jeroencr avatar image
jeroencr asked

Long distance private grid neutral bonding

Hello all,

I own a large farm in the jungle of Costa Rica, that we are converting to a permaculture farm with a B&B. We have some questions about our installation, that we would like to get resolved before investing in the equipment.

The site is a couple hectares big, and will have 3 buildings on it, about 200 meters apart.

The cable we have to run is 450m long, 180mm2 thick. So we would prefer not to run an additional neutral wire, unless necessary, because of the cost.

The public grid is 200 meters from the first building and supplies 120/240V or 240/480V upon request. We experience frequent short (seconds) power outages, about 10 per day, and bigger power outages (couple hours to a day) from time to time.

We are in the tropical rainforest, close to the ocean, and our lightning storms are 'spectacular'. We've been hit directly twice in the past 4 years.

The three buildings are 2 houses, and a B&B. We don't mind losing power in the houses, but would like to keep the lights and essential equipment running in the B&B during power outages.

Attached is an electrical diagram with the installation I would like to install. It uses a single 240V phase coming from the meter, and creates a neutral bond in each house.

The power grid supplies, 2x240V, of which we will only run 1 line. We have a 200A service breaker at the meter.

We use 3x victron 100A auto transformers, one in each building. And a 48/5000/70 multiplus with 48V 620Ah battery in the B&B, which is the furthest away.

The houses don't need a lot of power and will rarely draw more than 30A, only the B&B has various pumps for the pool, refrigerators and heat pump hot water/AC, that can draw large amounts of power, and can draw up to 100A.

electrisch schema hoofdvoeding2.pdf

My questions are as follows:

- Can we make this installation work, safely, bonding the neutral in each building, basically treating our line the way the utility company treats its lines? OR do we need to spend the extra money to get another 180mm2 cable running the entire length?

- Which Neutral/Ground relays need to be on/off, both the autotransformers and the multi have various options here. How do we need to configure these in this situation?

- Will the GFCI work correctly? We would like to use a main differential behind the auto transformers on all 3 lines (2x120V 1xN) in each breaker panel, securing the entire panel.

- Will power assist of the multi help us reduce voltage drop in the B&B?

- I am confused as to how many amps the 'AC out 2' of the multi will provide? Is this the transfer switch (100A) or auxiliary power switch (50A)? Most equipment will be on the AC out 2, only lights and essential equipment will be on 'AC out 1' using the battery. Can 1 multi give us 100A when the grid is on, so we can pass all power through it for sake of the protection it provides?

- Do we need additional surge protection on top of what is drawn in the schematic?

- Will the auto transformers reduce efficiency of the grid? Or does the 240V pass straight through without loss? I understand we will get some losses on 120V as it is transformed.

- We will invest in solar later, connecting to the battery side at the B&B.

Thanks for helping us understand this.

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1 Answer
ben avatar image
ben answered ·

Your questions are related to a complete system design, which is not something this community forum is set up to support very well. It also works much better if you split your questions up and post one Question per question.

That said, I think SWER at low voltage, like you're proposing, probably won't work very well. The ground impedance is likely to limit your power transmission enough that it will be impractical.

If you still want to ask some of the other specific questions regarding Victron gear, feel free to break them out. (Also, I don't believe your circuit as drawn will work.)

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