, you will be dead. If you hop, then you won't complete the circuit.

The reason for continuing to hop away from the downed wire has to do with ground gradient electricity. A downed wire produces a voltage gradient spreading outward over the ground in concentric circles. Especially if you're close to the center, even the foot or two of a normal stride will place one of your feet at a different potential than the other one, and current will flow up one leg and down the other into ground, and you will be shocked. Keeping your feet together helps to minimize this.

(BTW, this also explains why a squirrel can run along a power line, or birds can perch on one. They're charged to the same potential and no current flows. So long as the squirrel HOPS from the line to the power pole he's ok, but if he steps across, it's goodbye.)

5. Some interesting observations on an increasing problem - folks invading substations and stealing the copper wire out of the transformers. They tip the transformer over and spill out the oil that fills it, then cut out the copper coil and make off. Sometimes they leave a charred hand or two behind, in the process.

(The presence of large amounts of oil is, by the way, one of the main combustibles at a power substation. And sometimes they do catch fire. There was no equivocation here: don't even bother spraying water or foam into a substation - the equipment will all have to be replaced anyway so it's needless, and very dangerous to spray water into an energized substation. Suppress any fire that may be spreading outside the substation, but don't get anywhere near the substation itself.)

6. Over the last few years there has been an increasing availability of portable, gasoline generators that folks like to use for power outages. Improperly connected generators (and this is very common) can "backfeed" from the house wiring, into the transformer, get stepped up, and enter the grid. The danger isn't just to the homeowner, it's to the powerline workers trying to repair a line. From the power company's point of view the line has been turned off, they *think* it's de-energized, but the homeowner's generator is powering it with potentially lethal voltage and current. It wasn't such a problem before, with noisy generators that powerline workers would listen for, but Larry said that with the extremely quiet Honda generators now available, powerline workers cannnot hear them in the vicinity.

I'm guessing that home solar panels similarly connected to the grid could create the same sort of problem.

7. The last video, an amateur video that just happened to be made, was of an automated switching failure. Cherrypicker used by tree surgeon accidently touches power line, but instead of automatically switching out, all switches failed. The transformer blew, and then ten seconds later, the next one down the line blew. And ten seconds after that the third. And so forth. Each house connected was suddenly subjected to 12,000 volts instead of 240v. And *they* blew too - visibly erupting into flames and smoke anywhere there was wiring. The impression as the charge moved down the distribution line was of a ravening, roaring monster passing by houses and igniting them in order. The sound of the beast was unearthly. Very dramatic.

Very cool two hours, and again thanks to OCFD for the opportunity.

--Wayne