Why do street lights flicker in snowy weather?

wrote:


The plonk went to:

This is an attack ad hominem. I should check the definitions? Nobody forces me to read plain insults.
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Tzortzakakis Dimitrios
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No it's not. You don't appear to understand the term "ad hominem".

Yes. If you're going to pontificate about something which can be measured objectively then you would do well to check your sources before you start to talk about the subject. Otherwise you could end up looking like someone who doesn't know what he's talking about. You were being given good advice which you respond to like a child throwing a rattle out of a pram.

No one posted an insult, plain or flowery. No one can force you to read anything. You chose to read the post, you chose to flounce.
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wrote:

*plonk*
Do not reply to this generic message, it was automatically generated; you have been kill-filed, either for being boringly stupid, repetitive, unfunny, ineducable, repeatedly posting politics, religion or off-topic subjects to a sci. newsgroup, attempting cheapskate free advertising for profit, because you are a troll, because you responded to George Hammond the complete fruit cake, simply insane or any combination or permutation of the aforementioned reasons; any reply will go unread.
Boringly stupid is the most common cause of kill-filing, but because this message is generic the other reasons have been included. You are left to decide which is most applicable to you.
There is no appeal, I have despotic power over whom I will electronically admit into my home and you do not qualify as a reasonable person I would wish to converse with or even poke fun at. Some weirdoes are not kill- filed, they amuse me and I retain them for their entertainment value as I would any chicken with two heads, either one of which enables the dumb bird to scratch dirt, step back, look down, step forward to the same spot and repeat the process eternally.
This should not trouble you, many of those plonked find it a blessing that they are not required to think and can persist in their bigotry or crackpot theories without challenge.
You have the right to free speech, I have the right not to listen. The kill-file will be cleared annually with spring cleaning or whenever I purchase a new computer or hard drive. Update: the last clearance was 25/12/09. Some individuals have been restored to the list.
I'm fully aware that you may be so stupid as to reply, but the purpose of this message is to encourage others to kill-file fuckwits like you.
I hope you find this explanation is satisfactory but even if you don't, damnly my frank, I don't give a dear. Have a nice day and fuck off.
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wrote:

--
And how do you define demand and capacity? Please tell me.
I know the usual definitions of these as applied to a power system and these
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Tzortzakakis Dimitrios wrote:

Sigh... too bad.
Don's quite right on the matter. 'Capacity' is not the current production, but the current maximum possible by on-line equipment. So it is always kept greater than demand. 'Production' is matched to demand by a variety of techniques. Most notably, manual operation of base load settings and governors of regulating units.
'Spinning reserve' is kept on line to respond to sudden losses in capacity by a unit trip. Most system operators are required to maintain enough spinning reserve available for the tripping/loss of the largest generating unit. So if the system has a very large unit on line (say, 1000 MW), they must have at least that much spinning reserve. So you could say the system has a 'capacity' that is kept 1000 MW higher than demand.
daestrom
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Generating capacity, maybe? I think it's installed power. I might be wrong, of course (since many people seem to forget) I am greek and have gotten my degree in Greece. My English is acceptable, but only God is always right.OTOH, we mere mortals...

As long as base units are synchronised, their most efficient use is to operate 24/7 at full load. When they need to reduce output at night, they might eg reduce coal supply

Here, in Crete, we have fast units (gas turbines) that synchronise in 11-12 mins. Even the (small) steam units, 3-4 hours and the 2-stroke diesels 1/2 an hour. I think hydro can synchronise in quite fast, too.
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Tzortzakakis Dimitrios
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Tzortzakakis Dimitrios wrote:

I thought this might be the root of the issue. You are normally quite knowledgeable about such matters. I wondered why you went for 'plonk' so quickly on Don's post.

Although it might be the most economic operating point for a single plant, demand of course does not change in such increments. So some units operate as 'regulating units' and must 'throttle' their output to match demand.
As Don pointed out, in a traditional system a technique called 'economic dispatch' is used to decide which plants to control in this way. Typically this works out to those with the highest fuel costs. Plants with the lowest marginal cost are kept on line as long as possible as demand drops, and those with higher marginal costs are the first to cut back or be taken off completely.
Of course the choice to leave a plant on line at very low power or shut it down completely is another issue. Cost / time to re-start, expected schedule for re-start and fixed operating costs to name a considerations.
In an unregulated system, the choice is made simply on the bid price of each generator (not counting long-term purchase agreements).

Yes, we have 'peaking plants' that can be remotely started and auto-synch and load in a matter of minutes (gas turbine or diesel). And some plants schedule up/down based on predictions of demand.
But if you've lost a large plant's output due to a trip, even 10 minutes is too slow. Every moment that demand exceeds actual production means frequency is dropping. So the combination of the on-line spinning reserve units and the excess capacity in regulating units (sometimes counted in the 'spinning reserve' summary) has to respond within seconds.
Here in the US the FERC (Federal Energy Regulatory Commission), along with NERC, has specific guidelines / requirements to maintain a certain level of reliability in the transmission system. This
daestrom
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------------------ That is rarely the most efficient situation. In Crete, it may be the best approach because you may have some large fossil units and, apparently some hydro and the rest is high fuel cost gas turbines and diesels so that it is sensible. Since the 1930's the process of economic dispatch at any load is to load all generators on line (where possible) to the point of equal incremental cost per Kw modified for losses. This was first done intuitively by operators and later proved to be the optimum loading distribution. A further and more complex addition is to optimize unit commitment considering the costs of shutdown and restart of units.

------------- That's right but if you lose a major generation, do you simply drop loads and wait for more generation to come on line or do you have enough reserve capacity in on-line units to pick up the load if, for example, the largest unit on the system fails?
I would suggest that capacity is not installed power but the available power that can be generated by the units which are on-line. If you bring up and synchronize a100MW machine, you have then increased on-line capacity by 100MW.
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Tzortzakakis Dimitrios wrote:

Shit. I knew I wrote that badly. I'm talking about physical capacity.
/BAH
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Eddie wrote:

Cold temperature raises the strike voltage of discharge lamps. HID lamps have small arc tubes which warm up quickly and are less prone to this, but low pressure sodium lamps common in Europe (the saturated orange ones that are pink when they first come on) have long discharge tubes with a lot of surface area and are electrically more similar to fluorescent lamps may have more trouble in cold weather. If the strike voltage is higher than the peak voltage the ballast can deliver, the arc will extinguish. If the voltage is just barely sufficient, the lamp can flicker.
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This explanation confirms what I see with such lamps in cold weather. The older the lamp, the higher the strike voltage and so the more likely it is to flicker. Eventually, the energy from the flickering arc should warm the lamp enough to sustain it without flickering (unless the lamp is at end-of-life) so it would be interesting to hear from anyone who has watched a flickering lamp for a while to see if that indeed does happen.
Someone mentioned that the cause of the flicker might be due to the luminaire's photocell getting mixed signals due to reflection from the snow. Photocells usually have a delay circuit built in; otherwise, they would react to lightning flashes or headlight beams sweeping by.
TKM
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With the SOX I've seen doing this, the flicker is happening when fully run-up. I haven't watched one of these during run-up, so I don't know if it happens during run-up. Temperature wasn't low when this happened, and I suspect that's not relevant.
I don't have a sample dead one with this failure mode (which isn't common), so I can't inspect the lamp to see what visible failure indication there might be. As a pure guess, I might speculate that the emission material is sputted off the electrodes, and it can't sustain an arc in thermionic emission mode. The 35W SOX has an ignitor/starter which is probably repeatedly trying to start it. The larger ones use a leakage reactance transformer to provide both the starting voltage and current limiting, because the arc voltage is too high for a simple series ballast on 240V, and so don't need an ignitor/starter. I don't think I've seen the larger ones flashing; when the emission coating wears out, they seem to fail to light up at all (or with only a very dim glow around the electrodes which you can't see from the ground).
IME more common failure mode of SOX is the arc tube develops a leak and the sodium is ejected into the outer vacuum tube, where it often forms an opaque mirror coating on the inside of the bulb facing the ejection point, so the light no longer escapes through part of the bulb (can block out most of it eventually). The arc tube seems to be able to lose a lot of sodium in this way, yet still work, but eventually it turns into a dim red neon light which never runs-up (nicknamed a "red burner"), as there's no longer enough sodium left in the arc tube, just the neon starting gas.
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Andrew Gabriel
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Another characteristic of SOX is that the lamp voltage (and power consumption) rise rather significantly over the life of the lamp. This causes the same issue, eventually the voltage is higher than the ballast can supply and the arc will become unstable and flicker. These things usually fail due to either sodium depletion or the electrode seals fail from the corrosive action of the heated sodium, but an older lamp coupled with colder weather, especially if the ballast is a choke rather than a leak autotransformer, they can do this instead. HPS lamps will not restrike hot, so when they reach end of life they normally will cycle, but SOX will usually restrike even hot, so they can flicker.
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wrote:

What most often happens is that the lamp shuts off completely, and then restarts, which takes it just as long to pump up as before because the run temp is far higher than the shut off idle temp, even if after only a couple minutes.
I used to make a joke and said that I shut them off 'with my aura' all the time because we often saw them shutting off as we approached while out getting a buzz, back in 'the day'.
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MadManMoon wrote:

Yeah that's what I was saying with HPS (metal halide and mercury behave similarly). The higher pressure in a hot arc tube raises the strike voltage beyond what is available from the ballast. It has to cool until the pressure reduces to a point that the arc will strike.
SOX lamps are much lower pressure to begin with and will usually restrike hot.
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---------------- I have seen many such lamps flicker but have never associated this with temperature. I have not seen any more excessive flickering in cold conditions than in warm conditions By cold conditions, I mean central Alberta, Canada, -30 to -40C is not all that uncommon and windchill down to -50C equivalent. However, there could be differences in design that affect this. As an example we don't run exterior water or sewer pipes:)
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Many photocells, particularly older ones, are thermal. The CdS cell controls current flowing through a piece of resistance wire wound around a bimetal strip. When sufficient light falls on the cell, the strip is heated, it bends and opens the contacts. This inherently creates a delay. Electronic photocells are designed with hysteresis for the same reason, normally the delay is around a minute.
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| In the UK we currently have cold winds and snow. | | A radio phone-in got a lot of people talking about flickering street | lights. | | Is there a real connection between bad weather and flickering street | lights. If so then how does it work?

http://www.youtube.com/watch?v=eYUmdqQ94Ao

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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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What kind of lammps do you have, carbon arc, sodium vapor, mercury vapor, incandescent, LEDs?
It makes a difference.
Vapor lamps are sensitive to the cold, as they require a narrow range of pressure internally to function. Cold reduces the presssure, making operation less reliable.
Cold can also shorten wires. If you have a break internally in an insulated wire, cold could shrink the metal, weakening the connection at the break and raising resistance, which heats the wire which expands again, which drops the resistance, which lets the wire cool down again, ad nauseum. That is the mechanism for flashers in Christmas lights and automotive turn signals.
Tom Davidson Richmond, VA
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wrote:

What kind of lammps do you have, carbon arc, sodium vapor, mercury vapor, incandescent, LEDs?
It makes a difference.
Vapor lamps are sensitive to the cold, as they require a narrow range of pressure internally to function. Cold reduces the presssure, making operation less reliable.
Cold can also shorten wires. If you have a break internally in an insulated wire, cold could shrink the metal, weakening the connection at the break and raising resistance, which heats the wire which expands again, which drops the resistance, which lets the wire cool down again, ad nauseum. That is the mechanism for flashers in Christmas lights and automotive turn signals.
Tom Davidson Richmond, VA
From a practical standpoint, these days the only lamps that are sensitive to cold temperatures down to ambient temperatures of about 0 F. (-18 C) are fluorescent lamps. Even so, special fluorescent lamps are used routinely at -20F (-29 C) in commercial freezers, outdoor signs and exterior building lighting. High pressure sodium, high pressure mercury, metal halide, LED, cold-cathode ("neon") and, of course, incandescent all work just fine. Low pressure sodium lamps have a "thermos bottle" construction so they may just take a little longer to warm up. Discharge lamps do require somewhat higher voltages to initiate the arc at low temperatures, so in applications where cold temperatures are expected, so-called "minus 20" ballasts are specified.
The only discharge lamps that I've ever seen flicker in cold temperatures are CFLs and unprotected or reduced-wattage ("watt miser") fluorescent types which have been mis-applied. Rarely, a high pressure mercury lamp will flicker due to a faulty arc tube and there's an odd type of high pressure sodium lamp designed to work on mercury ballasts that sometimes flickers near end-of-life. I've heard that high pressure sodium lamps operated on old series (constant-current) streetlighting systems will flicker; but, if so, all of the lamps on the circuit will flicker, not just one. I've never seen that phenomenon, however.
Terry McGowan
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