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Theoretically optimal location of a distribution substation

Former Community Member over 4 years ago

Hello,
I have the following problem with the preliminary design stage of a residential area:

The software I use can calculate a theoretically optimal location of a distribution substation for low-voltage networks. This place is calculated as a "center of power demand" or "center of gravity" of electrical consumers.

If the substation locates in this optimal place, we can design 0.4kV distribution feeders with a minimum length and power losses in low-voltage feeders are minimal.

I understand it’s almost impossible to put it exactly there, and I consider some sites nearby. But the architect believes that this is unacceptable in terms of landscape design and wants to place the substation in a far corner.

Who should be the arbiter in this situation? DNO representative takes a neutral position. Local authorities are completely on architect side, they do not care that long power cables will heat the atmosphere for many years to come.

0 AJJewsbury over 4 years ago

I agree with OMS - 3x32A seems to be a pretty standard Teutonic setup (the Gallic tendencies seem to be moving towards 1x40A).

Cookers/hobs etc will be 2- or 3-phase - so draw relatively low currents per phase; larger single phase appliances (washing machines, tumble dryers etc) will typically be on their own individual circuits back to the DB, so relatively easy to balance and as a result the likes of a general kitchen socket circuit will be modestly loaded. Their electricians will be perfectly used to working within the constraints of their system.

- Andy.
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0 mapj1 over 4 years ago

A 3 phase instant or near instant water heater is a common sight in a German kitchen or bathroom,designed for 16A per phase, so all the cable is the same as the normal socket circuits.- internally not much different to your UK shower heaters with multiple elements, just more than one phase present. PSSC can then be quite a bit lower than we would have on a100A supply.

Compare this approach with the worries about 3 phases in the same room in another recent post ; -) Those of us who have worked abroad at some point are much less worried by low power 3 phase- like the bathroom sockets it seems to be a UK only fear.
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0 Former Community Member over 4 years ago

There's a page here that shows you just how little power our French chums have for domestic residences.

French Tariffs

In rural France, your average family are an order of magnitude more thrifty than our porridge eating neighbors up north - it's not unusual to have 4 bed or more properties on a 3 x 16A service - you just need to get organized as to what you do and when.

Regards

OMS
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0 Former Community Member over 4 years ago

Yes, with 3x32A main protection, you can supply a load with a total power demand of 21kW with a power factor of 0.95 for a long time.

With a 3-phase input, the loads of the house can be fairly evenly distributed between phases. Powerful consumers can be ordered in both 3-phase and 1-phase versions. Usually, the main protection is not fuse, but a 3-phase circuit breaker with a C-characteristic, which can keep overloads with asymmetries.

On the continent, 3-phase input is increasingly being used if the power consumption is more than 16 kW. I can also add that for a house with an area of 120-150m2, the main protection 3x25A is most often used.

But my main topic was regarding the optimal location of the substation. I wanted to understand how important this issue is and how much attention is paid to it in different countries. UK has its own electrical standards BS, which are widely used throughout the world and I am interested in the experience of electrical designers from UK. I would like to accumulate arguments (pros and cons) in my dispute with the architect. Thank you all for participating.
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0 Former Community Member over 4 years ago

Alex Juhanson:

But my main topic was regarding the optimal location of the substation. I wanted to understand how important this issue is and how much attention is paid to it in different countries.

I would like to accumulate arguments (pros and cons) in my dispute with the architect. Thank you all for participating.

Well optimum is always going to be a balance of competing factors - eg, value of the land taken, proximity to HV, length of LV, cost of cable, cost of trenching etc etc - we've probably covered most of them in this thread.

Obviously, these are all capital costs - the only counterpoint to the CAPEX, is the OPEX of owning those cables (ie I2R) - which is typically a DNO issue as the losses are with them not the consumer.

Given the load profile of a typical domestic house, the OPEX is very small compared to the CAPEX - it can be mitigated by cable size and route - but it won't ever be the dominant design factor - location, land value, access, trenching costs etc will all radically outweigh the OPEX figures.

Regards

OMS
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0 Former Community Member over 4 years ago

Thank you OMS. It was a great final answer.

Yes, you are absolutely right about the balance of various competing factors. I will only note that the search for balance is based on the experience of the designer only. Unfortunately there is no a tool for comparative economic analysis of projected distribution networks and substations.

One final note regarding I2R.

Since it is impossible to make an accurate forecast for 40 years ahead, I will try to give a very rough estimate of the power losses in distribution feeders of the projected residential area.

Calculations were made on following conditions:
The average monthly consumption of one house in this project is 300 Kwh.
Power losses in all 0.4kV distribution feeders is1%.
Electricity price is 0.20€ per Kwh.
Operation period is 40 years.

As a result, we got the power losses cost for the entire operation period equal to 8640€. If we take the price constant, then this is relatively small. We do not know anything about what consumption and the electricity price will be in 40 years, but I think that the price will only increase and I2R cost will be much more. In any case it confirms your point of view that CAPEX >> OPEX in such installations.
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Theoretically optimal location of a distribution substation

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