Transformer Adequate?

Charles Perry P.E.

When transformers are installed, the electrical company figures that not every customer will be running at there peak load at the same time, for a particular time period. So they put in a power rating that is suitable for this type of loading. Through meter reading reports, the electrical company can keep track of customer loading and can make plans for upgrade. But they probably won't do this until a customer complains about voltage problems due to another customer running his or her appliances. If only your voltage is having problems, then it is possible that you are on the end of a secondary main or have a small service wire. The company will probably make sure that there service wire is of the proper size. If that doesn't work, then they will start to consider an upgrade. That will probably be the last resort unfortunately.

Dan

Just something I was wondering about when when considering demand and diversity.

Do the power companies make a special allowance when it comes to climate? In this case, you might expect that the air conditioners connected to those six homes might run more or less continuously for a large part of the year.

Beachcomber

(200Ax240V)? How

secondary

doesn't

probably

The utilities' decisions will be based largely on empirical information... if certain types of loads have been seen to have certain demands and diversities then that's what they'll allow for (plus some margin). Allowances for climate-related considerations, etc. are all rolled up into that. The utilities here don't mind if their transformers go a little beyond rated load. In the winter they allow even higher overloading.

Something you can do that will help is to use as much natural gas as possible - clothes dryer; water heater, and range. Not only reduces your electrical load, but it will cost less for the energy. Aside from that you shouldn't have much load at all.

HR.

so if i was to consult you for an exorbitant fee you would recomend at least

This is something of an aside, unless the high tension lines themselves pass your property.

I was driving around Tasmania recently. There were long stretches of road in the country with just high voltage lines (~60kV maybe - not 132 I think judging by the insulators). These appeared to be the only supply for towns on the route. Great - no redundancy, and possibly a couple of hours to reach a fault by road from a main centre.

Occasionally it was clear that a low voltage line lead off to serve just a single property in the coutryside (only one phase). Attached to the power pole was a transformer about the size of a 10 litre bucket. It looked a bit silly really, having two large insulators stuck out of it where it attached to the high voltage line.

I've no idea how much these things cost, but could it really come to $US10,000?

BTW, I took note of which phase was being tapped, expecting to see a rotation between the phase chosen - but this wasn't the case. Presumably the current was so low relatively speaking that it didn't matter.

Sylvia

| 6 on a 75kVA is not that loaded. The average residence has a load of around | 3kW to 5kW. With diversity, the effective load is even less (when adding | multiple services together). Without knowing their planning standards I | can't say how many services they allow on each transformer. Unless voltage | sags (from HVAC equipment) become a problem, I can't imagine that they would | serve fewer than 8 or 10 homes (with 200A services) from a 75kVA | transformer. Now, if some of those homes are monsters with 600A services, | that changes things. | | Charles Perry P.E.

A home that can't do with 400A (even assume 320A continuous) and needs to go with 600A has some serious energy issues. Maybe they will be running

| I've no idea how much these things cost, but could it really come to | $US10,000?

They manfacture them in third world countries, now, so the cost is down to a few hundred dollars. Add the corporate profits and its back up to around US$6000.

| BTW, I took note of which phase was being tapped, expecting to see a | rotation between the phase chosen - but this wasn't the case. Presumably | the current was so low relatively speaking that it didn't matter.

New instalaltions are probably tapped into whichever phase has the general trend of a lesser load. In large enough numbers, selecting a phase at random (roll dice, don't pick from your head) is going to even out, anyway.

Stick to posting about subjects you understand. Most distribution service transformers in the US are manufactured in the US.

As for cost, the labor to install would likely be higher than the equipment costs. The original poster was talking about a padmounted installation. Those are very expensive since it would involve trenching, possibly conduit or concrete duct, a transformer pad, etc. Most padmounted transformers used in the US are made in the US also.

Try these links to educate yourself:

Also, I believe ABB still makes distribution transformers in the US. Sadly, it looks like GE has moved most of its smaller transformer business to Mexico and a jointly owned plant called GE-Prolec.

There are several other small transformer manufacturers still in operation in the US. I figured you could Google them if you like.

Charles Perry P.E.

You need to think a little more about how NEC recommends sizing things. Just because the NEC might require you to install a 400A or larger service, does not mean you will ever get anywhere close to that figure. Have you ever seen a 200A service running close to its rating? I haven't.

Charles Perry P.E.