Power re-distribution 7

[sto]

I have a house in Portugal with 3 phase el service rated 15.5 A /phase. This service can be increased up to 21 A/phase at a cost.
The house has a single phase air conditioner that draws 14 A at 220 V (25,000 BTU). This single phase load is a problem that can be minimized by redistributes the 1 phase load across the 3 phases with an efficient power conversion (or replacing the air conditioner).
Any suggestion??

 

[buzzp]

Can you redistribute your other loads instead of messing with the largest load (air conditioner)? This would sure be much simpler.
I am sure people have tried using a 3 phase source for single phase equipment (by this I mean hooking up to all three phases with the air conditioner) this would be a bad idea since each is out of phase with the other by 120 degrees. Can not make any recommendations to accomoate your question.
You would have to find some piece equipment to accomplish this task (or design your own) and I have not heard of any.

 

[wareagle]

Sto
A service rated at 15 amps is small wire. What size is it?
I would think you would want to up grade to something larger than 21 amps. Why go to all that trouble to upgrade only 5 amps? Do you use al conductor for services?

 

[sto]

buzzp and wareagle,
In my case it is first delivery (of more single phase current) and then cost of the service.
The utility wires are underground; for a non electric home, a service of nearly 10 KW is not a trivial amount of power.
You should also know that: up front, directly following the meter there is a “circuit line unbalance detector” that disconnects the service when the line-to-lines unbalance is 15 A. At startup the air conditioner has a current surge of 3 to 6 times 15 A. That is making any practical loading of the other 2 phases ineffective.
Excuse the naiveté, but I am looking for a way of solving this problem by using a transformer(s) in a way that I do not yet know how.

 

[dede61]

sto,

Have you checked the wiring inside the unit, it is well possible that is is basicaly a 3ph motor. Some simple rewiring could be sufficient.

regards

 

[RalphChristie]

Sto

If you don't want to grade the power up to a larger value you'll have to replace the single phase unit with a three phase unit. Or you can try to replace the single phase motor with a three phase motor, like dede61 suggested. I have to agree with buzzp, have never heard of something where you can balance a single phase motor between a three phase supply.

Regards
Ralph

 

[buzzp]

So the 'unbalance protector' is tripping out? I would change the trip time if this is the case. Your motor for your AC should only pull this current for a few seconds at best. Also, usually unbalance protection is given in 'percent unbalance' and not based on just a current difference (15A you indicated). Is this really how the trip point is determined of this 'unbalance protector"?
If the real concern is with this thing tripping I would definately increase the trip time (assuming it is set lower than the start time of the motor).
If the above is not the problem then your most cost effective solution will likely be a three phase AC system. It will save money in the long run by way of efficiency.
Otherwise, more details about the issues may give rise to other solutions.

 

[mc5w]

Any residential service here in the U.S.A. that is less than 200 amps 120/240 volts single phase is considered obsolete. This size provides 48 KVA for noncontinuous loads and 38.4 KVA for continuous loads if all of the wire strands are conducting. In some places local wiring rules make this the minimum capacity.

We also have quite a few places here that have outlawed 15 amp branch circuits and the minimum branch circuit size is 20 amps.

I have a hard time understanding why you have such a puny electrical service. If your system voltage is 220Y380 volts you should upgrade to at least 100 amps using 125 amp wire derated to 100 amps for 4 current carrying conductors in the same cable or conduit.

 

[mersin33]

electric power consumption per person (house, etc) in North America is not a typical value for the rest of the world at all.

Why would a house need 100A at 380V (approx 65-kVA)? ))

 

[mc5w]

I sometimes install 400 amp electrical service for a house. Depends on the floor area and on how much air conditioning, electric stoves, and so forth that they are running.

100 amps at 220Y380 volts would support 52.8 KVA of continuous duty load according to U.S. rules provided that ALL of the wire strands are conducting. Since most electricians have onoy 1/2 the wire strands conducting because they are too lazy or cheap to clean all of the wires and goop them with electrical joint compound as recommended by the Consumer Product Safety Commission, you would only be able to pull about 35 KVA from a practical 100 amp 220Y380 volt electrical service.

One of the power quality problems that I do encounter is that the residential distribution was built when a toaster was the heaviest load in a house. Throw in a few air conditioners and you have a 2 ounce bird airlifting a 1 pound coconut. I one time viewed an apartment building that only had 800 watts of continuous duty capacity per tenant. Your 15.5 amp electrical service is incredibly obsolete. If you have the bucks to pay for a room air conditioner the power should allow you to get at least 60 amps 220Y380 volts.

Here in Ohio we have a law that says that the power company has to provide adequate and reliable capacity. Does Portugal have similar law?

Since natural gas prices have gone up I suspect that add-on heat pumps that only use the natural gas during occasional cold spells and utility peak periods will become popular. In Northern Ohio and add-on heat pump would only need to burn natural gas during 1/4 or so of the heating season.

 

[AusLee]

Hi,

You can feed your 3 phases to a "static phase converter" that will give you your single phase output drawn equally from the 3 phases. $$$

If you insist on the transformer, you have to make sure that the stepped down phase to phase voltage is equal to what you need for the Compressor. Then you will use one of the two wires you just used with the third output to feed the fan. This is the least way you can disturb the input. $$$+!

If you have trouble with the tripping, replace the incoming breaker with a disconnect switch and unplug the annoying phase balance relay. !!!

My opinion is to throw money at the problem. Some people enjoy a new car, i enjoy the cost of a 100% simultaneity factor on my installations ~

 

[sto]

Thank to you all for the suggestions.
Here in the States I have a 200A service but use a small part of the service. Even here, if you know someone living off the grid, you will be surprised by how little electricity is sufficient to get by. European appliances typically use less then the American one.
Why did I come up with this problem? Because I know of a number of people with the same electrical load problem and felt that if I could come up with a solution, this would be also valid for others.
Next Monday I will be over there, able to read the complete label/description of the air conditioner/heater and Email this information to the Fujitsu-General man in California. This man is the only individual across the continents that has responded to my quest and tells me first that the motor and compressor are one assembly and typically a Panasonic unit. Plan one is to swap this unit for a 3 phase one and of course do the necessary electrical conversion at my risk.
If a suitable motor-compressor unit is not available, plan two will be implemented; get a transformer (how??) or even betters an autotransformer, with the proper turn ratio, and connect it across 2 of the 3 phases to supply the 4 HP unit. The remaining airconditioner’s loads, mostly fans, will be connected to the third phase. The electrical conversion is again at my risk.
Some of you have also suggested swapping the unit for a 3 phase one. Originally I tried the approach and it did not work. Plan tree is (not to swap but) to junk the single phase unit. I guess this is throwing money at the problem!
Thank you again for you advices and comments.
PS: If some of you has a better idea or solution I am still receptive to it.

 

[AusLee]

Hi,

If there are many who have the same problem as you and you are all i nthe same building, i think a 3 phase in - 1 phase out UPS with very little battery capacity can be quoted to compare the costs.

I know how little of the 100s of Amps normal dwellings go by, but the requirements of the permanently updated Codes have Safety, economic, legislative and other supporting reasons.

 

[Kim69]

Hi,
sto
probably is less expensive to change the air conditioning system (3-phase type) rather than performing the suggested modifications.
Besides, I suggest you don't modify the existing air conditioner: any modification declines warranty, CE certification, and YOU could be responsible for any accidents.
You already evaluated the possibility to have an additional contract (monophase 3 kW) with the Portoguese energy supplier.