Transformer too small for your business? Your options

If the extra power you need comes in peaks of a few quarter-hours or a few hours a day, a business battery system behind your existing transformer can deliver those peaks and keep the transformer under its limit. You avoid the new request, the study and the wait at the grid operator. If the extra load is constant, or your site keeps growing, a bigger transformer (and more connection power) is the right road, and a battery can bridge the time until it is there. Your quarter-hour data decides which case you are in.

You recognise the situation. A new cooling line, a heat pump, a row of chargers for the vans or a bigger press is on the way. Your electrician looks at the cabin and says what everyone says: "The transformer is at its limit, you need a bigger one." Maybe a breaker already trips on the busiest mornings, or the transformer runs hot in summer.

What that sentence hides is the real cost. You do not only buy a transformer. You ask the grid operator for more connection power, pay for a study, wait for an offer, adapt the protection in the cabin, have it inspected, and stop the whole site for the swap. And in a growing number of places the grid operator cannot say yes at all. Meanwhile, the new machine sits in its crate. Often the peak that causes all this lasts only a few quarter-hours a day.

A battery and a cabin are not either-or. In Beveren-Melsele a site uses about 350,000 kWh a year. We installed 200 solar panels and a battery of 154 kWh with 45 kVA, so that as much solar power as possible is used on the spot. The design leaves the remaining peak current to a high-voltage cabin. Each part does what it is best at.

How do you know if your transformer is really too small?

Compare your highest quarter-hour peak with the power of the transformer, not the sum of your machines. The Walloon energy knowledge site Energie+ gives the check: the apparent power of the transformer (kVA) against the maximum quarter-hour power on your bill (kW), divided by the power factor (cos phi).

An example: a 400 kVA transformer at a power factor of 0.9 carries about 360 kW. If your highest quarter-hour on the bill is 300 kW, there is still about 60 kW of room. If the new line adds 100 kW at the same moment, you are over.

People often ask how many amps a transformer delivers. On the 400 V side the rule is: current = kVA x 1,000 / (1.73 x 400). That gives these round numbers:

Look at when the peaks happen, not only how high they are. Ten minutes of overlap between start-ups is a different problem from four hours of extra load every afternoon. Your grid operator records your load per quarter-hour, and that profile is the base for every decision below. Our article on peak demand in a business shows how such peaks build up.

Transformer, connection power or access power: which limit do you hit?

A customer with a cabin has three limits, and a bigger transformer only lifts the first.

• The transformer itself (kVA). It is your property: with a medium-voltage connection you supply and place the customer cabin yourself, and the grid operator supplies the meter and the connection (Fluvius connection guide).
• The connection power in your contract (kVA). The grid operator studied your connection for this power. In the ORES connection contract for high voltage, the protection settings are set to match it, and the transformer protection must meet the Synergrid C2/112 rules. A bigger transformer on the same contract does not give you more power.
• The access power you nominate (Flanders). Since 2023, Fluvius bills about half of the capacity cost of a high-voltage customer on the access power you nominate in advance, and about half on your real monthly peak. If the monthly peak goes above your access power, an extra tariff applies.

In Flanders that monthly peak has a price. In the Fluvius Antwerpen tariff list for 2026, a customer on the 1-26 kV grid pays about 54 euro per kW per year for the monthly peak, plus about 34 euro per kVA per year for the access power. Other grid areas have their own figures. So every kW that a battery keeps off the peak also lowers the bill, even when the transformer is not the problem.

What does replacing the transformer involve?

More than the transformer. Because the connection power has to go up, the route is the same as for a new high-voltage connection, only on an existing cabin.

• The study. At ORES the detailed study for a medium-power connection is mandatory and paid, and it is the only step that reserves your place in the queue and the power you asked for. An offer is valid for six months.
• The cabin. A bigger transformer often means other protection settings, heavier cables to the main board and sometimes a bigger low-voltage board. The design must follow Synergrid C2/112 and the extra rules of your grid operator.
• The inspection. The modified cabin is inspected by an approved body before the grid operator connects it. After that come the yearly control visits that every high-voltage installation gets.
• The stop. The cabin must be dead for the swap. Plan it outside production, or rent a generator for the day.
• The meter (Wallonia). Below 250 kVA, ORES can place the meter on the low-voltage side of your transformer. If you then go to 250 kVA or more, the meter moves to the high-voltage side, at your cost.

Two more things are easy to forget. A bigger transformer also has bigger no-load losses: Energie+ points out that these iron losses run all year, whatever you consume. And transformers are not always on the shelf. The International Energy Agency reports that the price of power transformers rose by around 75% in recent years, and that the largest units take up to four years to get. The smaller unit in a customer cabin comes faster, but ask for a firm delivery date before you plan your new machine around it.

What if the grid operator says no or not yet?

Then the transformer is not your bottleneck any more: the grid behind it is. In March 2026, VILT reported on fruit growers in Bierbeek who wanted to raise their cabin from 250 to 400 kVA, so their farm battery could also work for the grid. Fluvius answered that their file sat "in a zone that is currently considered congestion-sensitive", and later that it needed more analysis and time before it could make an offer.

In zones where congestion is expected, Fluvius can also offer a flexible connection instead of a classic one: you get the extra power, but it can be limited at busy moments. Our article on a heavier connection that is refused or delayed explains what that means and what your options are.

For a business with a new machine waiting, "not yet" is the expensive answer. That is exactly where a battery behind the existing transformer earns its place: it does not need more connection power, because it charges in the hours when there is room.

How does a battery behind the transformer help?

The battery sits on the low-voltage side, next to your main board, and watches the load on the transformer. When the load comes close to the limit you set, the battery delivers the difference. When the load drops, it recharges, without ever pushing the total over the limit.

That is what peak shaving means in practice. In a Victron system, for example, the ESS peak shaving function limits battery charging so the grid import stays under the set current, and lets the battery assist when the loads go above it, as long as the battery allows. If one phase goes over its limit, power is shifted to the other phases. The same logic works behind a transformer: the limit is simply set to what the transformer and your contract allow.

Two conditions decide whether this works:

Is your connection still on low voltage, and do you wonder whether you need a cabin at all? That is a different question, answered in our article on a high-voltage cabin or a battery.

Example: a 400 kVA transformer and a new cooling line

Illustrative figures, not a customer case.

A food company has its own cabin with a 400 kVA transformer: about 360 kW at a power factor of 0.9. A new cooling line and chargers for the delivery vans bring the busiest days to 440 kW, for about two hours in the late morning and again in the afternoon. The rest of the day the site stays well under the limit, and at night it runs at about half.

• Power: the battery must deliver the 80 kW above the limit, so an inverter of about 100 kW gives some margin.
• Energy: 80 kW for two hours is 160 kWh per peak, so about 200 kWh of usable capacity leaves room for a busier day and for ageing.
• Recharging: between the two peaks and at night there is well over 100 kW of room under the limit, enough to refill the battery.
• Bonus in Flanders: each kW that stays off the monthly peak saves about 54 euro a year in the Fluvius Antwerpen example above.

Change one assumption and the answer changes. If the cooling line ran 16 hours a day at full power, there would be no room left to recharge, and the company would need a bigger transformer. That is why we start from measured data, not from rules of thumb.

New transformer, battery or both: how do you choose?

Choose on the shape of your load and on the answer of the grid operator.

Spreading the load is the cheapest first step: our article on chargers without a heavier connection shows how smart charging keeps a car park under a limit. The same thinking works for cooling compressors, presses and pumps. If that is not enough, the battery is the next step. Our business battery systems are modular up to 1 MW and are integrated with your existing electrical installation.

What else can a battery behind the cabin do?

A battery that only waits for the peak is idle most of the day. Give it more work.

• Store your own solar power. In Beveren-Melsele the battery is there to use as much solar power as possible on the spot. Read when solar panels pay off on a business roof.
• Lower the monthly peak on the bill. Our article on peak shaving with a battery explains how.
• Use cheap hours on a dynamic contract. See a dynamic energy contract with a business battery.
• Keep critical circuits running when the grid fails, if the system is designed for it.

On a farm in Tielt, the next step for growth would have been medium voltage. The battery system gives the site more power, so no reinforcement was needed. On a site with its own cabin the idea is the same, one level higher: the battery gives you more power than the transformer alone. Our article on more power without a heavier connection shows the same principle for a pump or a machine.

What happens when you ask us to look at your transformer?

We start from your data, not from a product.

1. Step 1: Analysis and sizing. We read your quarter-hour data, list the new loads and check how often and how long you would go over the limit.
2. Step 2: Technical design. We choose the battery capacity and the inverter power, and set the limit to what your transformer and your contract allow.
3. Step 3: Installation and commissioning.
4. Step 4: Monitoring and support. You follow the system in our monitoring software, and we can adjust the limit when your site changes.