Your plant grows, the utility delivers the energy at medium voltage, and the question arrives: who turns it into the low voltage that drives the motors? A transformer substation. In Colombia, RETIE (the technical regulation for electrical installations), under Resolution 40284 of June 23, 2026, calls it a "substation"; transformer substation is the equivalent commercial term. Here are its parts, how it works and when a pole-mounted transformer stops being enough.

What a transformer substation is under RETIE

It is the set of equipment that receives the energy at medium voltage (MV), switches it, protects it, steps it down with a transformer and delivers it at low voltage (LV). RETIE, Book 3, calls it an electrical substation: the assembly that transfers the flow of energy, redistributes it and safeguards the system with automatic protection. Its chapter 5 applies to substations above 1 kV, so every user-owned transformer substation falls inside its scope.

Distribution regulation places level 2 between 1 kV and less than 30 kV (in Colombia, typically 11.4 and 13.2 kV) and level 3 between 30 kV and less than 57.5 kV (34.5 kV being the usual value). With that kind of service, the delivery point is not a panelboard: it is a medium-voltage substation, the transformer substation shown on the drawings. Confirm the exact voltage of the connection point with your utility.

What the parts of a transformer substation are

A transformer substation is built from six blocks. Medium-voltage switchgear (incoming, sectionalizing, protection and, where it applies, metering): metal-enclosed switchgear from 1 to 52 kV to IEC 62271-200, air-insulated (AIS) or gas-insulated (GIS). The transformer, which RETIE covers in Book 2, Art. 2.3.32, from 3 kVA upward, referring to IEC 60076. A low-voltage switchboard. Grounding. An enclosure, either civil works or prefabricated, with ventilation and drainage. And auxiliaries: surge arresters, interlocks and signage.

For the rated voltage and the switchgear family, see the guides on 24 or 36 kV, on the CGMcosmos 24 kV switchgear and on the CGM.3 36 kV switchgear.

And if the fault current in the medium voltage substation goes above 10 kA, or if the measured resistance turns out to be twice the design value or more, RETIE requires step and touch voltages to be measured. It does not apply to the pole type.

How it works: the path of the energy in three steps

The transformer substation does three things in sequence: isolate, protect and transform.

When your industry needs a transformer substation

When the power goes above 250 kVA, or when switchgear, medium-voltage metering and protection inside a room become necessary. RETIE allows the transformer on a single pole in three tiers of pole breaking load: 510 kgf or more up to 112.5 kVA, 750 kgf or more up to 150 kVA, and 1,050 kgf or more up to 250 kVA.

That is where the pole ends. In process industry, hospitals, data centers and solar plants a transformer substation of its own is the usual answer, and that is where medium voltage metering, relays with settings instead of fuses, and space reserved for one more switchgear position tend to appear.

Indoor, pad-mounted or prefabricated: which type to specify

The type of transformer substation is decided by the site. RETIE regulates separately the indoor substation or the one inside buildings (Art. 3.23.2), the pad-mounted type (Art. 3.23.4) and the prefabricated type (Art. 3.23.5). Indoors it requires live parts to stay out of reach of unauthorized persons, vault doors that open outward and, as a general rule, with panic hardware, firestop seals, ventilation calculated at full load and, in basements, drainage or pumping and, when that cannot be guaranteed, submersible equipment.

In the pad-mounted type, intended for underground networks and set on a concrete pad, the primary and secondary compartments are separated, the primary can only be reached after opening the secondary door, and live parts stay in lockable compartments. If the outer surface exceeds the ambient temperature by 45 °C and is within reach of the public, a barrier and a hot surface warning are required.

In the prefabricated version, the product is designed to IEC 62271-202 and IEC 62271-212, with IK 07 indoors and IK 10 outdoors, and the installation is fully certified as a transforming installation, with a declaration of compliance from the designer and from the builder and on-site verification by an accredited inspection body. And do not accept "arc resistant" without the full designation: the internal arc class in IEC 62271-200 carries accessibility (A restricted, B public), classified sides (F front, L lateral, R rear) and current with duration, for example IAC AFLR 25 kA 1 s.

Specification lesson. Before ordering a transformer substation, define in writing the utility's MV voltage and the short-circuit level, the power and the growth in kVA, the environment (indoor or outdoor, altitude, salinity) and the full IAC class of the switchgear. If you prefabricate it, require the site preparation and the maintenance manual, and plan for full certification of the installation.

What is changing: demand, connections and less SF6

In August 2026, demand on the National Interconnected System (SIN) was 7,696.79 GWh, 6.75 % higher than in August 2025, according to XM's press release of September 28, 2026. And more load is on the way: on May 7, 2026, the Mining and Energy Planning Unit (UPME) reported the release of 6.3 GW of grid capacity, 4,016.4 MW of solar, 1,815.6 MW of wind and 320.95 MW of thermal. Every new project calls for a transformer substation of its own.

On the equipment side, the detail matters. Regulation (EU) 2024/573 phases out sulfur hexafluoride (SF6) in MV switchgear up to 24 kV from 2026, but it is a European rule and it does not apply in Colombia: here RETIE only requires that leakage not exceed what the manufacturing standard allows.

The other front is the monitoring of temperature, humidity, doors and water level, which moves maintenance from a calendar basis to a condition basis, and Art. 3.23.6 already requires a plan with records. Industrias Ectricol S.A.S. manufactures in Funza and is a Siemens Technology Partner. Verify every requirement in Book 3 of RETIE from the Ministry of Mines and Energy.

Frequently asked questions

What is a transformer substation?

It receives energy at medium voltage, protects it with switchgear, steps it down with a transformer and delivers it at low voltage. RETIE calls it a substation and its chapter 5 applies to substations above 1 kV (Resolution 40284 of 2026, Book 3).

What are the parts of a transformer substation?

Medium-voltage switchgear, the transformer, the low-voltage switchboard, grounding and the enclosure. References: RETIE Books 2 and 3, IEC 62271-200 and IEC 62271-202.

Which standard is mandatory in Colombia and what does it require of a prefabricated transformer substation?

The RETIE in force, Resolution 40284 of June 23, 2026: it requires the prefabricated unit to be fully certified as a transforming installation, with on-site verification by an accredited body, and the minimum working space of Art. 3.23.5. The product itself is governed by IEC 62271-202 and IEC 62271-212.

When is a pole enough and when do you need a transformer substation?

Up to 250 kVA, RETIE allows the pole-type substation (Art. 3.23.3). Above that, or when switchgear, metering and protection inside a room are required, an indoor, pad-mounted or prefabricated installation is used.

What does IAC mean on medium-voltage switchgear?

It is the internal arc class in IEC 62271-200: accessibility (A restricted, B general public), classified sides (F front, L lateral, R rear) and arc current with duration, for example IAC AFLR 25 kA 1 s.