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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Power Pole Transformer is too small
This is slightly off topic....
I live on a farm, and have a main disconnect switch on the meter pole, rated at 400A. That feeds 3 buildings (house, garage, and barn) each has 100A main breakers. It also feeds an old 60A fuse panel in a shed. (yea, that is still fuses but all it does in run a few lights, so I never changed it). This is mostly just my home, but I do a little "hobby farming". So my electrical needs are small. But this was once a large working farm with large power users, such as huge 240V motors that ran grain dryers on grain bins. Anyhow, the pole transformer has been there for ages, and I just noticed that it's rated at 15KVA. 15KVA is only 62.5 Amps at 240V. (Or 125A at 120V). Why would the power company install a transformer so under rated? -OR- Do they rate those transformers in a different manner? Like I said, it works for my needs, but in winter, I run several livestock tank heaters and I tell when they kick on by a very slight momentary (slight) dimming of my lights. (They are rated at either 500W or 1000W, but there are 9 of them). From what I am seeing, those transformers are all under rated. A friends house has 200A service and his transformer is only 8KVA. |
#2
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Power Pole Transformer is too small
What is coming into that transformer is typically 2,300V, and the rating is on the primary side. Meaning that if it is converting from 2,300V to 240V, for round figures and with losses thrown in, you are getting about 8 x the amps at the low end.
If watts is watts, again to be crude, 1 A @ 2,300 V = 10 A @ 230V v, each giving 2,300 watts. Now as there are two legs in the single-phase service, *EACH ONE* carries the nameplate rating. If that service is 3-phase, then you are getting even more. Not to worry, those transformers are fused always on the primary, side, often on the secondary side. You may not see the secondary fuses, but you will see the primaries. No utility wants a fire on a pole, and certainly not at a remote location. One more thing - we have a 200A service at our main house and at our summer house - the service was sized for electric heat, which we have never installed. At our main house, in the hottest part of the summer, we have never pulled even 150 A, (with 2 x 200 A available). That is with AC, a hot-tub, two refrigerators, freezer and a car charger. Our summer house - not even 60 A. No AC, but a hot tub, refrigerator, and car charger. Does that help? Peter Wieck Melrose Park, PA |
#3
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Power Pole Transformer is too small
On Sun, 19 Feb 2017 13:48:55 -0800 (PST), "
wrote: If watts is watts, again to be crude, 1 A @ 2,300 V = 10 A @ 230V v, [Quoting removed because of line lengths] Yes, that makes sense. I was thinking the output was the amp rating. Since you mentioned the fuses, I am aware of them on the input. In fact years ago, I had one of them blow during a storm. A shower of sparks was seen. The power company replaced it and all was fine again. I do question how much they are fused to match the loads though. Some years ago, I was at a yearly community meal at the small town's reception center. I think every woman in town brought their electric roasters, which use about 12 amps each. I counted 26 roasters, plus a few large elec coffee pots. The building this was in, was fairly new, with adaquate wiring. However, it was a very hot day. There is a trailer park across the road, and I bet half them trailers had their air conditioners on. That trailer park is to the same pole transformer. So, add it up. 26 roasters = 312A. 3 coffee pots at around 10A each, plus lighting, and that meal was drawing around 350A. Who knows what the trailer park was drawing, and the meal center's AC may have been on too. Then the power went out. We had to eat cool food by candle light, until the town's fire dept came with some generators for lighting. The power company came, and they went up on the pole. The guy burned his hand on that transformer. That thing was so hot they could not do anything with it till it cooled. It was rated at 25 KVA. Hours later they finally were able to replace it, and put in a 37.5 KVA. That transformer fried before the fuse blew ! If that transformer had been touching the wooden post, I bet there would have been a fire, but it was on brackets that held it away from the wood. Even a few hours later, when they brought in a crane with a steel cable to lower it to the ground, the guys said it was too hot to touch and they could not load it on their truck. One of the guys suggested hosing it with cold water, but I left before they did that. |
#4
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Power Pole Transformer is too small
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#5
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Power Pole Transformer is too small
On Sunday, February 19, 2017 at 7:52:20 PM UTC-5, Rheilly Phoull wrote:
AFAIK the fuses are to protect the tranny not the load. Yep. The utility could care less about the load. Peter Wieck Melrose Park, PA |
#6
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Power Pole Transformer is too small
On Mon, 20 Feb 2017 03:59:35 -0800 (PST), "
wrote: On Sunday, February 19, 2017 at 7:52:20 PM UTC-5, Rheilly Phoull wrote: AFAIK the fuses are to protect the tranny not the load. Yep. The utility could care less about the load. Peter Wieck Melrose Park, PA The fuses did not protect the tranny in this case..... |
#7
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Power Pole Transformer is too small
On Monday, February 20, 2017 at 7:46:53 AM UTC-5, wrote:
The fuses did not protect the tranny in this case..... There is this about fuses. They are designed to handle the regular load + a certain level of brief heavy overloads, and then on a time/load lesser loads for a greater period. There are rules of thumb, but consider that most fuses that could handle a 3x momentary surge can also handle a 10% overload pretty much indefinitely - at least as defined by the typical single-element fuse, even an oil-filled device. At 2,300 V and 15KVA, that comes to 1.5A x 2,300 or about 3,500 watts... That transformer is gonna cook!! And that fuse is going to smile and suck it up. Now, get me started on equipment fuses. I Will spare you the rant. Peter Wieck Melrose Park, PA |
#8
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Power Pole Transformer is too small
pf
There are rules of thumb, but consider that most fuses that could handle a 3x momentary surge can also handle a 10% overload pretty much indefinitely - at least as defined by the typical single-element fuse, even an oil-filled device. At 2,300 V and 15KVA, that comes to 1.5A x 2,300 or about 3,500 watts... That transformer is gonna cook!! ** Makes not one tiny bit of sense. But the Wieck troll rarely does. ..... Phil |
#9
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Power Pole Transformer is too small
On Monday, February 20, 2017 at 11:18:33 PM UTC-5, Phil Allison wrote:
Fair warning: I have come to the conclusion that Mr. Allison suffers from exposure to some sort of heavy metal - probably cadmium and lead - given his erratic behavior and the fact that it clearly does not respond to medication. And, if one wishes to understand the potential of these exposures, consider the case of Vincent Van Gogh. Which would do nicely to explain the basic intelligence rendered toxic by toxins. Very sad. And, irreversible. Peter Wieck Melrose Park, PA |
#10
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Power Pole Transformer is too small
On Sunday, February 19, 2017 at 2:33:12 PM UTC-5, wrote:
This is slightly off topic.... I live on a farm, and have a main disconnect switch on the meter pole, rated at 400A. That feeds 3 buildings (house, garage, and barn) each has 100A main breakers. It also feeds an old 60A fuse panel in a shed. (yea, that is still fuses but all it does in run a few lights, so I never changed it). This is mostly just my home, but I do a little "hobby farming". So my electrical needs are small. But this was once a large working farm with large power users, such as huge 240V motors that ran grain dryers on grain bins. Anyhow, the pole transformer has been there for ages, and I just noticed that it's rated at 15KVA. 15KVA is only 62.5 Amps at 240V. (Or 125A at 120V). Why would the power company install a transformer so under rated? -OR- Do they rate those transformers in a different manner? Like I said, it works for my needs, but in winter, I run several livestock tank heaters and I tell when they kick on by a very slight momentary (slight) dimming of my lights. (They are rated at either 500W or 1000W, but there are 9 of them). From what I am seeing, those transformers are all under rated. A friends house has 200A service and his transformer is only 8KVA. last stop before our cell tower...a wrok in progress at that time ...we saw several lightning strikes and 2 transformer blowouts. I watched one go directly...the top blew off straight up to ? with a BANG followed by a rocket trail off flame n debris...very entertaining. |
#11
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Power Pole Transformer is too small
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#12
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Power Pole Transformer is too small
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#13
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Power Pole Transformer is too small
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#14
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Power Pole Transformer is too small
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#15
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Power Pole Transformer is too small
Little Timmee got hold of mommy's computer again.
If, of course, it even has a mommy. |
#16
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Power Pole Transformer is too small
" writes:
On Monday, February 20, 2017 at 7:46:53 AM UTC-5, wrote: The fuses did not protect the tranny in this case..... There is this about fuses. They are designed to handle the regular load + a certain level of brief heavy overloads, and then on a time/load lesser loads for a greater period. The pole pigs around here have 2 fuses. Mine has a 10A and a 15A in series. I asked why two. Turns out the 10A is the rated one and cheap; the 15A is fast, $$$, and solely protects against lightning hits on the primary. But I know the "rated" load of such a transformer is continuous, and they are routinely overloaded for a few hours. -- A host is a host from coast to & no one will talk to a host that's close.......................... Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
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