The Why, what does the Overhaul of the electric network accomplish?

The wiring rules aren’t meant to be restrictive, but intentionally guide how electric poles connect.
A key goal is to reduce the need for manual wire disconnections.
Building isolated electric networks using vanilla wiring can be tedious and error-prone.
While these rules won't entirely prevent electric network short-circuits and cross-connections, they make them less likely.

A mini How-to?

With the Overhaul enabled, electric poles follow new connection rules that reshape how power is distributed.
Medium, big, and huge poles are used to transfer power across distance — they no longer supply power directly to machines.
Only small electric poles and substations have a supply area and can deliver power to your factory's entities.

Huge electric poles, in particular, form the backbone of a high-voltage network.
They can only connect to other huge poles or to Transformators, which means that any electric networks on either side of a huge pole line are automatically isolated.
When arranged in a grid, huge poles naturally divide your factory into independent power blocks.

A typical layout might involve connecting a power generation facility — nuclear, solar, or steam — to the high-voltage side of a Transformator.
The Transformator's low-voltage side then feeds into a backbone of huge poles, forming your high-voltage main bus.
This bus carries power across the factory without directly powering anything along the way.

To supply power to isolated zones or city blocks, Transformators can tap into the main bus.
Each one connects a huge pole (high-voltage) to a separate internal network (low-voltage) made of medium or big poles, which in turn feed small poles or substations.
This layered structure gives you more control over how and where electricity flows.

There’s no single correct layout — just possibilities.
Whether you want fine-grained control, modular factory blocks, or simply a clearer view of power usage, the Overhaul encourages you to think more deliberately about power design.

And yes, Transformators support both serial and parallel arrangements.

About existing blueprints?

Why I tagged this mod as an Overhaul, the power distribution portion will likely need to be modified.

What is this high voltage and low voltage nonsense?

Just an attempt to be thematic, it is equally correct to refer to them as: input/output, source/target, production/consumption, etc.

What are the four different selectable sections of the Transformator?

The two on either end are electric poles, to which you connect copper wires, but not across them. Circuit wires can cross.
There are two middle sections. The pump, which connects the Transformator to the circuit and/or logistics network, or can be disabled.
The final section allows you change the electrical rating, how much electricity is allowed to pass through, from pole to pole.
This is also the section to right-click and hold to pickup the Transformator.

How to connect a power source to the high voltage network?

Power always flows through a Transformator from the high voltage pole to the low voltage pole. A power source is always the "highest voltage".
This is true, even if the power source you are connecting produces less power than what already exists on the high voltage electric network.

How to connect a Transformator to a circuit network?

While the electric poles of the Transformator will carry circuit signals as any electric pole, they do not connect the Transformator to the circuit network.
To connect the Transformator, a circuit wire must be connected the internal pump, which is located near the yellow plug.

In modding terms, what is a Transformator?

A Transformator is a composite entity, comprised of the following seven base entities:
An identity unit, provides the visual representation
Two electric poles, providing the electric and circuit network connections
An infinity pipe, providing an infinite fluid source
A pump, allows the manual, circuit, and logistics enable and disable functions
An electric boiler, consumes power from the high voltage power pole to produce a heated fluid
A steam engine, which produces power from the heated fluid and provides power to the low voltage network

What is the effect on performance?

A tough question, but let me try.
This mod will add some load... it must, it adds both code and entities.

There are two primary areas... the code that runs when events occur (ex. you place an entity) and the code that runs on_nth_tick.
As much code as possible is assigned to events, minimizing the on_nth_tick code.
The code that runs when events take place should have little impact, I doubt it can be noticed in normal game play.
Usually the greater concern is the code that runs on_nth_tick, this code runs at quick intervals throughout the game session.
This mod uses the on_nth_tick to watch for when the Transformators are enabled/disabled via the circuit and logistics networks.

So adding a Transformator is the same as adding the seven entities. Quick enable/disable adds more.
I have tested 100 Transformators in operation with the on tick interval set to 1, it was not too much on my computer (M1 Mac Mini) and the performance profile was pretty good. Could you build with over 500 Transformators? Uh, maybe, maybe not. I could probably make code adjustments to split the workload. Please contact me if you do run into performance issues. I would want a save to test with, if possible, I am not a megabase engineer.

Why is there on_nth_tick code?

The Transformator's boiler and steam engine have an energy buffer and this buffer scales with the rating. When a Transformator is disabled, this buffer will continue to supply power until it is depleted. This can take some time depending on the rating chosen and power consumption. A fully buffered 10 GW Transformator with nothing more than an inserter as the consumer, will take a very long time to deplete the buffer. The on_nth_tick code flushes the buffers, so the power-off takes effect quickly.
When the underground substations are placed, the on_nth_tick is used to replace the displayer entity with the actual underground substation, on a 3 second delay. This allows the underground substation to the placed via pole dragging, like other electric poles.

Why can't Transformators be placed on Fulgora?

On Fulgora, the buffers of the internal components act as an over-powered accumulator. In the spirit of intended game-play, they do not belong there.