Should I be worried about a 345 kV transmission line in my street?

General Questions
#1

I learned last night that Com Ed plans to construct a 345 kV transmission line under the street in front of my house, to bring additional electrical capacity to downtown Chicago substations. It will only be 4-10 feet under the surface of the street because of the subway tubes adjacent. Now 345 kV is not your ordinary distribution electrical line; it’s what is normally run cross-country on 70-foot-high poles. I believe that folks further south objected to a new aerial transmission line, so Com Ed will be doing the much more expensive underground option, running north from 55th under State Street and then west under Ninth St.

I’m usually not much of an alarmist on EMF and health effects, but the use of a narrow residential street is a little worrisome, even if it’s just the effects on police radios and pacemakers. I’d really like to educate myself about this subject before I raise unnecessary alarms.

#2

345 kV underground cable is special stuff - there’s a metal shield around the center current-carrying conductor, so it’s rather like an enormous coaxial cable.

I don’t know for sure about HV cables, but with regular cable TV coax, the shielding keeps the signal inside the cable, so I can only assume the HV cable’s shielding keeps EMF to a safe level. There are many miles of HV powerlines just a few feet underground across the country, and I haven’t heard of pacemakers or radios misbehaving near them.

Frankly, I’d be worried about more of the things under the street like old steam and gas lines.

#3

I’m wondering what would happen if that thing accidentally shorted to ground. Giant explosion maybe? And would that short be detected quickly if the line was completely cut? The ground might not be conductive enough to increase the huge load already on that line.

#4

I suspect it’s DC, so no RF interference. Even if it’s AC, it’s only 60Hz, and nothing transmits on any frequency even remotely close to that.

And, FWIW, there has NEVER been a conclusive link to power lines and any health issues. There have been “suspicions” but there always will be…

#5

You mean proximity to power lines, at some minimum distance, right? I can think of a number of health issues with a conclusive link to power lines.

#6

More likely would be an internal fault in the cable with the center power conductor shorting or arcing to the outer shield. This would be detected quickly by automated equipment. The power system uses devices called reclosers that sense faults and disturbances as most faults are temporary - a hapless bird or squirrel in the wrong place, lines getting blown around in a storm, etc., and there’s no point in tripping a breaker and leaving it off if the problem is gone. The recloser will cut the power, count down a few seconds, re-connect and monitor conditions. If the fault is still there, it repeats the shut off, wait and reconnect sequence. Usually, these things will only do two or three reset cycles before leaving the power off.

#7

That’s correct, but usually a scheme that is used more for above ground distribution lines (2Kv to 25KV) and not so much for transmission lines. Transmission protection schemes might have reclosing but it would be based on something other than timing out. I would guess that with an underground line there isn’t much use for the relay logic to include a reclose since it wouldn’t be subject to the same kind of temporary actions as an overhead line like wind, lightning, ice, trees etc. The relay scheme would probably remove the line from service very quickly and leave it that way until somebody manually closed it.

#8

Is that a joke about touching the lines or are you saying you know of conclusive links between living/being near high tension lines and health issues. If it’s the latter, I don’t think you can just make a statement like that and not back it up. Do you have a cite?

I’ve always hear the same thing as Beowulff. Lots of suspicious, no proof. But I think we’re at the point that the people with the suspicions aren’t going to let them go no matter what proof (or lack thereof as the case may be) to the contrary they’re given.

#9

Touching the lines, or electrocution from being too close. Building code, and the power companies won’t allow houses within a certain distance of some overhead lines. But the health risk is always electrocution, or at least some pretty serious shocks.

#10

But since this thread is about electromagnetic radiation and not an actual electrical arc to a person, I’m not sure your point is relevant. Besides, I’m fairly sure 345K can’t jump 4 feet through the earth to zap someone standing on the ground anyways.

#11

I didn’t mean to hit submit, I walked away from my computer and apparently hit it before I was ready. That wasn’t meant to come off as snarky as it did. All I was trying to get across was that the OP is talking about an underground wire so electrocution really isn’t a concern and he’s really only concerned about EMF. My understanding is that there hasn’t been any real evidence that EMF from high tension power lines causes any health issues. I can understand why people might think it does. I mean, that ominous humming, how can you not think it’s doing something. I just wanted to make sure that when you said “I can think of a number of health issues with a conclusive link to power lines.” you were jokingly talking about touching them, since it was a bit confusing.

#12

But, the CDC review of studies does show there is a statistically significant increase in (cancer or whatever they were looking at). It was small and didn’t prove causation, but there is something there.

#13

I wouldn’t worry about any effects from EM radiation, but then I am not one to worry, especially given my hobby in electronics, where I regularly expose myself to some pretty strong EM fields, and at higher frequencies; e.g. a neon indicator bulb held in my hand can light up 6+ inches away from a flyback transformer (up to >25 kV and >100 kHz, many volts on an oscilloscope with the probe a good distance away), nevermind the strong fields from deflection coils and other (SMPS) transformers; when I was younger, my parents would complain about interference on their TV (before they had cable and I learned about EMI suppression) - on the other end of the house, yet I have thus far failed to see any health effects. Of course, at very high energy levels, like a microwave oven, you can literally be cooked (visible light, at several hundred terahertz, can do that too), but anything less than ultraviolet isn’t going to be able to cause harm otherwise (EM radiation != nuclear radiation, except for gamma rays).

#14

Not a problem.

#15

The only worry should be the traffic while they bury it. Nothing else.

#16

I think the dielectric strength (is that the right name?) of air is only 3KV/mm, meaning it could do about 4ft in the open. Through anything besides the air, you would have to be much closer. So (in case you had other ideas) if you ever see that line exposed after an earthquake, apacalypse, or godzilla attack STAY AWAY!

#17

No, that’s way wrong.
3KV/mm means that 345KV should only be able to jump around 4 inches or so (115mm).

Still- look but don’t touch!

#18

Not necessarily; I can make arcs 2 inches long with the voltage from a TV flyback transformer, which is 25-30 kV for a color TV; breakdown voltage is highly dependent on the surfaces (sharp points have a lower breakdown voltage, and corona is often observed even with no ground nearby, also depends on AC frequency if AC, with higher frequencies leaking more current through stray capacitance; think of Tesla coils). Incidentally, the same is also true of lightning; only the strongest positive lightning bolts have voltages in the gigavolt range (required to jump the several kilometers of an ordinary bolt, positive lightning is much longer though, being from the top of the cloud).

In any case, with the line underground, even slightly damp (or even what one would consider to be dry; there will always be some moisture, especially underground) soil is a VERY good conductor at 345 kV, especially once the heat melts the soil (even insulators like glass become very good conductors when melted); for example, 1 megohm of resistance at 345 kV will let 345 mA through, which will dissipate 119 kW, leading to very rapid heating and thermal runaway.

#19

are you striking the arc at 2 inches, or striking it closer and using the ionized air to pull it away and sustain a longer arc?

#20

Related Straight Dope: Is living under power lines harmful to your health?