Rough functionality of the European power grid
In central Europe we have a 3-phase power grid. This means that we have three conductors parallel to each other. What is the difference between Direct current, alternating current and three-phase current is, you can in the Wiki under the electrical basics topic.
Our three-phase network has many advantages over 1-phase networks, for example we can save a lot of copper with it. A three-phase network only needs 4 conductors, a comparable 1-phase system would require 6 conductors or 2 significantly thicker cables. In addition, a three-phase network has two possible voltages: 230 V & 400 V
And last but not least, you can operate a simple but powerful electric motor with three-phase current, which has no dead center and therefore starts independently from any position.
With that in mind, it is now clear why the 4.7 kW charger from the smart ED4 only gets 3.7 kW on the a European 11 kW box. (See FAQ: Why does my 4.6 kW / 7.2 kW charger only charge 3.7 kW at a 11 kW wallbox? )
So what is now a unbalanced load?
Whether a toaster or just the television in the living room, almost everything in our everyday life is powered by 1 phase. After all, it only has the small Schuko plug, no high-voltage plug. If you were to put everything on L1, you would have a classic unbalanced load. The three conductors would not be used equally.
Why is an unbalanced load a problem?
Using the power grid equally has many advantages, here are the most important:
- Due to the unequal utilization, the voltage difference between the heavily used phase and the phases that are not used, can become too high. 3-phase machines then no longer work reliably. Single-phase loads may also switch off because the phase drops too much (their voltage drops).
- If everyone only used one phase, the traffic on the transformer would be overloaded and would switch off, although three times the power would be available.
- A power plants can only increase and decrease the output in 3 phases, but not for individual phases. This is due to technical reasons.
How is unbalanced load prevented?
Logically, we cannot provide every vacuum cleaner and every room lighting with a 3-phase connection, that would simply not be in proportion to the benefit.
That is why an electrician has the task, for example, of making a house installation in such a way that we use the 3 phases as evenly as possible in everyday life. For example, he puts the kitchen with the dishwasher on L1, the laundry room with the dryer on L2 and the bathroom with his hairdryer on L3.
An example from everyday electric cars, 3 charging stations with 3.7 kW each:
Even if you have three 11 kW stations, you think of the unbalanced load. Then you roatate all three phases. This is a precaution in case there are cars at all three charging stations that can only charge 1-phase. Instead of all using to one phase, they use all three phases individually.
In addition, the German VDE has stipulated that electrical devices never single-phase use more than 4.6 kW (20 A, see formula collection). Anything that needs more power than this 4.6 kW must distribute its power over all three phases. Incidentally, this also applies the other way around: Solar systems with more than 4.6 kW must also feed at least two phases into the power grid. The purpose of this is to ensure that there are no individual consumers who can cause large unbalanced loads on their own.
In Switzerland and Austria, the unbalanced load is limited to 3.7 kW (16 A), that's why the smart ED4 is there only available with the 22 kW charger. As a side note, you can unlock the 7,2 kW of the 4,6 kW charger, how is described at the DIY battery tool.