Author Topic: NEMA head area light gets creamed by falling transformer  (Read 10813 times)
HPS Lover
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Re: NEMA head area light gets creamed by falling transformer « Reply #15 on: November 03, 2011, 08:15:10 PM » Author: HPS Lover
Whats odd is that all of the arcing happens on the low voltage 120 volt lines not the high voltage one, and the NEMA head looks OK it just needs a new optical assembly and it will be good as new  ;)
I don't think it would be fixable, because it looks like it fell into someone's pool! :'( :'( :'( :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv:
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paintballer22
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Re: NEMA head area light gets creamed by falling transformer « Reply #16 on: November 03, 2011, 09:48:35 PM » Author: paintballer22
The nema head is still up on the pole the arm bent over only the refractor and parts of the bulb fell to the ground.
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Ash
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Re: NEMA head area light gets creamed by falling transformer « Reply #17 on: November 04, 2011, 04:22:45 AM » Author: Ash
I don't think it would be fixable, because it looks like it fell into someone's pool! :'( :'( :'( :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv: :mv:

I managed to fall into a pool with a powered up (open apps on the screen and everything) laptop in my hands. The laptop drowned and screen wend black. After a quick dive, full disassembly, dry up of all parts and assembl it worked no problem - even the battery and hard drive

And i have some light fixtures that i found submerged in water (magnetic fluorescents) and they came out ok after drying up
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don93s
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Re: NEMA head area light gets creamed by falling transformer « Reply #18 on: December 27, 2011, 05:46:42 PM » Author: don93s
@Ash, I once found the rusted remnants of an old F40 fixture all smashed in the bottom of a stream. It looked like it had been there for many years. I got the ballasts out....they were very rusted...and took them home to let them dry under heat for a few days. In the end, one ballast was shorted but the other worked fine after that!
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dor123
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Re: NEMA head area light gets creamed by falling transformer « Reply #19 on: April 01, 2012, 07:03:23 AM » Author: dor123
What is strange, i never heard about any similar arcing/fires here, never seen any such arcing video from other countries then US...

But wiring damage does happen, mainly in the winter, while power microcuts (~0.5s outages) during storms are common, so i assume HV wires do touch each other and/or break in heavy weather as well, but the protections work well to shut these arcs down, so we have no such shows.

There is no such protection on these HV lines in US or what cause the arcing to continue for so long and even cause fires?
Ash said me that with the US 120V mains, the current that flows in the US electricity network is much higher than in 220-240V countries. This allows the arcing to last longer than usual.
Ash also said me, that the electricity wiring in the US, is done by wirenuts instead of screw terminals as the rest of the world (The last wirenuts disappeared from Israel in the 80' and are now considered obsolete and extinct wiring here).
Ash also said me a thing about the US ballasts vs European ballasts: While the european ballast are very simple chokes, without any PFC capacitors, Most US ballasts incorporates the PFC capacitors in them in a single unit. Thats why there are so many HPF magnetic ballasts in the US compared to the rest of the world (The only known HPF magnetic ballast we have in Israel, are the rapidstarts of Eltam and Shaingout for one F96T12 HO 110W, which consist of an open tray with a simple LPF rapidstart ballast, a replaceable PFC capacitor and a heating transformer starter (The second "ballast" in the tray).
« Last Edit: April 01, 2012, 07:05:00 AM by dor123 » Logged

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Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

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I lives in Israel, which is a 220-240V, 50hz country.

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Re: NEMA head area light gets creamed by falling transformer « Reply #20 on: April 01, 2012, 03:50:35 PM » Author: Ash
In residential circuits, US use 120V/240V while we use 240V/415V. For typical 120V (US) or 240V (here) loads, for the same power of load (since that is what have to be the same here and there), 1 phase appliances in the US take 2x the current they take here

Here in Israel we have 24KV (substations output in the north), 36KV (substations output in the south), 160KV (older main lines from power plants) and 400KV (newer main lines). In the US a common voltage for substation output is 11KV

This calls for 2x higher ampacity of the circuits, thicker conductors,.... So perhaps higher short circuit currents, if so then more exciing fireworks respectively

But those are not the actual problems. If the system is wrking well and is not failing. fireworks simply are not going to happen



So lets see where the more significant differences are :

Here, the final transformers on the line are 3 phase transformers - as far as i know D on the high voltage to Y on the low voltage. So, other than open neutral on the low voltage which causes moderate excitement (a lot of damage, but no big outdoor fireworks), there is NO condition where an opn in a wire can cause a show

In the US, the final transformers are 1 phase autotransformers - for 3 phase there are 3 of them. Now if here an open in the earth wire happens, the result is that 11KV through an inductive "ballast" (the primary of the transformer, add or take the secondary which is very small so unimportant) is supplied into the 120/240V output. Now we have a show, And the "ballast" limit the current so overcurrent protections in the substation dont respond

Besides, there may be differences in the protections in the substations. Maybe they are not made to immediately disconnect shorts. Maybe the current in some "fireworks" is too low to activate them

Once again protections - the phases to the high voltage side of the final transformer are fused (right above the transformer). If the rating of the fuse is too high (makes sense, as the working current is high), it will not fuse fast enough to prevent transformer explosion (pressure build up from arcing inside)



The 110W HO rapid start from Eltam is low power factor, but is capacitive (PF = 0.5C) - The capacitor is in series with the mains input, the rest of the ballast is inductor and heating transformer

The 110W HO from Shingot is high power factor. The inductor and heaing transformer are not just wired together - the capacitor is in series with 1 of them so theyballance each other power factor
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Medved
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Re: NEMA head area light gets creamed by falling transformer « Reply #21 on: April 06, 2012, 01:18:14 AM » Author: Medved
I think there is one other aspect: Big part of the electrical installation was in Europe destroyed during both WW1 and WW2, in Asia nearly didn't exist at all. So all the installation here is build, when already a lot was known about the transmission problems, so they were designed to already tackle them, so they do not make as big issues.

But in the US, many equipment still in use is dated far back to the pre-WW2 era, so way worse protected.
Other aspect is, than the HV lines are by far not as wide spread between houses, so it is handled with way better care (inspections,...). The same, in Europe are only few HV transformers (each serving tens of houses, compare to more than 1 barrel per house in the US), so again they allow (mainly financially) better, more expensive, protection equipment to be installed. In US this is not possible, as the 120V is too low to be distributed for longer than few 10's m from the transformer, so the transformers have to be nearly everywhere. So they are within reach of many "RepairEverythingYourselves", who instead of replacing the proper primary fuse put there some wire inside.

And more units in use mean higher chance you find some to fail with a show.
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Re: NEMA head area light gets creamed by falling transformer « Reply #22 on: May 18, 2015, 12:24:55 AM » Author: Solanaceae
Here in the Midwest, we always get severe storms in the summer. There was once a transformer that got shorted out by a tree and it punched out a streetlight with thousands of volts. The 120 volt output wire got crossed with a several KV wire and POP! We could hear the bang from the back of the neighborhood. The crappy HPS fixture has since been replaced, but I feel it's days are numbered.
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