100Kva 3 Phase transformer

[Anthony5]

- Taken into account having a 100Kva 3 Phase transformer supplying a foreigner housing estate with 3 phase 15/45A meters and living up to the maximum power that meter can pull. how many houses would that transformer be able to supply of sufficient power.

- For a house 200 meter from the transformer, which size of NYY underground cable would be needed ?

Edited October 1, 2014 by Anthony5

[Crossy]

You need to talk to a supply contractor, the following should be considered an outline guide at best.

How big are the homes?

A 15/45 3-phase supply can provide about 30kVA, in reality most homes, even big ones get by on an average of less than 10kVA, the UK supply authorities size substations based upon 2kVA per home but there's no heating load included, we have to take account of aircon.

I would guesstimate that your 100kVA Tx will supply 10-15 reasonably sized 'farang' homes without issue.

A 15/45 3-phase on the end of 200m of copper would need 25mm² cable assuming it feeds the one home, if homes are daisy-chained you'll be needing bigger cable.

[Anthony5]

My question was more rethorical. I'm in the process of purchasing a plot of land..

At the location is high voltage available at about a 350 meter distance.

The owner however who sells me the land has a 100Kva 3 phase transformer installed for personal use. I assume that this transformer, however it is installed inside the property of the owner, is now property from the PEA.

At this time there is only 1 house connected to the transformer, although a really large property with many amenities.

The land I want to purchase is located behind the house of the owner and borders also at another public road. The seller owns another 3 plots in that location, and all are adjacent to each other, so a underground cable to connect all plots can be buried without going over other people's or public property.

Since my plot is the furthest and is in a straight line about 200 meters distance from the said transformer, I thought that would be the cheapest way to get power, but I don't know id the PEA will allow this.He intends to sell all plots to foreigners, and I consider that an average foreign house has a pool, at least 6 aircons and probably another 5 waterheaters of 6Kw,. Add to that a kitchen with electric appliances, washing machine, irrigation system and some waterpumps and you may have an idea about the powerusage.

[Anthony5]

Crossy, since you say that such a transformer can provide approx 30Kva, can I assume that if I would use only 1 phase of the transformer it can be compared to a 30Kva single phase transformer on which I can install a 30/100A single phase meter ?

I only think this way as it would save me quite some money in NYY cable costs, and probably also installation cost.

[Crossy]

100kVA is about 130A per phase, so you could happily hook a 30/100 to one phase without issue.

The Tx probably does now belong to PEA, despite it having been paid for by the property owner. Assuming it's not going to be taken over the limit by your additional load PEA should be happy to install a 30/100 meter for you, you'll need to speak to the local office.

PEA will determine where the meter goes and to a degree how the power gets to your plot, if you're burying cable watch out for ownership issues of the property it crosses.

[Anthony5]

100kVA is about 130A per phase, so you could happily hook a 30/100 to one phase without issue.

The Tx probably does now belong to PEA, despite it having been paid for by the property owner. Assuming it's not going to be taken over the limit by your additional load PEA should be happy to install a 30/100 meter for you, you'll need to speak to the local office.

PEA will determine where the meter goes and to a degree how the power gets to your plot, if you're burying cable watch out for ownership issues of the property it crosses.

Do I understand correct that with a 30/100A single phase meter it is supposed that you use 100A? So since each phase only supplies 130A, in this setup it would only be possible to hook up 3 maybe 4 more houses, while if they use 15/45A 3 phase meters they will have the same powersupply but it is possible to connect more houses?

[Crossy]

Do I understand correct that with a 30/100A single phase meter it is supposed that you use 100A? So since each phase only supplies 130A, in this setup it would only be possible to hook up 3 maybe 4 more houses, while if they use 15/45A 3 phase meters they will have the same powersupply but it is possible to connect more houses?

No, it is not automatically assumed you'll be using the supply to its maximum at all times, at least not for a domestic situation.

Diversity is applied by the supply authority to define the average load per home in the same way is it is used to determine your maximum demand when designing your home electrics.

It is highly unlikely that everyone in the village will be taking a shower and boiling the kettle at the same time, aircons don't draw power continuously either, so whilst the total connected loads may add up to more than the supply rating, the actual power drawn at any one time is less.

As an example, most domestic supplies in the UK are fused at 80 or 100A but when sizing the substation transformer the supply authority use 2kVA (about 10A) per home as the average load. Our home in Thailand draws less than 3 Amps during the day, rising to 5 (with peaks to 10 when the A/C runs) or so in the evening when the lights and PCs are on and 35A when the shower is running.

In Thailand I don't know what load factor PEA would use, but since aircon is a significant load for expat communities I would be budgeting on, say, 10kVA per home (the UK figures do not include space heating in the 2kVA). So the Tx will provide for 10-15 homes whether they are connected to single or 3-phase supplies.

Transformers are extremely robust as well, your 100kVA Tx will be quite capable of supplying a 100% or greater overload for many minutes without blinking.

[Anthony5]

Do I understand correct that with a 30/100A single phase meter it is supposed that you use 100A? So since each phase only supplies 130A, in this setup it would only be possible to hook up 3 maybe 4 more houses, while if they use 15/45A 3 phase meters they will have the same powersupply but it is possible to connect more houses?

No, it is not automatically assumed you'll be using the supply to its maximum at all times, at least not for a domestic situation.

Diversity is applied by the supply authority to define the average load per home in the same way is it is used to determine your maximum demand when designing your home electrics.

It is highly unlikely that everyone in the village will be taking a shower and boiling the kettle at the same time, aircons don't draw power continuously either, so whilst the total connected loads may add up to more than the supply rating, the actual power drawn at any one time is less.

As an example, most domestic supplies in the UK are fused at 80 or 100A but when sizing the substation transformer the supply authority use 2kVA (about 10A) per home as the average load. Our home in Thailand draws less than 3 Amps during the day, rising to 5 (with peaks to 10 when the A/C runs) or so in the evening when the lights and PCs are on and 35A when the shower is running.

In Thailand I don't know what load factor PEA would use, but since aircon is a significant load for expat communities I would be budgeting on, say, 10kVA per home (the UK figures do not include space heating in the 2kVA). So the Tx will provide for 10-15 homes whether they are connected to single or 3-phase supplies.

Transformers are extremely robust as well, your 100kVA Tx will be quite capable of supplying a 100% or greater overload for many minutes without blinking.

Thanks again, so which setup would you suggest, cost-wise and efficiency wise, taken in consideration the details I have provided.