Please calculate my electrical transformer size?

Question

i am in Cost Rica and need to buy my own transformer. I dont need lectures on codes etc..Please just a close ballpark.

Thanks

Answer 1

Our codes require 200A service for separate homes, condos may be allowed 100A service.

Assuming the condo owners will be on separate meters and paying their own electricity, the power company owns and sizes the transformer. In some jurisdictions, they may allow consulting engineers to design the distribution system; in ours the engineering department of the power company (and phone company) handles that.

Their engineering department would make an estimate from a copy of the project plan. They use standard transformers and the  engineer would determine how many transformers, and he would determine the cost based on company policies as to how much of the initial cost the developer would be required to pay.

Much of the cost is site specific; they actually cost based on the number of poles and feet of wire to be laid.

It would be worth a visit or call to the engineering department for general numbers for your project; obviously they can't do an in-depth quote without building permits, etc.

If you are talking a hotel or cabins on a single meter, different story. The actual calcs you ask would be 100A * 240V * 40 services = 960kW, however, I believe they generally use a derating factor because not everyone uses full power at the same time. I'd have to go with hiring a consulting engineer for advice on this. You actually have no choice, as getting a building permit will require stamped drawings.

BTW, when figuring utilities, don't forget water, sewage, phone, cable, natural gas. Locally, contractors pay over $2k per unit in fees for utilities, which does not even count the actual hookups.

Answer 2

Your electrical load is:

15pcs,  12,000 BTU AC , ---------1 ton/hr, 3hp compressor,   33.45Kw

45pcs,9,000 BTu AC,     --------3/4 ton/hr,1 Hp compressor,  33.57KW

20 stacked washer dryer,---------20, 1 kw                              20Kw

40 instant water heaters, -----------40,2 kw                         ,   80Kw

325, compact fluorescent lamps, 11 watts                        ,  3.575

40 refrigerators, 1/8HP              , 93.25 watts                    , 3.73Kw

total Kw Load =                                                               174.32Kw

KVa required at 100 % demand = 174.32/0.8 =                  217.9 KVA

KVA at 70% Demand factor =174.32/0.8(0.70) =               152.53KVA  

Answer 3

The transformer size should be determined according to the electrical code requirements that apply to the location. That should be done by an engineer that is licensed by the authority having jurisdiction at the location. If you just want an estimate, or if this is an academic exercise, you should state the location and/or identify the electrical code that applies.

Edit 1

In addition to the estimate for the AC units etc, you should figure 5 kva per unit (200 kva total) for all of the microwave ovens, small kitchen appliances, table lamps, floor lamps, televisions, vacuum cleaners, computers etc. that people will plug into wall outlets.

Are there gas cooking stoves or is cooking limited to microwave ovens?

Edit 2

The 12,000 BTU A/C units probably need to be 230 volts. In the USA, units are available that only require 1.3 KVA each. The 115 volt 9000 BTU units available in the USA require 1.1 KVA each. If the stacked laundry units have gas dryers, they probably need no more than 1 KVA each. With electric dryers they would probably need 230 volts and 30 amps for 6.9 KVA each. For the instant water heaters you would need 12 KVA each for units that could supply enough hot water for a low flow shower head. What about dish washers?