One grid: transmission and distribution according to CIGRE, and what it means for the Bajío

Bajío Ventures · April 2026

Issue 345 of ELECTRA, CIGRE’s magazine, opens with an editorial by its president, Konstantin O. Papailiou, titled “Transmission and Distribution – ONE GRID”. Its thesis fits in one line: transmission and distribution are a single grid, and it has to be developed, operated and governed as one. This is what it says, what the same issue measures, and what it means for the Bajío.

Why it matters

Mexico closed 2024 with 518,019 distributed-generation contracts and 4,448 MW, almost all of it solar and all of it connected to the distribution grid. The 2025 Electricity Sector Law raised the size that needs no permit to 0.7 MW and created interconnected self-consumption from 0.7 to 20 MW. In other words, the market that can be built today comes in at medium voltage. The constraint sits higher up, in the links between transmission regions. The project is installed in one layer and its limit is in the other.

What the editorial says

• The distribution grid has changed in nature. It was designed for one-way flow and passive operation; it now integrates distributed generation, electric mobility, storage, flexible demand and power electronics.
• Phenomena no longer respect the voltage level. Inertia, fault levels and voltage control are changing across the whole grid: a local action can have a system-wide effect, and a system-level phenomenon shows up in distribution.
• The conceptual separation is no longer enough. Planning, protection, control and asset management have to evolve in a coordinated way on both sides of the boundary, with transmission and distribution as equal partners.
• It is an invitation. CIGRE, founded in 1921, has more than 300 active working groups and calls on distribution operators, their specialists and manufacturers to join. The Paris Session in August is the way in.

What the same issue measures

The “One Grid” section of that issue includes a real-world case in Milan, written by Terna (the transmission operator), Unareti (the distributor), Politecnico di Milano and Università di Pavia. It estimates how much flexibility resources connected at medium and low voltage could offer by 2030, aggregated by primary substation, starting from 2020 and 2021 data. Three results:

• There is a threshold. It takes 10 MW of active-power variation at a primary substation to appreciably change the flows on the lines leaving it, and 10 Mvar to move the voltage on the 220 kV busbars by about 0.5 kV. Some substations do not reach that minimum.
• The help is mostly on voltage. Distributed resources can support voltage regulation at most nodes. On active power, their main contribution is reducing generation when there is a surplus, not injecting more.
• Neither side has to open its network to the other. Each operator optimises its own: the transmission operator makes a request and the distributor responds, without handing over sensitive information about its grid.

Another article in the same section, by the chair of Study Committee C6, describes the relationship between the distributor and a customer who no longer only consumes. It sorts it into three interfaces: technical (grid codes, hosting capacity), operational (outages, flexibility dispatch) and digital (smart metering, portals).

What it does not say

The editorial is a position piece: it carries no figures, method or coordination architecture, and it does not mention Mexico. The Milan figures belong to an urban grid with 220 kV busbars and do not transfer as they stand to a grid like Mexico’s, which is mostly 115 kV. What follows is our own reading.

The reading for the Bajío

First: assess both layers. A self-consumption project connects at medium voltage, in the Bajío distribution division. The capacity available also depends on the transmission region — Querétaro, Salamanca, Aguascalientes or San Luis Potosí — and on its links. A study that looks only at the connection point sees half the picture.

Second: flexibility counts once it is aggregated. The Milan case gives an order of magnitude: below roughly 10 MW per substation, the transmission operator does not notice the difference. A 0.7 MW system with batteries fixes one plant’s bill; to count on the grid, many plants behind the same substation have to be added together. The industrial park is the natural unit for doing that, and the self-consumption group is the regulatory figure available.

Third: someone has to translate. In Mexico the operator, the transmission grid and the distribution grid use different borders: nine CENACE control offices, nine transmission offices and sixteen distribution divisions that do not line up with one another. The coordination CIGRE is asking for starts with knowing whom to ask what.

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Sources: CIGRE ELECTRA No. 345 — editorial “Transmission and Distribution – ONE GRID”, K. O. Papailiou, April 2026 · ELECTRA No. 345 — Estimating MV/LV DER Flexibility for Enhanced TSO–DSO Coordination: Italian real-world case study · ELECTRA No. 345 — Customer Empowerment in the Electricity Distribution Sector, SC C6 · pv magazine, distributed generation in Mexico reaches 4,447.92 MW in 2024, Feb-2025 · Electricity Sector Law (Chamber of Deputies) · Pérez-Llorca, self-consumption general provisions published, Dec-2025

Bajío Ventures — a Mexican energy-infrastructure investment group based in Guanajuato: capital, a data platform on the region’s industrial base, and a German industrial channel, with its own advisory presence in Berlin.